I recently got hold of a 1914 Gibson H1 Mandola (obviously no truss rod) that was a little neglected but structurally okay.
The neck relief was excessive (0.75mm at fret 8 without strings attached) although the fingerboard and neck looked fine. I decided to try and straighten it using dry heat by carefully clamping it the a solid metal plate (with cauls of course) then heated everything up to 60 degrees C (150F) for 30 minutes the allowed it to slowly cool and left it overnight.
Rather than improving thing the neck bend was now greater (hide glue on fingerboard letting go?).
I've now removed the fingerboard (dry heat) came of fairly easily and both neck and fingerboard are undamaged. Fingerboard is in great shape - very flat top and bottom.
The bow in the neck is a tad more than 1/8th inch and starts when the neck leaves the body.
My question is should I
A . Just build up the dip with mahogany veneer using hide glue, then sand flat fit fingerboard, new binding, touch up finish etc .
B. Try and heat bend the neck back as much as possible then build up any dip with a thinner veneer.
C. Is there any other bit of advice you can offer.
What the normal way of doing this repair.
Since you have the FB off, now is the perfect time to install a Carbon fiber reinforcement. It should be easy to clamp the neck straight without the added stiffness of the fingerboard; then rout and epoxy in a CF bar. Reglue the board and you're done.
Thanks for that - I've replied to both you and Andrew below.
Greg and Andrew.
Thank you both for your reply. The carbon fiber rod is a good idea. I'll think about the truss rod - it depends if it effects it value or not.
Has anyone any experience of heat bending the neck. If so how successful / unsuccessful is it and what temperature would you use.
A 1914 Gibson should have the big maple reinforcement in the neck, so I presume this one does.
My experience with these is that if the fingerboard is removed and the warped neck left untouched that re-gluing the board with a solid flat caul on top is sufficient to reestablish all the stiffness needed to keep things looking good in the future. Re-gluing the board with hide glue, combined with leveling and re-fretting afterward should provide a really solid, stable neck.
So far this simple old-time technique has worked for me every time, even on necks without the maple reinforcement.
Andrew and Frank
Thanks for the help. Frank is right it has a maple reinforcement that is firmly glued in place. Thinking about it, it's probably best not to heat the neck again as the maple might be dislodged.
I'll go with Franks suggestion
Mike from England
Frank, Andrew or Greg.
One final thing.
Would you suggest that (without strings) I get the fingerboard dead flat or should I allow a tiny amount relief. Not sure how much the mandola neck is likely to bend under the string tension. I guess I'd be aiming for around 0.3 - 0.4mm relief under tension - does that sound okay?
For mandolins, my ideal fingerboard is dead flat unstrung, and when tuned to pitch. Pretty much the same with mandolas, too. 'cellos get relief. Now, I don't always get my ideal, but I try.
Even flat fingerboards get the tiniest amount of radius, for fear of them looking slightly concave. . .
Frank and Greg
That's what I thought. Thanks once again for the advice.
This will be the forth "dead" Gibson I'll bring back to life. The others (all Gibson A's) sound wonderful - fingers crossed this is the same.
ps I recently re-glued a top brace on an A4 using method Frank describes on the "Frets" luthier resource page and it worked fine.
Best regards from a very wet London