A couple of times, I’ve talked about shimming a neck (the right way) to alter the angle the neck attaches to the guitar body. This is sometimes done on guitars to lower the action when the bridge saddles are bottomed out and have no more downward travel. Shimming is also used to get, sort of, the opposite effect — make it possible to raise the saddles (to give more string break angle over them) while keeping the action comfortable.
And it’s this latter that I want to touch on a little more. I’ve felt like I may not have explained it as well as I could. I’ll rectify that, but first, we need to consider neck angles in a little more depth.
What is a guitar neck angle for?
Right. Let’s go back to the old days. The days before djent and rock ‘n’ roll. Back then, you might have had a fancy, new-fangled flat-top acoustic or you might have had an arch-top guitar.
The arch-top guitar has a construction similar to older instruments like the violin. The strings are anchored in the tuners, at one end, and in a tailpiece at the other. Sitting on top of an arched top, with the strings passing over it, is the bridge.
The bridge’s job is to transfer the string vibration to the top so that it can vibrate. The vibrating top, vibrates the air in the body and that squirts out the sound hole(s) as sound.
If the angle the strings pass over this bridge is a bit too shallow, there’s not as much pressure pressing downwards. Less pressure means less efficient transfer of string vibration (a lot of energy is lost to sting floppiness) and that’s bad for tone.
So, to keep a decently steep angle over it, the bridge is made quite tall. When the bridge is tall, the neck has to be angled backwards to allow a comfortable action. Imagine the ridiculous situation below…
In this way, the instrument’s construction dictated it needed a tall bridge, which dictated it needed a backwards-angled neck.
Fast-forward a few years and you’ve got solid body instruments with pickups and crazy sci-fi-sounding names. Now we have a clean slate. These pickup things mean we don’t need to have so much downward pressure to get an olde-time arched top vibrating. What are we going to do?
Well, Gibson, decided to go down the solid instrument that looks like an arch-top route. The Les Paul had an arched top on a solid hunk of lumber. Cool. Their tun-o-matic bridge wasn’t archtop-tall but it was relatively tall and this meant the Les Paul retained a backwards neck angle.
Down at Fender, on the other hand, Leo decided he’d pick an easier route. You see, fashioning a neck joint for an angled neck is a pain in the… erm… neck. Leo was all about easy construction techniques and angled necks weren’t something he wanted to mess with.
So, he went and designed a shorter bridge and screwed his neck into a flat-bottomed pocket in the body. No nasty angles. Pretty obvious, really.
And here’s where we come back to the neck-shimming.
Even though these solid-body guitars don’t require a vibrating top to produce their sound, it turns out that the angle strings break over the saddle is still important. Floppy strings bring their own problems on a solid-body instrument.
This wasn't so much of an issue with something like a Tele or a Strat because the strings passed through the body (or anchored) right behind the saddles, automatically giving a steep angle. And it wasn’t a problem on a Gibson with the strings anchored in a tailpiece quite close to the bridge. All seemed well for a while.
Then Leo went and made a Jazzmaster. Enamoured with the whole ‘jazz’ vibe, he designed a cool vibrato tailpiece and he located it down the end of the body — like on an arch-top.
Of course, moving the string anchor point all the way back there made for a much more shallow string angle over the bridge. The shallow angle made for less downward pressure on the bridge. Less pressure made for floppier strings that wouldn't stay put, rattly bridge saddles and screws, and the issues Jazzmaster players have wrestled with for years.
Similar to the arch-top solution, having a taller bridge would help enormously but that means the action gets higher and it’s hard to play.
Unless you’ve got a neck angle.
Shimming the neck artificially creates our neck angle and means we can raise the bridge up without screwing with our action.
So, we’ve sort of brought Leo Fender full-circle and back to the archtop guitars — complete with tailpieces and neck angles — that his first designs had completely eschewed.
Gerry’s Last Word on Shimming
Remember to do it properly.
You must use full pocket, wedge-shaped shims. If you missed this stuff the first time (or second, or subsequent times), it’s important you don’t just shove a bit of card or something under the end of your neck. Doing that can cost you hassle and money. Check out Neck Shimming Made Easy and the other links for more info.