28.6" short scale bass neck question

[Eric Schmitt]

I'm planning out a new project, I'm wanting to do a 28.6" short scale fretless bass. On my plans the fretboard area will be about 21" long. I'd like to use a double action truss rod from stew-mac. My question is what length truss rod will be best? Will the 18" one they sell be long enough since the next size up is 24" (which is probably too long)?

[Peter Wilcox]

I think the 18" will be long enough if accessed from the headstock, since this will support the most elastic/weakest part of the neck. It would be too short if accessed from the heel end. Of course, the type of neck (bolt-on, set or thru), thickness and profile might factor in too.

[David King]

The greatest stress on the neck will be in the middle of the string's length i.e. at the twelfth fret. An 18" rod would be fine but I would reinforce from the heel to the 12th fret to make that part of the neck as stiff as possible.

[Peter Wilcox]

David certainly has much more experience at this than I do. My reasoning was that probably 3" of the heel end will be supported by the neck pocket and won't need the truss rod, leaving 18" of neck. Depending on the neck profile, the cross sectional area of the neck at the nut will be about half that at the heel, and will need more support. The 18" truss rod will extend close to the 18th fret length (18.49"), where the neck joins the body, giving plenty of support to the half scale (12th fret) area.

So maybe the 18" rod will work either way, whichever is most convenient for the design and construction.

[David King]

A lot of older bolt-on necks get a permanent kink over time right at the end of the heel. Keeping that area as straight as possible is very important and that means reinforcing with something that has a good "memory". Steel would be an obvious choice and it doesn't take very much but you definitely want it to overlap the end of the rod by 3-4 inches at a minimum. The material from 1/2" steel strapping bands is perfect as they only need a .020 kerf. You can taper them shorter at the 12th fret end to gradually allow the neck to flex and keep any relief where you need it most.

[Eric Schmitt]

Thanks guys, that's just what I needed to know.