Newbie- Vacuum clamping ?

[bherr]

Recently constructed a vacuum clamping system using Joe Woodworking plans. have a GAST vacuum pump going to -22Hg with a manifold system. I''m trying to mill flat aluminum stock and using the vacuum clamping system to hold the stock. However it doesn't seem to hold the stock solid using the no creep sealing tape that Joe sells. I'm milling out a 12.5" long by 2" wide by 3/8th thick aluminum and need to mill around the entire piece and then do a cut out in the center. I'm afraid the vacuum won't hold the stock tight enough and move messing up the cut. I though about milling out the center first with the stock clamped in a vice and supported on the one end, then clamp the piece using the center cutout to hold the stock.

Any ideas that I could use to increase the holding power of the vacuum system so I don't have to re-chuck the stock??

ben

[Geof]

I think your area is simply too small for vacuum fixturing. You have 25 square inches and a vacuum of 22 inches which is about 11 psi. Your total hold down force is only about 280 lbs even before you have removed anything. Even if you could get a full vacuum you only have around 350 lbs of force holding the part down. A single clamp exceeds this quite easily.

[Mike Stevenson]

Geof's right about the clamping force. Woefully inadequate. In my experience I haven't seen anyone using a vacuum clamp on large pieces of metal either. Wood and plastic are the only examples I have seen.

[Lillitaly]

I mill similar pieces. I mill out the inside first, then use them holes to hold down the piece while machining the outside. Only good way i found that works.

[Vac-Clamp]

You might want to look at putting a high friction material between the workpiece and the and the deck of your vacuum clamp. Naturally, this is used in conjunction with your vacuum clamp. We use a rubberised plastic on our clamps to increase the friction. Think of it as running shoes on your clamp
Errol