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I recently had a bridge come loose from one of my guitars. It was glued with a fresh batch of hot hide glue. I used a vacuum jig for clamping.
Is it possible that the pressure from the vacuum could have starved the joint and caused the faliure?
How long should the vacuum run for hide glue ups?
Humidity has been addressed and the instrument has been kept from direct heat.

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R.W. '' Rollo'' Scheurenbrand
http://www.koaguitars.com

I also use a vac clamp for my bridges and its my understanding that you cannot over clamp, as its the atmospheric pressure that does the clamping. I.e. remove air to achieve pressure.

Could the glue have cooled and gelled a little before you got it clamped down?

I usually leave my clamp on for 10 minutes then remove it, clean up the squeeze out and then reclamp for 45 more minutes. Then I wait one day to string it up.

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Lance@LuthiersForum.com

Hi Rollo

Was the underside of the bridge or the top completely clean ?

Sould of maybe been something stopping the glue from getting a clean bond ?

Speaking of vacuum clamps for gluing down the bridge, do any of our OLF vendors make one? The LMI version seems a little high priced to me.

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Dave Rector
Rector Guitars

Thank you members, for your replies.

My proceedure is standard: lay out the bridge, scribe around it, then scrape the top to bare wood. So I feel I did prep the surface correctly. I build a tape dam around the footprint of the bridge. It is pretty quick and easy to reset the bridge at that point. And as you know,Lance, it doesn't take much time to set the vacuum.I believe I left the vacuum on for more than an hour.

I finished the guitar in early May. In Late July, the guitar moved from Hawaii to Vermont.

The bridge detached only from the trailing , or back edge. Could there be other things at play here? Drier environment? I do believe the owner has taken care to control the humidity.

Aloha

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R.W. '' Rollo'' Scheurenbrand
http://www.koaguitars.com

I just asked that very question here last week. If you go to the joewoodworker.com website, there is a kit you can buy there for about $130 that you can use to make a vacuum clamp. I plan on buying one very soon.

Cheers!

John

Was the bottom of the bridge sanded to the same radius as the top or was it flat and then you just pulled [or clamped] it into position?

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tim...
http://www.mcknightguitars.com

Tim,
I did sand it to the radius of the top.

I am a little puzzled, and I sure don't want it to happen again. I will certainly be more mindful during the next glue up.

aloha

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R.W. '' Rollo'' Scheurenbrand
http://www.koaguitars.com

John, thanks for the info. I already have a vacuum pump, I was just wondering if there was a less expensive alternative to LMI's bridge clamp. I think I'm gonna just go ahead and order one.

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Dave Rector
Rector Guitars

A couple of things here I should point out...

Frank Ford and Dan Erliwine both actually heat their bridges in a heating blanket before gluing them down to the soundboard, if I am not mistaken Frank even mixes up a fresh batch of hide glue to this step. I've had two bridges pop up and both where because I thought I was scraping wood when in fact I left a super thin film of finish that was hard to see. By heating the bridge you are giving yourself some extra working time with the glue, and with bridges that's very important because with hide glue you want it to have time to penetrate the wood before setting...

That would be my guess is that the hide glue gelled before you finished clamping...

My procedure now is as follows (this is from the school of hard knocks):

1. I use a dremel like Lance and others to route out the saddle area, then use 220 to sand it flat. I want to make sure that I'm actually touching real wood with no finish at all between it and my bridge.

2. I check the fit of my bridge making sure that it seats all the way down, I chamfer the edges until I'm positive that I've got a full seat on it.

3. I usually make a new batch of fresh hide glue, just a little on the thin side.

4. I heat up the bridge and the top with a heating blanket, the bridge gets wrapped at high and a second blanket at medium is left on the top (with a soft cover). On the top my goal is to not have a hot top but just to get it warm.

5. when ready I put on a good amount of hot hide glue very quickly and then place the bridge down and start the vaccum clamp. Because the bridge is hot I know that the hide glue has time to actually do it's magic before gelling...

That's it... I leave it for 10 minutes, then get a q-tip and clean up the squeeze out (you WANT some squeeze out by the way) and re-clamp it for an hour or so. Then I let it dry for a day before stringing it up, once I started doing it this way I've not had one single problem. Also to get a clean edge I now leave brown tape around the edge when gluing (I actually use it when routing as an edge marker), then when I'm done I can carefully scrape any hardened glue with some dental tools without scratching my top, when done I just pull it up...

Hope that helps...

-Paul-

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-Paul-

Patriot Guitars

Paul, thank you for sharing your procedure. I will do as you suggest, although I am hesitant to apply a heating blanket to a finished top. I have not used a dremel to remove the finish. It certainly sounds thorough.

Mahalo and aloha

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R.W. '' Rollo'' Scheurenbrand
http://www.koaguitars.com

I too am new to vacuum clamping, & one bridge I installed has lifted at the back edge very slightly. I have a couple of theories... Any comments or suggestions would be welcomed.
This was an Ebony bridge on a Cedar top, using Titebond.
The bridge fit was was good & the top surface scraped down with no finish remaining.

1) I may not have used a sufficient amount of glue. I did have squeezeout, but it was in tiny balls along the very edge, not a full line of excess glue.

2)As the vacuum is applied, the rubber sheet seals on the finished top. It occurred to me that this seal may have prevented full vacuum from being applied right at the bridge. There is certainly full vac (28.5" Hg) at the edges of the clamp body, but no guarantee that the bridge is under the full clamping pressure indicated by the guage.
On the next bridge glueup, I layed a short piece of soft nylon cord over the bridge, to the inside edge of the clamp body. This leaves an open space to assure that full vacuum is applied evenly across the surface of the diaphragm. Am I out to lunch on this theory???

I haven't strung up the second instrument, so I don't know if I can expect a repeat performance. I also used more glue the second time around & had an even line of squeezout all around the bridge. If this one fails, I'm gonna be pulling my hair out!

TIA,   Dan'l

I made my own vacuum clamping caul.It's not too hard to do I'll post a picture hopefully later.
One tip when vacuum clamping is use some type of fabric to act as a breather or vacuum distribution if you will. This goes between the vacuum membrane and the parts you are clamping and helps to ensure that the vacuum doesn't get choked by the membrane next to the vacuum port.
Hope you can understand my ramblings, it's key to getting even vacuum everywhere.

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Jim Watts
http://jameswattsguitars.com

Thanks Jim;
That kind of confirms my suspicion that the bridge maybe wasn't under full vacuum. I hadn't thought of using a piece of fabric.
Good Idea!

Glad to help. You also might want to put a piece of wax paper between the fabiric and bridge to help avoid gluing the fabric to the squeeze out. Don't ask me how I know this

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Jim Watts
http://jameswattsguitars.com