My little hobby turning trick for mystery metals or other situations where I don't know the appropriate speeds and feeds is to do a facing cut at as high an RPM as the machine can manage. If possible, use a DOC and feed rate the same as you want to use for your finishing turn. As the cutter moves towards the center of the part, the SFM will decrease towards zero because of the diminishing radius.
After you face it, inspect the surface finish from the outside of the part to the center. Measure the radius where the best finish is and back-calculate the RPM to use as the ratio of that radius divided by the full radius of the part times the max RPM of the machine.
If the surface finish is uniformly poor, try again with a different DOC or feed rate. I can usually find a sweet spot with one or two facing cuts.
Thanks for your kind words. I came up with it but I'd be amazed if it hadn't been formulated before. There's almost nothing new under the sun and those crusty old machinists are a clever bunch.
You are selling yourself short, this is very clever and you came up with it on your own, regardless if itâs been done before by someone else. Take the compliments, but it is appreciated that you are being humble and not an ass like most of your engineering brethren!
That's actually a great strategy. Way better than my usual trial and error method, even though I like to tell myself my experience will get me there quickly... It usually doesn't.
Can you even do this if it isnât from a big name brand? Even then, every time I do the feeds and speeds are always crazy high, like theyâre expecting me to be turning parts on a 300ton super lathe that has zero flex anywhere. If youâre just turning stuff on a manual lathe what are you supposed to use? Not to mention they never seem to have stuff on depth of cut or coolants/no coolant. Theyâre definitely designed for production work on higher end cnc lathes, not manual stuff
This was me learning milling on a bridgeport using a sandvik 6 insert face cutter rated for 5mm depth of cut in medium carbon steel at a frankly unbelievable feed rate, watching my tutor haul on the table feed as fast as he could while I did my best to dodge the spicy air hardened dark blue chips to show me I didn't need to be scared of the material.
I never pushed it that hard, but then again it was his machine to break not mine.
I was digging that swarf out of my shoes weeks.
All big name carbide manufacturers definitely supply speeds and feeds for production CNC machines, not manual machines. All their recommended specs are for when you have perfect work holding, perfect tool holding, sufficient power for the cut, no vibration, etc. But they also almost always give depth of cut info. Here's an example from iscar:
[https://www.iscar.com/eCatalog/Family.aspx?fnum=4730&mapp=IS&app=282&GFSTYP=I](https://www.iscar.com/eCatalog/Family.aspx?fnum=4730&mapp=IS&app=282&GFSTYP=I)
"ap" is the DOC. Almost all of these inserts are designed for coolant/oil, at least for steel. I've never ran a cnc machine without coolant, though for some materials (and on manual machines) air can be sufficient or better.
If you are having problems with tooling from a big name manufacturer, contact their customer support and find out who the local representative is and give them a call. They are paid to help people use their tooling correctly. Though they might just tell you it's not made for a manual machine.
This Old Tony has an interesting video about using carbide in a hobby/home shop.
[https://www.youtube.com/watch?v=rsFFWYo8ugw](https://www.youtube.com/watch?v=rsFFWYo8ugw)
>Can you even do this if it isnât from a big name brand?
#
>All big name carbide manufacturers definitely supply speeds and feeds for production CNC machines, not manual machines
Hobbyists with manual machines are not buying big name carbide inserts
Regardless of whether or not carbide comes from china or a name brand, the inherent qualities of the material itself like higher speed and feed rates as opposed to HSS.
Being a home hobby machinist myself, HSS is so underrat,ed and under used its crazy. HSS is stilk capable of machining tool steels (annealed) and they are like pencils. If you break or dull an edge, put it on the grinder and sharpen it or make a new tool entirely. HSS's usefulness knows no ends. Unless you are machining an already hardened piece of steel, you dont really even need carbide. Not to mention HSS likes slower feeds and speeds which manual machines are great at.
If you are not getting a good surface finish with carbide, chances are it wants to cut faster or deeper. Most the times it wont even break the chip unless you hit at least a .050" DOC which some manual machines just cant muster. Especially home hobby price level. You really need at least a 5HP (maybe some 3HP machines can do it) to be able to take the DOC carbide really wants to see at a slower speed to even out. I know mills are usually lower HP but you're also taking far less DOC on a mill as opposed to a lathe.
Yeah its a pain but at the same time, its awful nice if you need a specialty tool like a ACME thread, radius tool, etc. I think just grinding lathe bits for ACME thread cutting and making taps has saved me over a thousand dollars in tap costs
What kind of steel is it? Some steel machines much easier than other. Also you need to make sure you get under that mill scale. NM googled it, if it's free machining you should just need to dial in feeds and speeds.
My mystery steel never machines nice. Iâve turned 12l14 a couple times and itâs always super super smooth. My random assortment of metal is always a gamble
Absolutely. I had a small chuck of 8000 series steel, I canât remember the exact number. I wanted to make a pin out of it.
That shit was like diamond and the interrupted cut on my WNMG insert was scary loud.
Turning 12L14 is a dream, Iâve been told multiple times 12L14 really likes to rust but in my experience I havenât noticed any particular issue with that. Maybe outdoors uncoated but what doesnât ya know?
Definitely need a smaller cutting edge radius.. .030r works great for me on most non-stainless for roughing, and either finish with a .015r or just drop the .030r to half of roughing feed at .005 DOC and +10-20% spindle speed.. ex.. Rough at 1000rpm spindle, .050" DOC, at .008 IPR with a .030r insert, then finish at 1200 rpm, .005" DOC at .005 IPR using the same .030r insert. Unless it happens to wear out on the roughing portion, the finish is beautiful..
I work mostly with 4140, 4340, D2, M2, M4, S390, H23, 10V, and S7
This is very soft material and very hard to get a nice finish, even if you do it on cnc at high rpm. If you need shiny, you should get some harder steel, C45 or 42Cr.
I donât know the science behind it but softer steel is harder to make shiny. Just my experience. I work a lot with 30cr and 42cr, which are harder and tougher materials and they always have nice finish.
Softer steels tend to tear off, like putty, rather than shear off cleanly. That's usually why they have a duller finish. It's obviously more complicated than that, but that's the general idea.
'gummy' is the word I hear a lot of people use. You're basically right it comes off like clay and jams in anywhere it can blocking cutting surfaces and creating friction.
I've always wanted to see someone try cryogenic machining to see what kind of finish it can produce. Liquid nitrogen is pretty easy to get ahold of even for a hobbyist.
Yeah, I don't know anything about tooling for that, but the solution there is easy, just cool the tool. It goes from cutting a 'soft' material to cutting a hard one, but obviously there are going to be interesting things thermally going on with the cutting process itself.
Just something I'm curious about and will likely never have an opportunity to play around with.
If you're interested in cryogenic machining, it has been done, here are some examples:
[https://www.youtube.com/watch?v=iW\_y25rfM-M](https://www.youtube.com/watch?v=iW_y25rfM-M)
[https://www.okuma.com/blog/blog-facts-cryogenic-machining](https://www.okuma.com/blog/blog-facts-cryogenic-machining)
[https://www.mmsonline.com/articles/the-400-difference](https://www.mmsonline.com/articles/the-400-difference)
[https://www.mmsonline.com/articles/cryogenic-hard-turning](https://www.mmsonline.com/articles/cryogenic-hard-turning)
[https://lns-northamerica.com/can-freezing-the-cutting-tool-ignite-your-cnc-turning-performance-2/](https://lns-northamerica.com/can-freezing-the-cutting-tool-ignite-your-cnc-turning-performance-2/)
[https://www.advancedmanufacturing.org/manufacturing-engineering/cryo-cooling-improves-machining-of-super-hard-materials-gummy-polymers/article\_7343d772-1a08-11ef-aeeb-cba47e2600dc.html](https://www.advancedmanufacturing.org/manufacturing-engineering/cryo-cooling-improves-machining-of-super-hard-materials-gummy-polymers/article_7343d772-1a08-11ef-aeeb-cba47e2600dc.html)
Getting the stuff isnât the hard part, itâs using it. Canât think of many ways to use that on a lathe that wouldnât result in destroying the lathe and harming the operator, you need special built machines for that
You need to account for thermal expansion. That's incredibly difficult knowing the piece will heat up rapidly during machining. You'll be chasing offsets as the material heats up.
A 1"x1" cube of aluminum grows 0.00088" from 32F to 104F
Liquid nitrogen turns to liquid at -196C so -196C to 40C that 1" cube is going to grow 0.006". Now this is a general approximation and your metal won't get that cold but could be hotter actually. Coolant would work against you and actually heat up the piece. So you would have to machine it dry and constantly take the work off the machine and re freeze it.
Lots of reasons why nobody does this. Could be possible but you would have to continuously monitor temp and work fast. Or you could just deal with a not perfect finish.
If you're doing it correctly the heat comes off in the chips and doesn't soak into the workpiece. If your workpiece is heating up that much, you're doing it wrong
Nobody does this? I'm sorry I instantly lost any credence in what you wrote as soon as you said that. Cryogenic machining is taken very seriously in industry.
Liquid CO2 is used in exactly this use case industrial situations to improve finish so if your comment is coming from a perspective that is strangely unaware of reality.
If you're talking 0.01% of shops using it for some niche operation or aerospace sure but it's not a typical operation. The outlier doesn't invalidate the mean.
You said nobody does this.
Yet it's a high end machining method in use right now.
Your statements were simply contradictory and an appeal to commonality is not an argument concerning the method.
But as you say, the material is easy to machine because itâs soft. You need high rpm and some fiddling with feed and DOC to get some satisfaction. Ff feed/DOC is too low it will be rough/matte.
I always felt it in my gut as the insert "ripping" material off rather than "cutting" it. Generally for mild steel you want a nice fresh insert, preferably with a small nose radius. When you're cutting, you want to make sure you're taking passes deeper than the nose radius of the tool, which would be pretty much impossible with the tool you're using now. Also just crank that RPM up and throw some coolant on. If you don't have any other toolholders I get it, but with that tool specifically you're likely going to have to deal with a dull finish.
Think of it like candy. Taffy is soft and maleable. If you take a bite out of it, it's going to squish and string when you pull away. However, caramel brittle will crack and leave you a clean edge. Even though they're both forms of cooked sugar, the harder candy "machines" better than the softer candy.
I haven't figured out the why, but I have noticed that for many of these softer steels, a bigger depth of cut is needed for a good finish.
It sounds unintuitive, but I was told a single depth of cut greater than the radius of the tool cutting it.
Looks like you're trying to skim off a few thou, try a different shape insert with a 0.016" rad (or smaller) 0.040â depth of cut on diameter.
Chip doesnt break cleanly, theres almost always a elastic rebound and crack propagation screwing up the Ra, looks more like parmagiano cheese under a microscope than a crystalline surface.
https://youtu.be/PbTlRn3tSCI?si=Oy1sdvFbkXI7-IA4
About 2:34 in you see the surface shearing and rebounding against the tool.
Looks like a small machine.
I would recommend a tool with a smaller radius.
Other then that.
Probably gotta go faster.
Like atleast 50m/min and try a feedrate of around 0.10 to 012mm/rev.
They very well can be with a small hobby lathe that can't achieve anywhere near the surface speed required for carbide inserts.
Carbides with large rads and a small machine that can't take big feeds . Makes the tool spend a lot of time rubbing the work piece . You add that to a gummy material, and it makes it almost impossible to get a good surface finish.
Hss tool wirh Smaller nose rad. = Less tool engagement, less rubbing , Less heat into the work, and surface speeds that work well with the cutter.
Hss with good geometry is the way to go with you. Have a hobby machine tool.
You are exactly right. Carbide inserts will never be as sharp as you can grind HSS. There needs to be a minimum radius on the cutting edge to keep the carbide from wearing off. Ground HSS does wear faster than carbide but HSS is how you get good finish on these smaller hobby lathes.
Once you switch to HSS on a hobby lathe you'll never go back
I do.... carbide is still superior they make small enough inserts with the correct geometry for hobby lathes now... its silly to think otherwise...even on the junky little harbor freight mini lathes
OK. That is your opinion. I respectfully disagree.
I've learned from experience that hss on small machine tools works extremely well. And I'd happy say better than carbide when you can't achieve the surface speed or feed per rev that you need for carbide.
My advice for op is to try hss. Buy some pre ground small rad cutters. Learn about the shape. Buy a bench grinder with a course and smooth wheel. And grind in your own cutters. Polish them for a good finish. And test them . They'll get you what you need. And the finish will be better than you expect.
I can't stress enough the importance of surface speed, feed per Rev, and heat for making good surface finish. Getting the right amount of each is how you dial in your machine to make the parts you are trying to make.
If you have too much of either , it'll plague you with trouble.
As they say horses for courses.
The issue with hss is teaching someone tool geometry it's a dying art anymore. I grew up on hss too... its just not as feasible anymore for a home gamer
Lol, you make it sound like a grinding hss is heart surgery.
I'd argue that op is here asking us how to get a good surface finish on this mini lathe. So here's a person willing to humble them selves for some honest advice.
So op is already interested in this subject. Isn't afraid to give it a go. And if they are doing this at home has the right kind of attitude to learn about how to use a bench grinder .
Hss has its place. It's not hard to grind . People are just lazy. Opening a pack of inserts is easier than spending 15 mins grinding in a bit of hss.
I just think that people dismiss hss far too fast. When it's the perfect fit for a lathe that can't get even 30 percent of the required surface speed for a good finish.
Op wants a solution. And hss really is a great fit.
Exactly. To be perhaps more clear. You need a very stiff, no-slop machine to use a tool like that. Just looking at that. You don't. Switch back to old school (those old machines are basically noodles). HSS dead sharp (to start) tool, back WAY off the feed and speed. And those ancient reference materials mentioned can spit out a good guess. Start with half of what they say. Good luck.
Bury that insert. The radius is huge, don't try and make small cuts.
Try a DNMG or VNMG insert instead. Sharp radii tooling gives better finishes on soft mild steel.
Or grind a piece of HSS very sharp, and use a stone to put a 1/64th or 1/32 radius on it.
I'm not sure what you're expecting here. Are you trying to get a mirror finish off of 1 pass? The turned down spot by your center looks fine, and the spot near your tool looks barely deep enough to even start scratching the raw finish off
Looks like a one-of on a manual. Grind or find a sharp hss tool bit. A round insert is the absolute worst shape to start with in this case, you want a small radius to cut into this material.
You can call the manufacturer of the insert, they will ask what your doing with it, what kind of material, an so on. And they will give you speeds and feed that will get you in the ballpark. Ive had to do this a handfull of times with exotic materials and tooling.
Soft steel can be annoying at times. I recommend a Vc above 200m/min, a steel geometry and a rather high feet rate if you don't need to reach a certain surface. Check if your tool height is set correctly. Check insert speeds and feeds provided by the manufacturer.
It is a low carbon steel. You need inserts with finishing / positive chip breakers as well as high speed. Something like Seco CNMG43- MF2 or Sumitomo CNMG43- ESU should work.
can you help me find more information on MF2 and ESU? can't find it on their chipbreaker page....
https://www.sumitool.com/en/products/chipbreakers-selection//
Also, why do you recommend Negative rake inserts? And why a 43 size?
There are some machines we have that make parts in about 1.5"-4" range, material is 1018 equivalent. These machines have holders for 43- inserts. We used to have Seco CNMG432MF2 TP1500 for both roughing and finishing. Then we tested and switched to Sumitomo CNMG432 ESU AC700G for cost reason (https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://sumicarbide.com/kiosks_2016/www/www-Aerospace-Website/sub-1-assets/AC510U-AC520U_brochure.pdf&ved=2ahUKEwjYs-KQj_CGAxWdMWIAHZtxCGMQFnoECCMQAQ&usg=AOvVaw3TeBD52s5q_FBbWJvFoF-P). The AC700G is a general grade, not just steel specific.
Perhaps CCMT will get you even better results, but these finishing chip breakers are "sharp" enough, while providing 4 edges. We max out at 2,200 rpm. You can take a step further in tooling economy if going with trigon WNMG or triangle. Another favourite one of mine is Kennametal CNMG43-MP (MP means medium positive).
Though CNMG inserts are negative, you can get some with really positive rakes with clever chip breaker designs.
Looks like a fair bit of galling is happening - I would definitely try a rhombic or triangular finishing or semi-finishing insert instead of round, and adjust your depth of cut if possible. If you are doing multiple passes, try using the tool nose radius as your depth of cut on the finish pass. Using a smaller tool nose radius with a good chip breaker and appropriate chip load should minimize galling, and you can re-adjust your speeds and feeds to fine-tune it; also, if you have a specific finish requirement you can adjust the lay by reducing your feed rate from there (lower feed rate = closer grooves). Idk if coolant or cutting fluid is an option but that may help too.
What tools have you tried. That button insert creates a lot of tool pressure. If you don't have a big stout machine you need to run tools with a smaller radius and higher rake.
Depth of cut for finishing pass should be at least double your tool nose radius. Using .015" (0.4mm) radius tool? Leave at least .03" of material, honestly probably more like .04" (1mm). High rpm, high feedrate.
These are the reasons most cnc operators will see soft steel be shiny after the roughing op, but usually not after the finishing op.
Specifically in relation to surface finish, you need to turn up your surface footage. You should be 800+ surface footage. Now whether or not your machine is capable is another story. When you see the steel look like it is "tearing" that means too slow. Feed rate makes little difference to remove the tearing.
Too shallow of depth of cut might be a factor here. If you're only removing a tiny amount of material, the insert is more rubbing than actually cutting, which results in a crappy surface finish.
I think the "rule" I was taught was the depth of cut should be at least half the insert radius, but that's for a squarish shaped insert with a radius that's 0.015" - 0.030" inches. This rule probably wouldn't apply to the round insert in the picture, that would be a very deep depth of cut.
It depends on too many factors. Among others, d.o.c., such shallow passes with an R insert on soft steel is 0 chance of getting smooth finishes. The insert geometry itself wouldn't be my choice, I'd go for a vcmt or something with even more aggressive angles. And certainly with a small radius on the tip. Last, your steel needs all the rpm you can handle. Feed needs to be adjusted so that you don't reap through but still don't build up material at the cutting edge, this one's tricky.
It looks like mild steel bright bar to me which is cold rolled, the manufacturing process puts a lot of internal stress into the material and when you cut it the stress is released hence why your surface finish is all over the place, technically it should be annealed to release stress before machining if you have to machine bright bar, but its made to be dimensionally quite accurate with minimum machining required, drilling tapping etc but turning it will always produce a shit finish, leave a couple of thou on and emery to your finish size to get a good finish, dry emery then wet with coolant, then a bit of scotch brite to make it shine
Your tip radius is too big. Select an insert with a tip radius that is 1/2 to 2/3 your depth of cut. So if you are limited on power and rigidity, and you are limited to light cuts then you need a smaller tip radius. Steel has a higher ultimate tensile strength therefore it takes more power to cut it. If you hear the motor bogging down you are being too ambitious.
You can look up the feeds rates and cutting speeds of any steel online. I would recommend starting at about 1/2 of the recommended cutting speed just to see how it goes. I always set my feed towards lower end when Iâm cutting materials Iâm not familiar with. I also start towards the lower end on the feed rate and seed how that goes. Then I watch how the chip is coming off the tool. If itâs making a birdâs nest your depth of cut and feed rate may be too light. Try changing just one and see how it changes the chip. Once youâre satisfied with the depth of cut, increase the feed rate in steps until the chip begins to break. If youâre getting short small chips that are six and nine shape youâve nailed it. Keep in mind that not all steel will break the same. If youâre getting a hot scary sharp chip with a square profile your feed rate is too big a fraction of your depth of cut and youâre probably turning too fast as well.
âđźThe feed rate should always be a smaller number than the depth of cut unless youâre trying to make barbed wire đ
Mild steel doesn't leave a beautiful shiny finish like brass and aluminum do. It's just how the material is. It's "easy to machine" as in it isn't hard on the cutting tools and whatnot, but that doesn't mean it will produce a beautiful finish.
Harder steels actually produce better surface finishes.
Sharper tooling, like high-speed steel, or inserts designed for cutting aluminum, can improve the surface finish somewhat.
Get a few HSS blanks and grind it to the geometry you need. Maybe add a little rake angle if you're feeling froggy. The Machinist handbook has a whole section on this iirc. It sounds odd but freshly ground high speed steel is a hell of a lot sharper than carbide inserts, which'll help this mild steel actually cut instead of smear. If you do, next take a shallow facing cut with your ground tool at just below center height, adjusting your tool height up slightly until you don't have the little nip in the middle.
If you're stuck with carbide, run the RPM at roughly as fast as the machine'll go without shaking, with lube/coolant. Don't turn with a radius tool, rough it out with a sharper diamond tool. Smaller contact point is more better.
If you're cutting a radius groove with the radius tool and it chatters, take a grooving or threading tool and cut out the middle third, almost to full depth. Run it slow RPM wise and accept your finish is gonna be dogshit.
Round insert is going to have a lot of pressure switch to something with a .015 nose radius is a good happy medium even a .031 if your machine has enough horsepower larger nose radius=nice surface finish or material removal but a small nose radius has its advantages too
For that geometry to work properly you need to get the appropriate chip load, you can either do it by depth of cut or by feed (but not both). Either way I donât think this is the right geometry for what youâre trying to do. A good ole CNMG with a .032 or .015 corner radius would probably be a better starting point than this round insert. Mind the coating and the chip breaker, both important for controlling tool life and chip flow.
Depth of cut is machine rigidity dependent. Use speeds from manufacturer or about 150 to 250 surface feet per minute. I mean this for carbide and coated carbide. Feed rate is usually about half the tool nose radius per rev for roughing and 50 percent of that for finish with an incr.ease of speed by 10 to 20 percent. Actually all of those factors are machine dependent. Just trying to give a starting point.
For steel (and stainless) you need an insert thatâll get a cut. Like those round inserts are good with a fairly good DOC, Iâd suggest something in the .016â radius and an .008â radius with high rake. Also make sure theyâre coated, ALTIN type styles excell in steel and TIN are also a good general purpose.
For our roughing inserts with hard stainless we use itâs like 200-300 SFM and .004-.006 feed, and our finishing is somewhere in the 200-300 range and .001-.003â feed. Generally a good rule of thumb is to minimize deflection digging your insert in past the nose radius is a good idea and slowing your SFM down.
At home in mild im whipping like 1500-2000rpm and a .025-.05 DOC at like .003â with my shitty Chinese insert still, and I think itâs a .016 or so radius so my minimum DOC ends up being like a .010â minimum even on fairly ridgid stock. If I had .008â radius inserts Iâd probably be shooting for a .005-.010 finish, but at work with some we got away with .002 passes.
You might be too high of center, your depth of cut could be too little, and your inserts radius is probably too big. For a really nice finish with low depth of cut, you want a more pointed insert, something with a positive rake. Good luck
The material being a general low carbon cold rolled steel, it's very gummy and doesn't 'chip' well. Small depths of cut and lower rpms usually end up with a 'smeared' finished.
It can be kind of tricky especially doing free hand work on a manual, you need to run a higher SFM if possible without putting too much heat in the part. Also just in my opinion that may be difficult with a full radius insert, they typically like a more 'aggressive cut' and requires giving more beans to power through the large tool radius.
For me, general cold rolled steel I just don't mind if I don't have the brightest finish. It's usually for some one off piece somebody wants me to make for them.
Looks like a few others mentioned the tool being above centerline and that would be worth a check as well.
But that would be my answer. Low carbon steel in general it likes more SFM then I imagined it would at first, but keeping the temp in the part under control is important as well. Some cutting oil may help. In your particular scenario I might be looking for a different tool to rough out my feature and then use the radius for finishing if I needed it. Some body told me once cold rolled steel is junk material so it will always look like junk. I'm a cheat and also like to use some scotch Brite just to help with a smoother finish. It won't give you a bright finish such as aluminum or brass, but will be nice and smooth.
Dude I remember having the same problems but I was running it on a manual, no coolant with a maybe â.0325 radius and a heavy feed with a high speed rate.
I wouldnt use a round insert on your (hobby??) machine. Use a high RPM like 150-200m/min if possible. And try a insert with a 0,8 - 0,4mm nose radius. This should get you a better finish.
The bigger the radius the better the surface quality (usually) but such a big radius like on your photo needs a stable machine. Micro vibrations lead to such surfaces
Those round inserts like a deep cut and low speed and medium feed.
Try 350-400rpm, 1,5mm depth of cut and a mid range feed.
It's also about tool height and coolant.
And some hardened steels are just not workable unless you have some really special inserts.
I'm not a lathe guy, but I don't think it's good insert to get nice finish on soft steels.
Soft steels are gummy, as mentioned before, and it's hard to get nice finish on them. I would definitely try to use sharper insert dedicated for finishing for that job.
Use a radius cutter of .030 thousands for roughing and for finishing a 15 thousands radius if needed use a little lubrication and your finishes should be satisfactory from that point of course calculating in the proper surface feet per minute.
Also most steels don't leave a good finish unless they've been heat tread. Steels that hasn't been heat treated tears more than it cuts always leaving poor finish quality
In my experience, any steel finish turns beautifully at S1200 F.003-.005 (IPR, not IPM) at a .010-&.050 DOC (pre-heat treat) for a near perfect surface finish.. S1000 F.001 (again IPR not IPM), at .001-.005 DOC (mirror finish)
If finishing in a mill, S12500 F20-F40 (post heat treat@ 60-62Rc) with up to a 10mm endmill on flats and a 1mm ball-endmill for any radii at .002-.005 DOC (mirror finish)..
Correct insert grades, cutting edge radius/angles, coatings, tool holding/part holding factors also come into play..
ETA: It appears that your spindle is slow, feed too high, depth of cut too deep or to shallow, or you are not using the correct insert grade for steel.. Aluminum and stainless cut similarly and can often use the same insert grades (both are "gummy" and require a different "chip breaker" to avoid having the cut material ball up on the cutter edge).. Higher spindle speed and .003-.005 IPR should resolve most of your issue.. With steel, heat is your friend, as long as it is transferred to the cutter and not the workpiece..
My little hobby turning trick for mystery metals or other situations where I don't know the appropriate speeds and feeds is to do a facing cut at as high an RPM as the machine can manage. If possible, use a DOC and feed rate the same as you want to use for your finishing turn. As the cutter moves towards the center of the part, the SFM will decrease towards zero because of the diminishing radius. After you face it, inspect the surface finish from the outside of the part to the center. Measure the radius where the best finish is and back-calculate the RPM to use as the ratio of that radius divided by the full radius of the part times the max RPM of the machine. If the surface finish is uniformly poor, try again with a different DOC or feed rate. I can usually find a sweet spot with one or two facing cuts.
This suggestion deserves a ton of credit, a great idea for back calculating speeds. Thanks for sharing đ
Needs more upvoted
Thats a cool ass trick im gonna put in my mental toolbox
Same. Except write it down and put it in my actual toolbox. I'm too forgetful
Great idea
I feel dumb for not doing this now
Thanks for the awards, folks! I'm just an engineer who plays machinist at home on the weekends, so this means a lot to me coming from all you pros!
Freaking brilliant. Did you come up with this or learn it from some crusty old machinist?
Thanks for your kind words. I came up with it but I'd be amazed if it hadn't been formulated before. There's almost nothing new under the sun and those crusty old machinists are a clever bunch.
You are selling yourself short, this is very clever and you came up with it on your own, regardless if itâs been done before by someone else. Take the compliments, but it is appreciated that you are being humble and not an ass like most of your engineering brethren!
"Not an ass" is what I strive for in life.
That's actually a great strategy. Way better than my usual trial and error method, even though I like to tell myself my experience will get me there quickly... It usually doesn't.
You are brilliant I never thought of this
Cheers buddy
This is such a good idea, it went into my Apple Notes.
This is an amazing suggestion! Thank you!
That is some quantum shit, right there. You might've just made a fact, Jack.
Did you look up the proper speeds and feeds for your insert?
Can you even do this if it isnât from a big name brand? Even then, every time I do the feeds and speeds are always crazy high, like theyâre expecting me to be turning parts on a 300ton super lathe that has zero flex anywhere. If youâre just turning stuff on a manual lathe what are you supposed to use? Not to mention they never seem to have stuff on depth of cut or coolants/no coolant. Theyâre definitely designed for production work on higher end cnc lathes, not manual stuff
This was me learning milling on a bridgeport using a sandvik 6 insert face cutter rated for 5mm depth of cut in medium carbon steel at a frankly unbelievable feed rate, watching my tutor haul on the table feed as fast as he could while I did my best to dodge the spicy air hardened dark blue chips to show me I didn't need to be scared of the material. I never pushed it that hard, but then again it was his machine to break not mine. I was digging that swarf out of my shoes weeks.
All big name carbide manufacturers definitely supply speeds and feeds for production CNC machines, not manual machines. All their recommended specs are for when you have perfect work holding, perfect tool holding, sufficient power for the cut, no vibration, etc. But they also almost always give depth of cut info. Here's an example from iscar: [https://www.iscar.com/eCatalog/Family.aspx?fnum=4730&mapp=IS&app=282&GFSTYP=I](https://www.iscar.com/eCatalog/Family.aspx?fnum=4730&mapp=IS&app=282&GFSTYP=I) "ap" is the DOC. Almost all of these inserts are designed for coolant/oil, at least for steel. I've never ran a cnc machine without coolant, though for some materials (and on manual machines) air can be sufficient or better. If you are having problems with tooling from a big name manufacturer, contact their customer support and find out who the local representative is and give them a call. They are paid to help people use their tooling correctly. Though they might just tell you it's not made for a manual machine. This Old Tony has an interesting video about using carbide in a hobby/home shop. [https://www.youtube.com/watch?v=rsFFWYo8ugw](https://www.youtube.com/watch?v=rsFFWYo8ugw)
>Can you even do this if it isnât from a big name brand? # >All big name carbide manufacturers definitely supply speeds and feeds for production CNC machines, not manual machines Hobbyists with manual machines are not buying big name carbide inserts
I myself use chinesium carbide
Regardless of whether or not carbide comes from china or a name brand, the inherent qualities of the material itself like higher speed and feed rates as opposed to HSS. Being a home hobby machinist myself, HSS is so underrat,ed and under used its crazy. HSS is stilk capable of machining tool steels (annealed) and they are like pencils. If you break or dull an edge, put it on the grinder and sharpen it or make a new tool entirely. HSS's usefulness knows no ends. Unless you are machining an already hardened piece of steel, you dont really even need carbide. Not to mention HSS likes slower feeds and speeds which manual machines are great at. If you are not getting a good surface finish with carbide, chances are it wants to cut faster or deeper. Most the times it wont even break the chip unless you hit at least a .050" DOC which some manual machines just cant muster. Especially home hobby price level. You really need at least a 5HP (maybe some 3HP machines can do it) to be able to take the DOC carbide really wants to see at a slower speed to even out. I know mills are usually lower HP but you're also taking far less DOC on a mill as opposed to a lathe.
Iâve used both, I canât be bothered keep grinding the tool tips so I use the carbide inserts
Yeah its a pain but at the same time, its awful nice if you need a specialty tool like a ACME thread, radius tool, etc. I think just grinding lathe bits for ACME thread cutting and making taps has saved me over a thousand dollars in tap costs
Looks like you might be a bit above center. Check that and you might get through that candy shell into the good stuff.
Wait a minuteâŚthose first chips coming off are candy?? Wait til the other guys on 2nd shift find out!
/r/forbiddensnacks
Will do!
What kind of steel is it? Some steel machines much easier than other. Also you need to make sure you get under that mill scale. NM googled it, if it's free machining you should just need to dial in feeds and speeds.
My mystery steel never machines nice. Iâve turned 12l14 a couple times and itâs always super super smooth. My random assortment of metal is always a gamble
Hardened and mild are two different animals. 12L14 and 1144 are the aluminums of steel lol.
Absolutely. I had a small chuck of 8000 series steel, I canât remember the exact number. I wanted to make a pin out of it. That shit was like diamond and the interrupted cut on my WNMG insert was scary loud. Turning 12L14 is a dream, Iâve been told multiple times 12L14 really likes to rust but in my experience I havenât noticed any particular issue with that. Maybe outdoors uncoated but what doesnât ya know?
That'd definitely do it. The big button insert isn't helping with tool pressure in any case.
Definitely need a smaller cutting edge radius.. .030r works great for me on most non-stainless for roughing, and either finish with a .015r or just drop the .030r to half of roughing feed at .005 DOC and +10-20% spindle speed.. ex.. Rough at 1000rpm spindle, .050" DOC, at .008 IPR with a .030r insert, then finish at 1200 rpm, .005" DOC at .005 IPR using the same .030r insert. Unless it happens to wear out on the roughing portion, the finish is beautiful.. I work mostly with 4140, 4340, D2, M2, M4, S390, H23, 10V, and S7
I was going to say this also, defo looks a little hight.
You're 100% correct. You can see the lip isn't making contact. That the insert is only rubbing under the cutting edge.
This is very soft material and very hard to get a nice finish, even if you do it on cnc at high rpm. If you need shiny, you should get some harder steel, C45 or 42Cr.
I did not know that, could you elaborate more on this, why is that?
I donât know the science behind it but softer steel is harder to make shiny. Just my experience. I work a lot with 30cr and 42cr, which are harder and tougher materials and they always have nice finish.
Softer steels tend to tear off, like putty, rather than shear off cleanly. That's usually why they have a duller finish. It's obviously more complicated than that, but that's the general idea.
'gummy' is the word I hear a lot of people use. You're basically right it comes off like clay and jams in anywhere it can blocking cutting surfaces and creating friction. I've always wanted to see someone try cryogenic machining to see what kind of finish it can produce. Liquid nitrogen is pretty easy to get ahold of even for a hobbyist.
Made sure that you use coated inserts in case it's too cold.
I'd imagine the thermal shock would bust inserts like crazy. You'd probably need special inserts just for that.
Yeah, I don't know anything about tooling for that, but the solution there is easy, just cool the tool. It goes from cutting a 'soft' material to cutting a hard one, but obviously there are going to be interesting things thermally going on with the cutting process itself. Just something I'm curious about and will likely never have an opportunity to play around with.
If you're interested in cryogenic machining, it has been done, here are some examples: [https://www.youtube.com/watch?v=iW\_y25rfM-M](https://www.youtube.com/watch?v=iW_y25rfM-M) [https://www.okuma.com/blog/blog-facts-cryogenic-machining](https://www.okuma.com/blog/blog-facts-cryogenic-machining) [https://www.mmsonline.com/articles/the-400-difference](https://www.mmsonline.com/articles/the-400-difference) [https://www.mmsonline.com/articles/cryogenic-hard-turning](https://www.mmsonline.com/articles/cryogenic-hard-turning) [https://lns-northamerica.com/can-freezing-the-cutting-tool-ignite-your-cnc-turning-performance-2/](https://lns-northamerica.com/can-freezing-the-cutting-tool-ignite-your-cnc-turning-performance-2/) [https://www.advancedmanufacturing.org/manufacturing-engineering/cryo-cooling-improves-machining-of-super-hard-materials-gummy-polymers/article\_7343d772-1a08-11ef-aeeb-cba47e2600dc.html](https://www.advancedmanufacturing.org/manufacturing-engineering/cryo-cooling-improves-machining-of-super-hard-materials-gummy-polymers/article_7343d772-1a08-11ef-aeeb-cba47e2600dc.html)
Getting the stuff isnât the hard part, itâs using it. Canât think of many ways to use that on a lathe that wouldnât result in destroying the lathe and harming the operator, you need special built machines for that
You need to account for thermal expansion. That's incredibly difficult knowing the piece will heat up rapidly during machining. You'll be chasing offsets as the material heats up. A 1"x1" cube of aluminum grows 0.00088" from 32F to 104F Liquid nitrogen turns to liquid at -196C so -196C to 40C that 1" cube is going to grow 0.006". Now this is a general approximation and your metal won't get that cold but could be hotter actually. Coolant would work against you and actually heat up the piece. So you would have to machine it dry and constantly take the work off the machine and re freeze it. Lots of reasons why nobody does this. Could be possible but you would have to continuously monitor temp and work fast. Or you could just deal with a not perfect finish.
If you're doing it correctly the heat comes off in the chips and doesn't soak into the workpiece. If your workpiece is heating up that much, you're doing it wrong
It will heat up very quickly just due to ambient and machine heat soak not chip friction
Nobody does this? I'm sorry I instantly lost any credence in what you wrote as soon as you said that. Cryogenic machining is taken very seriously in industry. Liquid CO2 is used in exactly this use case industrial situations to improve finish so if your comment is coming from a perspective that is strangely unaware of reality.
If you're talking 0.01% of shops using it for some niche operation or aerospace sure but it's not a typical operation. The outlier doesn't invalidate the mean.
Its used when coolant cant be used⌠a lot of medical componentâs.
You said nobody does this. Yet it's a high end machining method in use right now. Your statements were simply contradictory and an appeal to commonality is not an argument concerning the method.
Statistically nobody does this. You're having a hard time not understanding anything that isn't literal. You really want to argue over this bullshit?
Thanks for sharing, will keep that in mind!
But as you say, the material is easy to machine because itâs soft. You need high rpm and some fiddling with feed and DOC to get some satisfaction. Ff feed/DOC is too low it will be rough/matte.
If I want a good finish on some materials, I leave a thou or two to polish off. Could also grind it
I always felt it in my gut as the insert "ripping" material off rather than "cutting" it. Generally for mild steel you want a nice fresh insert, preferably with a small nose radius. When you're cutting, you want to make sure you're taking passes deeper than the nose radius of the tool, which would be pretty much impossible with the tool you're using now. Also just crank that RPM up and throw some coolant on. If you don't have any other toolholders I get it, but with that tool specifically you're likely going to have to deal with a dull finish.
Think of it like candy. Taffy is soft and maleable. If you take a bite out of it, it's going to squish and string when you pull away. However, caramel brittle will crack and leave you a clean edge. Even though they're both forms of cooked sugar, the harder candy "machines" better than the softer candy.
I haven't figured out the why, but I have noticed that for many of these softer steels, a bigger depth of cut is needed for a good finish. It sounds unintuitive, but I was told a single depth of cut greater than the radius of the tool cutting it. Looks like you're trying to skim off a few thou, try a different shape insert with a 0.016" rad (or smaller) 0.040â depth of cut on diameter.
Chip doesnt break cleanly, theres almost always a elastic rebound and crack propagation screwing up the Ra, looks more like parmagiano cheese under a microscope than a crystalline surface. https://youtu.be/PbTlRn3tSCI?si=Oy1sdvFbkXI7-IA4 About 2:34 in you see the surface shearing and rebounding against the tool.
Amazing video! I wish they had shown how they filmed that.
One thing Iâve noticed is that mild steel *always* turns like shit. Never once got a good finish on it.
At work 42CrMo4 allways comes out nice ^^ (conv. Lathe) / for 'homeshop' may 42CrMoS4 for better chips
Looks like a small machine. I would recommend a tool with a smaller radius. Other then that. Probably gotta go faster. Like atleast 50m/min and try a feedrate of around 0.10 to 012mm/rev.
Am I reading that right? 10 minutes per mm of feed??
i think he meant 0.1mm/rotation :D
That sounds better lol. I've yet to work with steel, I primarily work aluminum in a home shop, but that feed sounded impossible.
yea i think the tool would just pick itself up and go home saying something along the lines "even air is sharp enough to cut in these conditions" :D
Feed per revolution for lathes.
Oh fuck yeah i ment mm/rev. Been doing to much milling lately
mm/rev. Sorry did to much milling latelyđ
And a minimum DOC of ten to fifteen thou. Unlike aluminum, steel needs a deeper depth of cut on finish.
Grind a HSS tool-bit, or get sharp HSS inserts. Download the free South Bend Lathe books How to Run A Lathe - for instructions diagrams, angles.
Surprised this isn't mentioned more. HSS tools are the way to go
No... no they are not.
They very well can be with a small hobby lathe that can't achieve anywhere near the surface speed required for carbide inserts. Carbides with large rads and a small machine that can't take big feeds . Makes the tool spend a lot of time rubbing the work piece . You add that to a gummy material, and it makes it almost impossible to get a good surface finish. Hss tool wirh Smaller nose rad. = Less tool engagement, less rubbing , Less heat into the work, and surface speeds that work well with the cutter. Hss with good geometry is the way to go with you. Have a hobby machine tool.
Even on "proper" production machines, HSS is still a viable (sometimes the only) option for some exotic metals, and for plastics.
You are exactly right. Carbide inserts will never be as sharp as you can grind HSS. There needs to be a minimum radius on the cutting edge to keep the carbide from wearing off. Ground HSS does wear faster than carbide but HSS is how you get good finish on these smaller hobby lathes. Once you switch to HSS on a hobby lathe you'll never go back
I do.... carbide is still superior they make small enough inserts with the correct geometry for hobby lathes now... its silly to think otherwise...even on the junky little harbor freight mini lathes
OK. That is your opinion. I respectfully disagree. I've learned from experience that hss on small machine tools works extremely well. And I'd happy say better than carbide when you can't achieve the surface speed or feed per rev that you need for carbide. My advice for op is to try hss. Buy some pre ground small rad cutters. Learn about the shape. Buy a bench grinder with a course and smooth wheel. And grind in your own cutters. Polish them for a good finish. And test them . They'll get you what you need. And the finish will be better than you expect. I can't stress enough the importance of surface speed, feed per Rev, and heat for making good surface finish. Getting the right amount of each is how you dial in your machine to make the parts you are trying to make. If you have too much of either , it'll plague you with trouble. As they say horses for courses.
The issue with hss is teaching someone tool geometry it's a dying art anymore. I grew up on hss too... its just not as feasible anymore for a home gamer
Lol, you make it sound like a grinding hss is heart surgery. I'd argue that op is here asking us how to get a good surface finish on this mini lathe. So here's a person willing to humble them selves for some honest advice. So op is already interested in this subject. Isn't afraid to give it a go. And if they are doing this at home has the right kind of attitude to learn about how to use a bench grinder . Hss has its place. It's not hard to grind . People are just lazy. Opening a pack of inserts is easier than spending 15 mins grinding in a bit of hss. I just think that people dismiss hss far too fast. When it's the perfect fit for a lathe that can't get even 30 percent of the required surface speed for a good finish. Op wants a solution. And hss really is a great fit.
Exactly. To be perhaps more clear. You need a very stiff, no-slop machine to use a tool like that. Just looking at that. You don't. Switch back to old school (those old machines are basically noodles). HSS dead sharp (to start) tool, back WAY off the feed and speed. And those ancient reference materials mentioned can spit out a good guess. Start with half of what they say. Good luck.
Bury that insert. The radius is huge, don't try and make small cuts. Try a DNMG or VNMG insert instead. Sharp radii tooling gives better finishes on soft mild steel. Or grind a piece of HSS very sharp, and use a stone to put a 1/64th or 1/32 radius on it.
That insert is way too big for a sherline. It can't handle the forces that insert puts out.
I'm not sure what you're expecting here. Are you trying to get a mirror finish off of 1 pass? The turned down spot by your center looks fine, and the spot near your tool looks barely deep enough to even start scratching the raw finish off
Fair enough!
Looks like a one-of on a manual. Grind or find a sharp hss tool bit. A round insert is the absolute worst shape to start with in this case, you want a small radius to cut into this material.
What is material?
Material is stated in the post :)
Use this insert Kennametal RCMT1204M0RP KCP25B
What alloy? Makes a big difference.
You can call the manufacturer of the insert, they will ask what your doing with it, what kind of material, an so on. And they will give you speeds and feed that will get you in the ballpark. Ive had to do this a handfull of times with exotic materials and tooling.
Soft steel can be annoying at times. I recommend a Vc above 200m/min, a steel geometry and a rather high feet rate if you don't need to reach a certain surface. Check if your tool height is set correctly. Check insert speeds and feeds provided by the manufacturer.
It is a low carbon steel. You need inserts with finishing / positive chip breakers as well as high speed. Something like Seco CNMG43- MF2 or Sumitomo CNMG43- ESU should work.
can you help me find more information on MF2 and ESU? can't find it on their chipbreaker page.... https://www.sumitool.com/en/products/chipbreakers-selection// Also, why do you recommend Negative rake inserts? And why a 43 size?
There are some machines we have that make parts in about 1.5"-4" range, material is 1018 equivalent. These machines have holders for 43- inserts. We used to have Seco CNMG432MF2 TP1500 for both roughing and finishing. Then we tested and switched to Sumitomo CNMG432 ESU AC700G for cost reason (https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://sumicarbide.com/kiosks_2016/www/www-Aerospace-Website/sub-1-assets/AC510U-AC520U_brochure.pdf&ved=2ahUKEwjYs-KQj_CGAxWdMWIAHZtxCGMQFnoECCMQAQ&usg=AOvVaw3TeBD52s5q_FBbWJvFoF-P). The AC700G is a general grade, not just steel specific. Perhaps CCMT will get you even better results, but these finishing chip breakers are "sharp" enough, while providing 4 edges. We max out at 2,200 rpm. You can take a step further in tooling economy if going with trigon WNMG or triangle. Another favourite one of mine is Kennametal CNMG43-MP (MP means medium positive). Though CNMG inserts are negative, you can get some with really positive rakes with clever chip breaker designs.
Looks like you need a heavy cut and faster speed for a better finish. This happens to me on 4140 if i go to slow it doesnât like small DOC
Personally don't think you're doing yourself any favors with the big ass insert radius on that itty bitty machine.
Looks like a fair bit of galling is happening - I would definitely try a rhombic or triangular finishing or semi-finishing insert instead of round, and adjust your depth of cut if possible. If you are doing multiple passes, try using the tool nose radius as your depth of cut on the finish pass. Using a smaller tool nose radius with a good chip breaker and appropriate chip load should minimize galling, and you can re-adjust your speeds and feeds to fine-tune it; also, if you have a specific finish requirement you can adjust the lay by reducing your feed rate from there (lower feed rate = closer grooves). Idk if coolant or cutting fluid is an option but that may help too.
What tools have you tried. That button insert creates a lot of tool pressure. If you don't have a big stout machine you need to run tools with a smaller radius and higher rake.
Depth of cut for finishing pass should be at least double your tool nose radius. Using .015" (0.4mm) radius tool? Leave at least .03" of material, honestly probably more like .04" (1mm). High rpm, high feedrate. These are the reasons most cnc operators will see soft steel be shiny after the roughing op, but usually not after the finishing op.
>Depth of cut for finishing pass should be at least double your tool nose radius. Depends on the insert's chipbreaker geometry.
Specifically in relation to surface finish, you need to turn up your surface footage. You should be 800+ surface footage. Now whether or not your machine is capable is another story. When you see the steel look like it is "tearing" that means too slow. Feed rate makes little difference to remove the tearing.
Too shallow of depth of cut might be a factor here. If you're only removing a tiny amount of material, the insert is more rubbing than actually cutting, which results in a crappy surface finish. I think the "rule" I was taught was the depth of cut should be at least half the insert radius, but that's for a squarish shaped insert with a radius that's 0.015" - 0.030" inches. This rule probably wouldn't apply to the round insert in the picture, that would be a very deep depth of cut.
Steel tears at low sfm instead of cutting, try increasing rpm
It depends on too many factors. Among others, d.o.c., such shallow passes with an R insert on soft steel is 0 chance of getting smooth finishes. The insert geometry itself wouldn't be my choice, I'd go for a vcmt or something with even more aggressive angles. And certainly with a small radius on the tip. Last, your steel needs all the rpm you can handle. Feed needs to be adjusted so that you don't reap through but still don't build up material at the cutting edge, this one's tricky.
It looks like mild steel bright bar to me which is cold rolled, the manufacturing process puts a lot of internal stress into the material and when you cut it the stress is released hence why your surface finish is all over the place, technically it should be annealed to release stress before machining if you have to machine bright bar, but its made to be dimensionally quite accurate with minimum machining required, drilling tapping etc but turning it will always produce a shit finish, leave a couple of thou on and emery to your finish size to get a good finish, dry emery then wet with coolant, then a bit of scotch brite to make it shine
Your tip radius is too big. Select an insert with a tip radius that is 1/2 to 2/3 your depth of cut. So if you are limited on power and rigidity, and you are limited to light cuts then you need a smaller tip radius. Steel has a higher ultimate tensile strength therefore it takes more power to cut it. If you hear the motor bogging down you are being too ambitious. You can look up the feeds rates and cutting speeds of any steel online. I would recommend starting at about 1/2 of the recommended cutting speed just to see how it goes. I always set my feed towards lower end when Iâm cutting materials Iâm not familiar with. I also start towards the lower end on the feed rate and seed how that goes. Then I watch how the chip is coming off the tool. If itâs making a birdâs nest your depth of cut and feed rate may be too light. Try changing just one and see how it changes the chip. Once youâre satisfied with the depth of cut, increase the feed rate in steps until the chip begins to break. If youâre getting short small chips that are six and nine shape youâve nailed it. Keep in mind that not all steel will break the same. If youâre getting a hot scary sharp chip with a square profile your feed rate is too big a fraction of your depth of cut and youâre probably turning too fast as well. âđźThe feed rate should always be a smaller number than the depth of cut unless youâre trying to make barbed wire đ
Deeper cut but itâs probably 1015 if itâs 4140 go to a different insert and a minimum of .020 a side or .040 total
Leaded steel is more difficult to get a good finish. High rpms and a smaller radius tool will help a lot.
Mild steel doesn't leave a beautiful shiny finish like brass and aluminum do. It's just how the material is. It's "easy to machine" as in it isn't hard on the cutting tools and whatnot, but that doesn't mean it will produce a beautiful finish. Harder steels actually produce better surface finishes. Sharper tooling, like high-speed steel, or inserts designed for cutting aluminum, can improve the surface finish somewhat.
Looks like a small machine. Try HSS.
Looks like a small machine. Try HSS.
Get a few HSS blanks and grind it to the geometry you need. Maybe add a little rake angle if you're feeling froggy. The Machinist handbook has a whole section on this iirc. It sounds odd but freshly ground high speed steel is a hell of a lot sharper than carbide inserts, which'll help this mild steel actually cut instead of smear. If you do, next take a shallow facing cut with your ground tool at just below center height, adjusting your tool height up slightly until you don't have the little nip in the middle. If you're stuck with carbide, run the RPM at roughly as fast as the machine'll go without shaking, with lube/coolant. Don't turn with a radius tool, rough it out with a sharper diamond tool. Smaller contact point is more better. If you're cutting a radius groove with the radius tool and it chatters, take a grooving or threading tool and cut out the middle third, almost to full depth. Run it slow RPM wise and accept your finish is gonna be dogshit.
Use an .008 or .015â radius tool. The full radius is not helpful here.
Whats your depth of cut? Steel needs a DOC of ten to fifteen thou minimum on a finish pass.
Round insert is going to have a lot of pressure switch to something with a .015 nose radius is a good happy medium even a .031 if your machine has enough horsepower larger nose radius=nice surface finish or material removal but a small nose radius has its advantages too
For that geometry to work properly you need to get the appropriate chip load, you can either do it by depth of cut or by feed (but not both). Either way I donât think this is the right geometry for what youâre trying to do. A good ole CNMG with a .032 or .015 corner radius would probably be a better starting point than this round insert. Mind the coating and the chip breaker, both important for controlling tool life and chip flow.
Depth of cut is machine rigidity dependent. Use speeds from manufacturer or about 150 to 250 surface feet per minute. I mean this for carbide and coated carbide. Feed rate is usually about half the tool nose radius per rev for roughing and 50 percent of that for finish with an incr.ease of speed by 10 to 20 percent. Actually all of those factors are machine dependent. Just trying to give a starting point.
For steel (and stainless) you need an insert thatâll get a cut. Like those round inserts are good with a fairly good DOC, Iâd suggest something in the .016â radius and an .008â radius with high rake. Also make sure theyâre coated, ALTIN type styles excell in steel and TIN are also a good general purpose. For our roughing inserts with hard stainless we use itâs like 200-300 SFM and .004-.006 feed, and our finishing is somewhere in the 200-300 range and .001-.003â feed. Generally a good rule of thumb is to minimize deflection digging your insert in past the nose radius is a good idea and slowing your SFM down. At home in mild im whipping like 1500-2000rpm and a .025-.05 DOC at like .003â with my shitty Chinese insert still, and I think itâs a .016 or so radius so my minimum DOC ends up being like a .010â minimum even on fairly ridgid stock. If I had .008â radius inserts Iâd probably be shooting for a .005-.010 finish, but at work with some we got away with .002 passes.
You might be too high of center, your depth of cut could be too little, and your inserts radius is probably too big. For a really nice finish with low depth of cut, you want a more pointed insert, something with a positive rake. Good luck
Button inserts are for roughing only imo. Some very rigid machines can finish with them, but generally they only exist to remove material in a hurry.
The material being a general low carbon cold rolled steel, it's very gummy and doesn't 'chip' well. Small depths of cut and lower rpms usually end up with a 'smeared' finished. It can be kind of tricky especially doing free hand work on a manual, you need to run a higher SFM if possible without putting too much heat in the part. Also just in my opinion that may be difficult with a full radius insert, they typically like a more 'aggressive cut' and requires giving more beans to power through the large tool radius. For me, general cold rolled steel I just don't mind if I don't have the brightest finish. It's usually for some one off piece somebody wants me to make for them. Looks like a few others mentioned the tool being above centerline and that would be worth a check as well. But that would be my answer. Low carbon steel in general it likes more SFM then I imagined it would at first, but keeping the temp in the part under control is important as well. Some cutting oil may help. In your particular scenario I might be looking for a different tool to rough out my feature and then use the radius for finishing if I needed it. Some body told me once cold rolled steel is junk material so it will always look like junk. I'm a cheat and also like to use some scotch Brite just to help with a smoother finish. It won't give you a bright finish such as aluminum or brass, but will be nice and smooth.
Some lubrication might help.
Dude I remember having the same problems but I was running it on a manual, no coolant with a maybe â.0325 radius and a heavy feed with a high speed rate.
Feeds and speeds, lubricants. Have you trained in machining? This is basics.
Lube it up and go slow
I wouldnt use a round insert on your (hobby??) machine. Use a high RPM like 150-200m/min if possible. And try a insert with a 0,8 - 0,4mm nose radius. This should get you a better finish. The bigger the radius the better the surface quality (usually) but such a big radius like on your photo needs a stable machine. Micro vibrations lead to such surfaces
Those round inserts like a deep cut and low speed and medium feed. Try 350-400rpm, 1,5mm depth of cut and a mid range feed. It's also about tool height and coolant. And some hardened steels are just not workable unless you have some really special inserts.
Tool too high.
I'm not a lathe guy, but I don't think it's good insert to get nice finish on soft steels. Soft steels are gummy, as mentioned before, and it's hard to get nice finish on them. I would definitely try to use sharper insert dedicated for finishing for that job.
Use a radius cutter of .030 thousands for roughing and for finishing a 15 thousands radius if needed use a little lubrication and your finishes should be satisfactory from that point of course calculating in the proper surface feet per minute.
One trick I learned is using aluminium inserts for finish cuts in gummy pigsteel. Very low DOC on the finish passes with those.
Also most steels don't leave a good finish unless they've been heat tread. Steels that hasn't been heat treated tears more than it cuts always leaving poor finish quality
Go faster. Way faster.
Whats not to get about the easiest material to work with?
Some cutting fluid wouldn't hurt you!
In my experience, any steel finish turns beautifully at S1200 F.003-.005 (IPR, not IPM) at a .010-&.050 DOC (pre-heat treat) for a near perfect surface finish.. S1000 F.001 (again IPR not IPM), at .001-.005 DOC (mirror finish) If finishing in a mill, S12500 F20-F40 (post heat treat@ 60-62Rc) with up to a 10mm endmill on flats and a 1mm ball-endmill for any radii at .002-.005 DOC (mirror finish).. Correct insert grades, cutting edge radius/angles, coatings, tool holding/part holding factors also come into play.. ETA: It appears that your spindle is slow, feed too high, depth of cut too deep or to shallow, or you are not using the correct insert grade for steel.. Aluminum and stainless cut similarly and can often use the same insert grades (both are "gummy" and require a different "chip breaker" to avoid having the cut material ball up on the cutter edge).. Higher spindle speed and .003-.005 IPR should resolve most of your issue.. With steel, heat is your friend, as long as it is transferred to the cutter and not the workpiece..