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Unfinished NOS necks - slight backbow

PostPosted: Mon Mar 12, 2018 4:12 pm
by Beate Ritzert
Hi there,

i bought 3 unfinished necks dating from the end of the Framus production in 1981. All three have backbows. Truss rods have been are loose and put under very moderate tension for a few minutes on order to test them. The amount of backbow varies, but just reaches an amount which will be compensated by string tension.

Those necks are unfretted. The 4th - the only fretted one - came out perfectly under tension. So i would not mind if i planned to use them in fretless basses. But i am going to fret them, and thus am a bit afraid that that might increase the backbow.

So what would You do? Simple risk it and be prepared to straighten it after fretting (by clamping and heating) or try to straighten it before cutting the fret slots?

Re: Unfinished NOS necks - slight backbow

PostPosted: Mon Mar 12, 2018 5:53 pm
by Mark Swanson
If you tighten the rod just a bit and then plane and sand them flat, when you loosen the rod you should have a bit of relief built in. Then cut your slots and fret it.

Re: Unfinished NOS necks - slight backbow

PostPosted: Mon Mar 12, 2018 8:01 pm
by Dan Smith
Yes on Mark’s reply.
I’ve done this on a very stiff neck to ensure I could add relief by loosening the rod.
If you use a sanding beam rather than a plane, it helps to sand the middle hump first so the beam does not teeter across the hump.

Re: Unfinished NOS necks - slight backbow

PostPosted: Tue Mar 20, 2018 12:11 pm
by Mark Wybierala
I've had very good luck using a micro plane or what some called a scraper to achieve a flat neck. It removes more material quickly yet it is very controlled. It is what I use on a violin or a cello.

In a very well lit bench setting, I'll perform a light surface sanding of the fingerboard using something like 320 grit sandpaper -- I'm only prepping the surface. Then I'll use a precision straight edge to identify the apex of the backbow. Because of the surface sanding, the straightedge will leave contact marks on the wood as I teeter it and/or move the straightedge across the width of the fingerboard. You can see the contact marks of the straightedge and I may use a pencil to outline the contact points. I'll apply the scraper to only the contact points and then repeat the surface prep with the 320 grit sandpaper and do it all over again. If you understand what I'm describing, the whole thing becomes really intuitive and the process becomes a lot faster than using a sanding beam because you are only removing the offending high spots. You also reduce the tendency to to change the neck geometry from the downward pressure of the sanding beam. If the fingerboard/fretboard is slotted, you need to run the scraper at a 40 to 50 degree angle to the fret slots and pay attention a bit more.

Re: Unfinished NOS necks - slight backbow

PostPosted: Tue Mar 20, 2018 12:49 pm
by David King
As long as your fret tangs have a bit of clearance in the slots you should be okay. Jescar supplies several of their popular wires with different tang widths. You didn't say what the fingerboard wood is but I can't imagine Framus used anything terribly hard so the the fret barbs should be able to penetrate with a little forward-bowing pressure after the frets are in. If you glue the frets in make sure that the neck is either flat or has some forward-bow before wicking the glue in or the glue will take up all the extra room in the slots and lock in any back-bow.

Re: Unfinished NOS necks - slight backbow

PostPosted: Tue Mar 20, 2018 7:35 pm
by Beate Ritzert
David King wrote: You didn't say what the fingerboard wood is but I can't imagine Framus used anything terribly hard ...


It is most probably dalbergia latifolia.

I'll try to avoid glueing in the frets; in the few cases i fretted/refretted a fingerboard it worked flawlessly without glue. And i will follow all Your hints when i continue with these necks. A great thank You! (And scrapers belong to my favorite tools anyway ;-) )

At present it is a bit too cold in my workshop and i am also waiting for some new fret wire to arrive. The wire i already have better suits to a guitar, and it is by far not enough for all my projects.

Re: Unfinished NOS necks - slight backbow

PostPosted: Tue Mar 27, 2018 7:46 pm
by Beate Ritzert
Unfortunately i have don the 2nd step before the 1st and marked the fret slots. So i had to cut them before dealing with the backbow.

Image

Image

Upon close view You might see that about a handful of the slots have to be corrected. A bit frustrating, but these are my 2nd and my 3rd fretboard, and i am looking forward that in the end they'll come out better than my first (which plays really good).

Re: Unfinished NOS necks - slight backbow

PostPosted: Sun Apr 15, 2018 8:03 pm
by Beate Ritzert
Beate Ritzert wrote:Upon close view You might see that about a handful of the slots have to be corrected.


Unfortunately about 50% of the slots of the lower of the two fingerboards.
Repair or replace? I have Apple and Walnut available, and the bass will have a top of flamed maple and a walnut body.

Re: Unfinished NOS necks - slight backbow

PostPosted: Sun Apr 15, 2018 11:25 pm
by David King
On a bass, your frets can be 5 cents off and few will ever hear it in the bottom two octaves. I wouldn't worry at all about 1-2 cents. I'd print out a board to scale using the fretfind2D app and lay it over the frets to see how bad things really are. If these necks use a compression truss rod then I wouldn't use walnut, it's just too soft. Apple is a possibility but I'd think you could find a stick of ipé decking at the local lumber yard that could be resawn