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| the dreaded back bow - suggestions? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23733 |
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| Author: | ayavner [ Tue Sep 08, 2009 11:33 am ] |
| Post subject: | the dreaded back bow - suggestions? |
hi all - Glued up an ebony fretboard on an LMI preserviced neck. both were dead flat when i started, and the trussrod was more or less neutral. after removing the clamps, I laid a straightedge down the center line and there is (i feel) a pretty significant dip about mid-way (6th or 7th). Is there anything I can do about this, or should I use the trussrod to counter it? Obviously i would like to try to get it as flat as possible first so that won't be necessary. I used Titebond, and I have read somewhere that this is common. adam |
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| Author: | Jimmy Caldwell [ Tue Sep 08, 2009 11:45 am ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Adam, If you really have a "dip", you don't have backbow. Backbow is just the opposite and is characterized by a hump in the neck. It can be caused by the absorption of moisture from the glue. A lot of builders use epoxy to attach fingerboards to avoid this situation. If you have an adjustable truss rod, and as long as the condition is not too severe, the truss rod should be able to take care of it. Generally speaking, most players like about .005-.010" of relief in the neck when tuned to pitch. If you start out with a dead flat neck before tuning, you should be pretty close to that when tuned up. |
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| Author: | ayavner [ Tue Sep 08, 2009 12:31 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Hi Jimmy, I stand corrected - yes, this is a dip, i would say about 1/16th of an inch eyeballing it.. haven't measured yet. I would like to try to find a way to make it flat as possible before fretting and stringing up. Do you think if I support it in the middle (fretboard down) then lightly weight or clamp each end to try to counteract the dip that way, that it would work? thanks! adam |
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| Author: | tommygoat [ Tue Sep 08, 2009 12:50 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
I would skip trying to bend the neck with clamps. Adjust the rod until your straight. String it up and then check relief with the actual string tension. |
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| Author: | Tom West [ Tue Sep 08, 2009 12:53 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Doubt it's 1/16 of an inch.Ten thou gap under a straight edge looks like you could drive a truck through. Suggest you measure with feeler gagues and report back. |
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| Author: | ayavner [ Tue Sep 08, 2009 12:59 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
westca wrote: Doubt it's 1/16 of an inch.Ten thou gap under a straight edge looks like you could drive a truck through. Suggest you measure with feeler gagues and report back. will do... admittedly, that was a quick gander on my way out the door this morning, and quite likely it seems bigger in my mind's eye. But, I will say it does look much larger of a gap than I recall ever seeing. I'll measure it when I get home, maybe its a non-issue. And, perhaps its possible that it can straighten out as the titebond continues to cure over the next day or 2?? Tommy, what if i take all the dip out with the trussrod, then there's more dip when i get it strung up and not enough left in the TR? Is that likely? thanks all, Adam |
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| Author: | Fred Tellier [ Tue Sep 08, 2009 12:59 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Are the frets installed? if not the frets will flatten this out or may even cause a little back bow that the string tension will pull back. Fred |
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| Author: | ayavner [ Tue Sep 08, 2009 1:00 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Fred Tellier wrote: Are the frets installed? if not the frets will flatten this out or may even cause a little back bow that the string tension will pull back. Fred Hi Fred, No, the frets are not installed yet. That's a good point. |
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| Author: | Fred Tellier [ Tue Sep 08, 2009 1:07 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
That is what I thought, repair people actually use wider tang frets to combat what you are seeing on old no truss rod guitars. |
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| Author: | David Newton [ Tue Sep 08, 2009 2:15 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Fred's right, but don't go doing a strong compression fret job, then you'll really have dreaded back bow. Your regular frets in regular slots are all you'll need. |
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| Author: | Tom West [ Tue Sep 08, 2009 2:28 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
If you are going to work on the board tonite,make sure you take the dip out before installing any frets. |
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| Author: | Alan Carruth [ Tue Sep 08, 2009 3:02 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
I like to make the neck such that the fingerboard has the correct amount of relief just before I put the strings on it. It will pull up a bit under tension, but that's what the truss rod is there to counter. This way, there's as much back pull on the rod as there is up pull on the strings, and the forces are perfectly balanced. Even without trying to 'compression fret' the neck the frets wil push it back a bit. Personally, I put the 'board on at ful thickness and not radiused, then plane it down once the guitar is together. I don't see how you guys can get it accurate enough, gluing down a fretted and dressed 'board. |
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| Author: | Alexandru Marian [ Tue Sep 08, 2009 5:48 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Alan Carruth wrote: Personally, I put the 'board on at ful thickness and not radiused, then plane it down once the guitar is together. I don't see how you guys can get it accurate enough, gluing down a fretted and dressed 'board. I am quite amazed by this approach too, especially after getting used to the Spanish way. In my case, a thicker FB is better. I use fish glue liberally, and since there is quite a lot of neck and FB meat, a little backbowing (or dipping or anything else), if it happens, is not a problem. I don't recall having more than a half millimeter backbow at the 0 fret so far. Once the system settles in about 1 week, I do whatever geometry I want with a plane. (and the choice here is based on the targeted relief, and more important, on where the bridge location is, as the doming does not have the same exact height when using sprung-in braces. |
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| Author: | ayavner [ Tue Sep 08, 2009 7:03 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Well I got home today and started working on it immediately. As you suspected, the gap was not that much, and the trussrod was able to counter it. We'll see where it sits when I get it fretted. Thanks for the info and encouragement! I'll try to post a pic and some measurements later. adam |
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| Author: | David Newton [ Tue Sep 08, 2009 8:35 pm ] |
| Post subject: | Re: the dreaded back bow - suggestions? |
Alan, For the longest time I glued a fully finished and fretted board, and I used titebond. The bare surface of the unprofiled, thick, neck had a little bit of relief, and when glued down with titebond it would, of course, induce a little back bow and flatten things out. Then on stringing up, I got my relief. I did these with a neck reinforced with CF only. They were all short scale 12 fret necks, which made it all less scary, and more controllable. I've done it also with hide glue, but you don't get much back bow with that, so you start with a dead flat neck. I've changed methods now, and do it your way, but I don't think I've gained anything, maybe a little peace of mind. |
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