Shimming a p bass

[Stub Mandrel]

A ski jump is the endof the neck turning up a little, as we all know.

 

On a typical 19 or 20 fret neck the attachment screws are about 3 frets apart.

 

Any bending force would be due to the screws between the shim and the screws at the other end.

 

If you are worried, rather than worrying about wedges, just make your shim long enough that the screws penetrate it. The neck is then under no bending force.

[ezbass]

I had a 1963 P Bass that had had a wee shim fitted. There was no hint of end of the fretboard turning up and heaven knows how long that shim had been in there. 

[tauzero]

On 21/10/2025 at 09:19, Stub Mandrel said:

If you are worried, rather than worrying about wedges, just make your shim long enough that the screws penetrate it. The neck is then under no bending force.

 

That's what I do, albeit with poncey brass shims. They have handy locating holes, so I put them on the end screws.

[Andyjr1515]

My view is that there are decent reasons for using wedges instead of a simple shim at the end of the pocket but:

- it's not essential

- it has nothing to do with ski-jumps

 

The main decent reason that I might use wedges is that a wedge does provide a tighter contact between the neck and neck pocket - and the more rigid the neck fixing, then the less vibration loss.  Whether anyone could hear the difference is, of course, a totally different matter! 

 

And so to ski jump.  Ski jumps are real and not uncommon, but a single shim at the end of the neck pocket causing a ski jump is a 'challenge' to physics, materials science and, certainly in my case, practical observation:

 

- Physics.  The pair of screws at the shim end of the pocket is close to the shim.  The pair of screws at the other end is close to the other contact point.  The gap is in the middle - and on most basses (admittedly not all) there aren't additional screws there.  So the screw forces are holding the two contact points tight - there is no bending force

 

- Materials science.  The heel of the neck has one of the largest aspect ratios (thickness: length) of most of the other wood components.  Even in a hydraulic press, it would take some considerable force to bend that.  I think the wood round the screw threads would fail first.

 

- Practical observation.  Those who have followed my build threads over the years will know that I exclusively build through-necks.  And yes - you can and do get ski jumps with through-necks.  Basically: the neck is pulled  up by the string tension; the truss rod keeps the bendy bit straight but there remains a movement axis at the neck/body joint; the string tension wants to snap the neck at the joint for the neck and body to clap hands.  There is some flex upwards even when new.  And, over time, that continued tension can result in a set lift of the neck.  It's one of the reasons that many builders add a 'fall-away' of the frets that sit over the body bulk near the heel.  If you don't, then folks who like a super low action and play way up the dusty end will tend to get buzz of the upper frets.

 

   

 

 

Edited 2 hours ago by Andyjr1515

[Stub Mandrel]

Just s thought... if you want to transfer vibration a single point contact is best, not an area, I think.

 

An area contact damps vibrations.