Inexpensive vacuum holddown

[ezcnc]

I want to build something like this eventually:

Vacuum Table

In the mean time I need to cut some aluminum and acrylic and need a
quick and dirty solution. Cheap is good too.

I'm thinking about clamping 2 sheets of MDF roughly 34" x 52" together with
a grid in the lower sheet similar to the link above. The sandwich will be
clamped to my existing MDF spoil board. The sandwich will overhang the
front of my CNC by about 4" to allow a shop vac hose to be connected to
a 2" hole in the lower sheet connecting it to the vacuum plenum.

The lower sheet with the plenum will be sealed, the upper sheet surfaced top
and bottom and the sides sealed. I'll be able to replace the top sheet of MDF
as needed.

Would this be a waste of time or would it hold down .1" 24" x 48" sheet aluminum or acrylic?

[fixtureman1]

I have the shopbot style vac and I use 2 Fein vacs for hold down for the full 4x8 table I can get by with 1 for a 4x4 sheet of .062 lam.

[HelicopterJohn]

Hi,

What type of machining are you going to do? i.e. are you going to be drilling holes through the material, or engraving etc.

The reason I ask is that I engrave LED Edge lit signs and have made several Vacuum Fixture plates 11" X 14" and 11" X 28" from plexiglas. First, I surfaced the plexiglas and then cut vacuum seal slots near the outside edge of the the particular sign I want to cut. Then just inside that border I cut random vacuum paths that will allow the vacuum to be distributed evenly over the entire surface of the fixture. Then near one edge of the fixture I pocket a vacuum port and drill a horizontal hole into that vacuum port and insert a vacuum line into that port. I use the 1/4" X 1/4" adhesive backed low density foam tape from Allstar Adhesives and make the slot slightly larger i.e. .270 wide so that the tape will easily fit into the slot. Also, I only make the slot about .110 deep which allows for good compression and seal. I use a small Gast vacuum pump and can easily pull 25 inches of vacuum according to my vacuum gauge. I would think it would work equally well on larger sheets but that is something you would have to try.

If you would like any additional information let me know.

John

[ezcnc]

I think a small vacuum pump would not have the CFM to hold down
the sheets because I'm cutting many small parts out. I assume at some point
the vaccum loss would allow the sheet to move.

fixtureman1: I assume you are cutting large pieces of laminate not small parts?

I guess I'll have to test it and see how it works.