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Odd Bass Neck Response To Truss Rods


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Hey guys. I'm currently working on some basses (four) and with two of them am experiencing something kind of odd; the two effected necks seems to have a fairly pronounced bump near the first fret line, and then again farther up near the end of the neck. From what I've measured, these bumps do not correspond to the nuts in the LMI dual-action welded rods. Since they are bumps and not simple bow forward/back, truss rod adjustment doesn't seem to address them effectively.

The boards were good and flat when radius sanded (checked with precision straight edge). The necks were flat and level too. They were glued up with epoxy, and therefore I shouldn't be experiencing any reaction from the wood to water content. Glue up consisted of placing clear masking tape over the rod channel, cutting the tape to within a 1/16" of the channel so that nothing could leak in with the rod, then clamping all along the length with spring clamps.

When I glue fretboards on with titebond in the past I've glued them while using a straight caul as well. However, I did not do this with these necks as epoxy doesn't want "too much" clamping pressure so I didn't want to try and force anything to a straight caul and over clamp. But as mentioned above, it shouldn't have needed a straight caul since the neck and board were checked for straight and epoxy has no water to react to.

This really sucks as both the necks in question represent the most complex inlay work I've probably ever done. One of which I've already tried to level sand and am getting close to a point where I'm concerned about potentially sanding through the inlay (there's a section where one piece of pearl stretches across the entire 5-string FB's width), so naturally I have concerns.

Any suggestions to address this, or words from anyone who's encountered this before would be greatly appreciated.

Best,

Chris

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Wow, I both love and hate conundrums like this one Chris. Any chance of a side profile photo so we can visualise this a little more?

Totally on the mark regarding epoxy and clamping. It needs nowhere near the same clamping pressure as penetrative PVAc/aliphatics and doesn't bring water into the equation. I know you know this, just voicing for the purpose of the conversation. Humps around the first few frets might be indicative of a scarf pushing out, however I am presuming that this is simply not the case, especially with no moisture involvement. Again, photos would help confirm/disprove any correlation.

Not sure if we have enough information to work off on this one yet. I guess my only reaction to the methods used would be that I would use a caul and clamping, but only a fraction of the pressure required for standard wood glues. Epoxy doesn't starve that easily, and usually it has enough surface tension to resist clamping pressure up to maybe 25-50psi. Light trigger-clamp kind of pressure. I have to discount excess glue since you'd really need to lay it on thick and the board wouldn't conform over excess....I'm still suspecting the rod in some kind of way, however I can't see that getting past you either.

Game on Chris. Bring it. Hopefully we can have an eye-rolling or a Eureka moment rather than bad news about the inlay through mitigation. How does the glue line look, or have you bound it away already?

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Sorry, been actually getting work done (odd, I know). I can't take a picture sadly as I've gone and dealt with the situation. I adjusted the rod to the least evil setting and was able to get almost all of this out on the two affected necks. The scarfs of both of these necks are in the headstock, not the neck, so we can rule that out. West systems isn't the thickest of epoxies... so I'm guessing we can rule buildup out as well. My locator pins are all wooden toothpicks that I leave the pointy part on to help guide the fretboard into them... so they stick well out of the board and are then trimmed... so nothing there either.

I'm truly stumped too. But luckily, like with all things, I'm a harder judge on myself than I should be most times, and the unevenness wasn't as bad as expected. I agree that, regardless of the "need", a caul would be a good idea. Just seems odd that out of the 3 necks that were glued up like this, one did just fine while the others had this... also, the one that did fine had only dot inlays. I really have a hard time thinking inlay work could have any effect like this though.

Stumped as well, and now that I've leveled things and moved on I don't know if I'll come to a resolution here.

Chris

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Nope, didn't seem to correlate with inlay placement.

Woods that had issues (albeit now not as bad as I thought) are wenge over honduran mahogany and ebony over honduran mahogany. Wood that didn't was cocobolo over home-roasted curly maple.

Inlay glue was thin CA on the ebony board, mostly epoxy on the wenge board.

Yeah... I'm lost too,

Chris

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If you've had said Sapele, I would immediately have seen a potential issue. I've found that even the straightest Sapele is liable to internal tensions being baked in from kiln drying which release when shaped into a workpiece. Unsure on whether what you have might be doing this also, and I doubt it more than anything. Still, those are the kind of shitty invisible surprises that poor kiln drying can lay on you. Silent and deadly, a little like @MiKro's gift to this thread.

Drying faults existing in the same places in timber used identically might be worth considering, but we're getting to the limits of what we can prove or believe here. I just hope that you can recover the inlays, because that's just painful to consider.

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