Shimming the Neck - effect on intonation

[Tony Reid]

Has anyone noticed that the intonation above the 12th fret goes out more noticeably after the neck has been shimmed? Or do I just need to fiddle around with the bridge saddles to get it back to an acceptable level?
I have a very nice maple +RW neck from USA guitars, 22 frets (so I can play up high) - so no issues with fret spacing. The bridge is a Glendale with compensated saddles - so that should be O.K., too.
The reason for shimming is the Jamerson Guitars body - very lightweight (3.5 lb), 2 piece swamp ash, beautifully grain matched that I paid too much for on eBay. The neck pocket is a little shallow, so first choice was a small shim to angle the neck upwards.
Perhaps I need to pay someone to carve out the neck pocket...
I really would appreciate some advice.

[craigoslo]

shims work great and are easy to do. I prefer tapered shims. I used tin (aluminiums) foil folded in several layers in a wedge shape on my last partscaster. Then just reassemble, adjust saddle height and intonation.

[Guran]

Originally Posted by Tony Reid

Has anyone noticed that the intonation above the 12th fret goes out more noticeably after the neck has been shimmed? Or do I just need to fiddle around with the bridge saddles to get it back to an acceptable level?

Yes, that happens more often than not, and you fix it by adjusting the intonation screws holding the bridge saddles.

If the guitar goes flat on the upper frets (as in above 12:th or so), the distance between the bridge and the saddle should be shortened and vice versa.

Make sure the guitar is in tune when you do it. Then loosen the string you are about to adjust a little. Adjust, tune it and check again.

The note you get when you play 12:th fret should be the same as when you play it open. I also like to check it furter up. Take first string as an example. I tune it to E, I check at 12:th fret so that is an E as well, then at 17:th so that it is an A and 19:th is a B.

One reason to do this is that sometimes, not very seldom, one fret can be slightly out of whack for one reason or another. If that fret is the 12:th and you just check at 12:th you will have a guitar that is in tune at 12:th fret but not at 9:th, 10:th, 11;th, 13;th, 17;th and so forth. It has happened to me.

[Tony Reid]

Thanks Guran and Craigoslo!

[El Reclusa]

Can anybody point me to a decent tutorial on shimming? My '76 had a shim when I got it, and it played noticably better than it does now, but lacked some sustain and all-around tone...first time I pulled the neck, there was a square of thick metal mesh that looked like it came from a screen door in the pocket! I know my '76 needs a refret, but it's gonna be a while before I can afford it, so I'm thinking a better shim might help in the meantime...

[boris bubbanov]

Originally Posted by Tony Reid

Perhaps I need to pay someone to carve out the neck pocket...

Ah, the Crux question.

If you have someone in mind that can rout the neck pocket out correctly and for a reasonable sum, I would definitely do that.

A front shim on an already too proud neck is never going to yield the result you have paid good money for. Were I in your shoes I would be doing everything I could to make that proper neck pocket fit happen.

I have a pretty low opinion of neck shims, to put it mildly.

[Tony Reid]

Thanks Boris
I was hoping to get your esteemed opinion! You confirmed what I felt intuitively.
BTW many thanks for your insightful comments on this and other forums. I have learned much from you.

[Guran]

Originally Posted by boris bubbanov

A front shim on an already too proud neck is never going to yield the result you have paid good money for. Were I in your shoes I would be doing everything I could to make that proper neck pocket fit happen.

I have a pretty low opinion of neck shims, to put it mildly.

Well, I also believe that a proper fit is the best solution. To get a proper fit is something else...

On some of my guitars a shim has made the guitar so much better. A proper fit would probably be even better, but the shimmed version is still way better than the unshimmed guitar. Not only better playability, but also better soundwise (which is something I can't really understand (My guess is that it has to do with the sound that bounces on the body and influences the string on it's way back outwards)).

As I have not had it properly routed, I cannot testify to whether it's better or not. I believe it would be better.

Anyway, to shim it and set it up properly costs nothing but a few hours. If you don't like the result, go ahead and have it properly done (if there's someone around capable of doing it).

I'm not opposed to neck shims, as Boris is, but if you can get it properly done (for a reasonable amount of dough) that's the way to go!

[lonewolf]

It's a shame, but unfortunately many bolt on necks, need shims. This is usually done to raise the saddle height far enough from the bridge plate, to give good down-pressure, or seating of the saddles. This eliminates rattles, and improves stability and sustain. I always try to insure that the intonation bolts become farther away from the bridge plate (higher) on the end where they enter the back of the saddle, than at the end where they anchor into the back of the bridge. In almost all cases the shim needs to go into the back of the neck pocket (closest to the bridge). It is rare that you need to shim the headstock end of the neck pocket. True tapered shims that fit the entire neck pocket are ideal, as they eliminate air pockets at the end of whatever shim is used. But these are hard to make, and tough to purchase. Believe it or not, one of those giant square sided, tortoise shell Fender triangle picks, makes a very serviceable neck shim for the back of the pocket. In most cases the medium thickness works the best. Place it so that the wide edge is as far back in the pocket as it will go, with the point facing the headstock end of the pocket, The neck screw holes will almost always go right around the pick, and when the mounting screws are tightened down firmly (don't give it the gorilla treatment or you'll chip the finish), the pointed end will depress into the wood just a tiny bit, and eliminate some of the air pocket around the shim. I have used them for years and they work very well. The material doesn't compress or compact with age like cardboard etc. I believe that is the only use for those picks. Nobody really plays with them do they?
Gene Warner
repairman

[lonewolf]

Sorry I forgot to address the initial question, Yes it affects intonation, and action also. Intonating an instrument is the very last thing you do, and it is actually neccessary after any change in the adjustment of an instrument. In other words, almost anything you change, will alter your intonation.
Gene Warner
repairman

[redstringuitar]

You should check intonation and adjust as necessary whenever you alter neck angle, relief, action, nut-slot depth or trem(if applicable). Anything you change has a knock-on effect.