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.

[Hesh Breakstone]

Sir?  You are making me feel as old as I am Andrew my friend...:)

For us the word is always serviceability.  Be it with people or guitars I never want to do anything that takes any of anyone's future choices from them.  With this said we endeavor to do only serviceable and if need be reversible repairs.  

This likely means no Paslode 3.5" nail gun for attaching bridges...:) although it might be fun to try...

As a builder too serviceability was hammered into me enough that it's all I know now and anything else seems like taking short cuts.

We all know too that there were lots of practices that many very good Luthiers used to do or even still do that are frowned upon these days.  Examples are cutting off the fret board at the body joint for a neck reset....  Even planing down bridges on certain instruments, not all, is not well viewed either these days but it was done likely thousands and thousands of times in the past.

The "California reset" as known in these parts and maybe the "Michigan reset" as known in California perhaps...:) is also a practice that we don't subscribe too.  We were unfortunately a party to a near lawsuit (it was settled out of court) over another service shop having done a California reset on a rare guitar and permanently destroying the instrument.  

For us if results cannot be guaranteed and the complete scope of work is not well defined including a beginning and an agreed upon ending we don't want any part of...

Back to bridges.  If we glue bridges with serviceable glues, do a decent job of getting as much wood-to-wood contact as possible, use best practices with all materials i.e. glue, reading runout, etc AND keep in mind that this may have to be done again someday that's likely as good as it gets at least for now...

One major manufacturer glued bridges on in the wrong place in the early 70's and thousands of them were sold this way.  The cowboy chord players didn't notice it much but others who use the entire neck noticed it early on.  The remedy back then was to replace the bridge and that's an example of a bridge needing to come off before it tries to on it's own.

[Christopher Parker]

Thanks for taking the time to explain your methods! I am anxious to try my hand at rabbiting a bridge replacement or reglue, but I'll probably rehearse on a Yamaha or Kay before trying it on a nice guitar. Occasionally, I'll buy a junk guitar just to use as a guinea pig. This will likely be one of those cases.

A couple of questions: 

It seems like a router table would work at least as well as your dremel setup. Can you think of any reason why it wouldn't? I've got the same stew mac router base, but it seems like a router table would be more stable. Thoughts?

Sometimes I radius the bottom of the bridge slightly to more closely match the radius of the top. And sometimes an existing bridge will already have a radius on the bottom. However, it seems like this would be incompatible with your method of rabbiting the bridge, because the bridge would only contact the bit at the ends. They are usually pretty flexible though. Can you just force it flat while performing the rabbiting operation?

[Andrew]

Hesh, youre sir to me not because of age (although Im "only" 30), but because you're my superior when it comes to guitar stuff. A lot of folks here are sir to me lol.

Specifically, I was wondering your thoughts on later removal of rabbetted bridges. That rabbet could make getting a knife in there tricky.

Christopher, note that Hesh pointed out his rabbetting platform is slightly radiused to accomodate such bridges. That would be a little more complicated to set up on a full size router table. I think a dremel or laminate trimmer would lend themselves nicely to a job this size, and it would be easier to add the radiused platform.

[Hesh Breakstone]

Hey Andrew - Rabbitting a bridge  .003 - .005" deep still lets a bridge come off the very same way.  I got one crooked once and didn't notice until the next day....  Reading the runout I selected a bridge corner, heated the thing, and the spatula worked the same way as for a non-rabbited bridge.

Also what I just described was not a common thing and instead usually when we have to remove a bridge it's because it's already trying to lift on it's own - hence decent access in the lifted areas as well.

[Hesh Breakstone]

Hey Christopher - What Andrew said about the radius on the jig's table, that's going to be trickier with a full sized router table AND I would be a little concerned about having my fingers... anywhere near that much power.  Some bridges can be pretty narrow....

Another issue you might run into and I am by no means a router table expert having never even used one is micro-adjust capability.  Our jig is based on the Stew-Mac router base largely for the micro-adjustability of the product/jig.  This is key to the success of the jig being able to dial in only a thou or two at any time.

Regarding stability sure a full sized router table would be more stable but great stability is not needed here.  The cutter does the work, the RPMs are way up there even with a Dr*mel :) and the work piece is 32 grams give or take some meaning no real pressure is required on anything to get clean, precise cuts.

For bridges with a bottom radius, that's how I build my own guitars, the jig's table is radiused to 25' and that's served us very well with hundreds of uses.

The only concern that really can be a consideration you already mentioned, bridges that taper upward can lose a sliver or two of perimeter.  OTOH though because we are also leaving finish inset under the bridge say .025" inward losing a thou of perimeter should not show or matter.

There are some other advantages but that will depend on if your wedded to how you clamp bridges and what glue you use.  Although the rabbeting does not care how we clamp or what glue it is particularly well suited to using HHG and here's why.

My business partner Dave Collins developed a method for gluing bridges with HHG exploiting the benefits of rabbiting bridges that permits us to when regluing a bridge with HHG have it all in place and clamped down in under 10 seconds.  We have way more time than we need because the rabbit forms and mates with a "pocket" for quick, precise locating (even though I missed once....).  With the addition of some thought as to how to preposition the clamps, preheat the bridge all the drama of using HHG for bridges disappears.  This is also a technique that we teach in our classes.

What results is a bridge that was reglued using approx. 98% of available gluing area, not cutting the finish back to the perimeter making the repair invisible.  The bridge is glued with HHG, our favorite for bridges, and it's reliable and repeatable resulting in a repair that can be reversed or redone if it ever needs to.  

[Andrew]

Im thinking I might make a little adjustable scraping tool for this operation.

[Christopher Parker]

Thanks again for the info! 

[Hesh Breakstone]

You bet!