Adjusting Your Action: Shimming and Micro Tilt

neckshim

There are many different factors that go into the playability of a guitar, including the string height, the quality of the frets, the smoothness of the fretboard edges, the shape of the neck – the list goes on and on. One often-overlooked aspect for bolt-on guitars is the neck angle; get it wrong and you can run into difficulties in maintaining consistent action. Get it right and the guitar becomes a slick, playable machine. Let’s look at some common problems and how to fix them.

Neck Angle Too Shallow

If the neck angle is very shallow, you have the problem of the bridge or saddles not being able to go ‘low’ enough, which of course means you can’t get consistently low action should you want it. If the saddles go as low as possible and the action at the 22nd fret is still way too high, you have to increase the neck angle. There are a few different ways to address this.


1. A shim.

This is the easiest way to fix a shallow neck angle. You slide a piece of veneer (some luthiers use thin but rigid cardboard) between the neck and the body at the end of the neck pocket closest to the neck pickup. Reattach the neck and voila: the angle is more steep. Now you adjust the saddle height and you’re done. You may or may not need to adjust the truss rod. If you’ve made a drastic change which involved raising a vibrato bridge higher for more ‘back-pull’ you may indeed need to tweak the rod too.

microtilt

2. Micro-Tilt

If your guitar is equipped with a Micro-Tilt device, all the better. This is a simple inbuilt system which lets you adjust the neck angle without actually removing the neck itself. Just loosen the strings and the neck screws then adjust the bolt in the Micro-Tilt mechanism, which in turn adjusts the neck angle. Lock it all in place, screw down the neck, retune, adjust the saddles and you’re done.

3. Adjust The Pocket Itself

If you’re a confident luthier or if you know one, you can adjust the angle of the neck pocket itself. You need specialized tools like the proper template and a router, but this job isn’t something any luthier should be fretting about. If you’ve determined that the neck angle should indeed be more steep and you’re totally committed to that specific neck, a trip to a luthier would never hurt.

Neck Angle Too Steep

If the neck angle is too steep, you could be in bigger trouble than if the angle is too shallow. You could try to raise the bridge and be done with it but if the neck isn’t completely straight and you can’t seem to fix it with the truss rod, you could be in trouble. The effect of this problem would be that the strings buzz at the lower frets, the action at the higher frets is unattainably high and if you bend the strings, they choke. Raising the saddles is either not possible or not advised because the action would get even higher making it even less playable. Essentially: the neck has a back-bow that can’t be torqued out with the truss rod or the strings. The only way to get it fixed is to make the neck angle more shallow. This can be done in either of two ways.

1: Adjust The Pocket Itself

If the neck angle can be made steeper by router, it can surely be made more shallow, too! If you think you’ve done everything you can to adjust the action and you recognize your guitar in the description above, it may be prudent to visit a luthier and suggest this kind of surgery.

NeckShim1-638x358

2. Shim It!

But you can also tackle the issue yourself with a fairly simple mod. You can make a shim but instead of installing it at the back of the neck pocket (i.e.: the edge closest to the bridge) you put the shim at the other side (i.e.: the edge closest to the tuning pegs). The angle gets more shallow, so you can lower the saddles. By changing the location of the shim and altering the neck angle, the lower frets were ‘raised’ relative to the higher frets (with relative respect to the strings, if that makes sense). It’s a bit of a stretch, but this method (proposed by a friend of mine) helped to ‘save’ a Fender USA Strat where the neck and body had a nice fit, but a wrong angle relative to each other.

Just 30 minutes of your time, a few basic tools and common sense can help you a lot to diagnose the problem and maybe even fix it. If anything, your own experiments can help your luthier in his search to trouble shoot the problem. Just don’t drill, sand, file, rout or chop in the woods unless you’re a competent luthier: those fixes are often a hell of a lot more expensive than the adjusting some nuts, screws and bolts. If you’re not sure, stop with whatever it is you’re doing and go to a pro!

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8 Comments

  1. I’ve heard about shims warping the neck at the pocket to get a ski slope type of curve at the high frets. Any info on this?

    1. A shim would never cause that type of issue to my knowledge, (I’m a guitar tech as a living) but would be more likely caused by poor quality wood/craftsmanship used initially for the neck or fingerboard. As wood ages, it “settles in”, as we say. A shim would not fix that issue either. A fret mill or a complete re-fret would almost certainly improve the problem there. It would involve a re-radius of the fretboard and replacement, leveling, rounding, and polishing of the frets to get rid of the hump or dip.

    2. Yes it does indeed the pulling pressure from the screws puts a bow in the neck if the shim is only holding up one side. The shim needs to be the full length of the neck pocket. If it needed to be raised 2mm for example then the shim need to be 2mm down to zero the full length and width of the pocket.

    3. It MAY happen, on occasion, but only if the shim is really, really thick. Smaller shims aren’t that prone to recurving a neck.

  2. These shim adjustments are might tricky. You need to experiment with different thickness shims to get the perfect action you want. I have been working on guitars for over 30 years and one needs to adjust the bridge, the nut and the truss to get a proper action. The micro tilt is a very good device and if one can come up with a double micro tilt (front and rear of the neck), then it would be relatively easy to get the near perfect action. Over time, after the adjustments are done, the action again goes off and one needs to go through the whole process again. If a double acting micro tilt device is come up with, it would be fairly quick to carry out the adjustment quickly and easily. That’s my two bucks.

  3. Neck angle that is too shallow/ steep stems from the disparity between the position of the bridge and that of the nut (they are not parallel with each other). To correct that, raise/ put a shim under the goddam nut, not the bridge. This is just wrong from the getgo. Classic Orpheo.

  4. Ace, I’m afraid you’re not correct in this case. If you raise the nut, the string height at the nut increases, true, but maybe not at the end of the fretboard. A shim isn’t to set the action, perse, but to fix the neck angle. A shim is the classic way to fix the neck angle, too. Not the nut. Take a look at what these guys are saying:
    http://www.premierguitar.com/articles/19686-guitar-shop-101-how-to-shim-a-bolt-on-neck
    http://www.strat-talk.com/forum/tech-talk/318907-neck-shim-hows-whys.html
    http://www.strat-talk.com/forum/tech-talk/15273-how-shim-neck-step-step-photos.html
    http://www.tdpri.com/forum/telecaster-discussion-forum/112515-neck-shims.html
    Fender has been using shims as well for years in their guitars, too. Are they wrong as well? I guess not. You can bash me all you want, but it doesn’t invalidate a shim perse. Again, the shim is to change the neck angle in order to give the saddles more travel. If you want to lower the action but the saddles/bridge can’t go deeper, decrease the angle. If you want to go lower but the saddles can’t get higher (and you’re getting fretbuzz), increase the angle and work on your saddles accordingly.
    I know it’s a lot of fun to bash me, but I’m right in this case, I’m so sorry.
    P.S. If shims aren’t the way to go, why do microtrilt systems exist?

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