Vacuum Fixtures

[barrowj]

I need to make several individual hold down vacuum fixtures. Ideally a 12"x36" and a 24"x24" with the ability to seal off what I won't be covering. I have not gone down this route so not sure what is the best way to do this. I don't have any vacuum setup at all so would probably buy a small vacuum pump. Any ideas or suggestions would be greatly appreciated.

[steve_g]

Joe…
I think you’ll be better off making several small “pucks” and ganging them up in series… This method plays well to the advantages of a high vacuum / low volume pump and you can rearrange these at will or leave them as a permanent setup on a sub-base.
SG

[barrowj]

Steve, what material did you use for the pucks, that is a great idea btw and makes more sense that several larger ones. I was looking at 1/2" hdpe and a 3cfm or 5cfm 2stage vacuum pump, any thoughts?

[bobmoore]

Pucks are nice for some materials and/or sizes but if you have a flexible material (1/4 inch plywood) and get too far from the puck you will get vibration issues. Vacuum holddown is very material and project specific. If you are regularly making the same parts I recommend a dedicated fixture as that is the most efficient way to hold a project with vacuum. No system works for everything. If you are going to use pucks a 3/4 inch thick is more common because most of the vacuum tubing is 3/8 inch O.D. and 1/2 inch doesn't give you much room for the vacuum tube. HDPE is a fine material although any stable workable nonporous material works. Bob

[steve_g]

Joe…
Bob pretty much hit the nail on the head! One comment I’ll add is gasketing… Quick and dirty, you can just stick a gasket material on top of the puck. This leaves a gap that thinner material can be sucked down into. Even this is Ok for simple perimeter cuts, but if depth of cut is critical, use method two…
Method two uses an “O” ring gasket in a groove. The vacuum pulls the material down, compressing the “O” ring into the groove and leaving the material flat and undistorted…
SG

[barrowj]

Steve/Bob, both are great ideas, looking at 3/4" HDPE now. I will probably go with 2 12"x12" as I have a specific product that we are doing. The base is 11 1/8" x 28" so 2 would do that, then the tops are 2 1/2" x 12 and 2 1/2" by 20 1/2 so I will probably go 7/8 then plane or drum sand down to 3/4" or 13/16". That way I don't break the vacuum seal. Any thoughts on the a vendor for the "o" ring? Thanks for any advice, this forum is great..

[steve_g]

All Star Gasketing

http://www.talkshopbot.com/forum/showthread.php?t=20510&highlight=star

[scottp55]

Joe, Just learning myself, but met George Bradley from AllStarAdhesives at Shopbot Camp Saturday and Extremely helpful. Bet you a $1 that if you contact him and tell him what you are cutting/material/and bit, he or John have helped somebody set up something similar and could get you into production Fast. gbradley@allstaradhesives.com
One note, At Camp, Sallye mentioned when they first tried a small highvac/lowvolume cheapie pump---The main thing it pumped was oil into the shop air!! Pretty sure the small pump Dad bought for me is the "Oil Spewing" type. She mentioned another pump they settled on that works well, but I can't remember it "H something?"
I would be interested in small pump recommendations also, that don't cost an arm and a leg and would be suitable for Desktop sizes.

[barrowj]

Scott, TJ mentioned a Harbor Freight model 2 stage 3cfm on one of his training sessions. There are a number of those type on Amazon (Prime, my favorite) and I will get one of those and let you know how it works. I also found 3/4" HDPE on Amazon 12" x 24" for $33 (Prime again), cheaper than even eBay... All I need now is to nail down the gasket and I will make my purchases either today or tomorrow and hopefully be up and running by next week. I will keep you informed.

[scottp55]

Joe, PRETTY sure that the "Oil Spewer" Sallye from Shopbot mentioned WAS a harbor freight(95%sure). Try emailing TJ and asking what pump they eventually used as standard.