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| Author: | nickton [ Thu May 05, 2011 11:49 pm ] |
| Post subject: | cracks in bridge |
On my last two guitars I've found bridge cracks between string holes after a few months of playing and am wondering why this happens. Is it my ebony quality or am I doing something wrong? I guess it could be shrinkage. Any thoughts? I hope this picture shows it adequately. I tried drilling holes at an angle thinking it might help but no such luck. (I know my bridge pins don't all match but I drilled each one individually and etched little numbers on them so they stay with the correct hole) ![[headinwall]](./images/smilies/headbangwalluf8.gif "Mad")
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| Author: | Ken Franklin [ Fri May 06, 2011 9:17 am ] |
| Post subject: | Re: cracks in bridge |
It could be that the bridge blank was not seasoned well enough before it was made. I agree with Todd about the need to have good fitting pins and slotted holes. You can always turn your pins around if you don't have unslotted pins. Frank Ford has a good method for replacing your bridge now that it's cracked. http://www.frets.com/FRETSPages/Luthier/Technique/Guitar/Bridges/018Bridge/018bridge.html |
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| Author: | Barry Daniels [ Fri May 06, 2011 9:35 am ] |
| Post subject: | Re: cracks in bridge |
It doesn't look like you countersink the holes. This is just conjecture, but I think a sizeable countersink takes stress off the sharp edge of the hole, which is where a crack probably starts. |
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| Author: | theguitarwhisperer [ Fri May 06, 2011 9:45 am ] |
| Post subject: | Re: cracks in bridge |
That problem is most often caused by shrinkage and is more likely to appear after the bridge is glued down. What happens is that once the base of the bridge is held stable, then the wood can't shrink down as one piece because it is being held in place on each side of the potential crack by the soundboard, and so the bridge splits and each side shrinks away from each other where it is glued down in place. If it were free, it would simply shrink. This happens with unseasoned quartersawn ebony. Also, if you used a lot of glue and/or cleaned up the squeeze out with too much water, then the spruce as well as the ebony swelled up, and when the glue dried the bridge was fixed in place, and then when the woods returned to equilibrium, the bridge cracked. I put a one eighth inch rim of tape around my bridges and put a thin layer of glue on the bottom. Remove the tape and glue it down. If you put JUST ENOUGH glue, it will squeeze to just the edge of the bridge and no further, no cleanup necessary! Another thing that happens is the top domes up, and the bridge stays glued but splits in order to conform to the dome. This type of crack forms a wedge shaped crack. You can remove the bridge, glue it back together, and reshape the bottom of the bridge to the top of the guitar. Or you can make a new bridge and shape it to the dome, either way. It unlikely the bridge pins played much of a role unless the holes were WAY undersized and you were tapping 'em in with a hammer, or REALLY pressing hard, and even then the bridge is unlikely to split as it is being held down by the underlying spruce, unless it wasn't glued down well. If it cracks due to bridge pins, then usually one side of the bridge will become loose as well. In that case you can actually remove the bridge, glue it back together, and reglue it to the top of the guitar again. I've done this hundreds of times with great success. Ream the holes a hair to obtain a good fit without wedging, and no more crack due to loose glue. |
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| Author: | Michael Lloyd [ Fri May 06, 2011 11:15 am ] |
| Post subject: | Re: cracks in bridge |
Something else to consider. I believe is to be the wood as it looks to have the wrong orientation of the grain. I prefer flat sawn with the grain running from end to end length ways. It does appear to be a shrinkage and orientation problem to me. |
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| Author: | Michael Lloyd [ Fri May 06, 2011 11:16 am ] |
| Post subject: | Re: cracks in bridge |
Something else to consider. I believe is to be the wood as it looks to have the wrong orientation of the grain. I prefer flat sawn with the grain running from end to end length ways. It does appear to be a shrinkage and orientation problem to me. |
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| Author: | Michael Lloyd [ Fri May 06, 2011 11:18 am ] |
| Post subject: | Re: cracks in bridge |
Note to self. Clinking the back key generates a second reply! 
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| Author: | theguitarwhisperer [ Fri May 06, 2011 8:47 pm ] |
| Post subject: | Re: cracks in bridge |
Depends on the dome. Ebony can be pretty brittle and split very easily from just a slight deviation. I've seen PLENTY of guitar tops that while having a 25 foot radius overall have a much rounder bubble at the bridge region, sufficient to force bridges off the surface or crack the bridge at the weakest point (the holes, of course!). As far as the split stopping at the holes, the holes are in the thickest part of the bridge. Dome splits don't usually go all the way through and usually stop at about the point where the wings level out, so I can see how the holes would splt without slitting the wings in that case. Also, the bridge wings are more flexible because they are thinner. Why do splits have to go the whole length anyway? They rarely do. I HAVE seen splits where the bridge was only partially glued and the pins(or something) DID split the entire bridge in half, though. This is rare. One more thing, these splits in this particuular guitar are hairline splits, well within the lateral expansion/contraction range of ebony widthwise, especially if the bridge is particularly brittle. Since this is the second guitar that's done this, is the bridge made from the same piece of ebony? Might consider getting a new piece of ebony to cut bridges from.... |
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| Author: | gerry [ Sat May 07, 2011 7:33 am ] |
| Post subject: | Re: cracks in bridge |
I've seen a few discussions on these cracks along the bridge pin holes, but don't recall any mention of what affect the large amount of end grain being exposed by a series of closely spaced holes plays. It must be detrimental. We all know to seal exposed end grain when storing or seasoning lumber to protect against checking and cracking. Might it be a good idea to use a little shellac on a Q-tip or some paste wax to seal inside the pin holes? In theory, the pins themselve might help as a moisture barrier if fitted well enough and of course the guitar should never see such humidity changes . But in reality? Gerry |
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| Author: | alan stassforth [ Sat May 07, 2011 8:53 am ] |
| Post subject: | Re: cracks in bridge |
Interesting. Have you taken all the strings and pins off, an seen if the crack closes up any? My guess is the taper is off. Did you use a 3 degree reamer and use 5 degree pins perhaps? Wood!!!!! Bummer. |
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| Author: | theguitarwhisperer [ Sat May 07, 2011 2:50 pm ] |
| Post subject: | Re: cracks in bridge |
That's a good idea. Take the strings off, the pins, and the saddle out, see what it does. If it closes, put the pins in and see what it does. |
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| Author: | Mike Collins [ Sat May 07, 2011 5:13 pm ] |
| Post subject: | Re: cracks in bridge |
What ever repair route you take make sure you check the bridge plate for cracks also. Mike |
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| Author: | nickton [ Sun May 08, 2011 12:18 am ] |
| Post subject: | Re: cracks in bridge |
thanks for the many replies. For the record I just re-did my frets from 12 to the end, in order to flatten out that hump I had inadvertently made, thus overcoming my fear of re-fretting and hammering on a set neck. Worked like a charm after fashioning a few support blocks for inside the box. Meanwhile I simply wicked CA glue in the cracks and put a couple of clamps on the bridge. Seems to have worked. I also reamed the holes a bit more, made deeper counter sinks, and sanded down the back a bit because it seemed too thick. So far so good. Maybe in a month the cracks will re-appear. Anyways a new set of strings really made a difference in sound. I had thought it was my bracing or too thick a finish. DUH! It sounds to me from all your feedback that I should double check my reamer angles. I have a few of them but don't know if I used the correct one. Again thanks for the help. |
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| Author: | nickton [ Sun May 08, 2011 12:39 am ] |
| Post subject: | Re: cracks in bridge |
A few more thoughts: I was pretty worried about making the fit too loose, so I'd make them slightly small and slowly ream a little at a time. Perhaps I didn't know my own strength and went overboard with a tight fit, not wanting my pins to pop out. And the angles could be off, even though I thought I'd been extra careful. Here are some more pics: I am surprised at how much better it sounds and feels now. Those details really do count. |
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| Author: | nickton [ Sun May 08, 2011 1:10 pm ] |
| Post subject: | Re: cracks in bridge |
Will do. I was trying to get creative with my bridge shape there, starting out being influenced by a bridge I saw in the Sloane book I have. Always wondered about bridge shaping theories. Everyone seems to have different ones, from the curvy design on my Tacoma, to the angled front profile on Petros guitars--which is supposed to counter act pulling down tendencies over time (or something to that effect I think). I think my ebony batch had some problems. There is slight crack on the fretboard extension that showed up too. I got this ebony from a pile at McBeath hardwoods and I think it was discounted but I'm not sure. It was a few years back. |
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| Author: | Michael Lloyd [ Mon May 09, 2011 11:54 am ] |
| Post subject: | Re: cracks in bridge |
1) What is end-to-end lengthwise? Are you suggesting the grain run parallel to the fretboard? No. The grain on the bridge would run perpendicular to the top (Soundboard) grain. I just prefer flat sawn for all woods when it comes to bridges. One less thing to worry about and it’s what I’m use to. |
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| Author: | alan stassforth [ Mon May 09, 2011 10:08 pm ] |
| Post subject: | Re: cracks in bridge |
Lucky puppy, you live close to MacBeaths. I got a decent piece of bearclaw sitka there that's almost used up. Looks like you got a good fix there. Now I'm concerned about my bridge design. I think I'll start a new thread...... Good luck. Alan. |
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| Author: | nickton [ Tue May 10, 2011 3:19 am ] |
| Post subject: | Re: cracks in bridge |
McBeath's is nice, but so is PAL (plywood and lumber supply). Seems like ebony is really scarce of late, and of rough quality. Perhaps coughing up the dough for blanks from LMI or Stewmac is worth it. |
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| Author: | alan stassforth [ Tue May 10, 2011 10:31 am ] |
| Post subject: | Re: cracks in bridge |
I like Allied, beacause you can still go there and see what you're getting. LMI for the rest of the stuff Todd doesn't have.  Stew Mac for electric things, or what LMI doesn't have. Mt. Storm (Windsor), sometimes has usable wood. |
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