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Cumpiano workboard and vacuum clamping
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=27004		 Page 1 of 1
Author:  John A [ Thu Apr 15, 2010 9:59 pm ]
Post subject:  Cumpiano workboard and vacuum clamping
HI everyone,

I am thinking about gluing my braces with a vacuum clamp. But I do not have a radiused work board. I was planning to use the Cumpiano work board, which is flat, and uses a cork shim all the way around to create a slight dish in the middle. The braces will be arched. Will this work with my vacuum press ? or do I need a nicely radiused board ? I am building a classical. I figured I would skip all the cam clamps and the go bar deck and go straight to the vacuum clamping - bad idea ?


Thanks
John
Author:  JohnAbercrombie [ Fri Apr 16, 2010 1:04 am ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
John-
I've used vacuum a bit for laminating sides and also gluing a couple of bridges, so I'm no expert on vacuum clamping braces.
However, you should keep in mind that the vacuum will be causing the atmosphere to press down on the entire soundboard (not just the braces) with something like 14psi. I would be concerned about doing that to a soundboard that was supported at the edges.

The other thing to note is that glue squeezeout is a lot trickier to clean up with a vacuum setup. I much prefer go-bars or some type of clamping setup to vacuum if squeezeout is an issue. I used the vacuum for the bridges partly as an experiment.

Vacuum is great for gluing up panels, laminating sides, etc where there is a lot of flat surface that needs pressure.

Cheers
John
Author:  stan thomison [ Fri Apr 16, 2010 9:14 am ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
I would probably do a radius dish of sort. I would think if have something with some give in it to let the back press into and the braces with a radius should work, but never have tried that.

I used to use go bars for this, but since 05', I have been using vacuum. I disagree with the idea harder to clean glue squeeze out. Let it run in the press (I don't know if using a compressor and about 13-15 psi or a AC unit running at 18-22 hg) I use a AC unit. Anyway after about 15 minutes can take it off the vacuum and use a chisel to clean. By that time the glue is hard and cleans fast and clean. If want can put it back on the vacuum. That is way we did it at Bourgeois. I let mine dry about 20 minutes or more and then clean and voice. I let it run longer only because I take a break or get involved in something else in shop and forget it for awhile. I have never had a brace failure.

I won't go back to go bars unless my pump or have problem with frame at some point, but have extras for those situations. For me it easier, faster, and cleaner with vacuum. But that is me and how I look at it.
Author:  JohnAbercrombie [ Fri Apr 16, 2010 11:58 am ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
stan thomison wrote:
Anyway after about 15 minutes can take it off the vacuum and use a chisel to clean. By that time the glue is hard and cleans fast and clean.


I think this goes to show that if you are skilled enough (like Stan), you can use any technique you want.

I've never had much luck getting hardened glue cleanly removed without scraping up the wood surfaces. I prefer to use the 'sharp stick' to just scoop up excess glue squeezeout while it is still wet, followed by a slightly damp paper towel. By the time I release the vacuum, the glue (usually fish glue or LV2002) is rock hard and really sticking to the wood. Releasing the vacuum 'too soon' finds the glue joint separating in some cases, for me. Obviously, I've got a lot to learn.

Cheers
John
Author:  Jeff Highland [ Fri Apr 16, 2010 3:09 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
Using the vacuum clamp without full support by a radius dish will distort the plate and probably give you a sloppy glue joint with the braces.
Author:  Ken McKay [ Fri Apr 16, 2010 5:43 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
I would certainly give it a try. Do a dry run first to see of everything looks good with no gaps.

Another way to glue braces that is very effective and quick is to radius the brace the way you want it, put glue on and tape it in place on the plate. Put bleeder cloth around the plate making sure the bleeder extends to the evacuation port, (nylon screen works fine). Now slip the plate into a bag without a caul and evacuate the air.

Trust me it works fine. You can also glue on peghead veneer, fingerboards, and many other things this way.
Author:  JohnAbercrombie [ Fri Apr 16, 2010 6:11 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
Ken McKay wrote:
Another way to glue braces that is very effective and quick is to radius the brace the way you want it, put glue on and tape it in place on the plate. Put bleeder cloth around the plate making sure the bleeder extends to the evacuation port, (nylon screen works fine). Now slip the plate into a bag without a caul and evacuate the air.


Yup! [:Y:] that would definitely be a lot better than having the soundboard on a dish which didn't fully support it.
Author:  John A [ Sun Apr 18, 2010 7:21 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
Ken McKay wrote:
I would certainly give it a try. Do a dry run first to see of everything looks good with no gaps.

Another way to glue braces that is very effective and quick is to radius the brace the way you want it, put glue on and tape it in place on the plate. Put bleeder cloth around the plate making sure the bleeder extends to the evacuation port, (nylon screen works fine). Now slip the plate into a bag without a caul and evacuate the air.

Trust me it works fine. You can also glue on peghead veneer, fingerboards, and many other things this way.



Sounds interesting - I lie the idea of using a vacuum, although I can make a clamping jig pretty easy or even a go bar deck.
DO you have pic of what you describe ? What is breather cloth ? is that just nylon screen that you would use for windows ?
And as per the Cumpiano directions I would be radiusing my braces.
Author:  Ken McKay [ Sun Apr 18, 2010 7:46 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
If you curve the braces rather than press them onto a curve, this technique will work. No, I don't have a picture handy but have done this for many different kinds of gluing operations including double bass sized back.

If you already have a bag then it is a no brainer, if you don't then you will need put a little up front $ to get a decent bag. The poly bag from JoeWoodworker is great as are some other companies like Quality Vacuum products and others. Yes bleader cloth is just window screen, nylon type. Make sure the bleeder prevents the bag from sucking closed anywhere from the plate to the evac hole. It is easier than you might imagine. Give it a try. The skateboard makers even have a hand pump that looks like it would work fine.
Author:  JohnAbercrombie [ Sun Apr 18, 2010 8:39 pm ]
Post subject:  Re: Cumpiano workboard and vacuum clamping
John A wrote:
What is breather cloth ? is that just nylon screen that you would use for windows ?

Nylon window screen works fine.
You can also 'make do' with garbage bags for vacuum bags for experiments, though of course you can't see through them which is an advantage with the clear, heavy bags. Since a garbage bag won't have a flange fitting for the hose, just put some mastic or putty around the hose to help seal the bag to the hose. Tape it closed. Consider the garbage bags one-use only - they still work fine for garbage after the vacuum thing- though the top is usually messed up with the tape and mastic residue...
Really, for braces I'd go with the go-bar or clamps.....if you want to mess with vacuum you could laminate some sides...

Cheers
John
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