Holding Down 1/4-Inch Materials on a Vacuum Table

Thin panels can be hard to hold down, especially at the edges. Here's some advice. September 3, 2010

We recently bought a Panel Pro 145G18CD / 2007. The vacuum pump is a Dekker 40 hp. The table is a 3 zone 5x12. I was cutting out parts and all was well until I started on the 1/4" sheet and noticed the ends would not stick. The material was ply pre-finished one side. Has anyone had a similar experience? I also had a problem with 1/4" melamine MDF core finished two sides. The spoil board was just surfaced and the vacuum pump gauge indicated 24 hgv.

Forum Responses
(CNC Forum)
From contributor D:
Although our vacuum pump isn't as big as yours we too had the same problem. I think it could simply be that the 1/4" material isn't rigid enough to stay flat. Have you tried a down cutter?

From contributor Z:
Have you boys tried flipping the work piece over? Often the thinner material will have a tendency to bow. Face the bow down and the vacuum should suck the panel flat.

From contributor D:
I cut 1/4" material all the time, using a 12hp pump and a homemade spoilboard on a pod and rail CNC. I jumped through a lot of hoops until I finally had it down. It came down to a combination of using Trupan ultra light, 1/4"Onsrud spiral-O single flute downshear bits, and tabbing all small parts. The small parts need to be snapped off after cutting, much like model airplane kits I had as a kid.

I tried many different sized bits, up and down, compression, and combinations of downshear first and upshear for a final pass, with 1 to 3 flutes, hoggers and chipbreakers as well, but with only 12hp, the best performance was 100in/min at 16k with the above spiral-O bit, as the chips crammed into the groove nicely and aided in holding my parts, which in some cases are only 5/8" wide. Some on this forum advocated the use of screws a while back, and that works too, but I don't like the hassle myself.

From contributor K:
When I use tabs I trim the parts out with my trim router and a flush cut bit.

From contributor S:
I had a similar problem with 1/4 inch x grade phenolic. I had to seal the spoilboard with spoilboard tape and added a 60 gallon vacuum rated tank close to the router. Pumped down the tank (24") and opened up the valve. The extra negative volume in the tank snaps the board down fast. It makes the board lay flat. I noticed, however, that the phenolic let air suck into the table. That is probably a factor when cutting faced MDF.

From contributor J:
I have found a lot of people run into this issue due to the speed of cutting the spoil board and the flow they have through it. Remember to check your spoil board without any material on it to see what the difference is. I have found many people read the gage and come up with 14 to 18 hg with no sheet on the spoilboard. This is a problem as it is not getting to your sheet. sacrificial panels should be ran around 30 meters per minute and around 8500 rpm for optimum flow of Vacuum I have found after working on the flat table since the first one came out from Italy. Give it a try you might find a different result.