old Gibson acoustic repair help

[Henry Rancourt]

Hi Mr Ford,

My old gibson has badly worn pin holes in the bridge and bridge plate. I removed the bridge and found it was glued in a recess for the full periphery of the bridge. The surface of the recess was in bad condition...missing wood and way out of flat. I scraped it down a bit and it is now flat within about .003. The depth varies from .030 to .050. The original bridge plate is solidly glued and in good condition except for the worn pin holes. My repair plan is to put a thin layer of a metal filled epoxy in the pin holes and then glue on a bridge plate overlay with the grain matching the top grain. My real concern is improving the structural integrity of the recessed area, since the top is thinned, where the most torque exists. I saw that you used an epoxy made by West System. I called their technical group. Bottom  line is the they said it has a very low viscosity and would wick into the end grain of the recess walls. My thought is that I could fill the whole recess making it flat where the bridge will sit. After it cures I would use a thin layer of the same epoxy to glue the bridge. They told me that the bridge could be removed by using a heat gun and pry it off with a thin putty knife. They also have a slow hardener 206 that has a light amber color. Also heating the 5:1 epoxy mixture and the top wood around the recess would lower the visocity allowing better penetration into the end grain. What are your thoughts on this repair?

 

Thanks,

Henry Rancourt

[Pierre-Antoine Roiron]

I think a picture would be a great help in giving you any advice.

Most of the time, I use epoxy only to glue a thin patch of wood between the top and the bridge. Then I glue the bridge on the patched area using hide glue, because most of the surface is wood. I you want to do it quicker, I guess you could use epoxy to fillthe void and glue the bridge in the same time. I can't see why you would do it in two steps.

Considering the worn pin holes, I would use stewmac tool to plug the areas.

[Gregory Hites]

I see no reason to use epoxy for this repair.  Just my two cents worth.

 

peace,

littleguitargreg

[Henry Rancourt]

One of the the best luthiers working today, and I have discussed this problem a number of times. He believes gluing a shim in the recess will only raise the bridge and, not return the structural integrity of the thinned area of the top, which takes the highest torque from the pull of the strings. He believes the end grain fibers, of the walls of the recess, need to absorb a strong bonding agent and, the wood shim has to fit very well and, also absorb the bonding agent into it's end grain fibers. A bonding agent or glue would also be used between the bottom surface of the recess and the shim. Then the bridge would be glued onto the shim. Any thoughts or other suggestions?
Thanks,
Henry Rancourt

[Joshua Levin-Epstein]

Have the luthier with whom you've discussed this do whatever he thinks is neccesary.He's seen the guitar and "we" haven't.

[Paul Verticchio]

@ Joshua...  +1 (add applause & fade to black).

[Henry Rancourt]

I feel, because of the sarcasm and superiority complexs of some members, it is time to exit this site.

[Ned Knepp]

If you don't mind me asking... What "sarcasm"?  It seems to me that the answers you got are good answers given the information submitted. We don't have access to the guitar. We don't have pictures. We only have your description and your ideas. It's not uncommon for people to start a thread here that addresses Frank Ford directly but this isn't Frank's email, it's a forum that Frank as opened up for our use. If you only wanted to address Frank, posting here isn't the way to do that.

 

Anyway,  in the end it seems to me that you have already determined what you want to do or at least have access to someone that you think highly of that has a plan. If you want it done that way, take the guitar to the man and have it done that way. If you don't want opinions, please don't ask for them. 

[Russell Vance]

Henry, take a chillax pill and listen to what prevails - the Email/forum format is in-personal and often our sentiments and delivery of information can be misinterpreted depending on the readers state of mind or predisposition towards alternative or contrary views.   

Firstly, end grain bonding with glue, especially with a low "butt joint" surface area such as the end of a shim is probably not an optimum solution but, if it needs to be done I would use an expanding polyeurethene glue which is optimised for end grain bonding and has some gap filling properties.  It is very messy to work with and needs good masking (brown plastic packing tape is the go) and a pressure caul to set it off. I would use this glue around the edge of the shim leaving the main surface to be glued with yellow of hide or whatever you choose.

Secondly, West system will wick-in very well but you will need to 'float' a layer to get a good coverage as the WS has no useful viscocity to stiffen the mix and seeps in.   Glueing another layer of epoxy to a sunken and cured>>  previous layer of WS is not an option as this will be a weak joint.  If you wish to bulk up the west system,  mix in some chopped fibreglass mat and glue the whole lot up (including the bridge if necessary) in one process. Use the aforementioned brown packing tape to mask off.

As far as the pin holes go, for a wrecked bridge and bottom plate we just glue everything in place, block off the bottom of the pin bore with a caul and tape (so you dont stick the caul to the bridgeplate) and layer the holes (fill it up gradually) with a mix of ebony/rosewood dust and thin superglue - redrill the holes and ream to fit which gives a cohesive and strong new bore from the top of the bridge to bottom of the bridge plate for the pin to rest in.  Alternatively, you can use some oversized preslotted bridge pins available from Stewmac and ream accordingly if the damage is not too great.

Always more than one way to skin a possum in this business. Rusty. 

[Doug T]

Henry, a picture would certainly help.  Depending on the finish thickness, this .03 may not be much wood actually removed.  There is a lot of good advice here, and a lot of different approaches.  Some guitars are made with a scraped surface that is exactly the profile of the bridge, while some leave a small 1/10 - 1/16" band less than the outline.  I've even seen some where it appears that the top appears to have been refinished heavily with the bridge on and no properly masked, where buildup of finish makes it look like the bridge is sitting in a recessed area removed from the top.  That needs to be assessed carefully.  If you have access to long throat instrument making calipers, you can actually see the thickness at the bridge plate.  If the thickness at the plate is roughly twice the thickness of the top, there's probably not much wood missing.  I've not used the stewmac hole-patching tool, but it looks slick.  That might be all it needs.  Without an inspection of the underside, you won't know exactly how worn the bridge plate is, or if it is cracked.  I hate the thought of using epoxy to glue a bridge, you may use it to fill the holes (if that's your choice) but once it's all leveled and the excess material scraped away, there really doesn't appear to be any need for the bridge to be epoxied.