How To Shim A Neck
Posted 23 May 2009 - 07:26 PM
The following describes how to shim the neck of a Fender-style bass (e.g. a Precision or Jazz) or any bass with a traditional bolt-on neck construction.
Posted 23 May 2009 - 07:27 PM
You would do it if you need to lower the action but find that the bridge saddles are already at their lowest position and will not go down any further.
How Could This Happen ?
There are several possible reasons - including manufacturing variations - but the most common one is that the bridge has been replaced (e.g. with a BadAss bridge) with one that has a thicker bass plate so that the bridge itself is actually sitting higher than it was meant to. For example -
Posted 23 May 2009 - 07:29 PM
Some space. An empty kitchen table is good enough but put some towels down to protect the guitar finish. You'll need a medium sized cross-point screwdriver to remove the neck bolts, a capo (or elastic bands), and something to make the shim from.
Posted 23 May 2009 - 07:30 PM
Once you know what you are doing it can be done in abouit 10 minutes. If it's the first time then allow up to an hour.
Can I Undo it if it Doesn't Work ?
Yes. The neck shim can be removed easily and quickly, returning the guitar to excatly the condition before you started.
Posted 23 May 2009 - 07:31 PM
Ok. You've got some space and a covered surface to work on. First step is to loosen (but don't remove) the strings. Loosen them off until there is no tension on the neck and they're all flappy.
Posted 23 May 2009 - 07:32 PM
Now put your capo on at the first fret. This will hold the loose strings in place when you remove the neck.
If you don't have a capo use an elastic band - it's just to stop the strings falling out of the nut. If you don't have an elastic band then follow your postie around for a day or so - he'll be dropping those pinks ones all over the place so you can use a few of these.
You can put a second capo/elastic band halfway down the neck if you wish, but it's not essential.
Posted 23 May 2009 - 07:34 PM
Turn the bass over onto it's front. You'll see the neck plate and (usually) 4 neck screws. You'll need to remove all 4 screws.
Posted 23 May 2009 - 07:35 PM
Use a well-fitting screwdriver to avoid burring the screws.
Unscrew each screw a little at a time so that they are all loosened evenly.
DON'T unsrew one screw completely then move to the next - this will put pressure on the neck. Undo each one a turn or so, then go back to the first and do another turn, and so on until they all come out.
Remove the screws and the neck plate and put them aside.
Posted 23 May 2009 - 07:37 PM
Now - nothing is holding the neck on. Lift the bass carefully. If the neck slides out then that's ok, but if it doesn't then it's just a tight fit in the neck pocket. Turn the bass over onto it's back.
If the neck is still in place, carefully ease it out straight up - don't wiggle it from side to side, you may damage the neck pocket.
Move the neck, with the strings still attached, to the side.
Posted 23 May 2009 - 07:38 PM
Check the neck pocket and the underside of the neck for any signs of a previous shim.
If there is a previous shim you can either remove it completely or replace it with a new one.
Posted 23 May 2009 - 07:41 PM
Make the new shim.
There's a big debate over what material the shim should be made of - wood veneer, sandpaper, cardboard. But remember - it needs to be thin. In most cases, cardboard the thickness of an ordinary business card will be enough to allow you to lower the action.
Sandpaper to grip the neck ? Well it's held tight by 4 screws so it's not going to move, so what will the sandpaper do (apart from being thicker than a business card). Wood veneer ? Yes, if you have some thin enough then this is a perfect material.
Wedge shaped tapered shim ? Well if you can make a tapared wedge with the thickest part as thin as a business card then that is perfect too.
For simplicity I have used an ordinary cardboard business card.
Place the neck over the cardboard and use it as a template to draw around and mark the shape of the shim.
Posted 23 May 2009 - 07:43 PM
Cut the shim.
Cut inside the line to ensure the shim will fit.
To allow you to lower the action the shim should be fitted at the back end (closer to the bridge) of the neck pocket. Check the fit is ok with no wrinkled or bent edges - it should be perfectly flat in the neck pocket.
Posted 23 May 2009 - 07:44 PM
Replace the neck. With the shim in the back of the neck pocket, carefully replace the neck in the socket. Put the neck straight down and don't wiggle it from side to side.
Posted 23 May 2009 - 07:45 PM
You now need to turn the bass over onto its front, keeping the neck in the pocket. It doesn't matter if the neck moves a little here but try to minimise movement and keep the back edge of the neck against the body so as the shim doesn't move.
Posted 23 May 2009 - 07:46 PM
Refit the screws.
Leave the screwdriver aside for now. Drop each screw into the hole then finger tighten them - you should feel each screw grip the wood in the neck. Go round each screw and get them all finger tight.
Posted 23 May 2009 - 07:47 PM
Tighten the screws.
As with removal do NOT fully tighten each screw individually. Go around the screws and give each a single turn, then mve on to the next one. Tighten all the screws evenly in this way. Make sure they are all good and tight, but do not use excessive force - just tighten with a normal screwdriver.
Posted 23 May 2009 - 07:48 PM
Turn the bass over and remove the capo/elastic bands.
Retune the strings to pitch. Once they're up to pitch check the tightness of the neck screws again.
Posted 23 May 2009 - 07:50 PM
Adjust the action.
You should find that the action has been lowered by putting the neck shim in place - the strings will probably rattle on the frets. You can now raise the bridge saddles to get the action you want. Job done.
Posted 23 May 2009 - 07:51 PM
A shim place at the back of the neck pocket (as described above) will change the neck to body angle by effectively pushing the headstock backwards. This has the effect of lowering the action.
A shim placed at the front of the neck pocket (furthest away from the body) will effectively push the headstock forward and should slightly raise the action.
Thanks for reading this - I hope someone finds this useful.
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