Severe back bow on Modern construction neck, any way to fix it ?

docteurseb

Senior member
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743
Spud said:
Whatever you do don't take the heat gun to it!

Yep I agree, I think the potential to overheat and damage the finish/frets/glue is too high; and exposure to heat too short to likely do much.

Here's what I have:
- clamp
- heating pad (sorry kitty, the guitar neck comes first this time around)
- rice sealed with plastic film

SaYodCx.jpg

OW5deg2.jpg


I suppose I'll leave it that way for at the very least a week.

Thanks all for the advice(s).
Crossing fingers this works. Just cleaning the finish off the fretboard edges and blending it in was such a pita (nearly two full afternoons...) that I'd rather see this neck go back to a usable state than dispose of it.
 

TBurst Std

Senior member
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2,591
Cagey has a jig to tension necks. He has to do it to my canary neck as it would not adjust flat before stringing up. He put it in the jig and in an oven (no idea of temp).  That was 4-5 years ago.  No issues.
 

docteurseb

Senior member
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743
TBurst Std said:
Cagey has a jig to tension necks. He has to do it to my canary neck as it would not adjust flat before stringing up. He put it in the jig and in an oven (no idea of temp).  That was 4-5 years ago.  No issues.

Thanks, I’ll message him to see if I should send him the neck or wait and see if my crude way of doing this will work
 

Sadie-f

Senior member
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427
That's the problem: I'm not the patient kind.

Fair enough, your build threads have evolved over enough time, I'd have thought you quite patient :).

Your adjustment rig looks great, sad for the kitty, however I'd make the same call 🐈.
 

Cagey

Senior member
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24,425
I got your PM but thought I'd answer here in case anyone else was interested. I wrote a how-to thread here describing how I bent the first one I did. The process seems to work well and the effects seem to be permanent. I've done it a number of times now with good results.
 

stratamania

Senior member
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9,217
I added Cagey's link to the Welcome to the forum thread post for build guides and tips so it can be found easily in future.
 

docteurseb

Senior member
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743
Cagey said:
I got your PM but thought I'd answer here in case anyone else was interested. I wrote a how-to thread here describing how I bent the first one I did. The process seems to work well and the effects seem to be permanent. I've done it a number of times now with good results.

Thanks Cagey. It appears this was a fairly quick process with the oven.
My neck is however already finished with poly and I'm hesitant warming that up to 175F.

The heating pad I use is probably going only to 85-90F; more than that and I'd expect a Sphynx cat to cook/die from overheating. It may take longer but I think I'll err on the side of caution here.
 

Cagey

Senior member
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24,425
It's a valid concern, but I've done it before without issue. Polyurethane is remarkably durable.

I think the first time I did it and wondered how the finish would fare, I considered that the neck was useless as it was so if I borked it up, there was little loss. Worst case, I'd have to refinish it or use it as a dog's chew toy, but it turned out fine.
 

docteurseb

Senior member
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743
Cagey said:
It's a valid concern, but I've done it before without issue. Polyurethane is remarkably durable.

I think the first time I did it and wondered how the finish would fare, I considered that the neck was useless as it was so if I borked it up, there was little loss. Worst case, I'd have to refinish it or use it as a dog's chew toy, but it turned out fine.

A very fair point. I'll see how successful the method I'm using now is; if it doesn't improve at all after a few days or a week then I don't have much to loose cranking up the heat.
 

Sadie-f

Senior member
Messages
427
I think you've got plenty of heat, also maybe move the clamp closer to the bolts end? Maybe 3-5 frets?

I look forward to seeing your results!
 

docteurseb

Senior member
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743
It's been 3 days, and there is definitely some improvement with the backbow maybe cut in half (with the caveat this was measured right after unclamping it).
I'm going to try the oven method today though to speed things up a bit; plus I feel the position of Cagey's clamping is more logical and safer than mine.
 

Cagey

Senior member
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24,425
Remember what I said in the how-to - don't overbend it thinking it'll spring back. The bend you put in it is the bend it will end up at when it's done cooking. If you overbend it, the truss rod may not be able to compensate, and you'll have to bend it again.
 

docteurseb

Senior member
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743
Definitely saw that but thanks for the kind reminder.
I’m just putting a 0.032” gauge feeler as shim.
 

Rick

Senior member
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4,323
Interesting ... I try to get it almost dead flat at .004 at the 7th fret.  Use a feeler gauge and metal ruler straight edge.  Or maybe I'm not remembering right ...
 

docteurseb

Senior member
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743
rick2 said:
Interesting ... I try to get it almost dead flat at .004 at the 7th fret.  Use a feeler gauge and metal ruler straight edge.  Or maybe I'm not remembering right ...

I think I do want a slight forward bow, to be safe in case it decides over time to spring back a bit.
The truss rod will easily compensate for that amount of bow; and yes I realize spring tension will add even more relief. Maybe that's too much, well there's still time to address that as it's only been cooking for 5 min...

Worst case, I'll cook it again...
 

docteurseb

Senior member
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743
rick2 said:
So ... what does it smell like after being in the oven?

I doubt it'll smell anything at that temperature but I'll let you know once I open it
I cooked maple at twice the temp to roast it though, and that was a nice smell.
 

docteurseb

Senior member
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743
No smell from the poly-coated maple + ebony fingerboard.

I'm at the 3rd baking session, it wasn't quite where I wanted it to be after the 2nd round:
- nearly flat, but far from the 0.032" relief expected from the feeler gauge. I'm adding an extra  0.014" this time around.

- odd curve in opposite directly around the last few frets. Hoping to rectify that clamping by at the last 2 frets this time around.


A few "downsides" of the procedure so far:

- small but clear cracks from the ebony fingerboard getting overly dry. I'm conditioning it before the 3rd session, and should have done that after the 1st session as I could feel it was dry but don't remember noticing the thin cracks then. I'll stabilize with superglue if the neck ends up being usable after all those cooking sessions.

- clearly the fingerboard shrunk a bit width-wise, as you'd expect from the drying: minor fret sprout / finish clouding of some fret ends, the side dots are 'sticking out' ever so slightly (you can see the tiny bumps at the surface of the poly, hard to feel though).

- apparent shrinkage of the joint between the ebony fingerboard and the maple veneer right behind the nut. There is a thin white line now apparent at the glue joint which is likely clouding as the poly lifted up from the joint from the shrinking wood.

- marred poly finish around the 1st/2nd frets where the clamping was. Likely easy fix by light sanding and buffing again if there is a sufficiently thick finish (if not it's OK, I wanted a satin finish and the shop did gloss...)
The first time I clamped just enough so frets touched the rod; by the time the baking session was over there was a gap...
The second time I clearly over-tightened which marred the finish; also it's a Clapton profile and the sharp V is limiting the contact area when clamping.


The primary concern is whether the 3rd session will finally put a proper forward bow and rectify the uneven slope at the heel.
The onset of fingerboard cracks is a slight concern, but those are manageable if they don't get worse. Last would be the finish issues starting to appear from shrinking, it can be redone if the neck ends up otherwise perfectly usable.
 

PhilHill

Senior member
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1,654
I think your doing well so far, only thing I might suggest is, considering how many times it's getting heated up, keep a notice of the condition of the fingerboard/neck joint and whatever adhesive is holding it together. Each time it's clamped that joint gets strained... :icon_thumright:
 
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