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  #1  
Old 09-10-2019, 07:36 AM
emmsone emmsone is offline
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Default bridge removal and re-attachment - which glue?

Hello all
Unfortunately the crazy weather this summer here in Switzerland has caused some problems with my number 1 self made acoustic guitar from a few years ago. The crazy up and down heat (it got above 37C IN my apartment at one point!!) and inconsistent humidity has caused the top to belly and the bridge to lift in the centre. I would have been tempted just to fill the gap with glue and be done with it, except that it sounds like there is some glue rattling around under there so I will probably have to remove the bridge and re-glue it just to solve that.

My question is which glue I should use? I originally used Titebond Original to glue it on, i'm under the impression that it does not stick to areas of previously titebonded wood. Is this correct?
Or would Titebond still work if both the underside of the bridge and the guitar top were cleaned up well enough?
Should I go with a PU glue? (unfortunately the PU glue I have is a subtly expanding one, i'm not sure thats the best plan but i'm sure it would hold).
Should I go with epoxy?

I also have to work out what type of jig/system i'm going to use to clamp the bridge down as I would preferably not want to remove my Dazzo SBT pickups but i need to know which direction to go with the glue first.

THANKS IN ADVANCE!!
David
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  #2  
Old 09-10-2019, 07:52 AM
Silly Moustache Silly Moustache is offline
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I had the same issue a few months ago. My tech offered to use epoxy, with the warning that it cold NEVER be separated.

We went with white glue, and all seems well.
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  #3  
Old 09-10-2019, 08:34 AM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by emmsone View Post
I would have been tempted just to fill the gap with glue and be done with it
On any fine instrument, in my opinion, that isn't the correct way to repair it. If the bridge is coming off sufficiently that it warrants re-gluing, then the bridge should be removed, the glue fully removed from the gluing surfaces and then re-glued.

Bridges do come off and removing and re-gluing one is a simple repair.

Quote:
I originally used Titebond Original to glue it on, i'm under the impression that it does not stick to areas of previously titebonded wood. Is this correct?
Yes and no. For large gluing areas, it is true that it will not provide the same bonding strength as Titebond used on clean wood. On smaller gluing surfaces, such as braces that have come partially un-glued, it has sufficient strength, where the alternative of attempting to clean the surfaces back to bare wood would likely compromise the fit of the joint to the point that there would be no strength advantage to removing the old glue. I've successfully re-glued loose braces that were originally glued with Titebond - or similar glue - by adding more glue and clamping. In more than three decades of doing so, I've never had one come loose that was glued in that way.

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Or would Titebond still work if both the underside of the bridge and the guitar top were cleaned up well enough?
The "correct" repair, in my opinion is to do just that, regardless of what type of glue was used. Probably, you don't need to with hot hide glue, IF hot hide glue was initially used, but I'd still remove the old glue and reapply fresh glue.


Quote:
Should I go with a PU glue? (unfortunately the PU glue I have is a subtly expanding one, i'm not sure thats the best plan but i'm sure it would hold).
I'm of the opinion that polyurethane glue probably isn't a good choice for any component in acoustic guitar making.

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Should I go with epoxy?
Definitely not. It's what one uses for a bridge re-glue on a guitar that isn't worth a "proper" repair but you still want to make the thing playable for as little cost as possible.

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I also have to work out what type of jig/system i'm going to use to clamp the bridge down as I would preferably not want to remove my Dazzo SBT pickups
On any pin bridge, I use two 3/16" bolts, one in each of the two E string pin holes. I use a gluing caul inside the guitar against the bridge plate and another on the outside on top of the bridge. Both are drilled to accommodate the two bolts. For the interior caul, you'd probably drill blind holes to accommodate the pickup elements and chisel out as necessary to accommodate the wires.

With the bolts use appropriate washers and wing nuts inside and out. I tighten the wing nuts, rather than use a screw driver that can slip in its engagement with the bolt heads. The inside wing nuts can be held and tightened by hand, the exterior wing nuts can be tightened with pliers. A couple of wooden wedges between the outer caul and the wings on the bridge clamps the wings down.

Wax the surface of the interior gluing caul so that it doesn't inadvertently become a permanent part of your guitar.
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Old 09-11-2019, 01:05 PM
emmsone emmsone is offline
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Thanks for the information Charles!!

As much as i've started down the being totally addicted to building guitars route, i'm yet to really get my head into doing repairs and I was kind of hoping I might not have to do anything here either. But if I do have to do a repair, i would likely undertake it "properly"

If you've ruled out epoxy and PU then that pretty much narrows it down to Titebond. If I can use Titebond here I do feel like thats a bonus, it will make things much easier to manage, plus I already have some. Would you say I need to really slather it on or use it as per normal?

I was tempted to try out vacuum clamping but several reasons are against me there at the moment. 1) is that I do not have nor have access to a vacuum pump. 2) The venturi adapters that would allow me to perhaps used a borrowed compressor are expensive and 3) my last idea to actually use hand pumps has been laughed at by the few people i've suggested it too. Personally i don't see the difference vs the hand pump activated RoaRockit bags that numerous people (and I) use for side laminating as long as the valve on the hand pump is good enough and the seal around the bridge holds but the LMI vacuum bridge clamp would be an expensive experiment if the hand pump didn't cut it.

I had already thought about using a bolt type jig to clamp the bridge on in this instance anyway because it's probably more important now than when the bridge first went on that the bridge holes are where they actually are and line up with the holes in the soundboard. also it would allow me to keep the holes reasonably clean if i just dropped a bolt through the holes even the ones that aren't being used to actually clamp the bridge on.
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Old 09-11-2019, 02:00 PM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by emmsone View Post
As much as i've started down the being totally addicted to building guitars route, i'm yet to really get my head into doing repairs and I was kind of hoping I might not have to do anything here either. But if I do have to do a repair, i would likely undertake it "properly"
You've already performed a variety of repairs while making your instruments.

There isn't much difference between initially gluing a bridge on and re-gluing one, other than the need to remove the old glue and resurface the gluing surfaces.

Quote:
Would you say I need to really slather ion or use it as per normal?
Use a "normal" amount. Excess is only going to get squeezed out and increase the mess.

Quote:
I was tempted to try out vacuum clamping
You can make your own if you are so inclined. You can experiment with a hand pump to see if it is viable. But, don't experiment while trying to glue the bridge.


Quote:
I had already thought about using a bolt type jig to clamp the bridge on in this instance anyway because it's probably more important now than when the bridge first went on that the bridge holes are where they actually are and line up with the holes in the soundboard. also it would allow me to keep the holes reasonably clean if i just dropped a bolt through the holes even the ones that aren't being used to actually clamp the bridge on.
The re-glue is no more important Than the initial gluing.

There are a number of ways to ensure the holes line up. Using bolts is just one method. If you use bolts, apply wax to the length that will be in contact with the glue.

Expect there to be some glue in the pin holes. After the glue dries, re-drill the holes ( 3/16" bit) and then ream them to fit the pins.
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  #6  
Old 09-11-2019, 02:52 PM
Howard Klepper Howard Klepper is offline
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Vacuum clamping cannot ever get you more pressure than the ambient air pressure. And you are not at sea level. Of course, no pump will get you the full ambient pressure--good ones get to maybe 80%. That is far less than the pressure you get from ordinary clamps. A hand pump won't likely get you half of ambient. IMO vacuum clamping is a lot of complication for no benefit in an individual maker's shop. It might be worthwhile in a factory where many guitars are being clamped simultaneously every day, and it could pay for itself over time.

I tried bolts a couple of times. They were the only bridges I have had come loose. The pressure was not where it needs to be, which is in the belly and the wings. You might come up with an elaborate caul that directs the pressure there, but then you are doing more work for the same result you could get from clamps.
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Last edited by Howard Klepper; 09-11-2019 at 02:58 PM.
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