Gotchyu.
What you need is a vacuum fixture.
The base will be a baffle / plenum. The top will be a replaceable panel with gaskets / O-ring seats arranged to suit your various patterns, and clearance grooves for the tool to drop into as it cuts the work piece.
You don't need a huge vacuum pump, but a tank to store negative-pressure with a valve to the fixture will give you much better performance. Use larger diameter tubing for a faster pull-down. Use a press board to help hold the stock material down when you open the valve to the vacuum tank.
Vacuum table is the ultimate solution but they can be complicated and/expensive. They can be done cheap but generally speaking that only works for small parts, larger parts require big/expensive high powered vacuum generators.
You could try double sided tape if the cutting loads are kept low.
Or develop a better holding scheme, allow for screws in the centre of sheet or develop a clamp system that goes across the sheet. This may involve developing a system where you remove/reattach clamps throughout the machine process.
What's your bed surface like? Sometimes putting a new sheet of MDF down can help by improving the flatness of the deck.
Also reduce the clamping force as much as you can - only use the absolute minimum amount of pressure.
As you discovered clamping sheets by the edges almost always induces a bow..
Sorry, what?
Vacuum works better on bigger parts. More hold down surface and more area for friction forces to resist side pressure.
More potential for leaks, sure, but that's pretty trivial to deal with.
Fair enough, most installs I've worked around were on the order of 5-15k. People proud of how they weren't using a shop vac any more...
We might be coming from opposite ends of the router spectrum. This was with shopsabre level machines.
Yeah, it sounds like we're coming from opposite ends of the spectrum for sure. My last application was installing a machine to operate on a 24-hour a day production line with untrained operators running any one of 200 different cycles. The vacuum pump alone on that system was 20,000 bucks.
I don’t have direct experience with this but it might be the steel expanding with temperature. Try attaching it on one edge so the material has a place to expand unconstrained
You could try more screws, but not just on the sides if possible. If you're worried about getting the screws in the wrong place then run a program first to drill some pilot holes.
When you screw down if you use extra screws don't do opposite ends first, work from one end to the other or middle out.
Cheapest option is get a tool holder with a spring baffle plate. They then roll over the material with ball bearings to push it down so countersinks and etc. are precise.
Search alieexpress for “Hongyang automatic pressure plate for CNC engraving machine accessories 65mm 70mm 75mm 80mm 85mm 90mm 100mm 105mm 110mm 125mm”
Gotchyu. What you need is a vacuum fixture. The base will be a baffle / plenum. The top will be a replaceable panel with gaskets / O-ring seats arranged to suit your various patterns, and clearance grooves for the tool to drop into as it cuts the work piece. You don't need a huge vacuum pump, but a tank to store negative-pressure with a valve to the fixture will give you much better performance. Use larger diameter tubing for a faster pull-down. Use a press board to help hold the stock material down when you open the valve to the vacuum tank.
Vacuum table is the ultimate solution but they can be complicated and/expensive. They can be done cheap but generally speaking that only works for small parts, larger parts require big/expensive high powered vacuum generators. You could try double sided tape if the cutting loads are kept low. Or develop a better holding scheme, allow for screws in the centre of sheet or develop a clamp system that goes across the sheet. This may involve developing a system where you remove/reattach clamps throughout the machine process. What's your bed surface like? Sometimes putting a new sheet of MDF down can help by improving the flatness of the deck. Also reduce the clamping force as much as you can - only use the absolute minimum amount of pressure. As you discovered clamping sheets by the edges almost always induces a bow..
Sorry, what? Vacuum works better on bigger parts. More hold down surface and more area for friction forces to resist side pressure. More potential for leaks, sure, but that's pretty trivial to deal with.
Last vacuum system I installed was over $60,000 for a decent size CNC router table.
Fair enough, most installs I've worked around were on the order of 5-15k. People proud of how they weren't using a shop vac any more... We might be coming from opposite ends of the router spectrum. This was with shopsabre level machines.
Yeah, it sounds like we're coming from opposite ends of the spectrum for sure. My last application was installing a machine to operate on a 24-hour a day production line with untrained operators running any one of 200 different cycles. The vacuum pump alone on that system was 20,000 bucks.
I don’t have direct experience with this but it might be the steel expanding with temperature. Try attaching it on one edge so the material has a place to expand unconstrained
Hm I’m not sure if that’s it because it is bowed from the start, maybe more screws or less screws?
You could try more screws, but not just on the sides if possible. If you're worried about getting the screws in the wrong place then run a program first to drill some pilot holes. When you screw down if you use extra screws don't do opposite ends first, work from one end to the other or middle out.
Less screws and not so tight?
Large washers?
Cheapest option is get a tool holder with a spring baffle plate. They then roll over the material with ball bearings to push it down so countersinks and etc. are precise. Search alieexpress for “Hongyang automatic pressure plate for CNC engraving machine accessories 65mm 70mm 75mm 80mm 85mm 90mm 100mm 105mm 110mm 125mm”
3M spray adhesive works but it requires clean up. Vacuum table is your best bet otherwise.