Cutting Stacked Sheets on the CNC

      Suggestions for how to hold thin sheets of material down while cutting multiple sheets in one pass. August 24, 2008

Has anyone attempted to stack and cut two or more plywood sheets (1/8" in my case)? Is there two-sided tape used for this purpose or am I asking for trouble. I cut a lot of sheets and it would be a huge cost savings if it could be done.

Forum Responses
(CNC Forum)
From contributor H:
Sounds like maybe the prep time would defeat the purpose.

From contributor T:
Most people cutting stacks of plywood utilize a roller hold-down on their machines.

From contributor O:
I often cut two narrow sheets together but you need to be careful as vacuum doesn't work well on the top sheet obviously (I don't have a roller). The biggest problem is dust/chips building up between the sheets. I used some mechanical fastening (nails around the edges and a couple in the centre) along with vacuum and it works well but not for more than two sheets. The smaller the sheets are the better.

I do know of someone who cuts a whole bunch of thin ply sheets together as they do mass amounts of smaller parts. I believe they screw fix all around the perimeter of the part to be cut; wouldn't work for full sheets though.

From contributor T:
I have seen the screw down approach used for cutting aluminum sheets, so it should work as well for plywood. They separated the parts a little further apart than normal in the nest and then fastened the sheets down to the table with screws in the dead areas.

From the original questioner:
I do have a pressure foot below the spindle and will experiment with it now that I know this type of thing is done.

From contributor A:
I had a similar problem on a project. A friend told me that a sheet of visqueen could be placed over the thin plys, turn on your vacuum and the parts suck down to the table. At the point when you cut your part, at least you won't be losing vacuum through the top of the part. It sounded like a good idea and I haven’t needed to try it since.

From contributor M:
If you can figure out how to do this on a standard spoilboard I would love to know how it works out. I think you are asking for trouble though. It would be a great innovation. I think Thermwood makes that roller type hold down.

How about using a light coat of contact adhesive sprayed between the two sheets through a template? That way you would not ruin the finished part, just stick the waste? It depends on how tight the nesting is though. Maybe plastic nails or staples would work too

From contributor O:
Sheet plastic helps the vacuum a lot - until it gets caught in the spindle and then sucked up into the dust extractor.

From contributor B:
The best thing I know to use that would be fast is machinable screws or staples. These are made of plastic and you can run a drill program even as your first tool to mark the locations where you want the screws or staples. Ideal would be to put them right in the tool path and use tabs on smaller parts. You have to consider the expense of prep time and screws etc. verses your time savings, if any.

From contributor A:
I have seen an older Thermwood router that had a drilling unit, automatic screw driver and a router spindle. They would stack several sheets of aircraft aluminum, then the machine would drill holes and automatically screw down the parts into the plywood spoil board. No vacuum was used on the machine. Then the router would cut the parts out. It is somewhat time consuming but it works.

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