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| making a vacuum frame press http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=3713 |
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| Author: | rlabbe [ Thu Nov 03, 2005 5:28 am ] |
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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. |
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| Author: | Don Williams [ Thu Nov 03, 2005 5:42 am ] |
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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. |
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| Author: | rlabbe [ Thu Nov 03, 2005 5:55 am ] |
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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. |
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| Author: | Don Williams [ Thu Nov 03, 2005 5:59 am ] |
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Anytime... |
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