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PostPosted: Mon Jul 24, 2017 4:02 pm 
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Cocobolo
Cocobolo

Joined: Fri Mar 16, 2007 7:42 am
Posts: 112
Location: Canada
Hey folks

I have a cedar top steel string with a cracked bridge and there's also a crack running through the holes of the bridge plate. I took the bridge of this morning. I thought I had enough heat to soften the glue joint but it turns out I split alot of cedar. I looks kind of chewed up there. gaah I'm kind of hoping I can level the surface as best as possible and just glue a new bridge on there, but I'm open to advice on this.

I don't want to try to take the bridge plate off. After the bridge I don't think I have it in me. What do you think about a maple overlay, grain running parallel to the top grain? What thickness maple would you recommend? I'd run it to back edge of the bridge plate, but how much should it go front of the bridge holes?

Feeling a bit over my head right now :oops:

Thanks for any advice,

Stefan


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PostPosted: Mon Jul 24, 2017 7:35 pm 
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Koa
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Location: Durango CO
First name: Dave
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I'd focus on the bridge first. The bridge is going to be doing the work here. The plate crack is less relevant. It looks like most of the torn wood is on the forward edge and there is lots of acreage of finish to remove along the back edge. thast's good. It should be ok with a good glue joint provided you clear the finish under the entire bridge and don't slice fibers at the back edge.
I'd make a new bridge, rift cut, with grain not exactly parallel to the pin holes. maybe an extra 1/32" of width on the back if your really nervous. Cedar needs extra surface area.

Clamp the bridge in place and score very carefully around the outside of the bridge and remove all the finish to the score line.
There are lot's of threads on prepping and gluing bridges on if you use the search function here.

A photo with a very low angle light would illustrate the situation better.


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PostPosted: Tue Jul 25, 2017 4:59 am 
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Old Growth Brazilian Rosewood
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Joined: Fri Nov 02, 2007 9:49 am
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Location: Ann Arbor, Michigan
First name: Hesh
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And after doing what Dr. David F. prescribed for the top side you can make a bridge plate cap. Maple is a decent wood, flat sawn is fine approx. .065 - .085 thick 3/8" longer on each end than the pin hole spacing. Bevel the edges. Glue, clamp, ream strum. I drill the holes in the cap before installation and buy 3/16" plastic rod stock for locating pins that are pulled when I snug down the cap. After gluing drill with a 3/16th" drill and ream for your pins, likely 5 degree.

If the bridge plate is actually split or has a physical crease in it and not just worn pin holes a cap is insufficient and you may be into replacing the bridge plate. By the way this is what cheap, mass produced plastic bridge pins can do to ruin a guitar and why unslotted pins are superior. Alverez?


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PostPosted: Wed Jul 26, 2017 11:11 am 
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Cocobolo
Cocobolo

Joined: Fri Mar 16, 2007 7:42 am
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Location: Canada
Thank you guys for your advice.

Hesh, yes this is an Alverez. The md60

After photographing the bridge plate with my cell phone camera I think I may have been wrong about it being cracked. Originally it seemed bent, the bend running through the holes, but I think now that is simple due to the radius of the top. Also, the bridge plate was finished with a thin layer of lacquer but had pores or grain texture running parallel to the holes. I think I mistakenly took the textured groves to be a crack. I sanded it is smooth as I figured I was going to glue a maple cap. Although perhaps this has obscured a crack?

I feel like I should I should patch the top with spruce where the worst of tear out out is, especially left of center. What are your thoughts on this?

I thinking of making a more traditional belly bridge to replace the original. The plan shown in the photo below is from Kinkead's book "Build your own acoustic guitar". One thing of note is that the string holes on the Alverez guitar are almost 0.25" further back from the saddle than the one shown in the Kinkead plan. The Alverez bridge is only .11" thick where the string holes are, so it still had a sufficient string break angle. But I'd like to make the bridge a bit thicker for strength. However, if I make a thicker bridge with the same hole location it will result in smaller string break angle over the saddle.

Some ideas I've had are:

1) plug the holes in the spruce top, make a bridge according to the Kinkead plan and re-drill when its joined on the guitar. But if I don't end up replacing the bridge plate it will suffer from having another set of holes in it, bridge plate cap maybe?

or 2) drill the holes in the new bridge so they line up with the original Alverez holes. Recess the top of the bridge just around the holes and cut groves for the strings to pass through on their way up to the saddle.

Much thanks for the advice you guys have given so far. I'm feeling better about this repair now,

Stefan


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PostPosted: Wed Jul 26, 2017 11:18 am 
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Cocobolo
Cocobolo

Joined: Fri Mar 16, 2007 7:42 am
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Location: Canada
Here's another picture of the bridge plate


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PostPosted: Wed Jul 26, 2017 12:39 pm 
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Old Growth Brazilian Rosewood
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Hey Stefan, happy to help.

The plate looks better than I suspected and you could cap it or not IME. I cap when the pin holes are so worn from slotted pins that the string balls are starting to migrate upward through the holes. If when a 3/16" drill bit is inserted in the holes if there is not much wiggle room no need to cap. If there is then cap.

The saddle location will be key to this guitar ever playing in tune all the up and down the neck again. I speak of intonation. If a substitute bridge moves the saddle 1/4" that's huge and will destroy the instrument's ability to play in tune.

No insult intended but this is not a rare or valuable instrument. When there is less than the ability to have 80% wood-to-wood gluing area under the bridge AND "when appropriate for the instrument..." epoxy is an option for regluing a bridge. Titebond, hide glue, fish, etc are not gap fillers making epoxy a good choice again when appropriate for the instrument.

On FRETS.net Frank Ford's excellent site he has a pictorial tutorial of how he removes a "scoop" of the top and then glues a new scoop back in place. It's a very good fix but only again.... when appropriate for the instrument.

In this case if you have to mess with matching finish or doing any refinishing at all the scope creep of the project makes it not worth pursuing in any commercial sense. For experience and fun it's a different story I understand and can appreciate.

If it were me I would enlarge the bridge foot print of cleared finish to close to .010" from the bridge perimeter all the way around. I could clean up the bridge bottom on a belt sander and then use a single edge razor blade as a scraper to refine the fit to the top distortion. I like to clamp a bridge when minimal pressure is required to get it down everywhere requiring some careful fitting. I'd make a masking tape well for positioning and ease of cleanup since you can only use water with epoxy and then use a quality epoxy (West Systems, System III, etc) wetting both surfaces and glue the bridge back on.

Epoxy is thick, dampening, and ugly with thick glue lines but it will fill voids and does not have the same dependencies on perfect prep and surfaces that other glues have. Epoxy is not a good choice but it is an appropriate choice for inexpensive instruments with enough top damage to warrant perhaps not fixing them at all......

We repurpose donated guitars for homeless folks and have found that epoxy does well living outside in Michigan's winters. I just wish that no humans had to do that......

While you are at it how's the neck angle, this beast is old enough that it may need a neck reset.

Lastly there are about three approaches to this one that I can think of. None of them is more correct than the other and they all basically suck in some way. Or, in other words like many repairs there is always more than one way to go about it.


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PostPosted: Wed Jul 26, 2017 1:22 pm 
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Koa
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Location: Durango CO
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If your not bound to the Alverez bridge design I'd definitely ditch it. Regardless of the implications to the pin placement.

Even if there was a crack in that plate I wouldn't replace it. If you struggled to get the bridge off cleanly, getting the plate out, especially on cedar I see as an unnecessary roll of the dice. A good bridge and a plate cap, grain running north/south, should be plenty.

Make sure the saddle location was correct originally. Frequently they are not and I've seen quite a few bridge replacements that just duplicated the error.

Do you know how the neck set was under string tension? if it was bad, would you reset it or correct it with the bridge thickness/ saddle height? This may be relevant to break angle and pin location.

I laminate spruce/maple(ebony in the pic's) sandwiches and cut plugs from that. Probubly not necessary with a cap.
I like to use a tapered reamer to clean up and taper the pin holes. I glue the squares to a dowel and spin the square plugs on a drill against a disc sander. Judging the taper by eye is surprisingly easy and allows a squeak fit of the plugs.

I'm pretty sure I have photo's of filling top voids with spruce but I'll have to dig for them.

Hide glue for plugs and top inlays ensures a good glue bond with the bridge.

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PostPosted: Tue Aug 01, 2017 12:22 pm 
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Cocobolo
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Joined: Fri Feb 18, 2005 6:18 am
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First name: Frank
Last Name: Ford
City: Palo Alto
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Zip/Postal Code: 94301
Country: USA
Focus: Repair
Status: Professional
A bridge that thin at the pin holes is absolutely weaker and more prone to cracking than a heavier one. Too many folks underestimate the bridge plate's role in preventing such cracks by keeping the area flat.

So, without any question, I'd overlay the bridge plate with a maple cap, GRAIN RUNNING PARALLEL TO TOP GRAIN, for the simple purpose of avoiding the bending that caused the cracks in the first place. Thickness? About a tenth of an inch is appropriate, I think.

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Cheers,

Frank Ford

FRETS.COM
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PostPosted: Fri Aug 04, 2017 6:06 am 
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Cocobolo
Cocobolo

Joined: Fri Mar 16, 2007 7:42 am
Posts: 112
Location: Canada
Thanks again for the advice.

One question about inlaying to repair the gluing surface. Is it ok to route out a rectangle, say 1" by 1.5", glue in a corresponding spruce rectangle then level with the top? This would mean edges of the inlay pocket meet the top perpendicular to the surface rather than at a shallow angle as would be the case in the scoop method described on Frank Ford's website.

The top has also been distorted, the bellying is a almost a sharp bend at the back of the bridge plate so that the entire bridge footprint is tipped forward. I don't think its bad enough to need a neck reset, however.

Stefan


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