Double Bass vintage Kay fingerboard question.... relief?

[Dennis Ramsey]

What amount of relief should the fingerboard have in it? ....
If I put a straight edge at the nut and allowed it to sit at the end of the extension, is there a measurement in MM or Thousands that I can look for to know it's within proper range?
Also should that measurement be at the very center of the fingerboard?

 

[Greg Clinkingbeard]

The necks on most old Kay’s are bowed badly because both the maple and fingerboards are thin. To modify my advice on correcting overstand, if it’s time to replace the fingerboard, set the neck as it is and add a tapered shim before a new fingerboard.
I shoot for the diameter of the string at the octave. Anywhere from 1/8” on the G to no more than 1/4” on the E will be OK. Chances are you have 1/4” or more in the middle of the neck now.

 

[Greg Clinkingbeard]

Put the most scoop in the middle of the vibrating length. Not the fingerboard.

 

[Dennis Ramsey]

Thanks Greg….
ok so just to clarify the bow your discussing is without the strings on as I described the straight edge on the fingerboard or are you saying that with the strings on the bass the setup clearances should be 1/4” from the bottom of the string to the fingerboard thus final set up adjusting bridge height…. If not …. Then I’ll ask what are proper set up clearance at nut and at mid point of scale length.

 

[Greg Clinkingbeard]

The neck will move a bit under tension, less with a stiff fingerboard. With a straightedge, I eyeball the maximum scoop at the octave, or about 21” from the nut.
For a well dressed fingerboard, 1/8”-3/32” is usually plenty before it’s strung up. Got to be a consistent scoop with the same amount of daylight over the entire board.

 

[Dennis Ramsey]

Thanks…..

 

[Greg Clinkingbeard]

I also use a short (about 4”) straightedge to judge consistency.