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Hello friends.
I started to make an electric guitar several years ago (something similar to Ibanez JS1600). So I didn't touch it for those years. Yesterday I took the neck and it appeared that it has a bow. I suppose it is because of the wood drying? How can repair it. The neck doesn't have finish and frets yet. The truss rod is one way action, so it wouldn't help. I attached the photos showing both ends of the fretboard. The gaps are about 1.5mm

What do you mean the truss rod won't help? That's exactly the kind of bow they are meant to help. Also, how about a wider view in your pix?

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"Act your age, not your shoe size" - Prince

It is a back-bow. I think that the tension of strings would not straighten the neck to a necessary degree. The truss rod in my case can only resist string tension, so it cannot work in a up-bow direction. I draw my case, see the attachment.

The pictured amount of back-bow is without any additional back-bow that may happen after the frets are installed so I would be thinking that string tension resolving the issue is a very long shot. (not to mention trying to do a fret job on it)

I know of only 2 possible solutions.

If the neck is thick enough to reshape and the fretboard can be sanded/radiused to level then maybe. Then there is still backbow from fretting to be considered and the fretboard is not going to look right with varying thickness if that even worked.

If the fretboard can be removed - replace the truss-rod with a double action one. ( probably the move I'd consider first before scrapping it and building a new neck)

This is a good example of why I install only double action truss-rods.

Guess I should have read your first post a little closer.

_________________
"Act your age, not your shoe size" - Prince

It would be a pity if I have to throw away the neck )
I heard about making some wet enclose and putting a neck there for about two weeks with bowing it against the wrong bow...
Does somebody know how to do this?

A friend of mine received a neck with about the same amount of back bow and my advice to him was to send the sucker back...

Since you made this one it's likely that the wood is moving with humidity changes and also likely that the wood may not be seasoned enough to be stable.... If this is the case the neck may not be done moving, fretting will only add more back bow, you used a single action rod so that's no help.

If it were mine and especially if this is a set neck glued to the body I would make a new neck with well seasoned wood and read up on maintaining proper RH range while building guitars.

This one looks like it may be the problem that just keeps on being a problem if it is used.

When I apprenticed we did a couple of Martin's with a back bow. They were made with the square tube in the neck and no truss rod. We put fixture with felt covered v cut outs at the ends and clamped a block on the fret board side in about the middle of the bow and slowly tightened it. It took a week or more then let it sit for a couple days strung up checking tune and bow. I'm worried about the width of the fret slots 1.5mm is close to three times what it should be. do you remember what they were cut at? if you can't get the slots down to .023 to .025 you may need to replace the finger board. It may cost you less in time and aggravation just to make a new neck. hope I helped.

I think he means the gap between the rule and the board. I'm no expert, far from it, but my guess would be the neck wood has shrunk while it dryed out more than the fretboard giving the tension and bow. Depending on what glues you used removing the fretboard could be a pita but it might release the tension somewhat. If it were me I'd probably just make a new neck because it would be the fastest option for me. Good luck with whatever you decide.

Brian.