Caculating Neck Height

[mfratto]

I am planning my first electric based on Martin Oakham's design in his book Build your own electric guitar. I also have hiscocks book as well.

Trying to figure out whether I need a neck angle or not. Oakham has a formula used to derive neck angle. Trig, scary stuff. Divide the bridge height by the scale length and then get the arc tangent of the result.

In my case, the scale length is 647.7 mm (25.5 in). I measured my Schaller TOM max height from the base of the bridge with the tumbscrews out (no threads showing) at 18mm. That gives me a neck angle of 1.59 degrees. Does an angle that fine make a difference?

Does it make more sense to angle the neck pocket, the neck heel, or cut/shape the neck by that angle?

thanks

[Keegan]

That formula would only be valid if you wanted the strings to touch the frets and the frets were level with the body, which is crazy. More accurate would be Angle = Arctan((Neck thickness + fretboard thickness + fret height - Neck pocket depth - minimum bridge height)/647.7). All measurements are taken from the Low E side(on a TOM, measure from the bottom of the lip on the bushing straight up to the breakover point of the Low E). That way the strings would only touch the frets if you had the bridge all the way down.

For example, my neck/bridge(stock Fender, so no neck angle) would look like Angle = Arctan((25mm-16mm-9mm)/647.7), and indeed, you get 0. I took those measurements straight off the guitar. The real angle(the angle when set up at a typical action of 3/32") is about .3 degrees. So yes, an angle of 1.59 degrees is huge on a guitar, when .3 degrees is the difference between playable and not. If I use the original formula on my guitar, I get something ridiculous like 1.1 degrees.

It makes the most sense to angle the neck pocket, since you can do it fairly easily while you're routing the neck pocket, just by raising the guide rails the right amount. If you don't want to angle the neck pocket, you can either lower the bridge or raise the neck, both, or just get a shorter bridge than a TOM.

Edited December 7, 2008 by Keegan

[j. pierce]

Small angles like that equal a fair amount of change as the distance increases. Think like shooting an arrow or a gun - if you're aiming just a little bit too far left, you might be a couple inches away from your target at 10 feet. At 50 feet, it's a wide miss. This is why it's harder to hit a target or make basket at a long distance.

If you want to see what a difference it really makes, get a long ruler (a yardstick or what have you) , a reasonably flat surface like a table. With the "zero" on the table, find your scale length (25.5 inches or whatever it is.) Put your bridge (or something as thick as you measured your bridge as tall under the ruler at this point. See the line the ruler makes? The table is your fretboard - the ruler is your strings. That's your action. If you measure the angle right now, between the table and the ruler, it's going to be "fairly small".

If you want to assume there's the additional thickness of your fretboard there, you can put your fretboard, or something as thick as it, between the table and the ruler, and use that as your surface, with the bridge still on the table. Chances are your action is still a lot higher than you'd like it. And the bridge may be even a little bit higher than it is now, since we didn't put the studs in there.

If you've got a protractor to measure the angles, you can see how much of a difference it makes over the couple of feet of scale length we have - quite a bit!

Short answer - with anything TOM styled as a bridge, you're going to have to either: a) angle the neck, b)recess the bridge into the body, or c) raise the neck in relation to the top plane of the body (like many archtop guitars are) or some combination of the three.

[j. pierce]

FWIW - I always used to draw out my neck angles from a side view and measure my "answers" from there, but because such a small difference in angle can change things so much, I prefer to do it the math way. I still draw out the whole thing from the side so I can mark everything down and keep track of the numbers and what they're measuring as I figure it out, but if you know the math (and really, it's just finding the unknown measurements of a triangle - there are plenty of calculators for doing this online once you determine the other measurements - you already know two sides and an angle) you can be much more accurate, unless you're much better at reading angles off of pencil lines than I am.