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Vacuum Press - I quit!!
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=20215		 Page 1 of 2
Author:  peterm [ Sun Dec 28, 2008 10:07 pm ]
Post subject:  Vacuum Press - I quit!!
Geez, after countless amounts of wasted hours I decided to give up and by an already made vacuum press. [headinwall] [headinwall]
I made one that has hinges on the back and the lid closes down onto the base but it leaked.... I sealed and re-sealed but never managed to pull more than 7-8 psi. [uncle]

Anyone has any input? or one for sale?

thanks,
Author:  Rod True [ Sun Dec 28, 2008 10:10 pm ]
Post subject:  Re: Vacuum Press - I quit!!
The other thing you could do is go with a vacuum bag, put the dish, plate and braces in the bag, seal it up and throw the switch.
Author:  Tai Fu [ Sun Dec 28, 2008 10:29 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Has anyone seen those vacuum bags designed for clothings and bedstuff? I suppose if you needed more pressure than what a vacuum cleaner can provide (how much pressure do you need to glue braces and stuff?) you could subsitude a vacuum cleaner with a pump...
Author:  peterm [ Sun Dec 28, 2008 10:31 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Thanks for the input. I do have a vacuum bag but that's not what I'm after....
Author:  Brock Poling [ Sun Dec 28, 2008 10:45 pm ]
Post subject:  Re: Vacuum Press - I quit!!
You know... I just took 2 pieces of MDF and laminated them together in a vacuum bag, then cut a hole in it to fit my radius dish in it (I also sealed it with an epoxy wash). On the bottom I routed a channel to put a strip of closed seal foam. I just throw it on my granite plate and it seals pretty decent, not enough to shut the pump off, but it pulls almost 20". I suspect it would grip to a piece of hardboard or a well finished work bench. It seems rather forgiving.
Author:  peterm [ Sun Dec 28, 2008 11:15 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Brock Poling wrote:
You know... I just took 2 pieces of MDF and laminated them together in a vacuum bag, then cut a hole in it to fit my radius dish in it (I also sealed it with an epoxy wash). On the bottom I routed a channel to put a strip of closed seal foam. I just throw it on my granite plate and it seals pretty decent, not enough to shut the pump off, but it pulls almost 20". I suspect it would grip to a piece of hardboard or a well finished work bench. It seems rather forgiving.



sounds interesting.... how did you attach the membrane to the MDF?
Author:  Daniel Minard [ Sun Dec 28, 2008 11:49 pm ]
Post subject:  Re: Vacuum Press - I quit!!
You should sandwich the membrane between two pieces of sheetstock. (I used MDF, because it has no voids like most plywood) Seal the membrane with contact cement to both surfaces. Then install a screw every 1 1/2" to hold the whole works together. My table has two layers of 3/4" MDF below the membrane & one layer above.
Make sure you pre-drill everything & punch holes in the membrane for the screws. Clean up all the shavings, glue & screw it together. It helps to paint all the pieces before you assemble the lid. MDF needs to be sealed (I used waterborne Varathane) or you will get leaks.
Did you slot your hinge screw holes so the lid "floats" up and down as the seal compresses? Also... leave the hinge screws a little loose in the slots so they allow the lid to settle as the seal compresses.
You should get a good seal at about 7 or 8 inches of mercury. I can't lift the lid on my deck, 'till the vacuum has almost completely bled off.
A three way brass fuel selector valve (available at most marine stores) will let you open & close the vacuum line, & leave one position open to vent the vacuum deck to atmosphere without bleeding vacuum from your reservoir.
Hang in there... It's just another learning curve, Right???
Good luck.
Feel free to PM me if you need more help.
Dan
Author:  SimonF [ Sun Dec 28, 2008 11:49 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Peter,
I don't even use a hinge. I made my frame out of MDF and sealed it - the gasket material is from the Joe Woodworker site and it works very well. And my radius dishes are made out of acrylic and were purchased from Bob Garrish.

--
Simon
Author:  Daniel Minard [ Sun Dec 28, 2008 11:59 pm ]
Post subject:  Re: Vacuum Press - I quit!!
P.S. With my old fridge compressor, I got 28.5" of vacuum in about 2 minutes. (I use a 20 lb propane tank for the resrvoir.) I now have a "real" two cylinder vac pump. It works hard to get 28", but the recovery is a lot faster. I wouldn't be happy with much less that 25" for gluing.
Dan
Author:  Brock Poling [ Mon Dec 29, 2008 8:02 am ]
Post subject:  Re: Vacuum Press - I quit!!
peterm wrote:
sounds interesting.... how did you attach the membrane to the MDF?


I just put it on the top with a piece of lexan over it with some holes drilled into it. I epoxied the edges then drove screws (with grommets) through it ever half inch.
Author:  Jim Watts [ Mon Dec 29, 2008 12:19 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Peter, the most fool proof seal I worked with in the composites world comes from http://www.torrtech.com. it's their T-7 seal, it works really well. Check out their site you probably get some ideas.
That said, your leak may be caused by the hinge in the back, as the back of the frame can't pull down tight due to the hinge. Try removing the hinge and placing the frame down against flat surface and see how many inches of Hg you get.
Author:  BobK [ Mon Dec 29, 2008 1:58 pm ]
Post subject:  Re: Vacuum Press - I quit!!
My press is a ring that fits over my sanding dish and seals to my epoxy painted cement floor. Simple, no hinges. The ring provides even tension on the membrane and there are no issues with having empty spaces that need to be supported during the vacuum process (ie. round dish in a square press).

Also, silicone caulk is your friend. If you make your press out of wood, coat inside and outside with caulk. My press pulls almost the same as my LMI bridge clamp. (25" if I remember correctly).
Author:  peterm [ Mon Dec 29, 2008 6:20 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Jim Watts wrote:
Peter, the most fool proof seal I worked with in the composites world comes from http://www.torrtech.com. it's their T-7 seal, it works really well. Check out their site you probably get some ideas.
That said, your leak may be caused by the hinge in the back, as the back of the frame can't pull down tight due to the hinge. Try removing the hinge and placing the frame down against flat surface and see how many inches of Hg you get.



Thanks Jim,
I did try without the hinge with the same results.....
Author:  Shane Neifer [ Mon Dec 29, 2008 6:38 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Peter,

Can you post a picture of your set-up? I have some suggestions but it is best I see your set up so that one can be specific about advice. Include your pump as well. Also, I trust that you have tried your pump with a different fixture, like a bridge clamp, and it works fine?

Shane
Author:  Chas Freeborn [ Mon Dec 29, 2008 7:14 pm ]
Post subject:  Re: Vacuum Press - I quit!!
I've been vac clamping for years and have come to a few conclusions along the way.
MDF, plywood, whatever has to be sealed to beat the band. I mean saturated with epoxy to seal it up. I had a 4' x 8' press at one time for veneering table tops that could pull 17" with a pump only capable of 20".
For a smaller press, such as what's required for guitar bracing, etc. laminate 2 pieces of corian together and then rout the escape channels directly into it. I've also heard of laying a piece of screen door screen under the top/back to provide escape route for the air.
Hinges will have to be of the engineered (adjustable) variety to seal properly along the hinged edge. Better to use a fairly resilient hinge and clamp shut on all 4 sides. If you're going to be using it allot consider a d-staco type latch. Fumbling with clamps with wet glue going is a drag.
The frame holding the membrane must be rigid. Metal is good.
Weather stripping should be of the closed cell variety, and preferably the smooth faced rope kind that fits into a groove like the stuff lmi sends with their circular vac body holder jig. Look in your phone book under gasket materials.
The west systems people have a whole variety of sealants, membrane, etc.
http://209.20.76.247/ss/price-list/ (scroll down to vacuum bagging materials)
These people are great too:
http://www.vacupress.com/

-C
Author:  BobK [ Mon Dec 29, 2008 7:30 pm ]
Post subject:  Re: Vacuum Press - I quit!!
FWIW,

Here are some pics of mine.
Author:  Chris Paulick [ Mon Dec 29, 2008 8:13 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Have any of you tried painting your frames with a epoxy paint to seal it? Down here in tampa there is a Pilgrim Permacoat epoxy paint that I used to paint over plywood when making an aquarium from plywood with a glass front. Never had a leak.
Author:  peterm [ Mon Dec 29, 2008 9:00 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Chris Paulick wrote:
Have any of you tried painting your frames with a epoxy paint to seal it? Down here in tampa there is a Pilgrim Permacoat epoxy paint that I used to paint over plywood when making an aquarium from plywood with a glass front. Never had a leak.


That sounds like a good idea... wonder where they sell that.
Author:  j.Brown [ Mon Dec 29, 2008 9:18 pm ]
Post subject:  Re: Vacuum Press - I quit!!
I'd love to see more photos of some of your setups.
-j.
Author:  Chas Freeborn [ Mon Dec 29, 2008 11:44 pm ]
Post subject:  Re: Vacuum Press - I quit!!
No no, the corian is the base / platten. It gets the grooves routed into it to allow air to escape, and a groove that's at the perimeter to hold the weatherstrip rope. The metal frame is hinged to the rig and has the membrane affixed to it.
I don't have one set up that way now, as I'm using a bag, but I could draw it up.
BTW, I assume we're talking about a bench top vac rig for bracing, etc, and not a little frame for gluing bridges, etc.
The advantage of corian it isn't permeable, so you don't have to seal it.
Drawing attached is a cross section. The grooves form a grid pattern when viewed from above.
-C
Author:  Brock Poling [ Tue Dec 30, 2008 8:02 am ]
Post subject:  Re: Vacuum Press - I quit!!
I had a thought.... what are you using for a base? Could you be getting leakage from the substraight you are connecting to (i.e. porous?)
Author:  Chas Freeborn [ Tue Dec 30, 2008 12:29 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Yes, Brock that's the likely cause of the troubles. Hence the corian recommendation.
Even with a ply or mdf substrate that is fully sealed if you ding a corner or scratch the surface it'll begin to leak. Corian is consistent throughout and air tight.
-C
Author:  Bob Garrish [ Tue Dec 30, 2008 7:07 pm ]
Post subject:  Re: Vacuum Press - I quit!!
A piece of melamine shelf stock (it's like $10 for a 2'x4' piece at the building supplies place) works fine as a base and seals well. You can't groove it, of course, but there are ways around that.
Author:  peterm [ Thu Jan 01, 2009 11:55 am ]
Post subject:  Re: Vacuum Press - I quit!!
Bob Garrish wrote:
A piece of melamine shelf stock (it's like $10 for a 2'x4' piece at the building supplies place) works fine as a base and seals well. You can't groove it, of course, but there are ways around that.


So, I sealed everything real well with epoxy and now the press is pulling almost 20 inches. (about 17) I'll have to do a try run and see how much squeeze out I get out. I would like to get 22-25" but can't get it...
Author:  Chris Paulick [ Thu Jan 01, 2009 1:06 pm ]
Post subject:  Re: Vacuum Press - I quit!!
Is this correct or not? I once read that the most pressure you can get from a vacuum bag or a frame is really only 15 psi. because what is happening is all the air is being removed out of the bag or under the frame so you have the atmospherical pressure applied to it which is 15 psi. and to increase that the bag would have to be in a pressure chamber where the ambient pressure is higher then 15 psi. So then the inches would apply mostly to holding suction something like the guitars weight being held to one of the vacuum vises.
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