Vacuum bridge clamping

Pegasus Guitars

Pegasus Guitars

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I posted this on a guitar building forum, but thought there might be some experience here too. Just wondering whether to continue vacuum bridge clamping. When I vacuum clamp veneers in a large bag, my vacuum system quickly evacuates the air and shuts off. It will stayed sealed for at least a half hour or longer before the vacuum pump starts up again. When I vacuum bridges my pump never shuts off. It hovers around 22-23# of vacuum. The noise is annoying and I'm not sure the clamping results are any better than just using regular clamps. I've never really had any trouble with bridges coming off using my regular clamps, but the vacuum set-up is a little less dangerous. No clamps to fall over on the top or come loose. Just wondering if others are able to get the vacuum pressure high enough for their pump to cycle qnd shut down. I definitely have more line connections on my bridge clamping system, but have not been able to find obvious leaks. Thanks, Bob

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Aaron,
I built that same Joe Woodworker system a few years ago. I mainly use it to veneer the tops of my lap steels in a vacuum bag. It's a winner. I love the system. I've tried a few times, unsuccessfully to make bridge clamps for guitars and ukes. I have an official (read expensive) uke bridge clamp, but just have not found out how to make the system airtight. I noted your use of silicon as a sealant. Probably was in Joe's instructions, but I never saw it. Sounds like he next thing to try. Only thing with Joe is that he is merciless on the shipping cost. I had to buy a new gauge last month. $13.00 for the gauge and $16.00 for the shipping! He won't use flat rate. Take care1-Bob
 
I think the leakage is through the thin tops under the bridge where there is no finish, acting like a very fine filter drawing tiny air bubbles into the glue...Just a theory ;)
 
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I use clamps with a cardboard mask to protect the top. I cannot stand the constant noise from the compressor even though it is in another room. And then there is the clamp on clamp off performance with squeeze-out.
 
For all my guitars and ukes I use shop made Stew-mac style bridge clamps. Works great. If the vacuum would work the way I want it to, I think the constant, even clamping pressure would be better. Since I use it a fair bit for other shop projects, I like the technology and am challenged to make it work. My vacuum pump is not too loud, but still can be annoying after an hour of so. During normal vacuum use it shuts down when the desired amount of vacuum is reached and cycles on and off very little. For most projects, I do the vacuum clamping outside my dehumidified work space, so the noise issue is not relevant. Bridge clamping I do inside my dry workspace. Aaron, your theory is possible. I've had my vacuum system suck air through 1" solid mango and let loose! Certainly does not work good on porous surfaces and works best on surfaces with a finish on them.
 
I set my bridges with two holes drilled in the saddle for pickup installation, and a pvc rod to hold it in place while gluing. When I vacuum clamp the bridge, a piece of tape to cover the saddle slot is enough to hold the vacuum.

Also, I use 315 HHG on the bridges. Clamp for a few minutes, pull to cleanup, then clamp for another 15 minutes, and let it dry overnight. I actually did a test after 20 minutes of vacuum, and the “bridge” pulled away the “top”, meaning, the glue joint didn’t fail. I STILL let it dry overnight.
 
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My first guitar had me building equipment also. Although it is a short scale instrument at 22" it is a steel string guitar. Low buck method, funny it even worked. Plastic food wrap, masking tape, tubing and a vacuum cleaner. Doubt I got more than a couple of inches vacuum, stuck the bridge on. Guitar is almost ten years old. Cam clamps do not give all that much pressure spread out over the square area. If you could maybe set the vacuum set point lower that the pump does not kick on as much?

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Printer- That is an interesting take on vacuum clamping! If I run the vacuum up to 22-23# and turn off the pump, the pressure drops within 20--30 seconds or so, so setting the pressure on/off switch lower won't help. I tested the system yesterday with a bridge on plastic and the pump cycles just as it should, so the leak is through the top somehow. Still working on it.
 
Hey Bob. Just off the top of my head, in your case would it help to have a vacuum clamp that has a radius the same as your ukulele top?
 
My vacuum clamp works just fine on the back, which has a tighter radius than the top, so the radius is not the issue. Good question though.
 
Pegasus Guitars said:
Printer- That is an interesting take on vacuum clamping! If I run the vacuum up to 22-23# and turn off the pump, the pressure drops within 20--30 seconds or so, so setting the pressure on/off switch lower won't help. I tested the system yesterday with a bridge on plastic and the pump cycles just as it should, so the leak is through the top somehow. Still working on it.
Click to expand...

Within that time period I would say you need to look for your leaks. I used to work for a place that autoclaved parts for the big airplanes, not sure if they would approve of my methods but then again that might be why I was in maintenance rather than production. At the time I was just winging it, now days if I saw something like that with no experience doing it I would raise an eyebrow.
 
Kekani said:
I set my bridges with two holes drilled in the saddle for pickup installation, and a pvc rod to hold it in place while gluing. When I vacuum clamp the bridge, a piece of tape to cover the saddle slot is enough to hold the vacuum.

Also, I use 315 HHG on the bridges. Clamp for a few minutes, pull to cleanup, then clamp for another 15 minutes, and let it dry overnight. I actually did a test after 20 minutes of vacuum, and the

Well that didn't work, got truncated. I was asking what 315 HHG is, as I've never heard of it before and Google isn't helping. Thanks.
Click to expand...
 
As soon as I finish my current projects, I plan to return to the bridge vacuum clamp issue. I would be interested in seeing, or getting a description of, any shop made vacuum bridge clamps that you have that work. Enjoy your building. Thanks, Bob
 
Pegasus Guitars said:
As soon as I finish my current projects, I plan to return to the bridge vacuum clamp issue. I would be interested in seeing, or getting a description of, any shop made vacuum bridge clamps that you have that work. Enjoy your building. Thanks, Bob
Click to expand...
Bob, from 2:28 in the vid I posted, you can see the jig I made, super simple. Its a 3/4” plywood frame, with bladder material from LMI wrapped and stapled on the top, and a tire valve with cross slots cut into it with a hacksaw. There no “seal” per se, and the bladder itself sticks to the finish of the instrument. Honestly, I saw Joe Souza’s vacuum setup, and all of his bracing jigs work similarly, with the bladder sealing directly on the UHMW bases (he has vacuum plumbed in the from the bottom). My brace jig is similar to the bridge jig, with a tire valve through the bladder, just a lot bigger. Bladder against the base is the key - less places to leak/fail.

Hope this helps.

F5DFB671-7160-449E-93A6-26BAEA7773D4.jpg788750F9-F960-44E5-9492-48FF7EDA578E.jpg
 
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