Shimming a neck

[Mid Life Crisis]

I've read a lot of posts about fret buzz and installing a shim to correct it. What I don't understand though is how shimming a neck is any different to adjusting the saddle height. Shimming a neck at either end of the neck pocket increases or decreases the angle of the neck. However it also affects the string angle, since they touch the neck at the nut and as the other end of the strings is at the bridge, the overall effect is to alter the string angle relative to the neck. If you adjust the saddle height, then (as long as there is enough travel possible given the saddle screw size) you will also alter the angle of the strings relative to the neck.

If you have a certain action, say 5/64 on the low E at the 12th fret, then after shimming the neck the saddle must be adjusted to maintain that action.

So, my question is, doesn't shimming have the exact same effect as adjusting the saddle height, with the exception that shimming increases the range of saddle screw adjustment that is possible?

Hope I've been making sense.

[Nick JD]

You make perfect sense.

Shims are for when your saddles are maxed-out either way (high or low).

Sloppy neck pocket routing and/or a badly made neck heel are the main culprits if you discount paint build up.

A well-made guitar shouldn't need a shim.

[leebman]

That would be true if the neck is flat but they aren't the relief in the neck means that its not quite as simple. I just set up a tele that had a shim in it the action was 2mm but it buzzed on the high frets ? I removed the shim and set the neck back to flat lowered the action to 2mm no buzzes. So if the neck is slightly shaped with a curve by shimming the neck to tilt back you raise the saddles but also raise the end part of the neck. If you see what I mean.

[Mid Life Crisis]

Originally Posted by leebman

That would be true if the neck is flat but they aren't the relief in the neck means that its not quite as simple. I just set up a tele that had a shim in it the action was 2mm but it buzzed on the high frets ? I removed the shim and set the neck back to flat lowered the action to 2mm no buzzes. So if the neck is slightly shaped with a curve by shimming the neck to tilt back you raise the saddles but also raise the end part of the neck. If you see what I mean.

I see what you mean but that's my point - the end (I assume you mean body end) of the neck comes up so you have to make a corresponding adjustment to the saddles to raise them up; consequently the angle of the strings to the neck is the same as it was before. As far as I can see (and I freely admit I may be missing something here) the only thing that has changed would be the break angle of the strings over the saddles.

[leebman]

Originally Posted by Mid Life Crisis

I see what you mean but that's my point - the end (I assume you mean body end) of the neck comes up so you have to make a corresponding adjustment to the saddles to raise them up; consequently the angle of the strings to the neck is the same as it was before. As far as I can see (and I freely admit I may be missing something here) the only thing that has changed would be the break angle of the strings over the saddles.

what you say is true but the important factor that makes the difference is that the neck is not flat in an exagerated demonstration think of the neck as a banana and your string as a piece of paper if you tilt the banana back away from the paper edge you can see the middle of the banana has dropped further behind the end nearest to the paper meaning the compensation on the saddles would be greater. Thats probably made it as clear as mud but without a diagram am struggling.

[Mid Life Crisis]

<goes off to find banana and paper>

I might just give it a try and see what happens. I can always put it back to where it was before.

[Ricky D.]

The issue is the height of the strings over the face of the instrument, and by implication, the height of the saddles over the face of the instrument. If these are within acceptable limits, no shim is needed.

A really nice touch for a setup is to have all the saddle height screws flush (or close to) the tops of the saddles.

[Guitarmadcat]

Mid Life Crisis, just take note of Nick J D - shimming retains the status quo as far as the neck is concerned. All it affects is the required height of the saddles.

[woodman]

a shim can also help if your action is fine on the first 12 frets but breaks high on the upper-register frets (at least it did for me).

[vinniger]

Originally Posted by Mid Life Crisis

What I don't understand though is how shimming a neck is any different to adjusting the saddle height.

If you want more clearence (height) in the picking area, you'll have to rise the saddle.

But saddle adjustment also affect the action in the fretting area. So if you want high picking area, you'll have to live with high fretting action; If you want low fretting action, you'll have to live with low picking area.

You can solve (resolve?) this dilemma by shimming the bridge end of the neck pocket.

Tall bridges (saddle) need a little bit of neck angle to maintain low fretting action. I learnt this lesson when I put a Floyd in my 1st guitar (RIP) back in the 80s!

[Astro1176]

Originally Posted by leebman

That would be true if the neck is flat but they aren't the relief in the neck means that its not quite as simple. I just set up a tele that had a shim in it the action was 2mm but it buzzed on the high frets ? I removed the shim and set the neck back to flat lowered the action to 2mm no buzzes. So if the neck is slightly shaped with a curve by shimming the neck to tilt back you raise the saddles but also raise the end part of the neck. If you see what I mean.

If shimming did exactly what it says on the tin - ie changed the angle or the neck with respect to the body - then geometrically this would have an identical function as raising the bridge saddle height, and the main need for this would be if the bridge was maxed out or couldn't go low enough.

Some feel that the height of the bridge can affect the tone on some guitars, maybe due to altering the break angles, maybe due to the length of screws holding the saddles off the guitar, so shimming would allow you to play with that if you were really really bored.

Changing the access to the upper frets? If you use a wedge shaped shim lining the neck pocket, then geometrically not possible, a shim does not change the relief of the neck, 2mm is 2 mm and the shape of the neck is the same. If you use a bit of chunk at the body end only, and screw the neck in really tight, maybe you will cause some extra curvature between frets 16 and 21, which could theoretically give the results Leebman speaks of. This isn't really what shimming is all about though, and high fret problems might better be addressed with some fret work? However, if it fixes the problem, it's all good.

[leebman]

Originally Posted by Astro1176

If shimming did exactly what it says on the tin - ie changed the angle or the neck with respect to the body - then geometrically this would have an identical function as raising the bridge saddle height, and the main need for this would be if the bridge was maxed out or couldn't go low enough.

Some feel that the height of the bridge can affect the tone on some guitars, maybe due to altering the break angles, maybe due to the length of screws holding the saddles off the guitar, so shimming would allow you to play with that if you were really really bored.

Changing the access to the upper frets? If you use a wedge shaped shim lining the neck pocket, then geometrically not possible, a shim does not change the relief of the neck, 2mm is 2 mm and the shape of the neck is the same. If you use a bit of chunk at the body end only, and screw the neck in really tight, maybe you will cause some extra curvature between frets 16 and 21, which could theoretically give the results Leebman speaks of. This isn't really what shimming is all about though, and high fret problems might better be addressed with some fret work? However, if it fixes the problem, it's all good.

I agree shimming doesn't change the amount of relief its the relief that is present in the neck that may cause problems when the neck is shimmed. It depends on the set up your after and the neck. The angles change proportionally due to the design of the neck.