Official Luthiers Forum!

A week ago I made a vacuum frame press, and it leaks like a sieve. I can't really tell where the leak is. I built it by making two separate rectangular frames of poplar. I used epoxy to try to make sure each of the corner joints was airtight. I took the rubber sheet, and used barge cement to glue it between the two frame. After 24 hours, I used a bunch of #12 screws to screw the two frames tight (they were already together, of course, thanks to the barge cement).

I then drilled a hole in the frame, and put in a brass nipple to connect the air line to. I used a liberal amount of epoxy around the threads when I screwed it in.

After everything was done, the frame didn't work. If I plugged the hole drilled into the frame with my finger, the pump only pulled 5lbs. Putting my mouth on the nipple, I could easily create air flow by blowing into the nipple, though I couldn't tell where it was going. The hole looked kind of torn up (the nipple only goes partway through the frame), so I dumped a bunch of epoxy into the hole, then put a bunch more epoxy all around the front of the nipple where it connects to the frame. Now, if I block the hole with my finger the pump pulls 10lbs - better, but still not the 20-25 that it pulls if I directly plug up the hose to the pump.

If I press the frame onto a smooth surface, I get enough suction to pull the rubber sheet down loosely, but there is absolutely no clamp pressure. I used 1/2x1/2" foam around the bottom of the frame, with one long continuous strip wrapped twice around to mimize any air leaks.

So the upshot is I don't know if the leak is from the rubber sheet/frame interface, the foam, or what. I'd like to fix this thing rather than start from scratch. Does my construction sound reasonable?

Alternatively, I did find Don Williams' site for his homemade frame. If I can't get my frame to work I'll try his technique - Baltic Birch ply frame, with the rubber sheet attached to the frame with a plexiglass cover. I assume there is no glue used in that technique? But I still have the issue of making the brass nipple airtight, and the foam as well.

Any pointers?

Seriously, this has been a big time and money drain, and if someone wants to sell me one, I'll bite. I don't have a table saw, a router table, or much else in heavy equipment, and so whipping these jigs out isn't as easy as you might think.

2 things immediately come to mind.
1. Seal the wood. A vac pump can pull air right through wood, and you will need to seal it to keep that from happening. A good shellacing or better yet, a coat of epoxy over all the wood surfaces.
2. Are you using closed-cell foam or open cell? BIG difference. You can also try routing a channel and using surgical tubing instead.

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Don,
It kind of felt like air was being pulled through the wood itself (it sure tasted like it when I used my mouth to test the seal) but thought I was being foolish. 1 epoxy coating coming up.

I just checked what foam I ordered from McMaster. Open cell. Doh! Looks like I'm making a trip to the hardware store tonight.

Thanks Don.

Anytime...

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."