Bent Gibson H1 madola neck - what is the best course of action

[Mike Keen]

Hi All

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.

Cheers Mike

[Greg Mirken]

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.

[Mike Keen]

Thanks for that - I've replied to both you and Andrew below.

[Andrew]

I was thinking something along the lines of what greg suggested. I would also want to take into account how much flex the neck has without the fingerboard. If you can straighten it out with a reasonable amount of clamping pressure then it should be no problem to glue the fingerboard on with a good straight caul. If it takes a lot of pressure to straighten out then just clamping it straight may not be an option. If course if you add no reinforcement the neck will presumably bow again under the tension of the strings.

What are the concerns regarding originality of the mandola? Would it be worth adding a truss rod at the cost of some originality if it gets you a more functional instrument?

[Mike Keen]

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.

[Andrew]

Ive never had to straighten a neck with heat but Ive straightened a few other pieces, i.e. Bridges, to get a better glue joint that required much less force to glue up. Straightening wood with heat is different than bending wood with heat, and it seems as though the results are different between each piece of wood. I never expect to get a piece perfectly straight. Usually adding some moisture with a very damp cloth before clamping/heating seems to help. Id go for about the same temperature range you were already at. Let the neck sit with the clamps on for a few days, and measure your results once you take them off, then again a while later. If it springs back to where it was, you probably wont get it to stay with a safe amount of force or repeated sessions.

[Frank Ford]

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.

[Mike Keen]

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

Thanks again

Mike from England

[Mike Keen]

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?

Cheers Mike

[Frank Ford]

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. . .

[Greg Mirken]

Agreed; dead flat unstrung. It might wind up with the tiniest bit of relief under tension, and that's OK.

[Mike Keen]

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

Mike