bridge r&r

[Matt Atkinson]

I am working on a friend's 1970's Martin D35.  There are a number of issues including the need for a neck reset, a B string pickguard crack, a very badly place bridge and a concave top.  I have pulled the neck and adjusted for the reset.  The saddle was only 1/16" above the bridge and action was high.  Also the bridge had been shaved down.  I have also removed the bridge and will replace it and fine tune the neck reset to it.  The bridge appears to have compressed the spruce beneath it (?) or perhaps previous work scraped a little too much away?

 

 The scratch line is how far back the new bridge has to go!  Also maybe you can see how deep the pocket is where the old bridge was.

Question:  Can I glue on some top wood fit to the old footprint, level it to the finish, and then glue on a new bridge?

Also the top is slightly concave.  I am humidifying it with sponges inside open baggies and the soundhole covered.  Hoping it comes up at least to flat.  Suggestions if that doesn't work?  

 Thanks for looking.  Advice appreciated.

[Glen Choitz]

I don't work as a luther, but have been doing guitar repairs for a long time...so take my words as non professional but what has worked for me....and may or may not be the 'right' way to go about this repair..

I would level the area where the bridge sits and use a thicker bridge to make up the difference...but I have heard of people adding in a piece and then leveling to the top before setting a new bridge..Either way seems to accomplish the same goal, so I would choose the less likely to damage the surrounding area, finish etc.

Something I have had luck with in top repair is to cut a polystyrene block (same stuff those cheap coolers are made of) just slightly smaller in height than the sides of the guitar minus any braces, or bridge plate, at the bridge area or wherever the concave section is and then using it as a mild jack while humidifying...Place under the section you wish to raise, firmly but not so much as to force the top up. You just want to encourage the top to move back into position..not force it. The springiness of the foam will help move the top as the humidity adds moisture to it...let dry in that position and then remove the block. If not enough, add a shim under foam block and do it again..

This has worked for me...

Glen

[Matt Dreher]

 

i cant tell from the photo, but if it is a slight impression, i believe the glue will fill the gap with no problems. if you don't think that will do, have you considered that you could shape bottom of the new bridge to fit the indentation? I am not a big fan of laminating a piece on top, but i then again i have not tried it. 

As far as the top being slightly concave, check if the braces are good and not loose. If they are good, then a solution i have used is to get a board that is slightly cupped and clamp it to the top (cup face down) with sound hole clamps while humidifying. this sometimes is all it needs. If it does not work you could pull the existing bridge plate and put in an oversized plate and repeat the process with the cupped board while the glue dries. a new bridge plate may also remedy the first problem as well and bring it level.

[onewent]

Matt, one thing to clarify with your customer: will he or she accept a larger bridge than original?  Sounds to me like the plan is to cover the 'witness' mark of the old bridge, while also moving it back an eighth or so to adjust saddle/intonation, resulting in an oversize bridge than original, correct?

Vintage guitar owners are really (accent on the really) fussy about bridge dimensions.  It can negatively effect value.  D-35s are effected by details like this these days.  Maybe you've already discussed this with your customer?  

Also, is the top concave (sinks in I assume) between the bridge and sound hole?  Seems odd to sink below the bridge.

Tom

[Matt Atkinson]

Thanks all. The guitar belongs to a friend. He is not overly concerned about preservation and just wants it to play well. I will probably buy it from him anyway. I don't care for an oversized bridge and was planning to repair the finish as needed around the bridge. I am leaning towards gluing down some spruce and then leveling it off and replacing the bridge at its typical size. Thanks for all the helpful advice. Great forum.

[Russell Vance]

Hi Matt,

Rebate the edge of the replacement bridge so you get good contact with the bridge and the top.  Clean up and flatten the top and glue on the new bridge with appropriate clamps.  Any attempt to "fill the gap" with glue will likely result in a poor glue joint and encourage failure of the glue.    

The compression you talk about is probably an original or subsequent scraping to get the lacquer off the surface of the spruce to get good adhesion and unless it is such a depth that structural integrity is in question I would not think about an additional shim/filler strip.

Regards,

Rusty.

[Matt Atkinson]

Yes!  I had not thought of a rabet (UK vs USA).  I will certainly do that.  I was just now thinking of the visible line between the spruce shim and the top where it would be exposed by the relocation of the bridge.  Thanks!

[Andrew]

Just be aware that such a rabbet will make future bridge removal more difficult should it be necessary - although you dont have much option and this is likely your best bet. You could also chamfer the bottom edges of the bridge so you get good contact of the mating surfaces. This should make the joint easier to get at with a removal knife - but it will be a bit more visible, and if the bridge sits low enough in the recessed area joint access will be difficult either way so the chamfer becomes moot. Six of one, half dozen of the other.

Also be aware that you would have been better to adjust the neck set after sorting out the humidification/concavity/bridge location and level, since you could be effectively changing the plane of the top relative to that of the neck. You should be fine, but after all that is done, double check the set before reinstalling the neck in case final adjustments are required.

[Howard Klepper]

1.  Don't fine tune the neck set to the bridge; set the neck first, taking account of what the bridge height will be, and fine tune the bridge set to the neck if needed.

2.  What it looks like to me is not that the whole area under the bridge is recessed a lot, but that the scribe line around the back of the bridge is overly deep.  If that is so, then you have no need to add wood--your new bridge can bridge the scribe line.  I would think that this is from a prior reset of the bridge--it doesn't look like original Martin work.  In any case, do not fill a gap under the bridge with glue.  If the whole area is recessed by much, add wood.  But it's impossible to tell the depth of that and how much is finish thickness from the photo.

3.  Don't make an oversized bridge that runs from the front line of the old to where you have scribed the back line.  Use a standard size and then a retouch and lacquer fill in front, or possibly a wood fill first if there is wood missing.  It will be easier to do the lacquer work before you mount the new bridge.  I would clear the lacquer to the back of your bridge rather than rabbet the bridge; you are in any case not going to have the cosmetic perfection where the lacquer disappears under the bridge as with a new guitar, and that is a lot of bridge to have glued only to the lacquer, which is about the same as not glued at all.

4.  Concave top is worrisome, and I do not think high humidity is a solution; what happens when the humidity goes back to normal?  If it stays concave at a room humidity in the 50% range, more work is needed.  Check carefully for loose or cracked braces.  If they are OK, I would replace the bridge plate--something you may want to do anyway, even if your top doesn't stay concave-- since you have the bridge off, and  it can improve these 70's Martins a lot.  Glue the new plate (a smaller maple one) in with a slightly convex caul.

[Paul Breen]

70's Martins are not Martin's best years. I believe that your bridge has never been off before and what you call compressed wood, is a result of heavy handed toothing chisel work, by Martin.

Here is an example, a 70's D 28.

Bridge came off clean and you can clearly see the marks from a toothing chisel and lots of glue!

Here is another.

I have only had one of these so bad that I felt compelled to fill with a Spruce patch. It is a LOT of extra work do a good job of it.

I just clean them up reasonably and don't try for 100% clean, flat wood, that will only lower the surface even more. If I can get 75% or more clean flat wood, evenly distributed, I call it good enough. It results in the bridge being slightly inset and could mean extra finish work if for some reason it failed and it needed to be done again but why worry about it. If a bridge is failing, there will be usually be a place to get your removal tool under it, even if it has been slightly inset.

Use hot hide glue to go back together.

[Matt Atkinson]

Thanks, guys.  I have decided to remove the small step at the back of the bridge and glue the new one in it's own slight recess.  Too damn hard to fit it otherwise.  Paul, that pic you posted is pretty much the same thing.  I added a thin patch over the bridge plate (much smaller) to back up the bridge pin holes and filled them in.  

[Matt Atkinson]

Another question:

The area beneath the bridge is quite flat.  Looking for opinions on whether I should just glue the new bridge on flat or radius the bottom of it and clamp it with a radiused caul.  Thoughts?

[Paul Breen]

Flat caul, no radius.