# Building for playability

#### Freeman Keller

##### Doctor of Teleocity
Geometry 101

I’ve been thinking about doing this thread for quite a long time but several recent threads tell me this might be the time.

If any of you have followed my ranting, er posting, you know that I am quite focused on the geometry of the guitar. I frankly don’t care what your guitar looks like or sounds like or what fancy pickup you put in it or how many coats of whatever you put on it – if it doesn’t play easily it is not a good guitar. Geometry is simply all those parameters that define whether or not you can make the guitar play easily. Basically if you have good geometry you can adjust the action to play well and easily, without buzzes, and have enough adjustment to change the action as needed.

Geometry is not the same as action – action is the height of each string above each fret, geometry is the thing that allows you to adjust the action. Another way to say that is geometry is the relationship between the ends of the strings (nut and saddle) and the fretboard. I’m going to define some terms so I can use them later – these are my definitions and there is nothing sacred about them.

- Fret plane. The tops of all of the frets on the center line of the neck. This assumes that the frets have been leveled and at least for now, there is no relief in the neck. If you lay a straightedge on the frets between the 3rd and 4th strings it follows the fret plane. The fret plane can be extended to the bridge

- Neck angle. The angle between the fret plane and the body of the guitar, usually measured relative to the side next to the neck heel. Neck angle can be positive or negative, zero is an acceptable angle. I will show measuring the neck angle with a protractor that will read somewhere around 90 degrees, the actual angle is 90 minus that reading.

- Overstand. This is a term from the bowed instrument world (violins) that indicates how much the fretboard is raise above the body of the instrument. It normally does not include the thickness of the fretboard itself. It may be angled or wedge shaped, in that case it is usually taken at the neck/body joint. It will make more sense when you see some pictures.

- Arching. Some guitars are flat on top, some are not. The amount that the top is arched or domed is important when we talk about geometry. I will assume that the outside rim (top of binding if the guitar is bound) is in a level plane, by laying a straightedge across the top behind the bridge we can measure the difference at the rim, assuming the gap is the same on both sides.

- Action. We have already mentioned action but my formal definition is the height of the strings above the first and twelfth frets. Action is a very personal thing – different players like totally different feeling guitars. Action often varies with different styles of guitar and sometimes style of playing (a Flamenco player or bluegrass flat picker might like a completely different action than a heavy metal shredder or an acoustic finger picker). For the sake of his discussion I am going to use a very average “medium low” action that I happen to prefer (and many people who play my guitars seem to agree). However this is one of the things that YOU should change in the following discussion to fit your preferences

- Action values for this discussion are first fret clearance between 15 and 20 thousands of an inch and 12th fret clearance between 60 and 100 thousands. Note that I am going to use decimal inches in all of this – sorry, that’s the way I think the best. Most players prefer action rising slightly across the neck – I might set the high E at 0.014 (1st fret) and 0.060 (12th) and the low E (0.018 and 0.090). I’ve done a whole ‘nother thread on setups and this is discussed in lots of detail. For most of this discussion we will assume that the relief is so small as to be negligible. Relief however is a factor in action and needs to be considered when you actually set it.

- Electric vs acoustic vs other instrument. The following discussion works equally for both acoustic and electric guitars, and interestingly, I find I like the same range of action values for both. My electric and acoustic guitars have a completely different feel when playing, but that comes from my choice of string tension and not action.

- Fretboard radius. I’m going to make all of my measurements on the center line of the fretboard, with the assumption that the radius is consistent (no compound radius here) and that the saddles are the same radius (or can be adjusted to be the same).

- Future fudge factors. I think it is very important to have some fudge room in any adjustment. I don’t like things at their maximum or minimum setting. Guitars change over time (particularly acoustics), playing style change, I want to be able to change my action accordingly.

So my refined definition of geometry is those parameters (neck angle, overstand, thickness) that allows me to have playable action (0.015 at the first fret, 0.075 at 12) and some adjustment in case something changes. There are an infinite ways to get there.

The last part of this little preamble is my observations that if I make the fret plane just hit the tops of the saddles at their lowest possible adjustment for most guitars (and bridges). It works for most guitars, most bridges and most players but it is up to you that it is going to work for yours.

OK, what I propose to do is design the geometry for two guitars, working backwards. I’ll start with a few assumptions about what I want to build and playable action. From that I’ll try to derive the geometry, with luck that will be recognizable and then I’ll show the actual guitar. Being that I am a total retro grouch I’m going to do this with pencil and paper (and some colored markers to make it easier for all of you to see). Obviously a nice computer aided design software would be faster and more accurate (particularly the “offset” command) but pencil will be accurate enough. Besides, I can’t cut wood to three decimal places…

#### Freeman Keller

##### Doctor of Teleocity
Here are the parameters for the first guitar. As simple as possible, slab body with a flat top. I’m going to use a commercial bridge designed for slab bodied flat topped guitars. I want to do everything with a band saw and a router, and I frankly don’t want to futz around with fancy angles. I don’t mind the neck standing proud of the body, I just don’t want an angle. I’ve got a nice piece of rosewood ¼ inch thick for the fretboard and I’ve got a ¾ inch thick hunk of wood for the neck. Sound familiar?

First thing is to draw the side view of the neck cut down its center line that’s the green thing. Mark the nut, 1st, 12th, 16th and 22nd fret locations and the scale length. Draw some little 0.040 bump to represent frets and draw the fret plane in red.

Take the bridge and screw the 4th string saddle all the way down. In fact I took one screw out so I could get my calipers in there. At its lowest setting the saddle is 0.249 over the mounting plate which is 0.119 thick. That’s 0.368 which is pretty darn close to 3/8 of an inch.

Draw my acceptable action of 0.020 (1st fret) and 0.070 (12th), connect them with a blue line and extend it to the scale length. That represents the D string over the fretboard at a nice reasonable action. Measure down from the red line (fret plane) the height of the bridge and make a black line parallel to the fret plane. That represents the top of the guitar.

If I measure from the red line to the blue line I get right at 0.125 – that is the amount that I need to raise the D string saddle to get my playable action. That is a very reasonable number – it puts me about the middle of the height adjusting screws. That satisfies my criteria for fudge factor.

Since my neck heel will be 1 inch thick I measure down from the top green line and that establishes the bottom of the heel or the depth of the neck cavity, measuring gives me 0.625. The distance from the bottom green line to the black one is the overstand, 0.125.

Pulling out my Tdowns telecaster plans I see that the neck pocket is 0.625 and flat on the bottom. Success so far.

So we build this critter with a 5/8 inch deep neck pocket

And here it is all done. 1/8 inch overstand, action at 0.075 for the D string and saddles nicely centered in their screw travel

#### Freeman Keller

##### Doctor of Teleocity
Parameters for the second guitar. I want an elegant carved body with graceful curves from the top down to the bound rim, the top 3/8 higher than the rim. I want the fretboard to sit on the carve top without any overstand. I’ve got the new style tune-o-matic bridge. I’ll glue the neck into the pocket so it better be right. Once again, sound familiar?

Basically the same game as before. Draw the green fretboard, put some fret bumps on it and the red fret plane. Draw the blue “acceptable action” line. Measure the total height of the ToM – is 0.4570 for the bridge, 0.1500 for the studs and knurled adjuster, minus 0.073 for the little recesses at the end. Total height is 0.534 – a skitch over a half inch. That establishes the top under the bridge.

Add the thickness in the center (the amount of the arching) and that establishes the rim, which meets the fretboard at the 16th fret (no overstand). The top will be planed flat under the fretboard but at an angle, then the top gently arches up to the bridge. The whole thing looks like this.

Here is an important measurement – this is the angle between the neck and the sides at the heel – subtract from 90 and you have a neck angle of right at 4 degrees. Checking my StewMac plans they call out that angle as 85.6 degrees – I’ll accept that.

Lets build it. Do the beautiful elegant arching of the top and angle the upper bout at 4 degrees.

Here it is, all set up, action is right at 0.075. The bass side bridge post is a bit above the calculated 0.125 because its on the outside and I want a hair more action on the low E.

So, totally different guitar, totally different parameters yielded totally different geometry. The action are almost identical and they play very similarly. The rest of the ergonometrics are different due to weight, shape, scale length and the angle of the neck relative to the body, but the fretboards feel the same.

#### bender66

##### Poster Extraordinaire
Thank you for taking the time to post the thread Freeman. I've seen a few of those recent threads. They're entertaining & enlightening.

I'm lucky to know a great local luthier/retired math teacher. He's all about numbers & geometry.

#### Bergy

##### Tele-Holic
I always learn a lot from yer posts, thanks for ranting!

#### Freeman Keller

##### Doctor of Teleocity
Here are a few random pictures of geometries that work.

My hollow body jazz guitar. 3/8 arch, floating ToM, 3 degree neck angle, small wedge under the f/b tapering to zero at the joint

Here it is under construction

The little wedge is really funky when you look at it this way

Here is another hollow body, an old Guild X-150. 3/8 arch, 5/16 overstand, 4 degree neck angle, very tall bridge. These big wedges are pretty common on archtops

Here is another old Guild. Almost 1/2 inch of arch, 5/16 overstand, and a negative 1 degree of angle.

#### Freeman Keller

##### Doctor of Teleocity
And we can talk all day about neck angles on acoustics - their geometry changes with age and it becomes necessary to take them apart and fix it. However this one is a year old, 1/8 inch of arch, one degree of angle

#### hopdybob

##### Friend of Leo's
may i ad another aspect that has to do with play-ability?
body shape.
my first homebuild solid body guitar had the body size of a Spanish acoustic with a strat scale neck.
i only play guitar sitting on a chair.
it sounded good but somehow the proportions were not right.
so the position where the guitar rest on you knee and were the nut is from that position does a lot to, i think?

#### gregulator450

##### Friend of Leo's
This thread is priceless. Thank you for the information!

#### mkster

##### Tele-Afflicted
Thanks For sharing !

Best regard

Marc

#### nickhofen

##### Friend of Leo's
I could have paid for a tutorial like that !

##### Tele-Afflicted
Feeeman,

As it relates to geometry. Things that should be obvious get hidden/confused/muddled with guitar folklore (and misapplied facts). Some facts that muddle my mind. If a guitar neck/pocket needs a shim something is probably wrong. You may not get as good contact between the screwed on neck and the body…you will not get as good sustain. Thinking about neck relief, you set the angle of the relief to be the maximum relief at about the 8th fret…midway in distance between the 1st fret and the end of the fretboard. So the vibrating string over the 8th fret has more room to vibrate. So what if you are playing a barre chord on the 8th fret. Didn’t you just create a hump that would cause fret buzz. Yes if you have too much relief…Won’t we now not have enough bow/relief between the 7th fret and the end of the fretboard? Maybe we don’t have a problem because shorter strings do not move as great a distance when they vibrate as longer strings. My whole point is that your explanation of the “geometry” of the fretboard is obvious. It only took me about 3 builds (fighting the misapplication of this obvious fact) caused by a template/router base combined error of about .5 degree in the neck pocket for me to figure it out. Oh, and more than once I have had to build a temp template late in the build to cut the pocket just a little deeper after fitting a new bridge…or usually not being careful enough measuring the depth of my original routing of the pocket or my neck was just a tiny bit thicker that one inch. It took me all this to say thanks for taking the time to explain this “obvious” relationship between the fretboard and the bridge.

Now that you have shown us the geometry between a Fender tele/strat zero angled neck and those other guitars with a 3 degree angle or so. Why would we ever want to have an angled neck …. in order to accommodate a badly designed bridge maybe… Leo must have gotten it right, right?

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#### Greggorios

##### Poster Extraordinaire
Outstanding effort. Thanks so much for your time and expertise. Very informative and practical. Will add it to my library.

#### Freeman Keller

##### Doctor of Teleocity
Feeeman,

As it relates to geometry. Things that should be obvious get hidden/confused/muddled with guitar folklore (and misapplied facts). Some facts that muddle my mind. If a guitar neck/pocket needs a shim something is probably wrong. You may not get as good contact between the screwed on neck and the body…you will not get as good sustain. Thinking about neck relief, you set the angle of the relief to be the maximum relief at about the 8th fret…midway in distance between the 1st fret and the end of the fretboard. So the vibrating string over the 8th fret has more room to vibrate. So what if you are playing a barre chord on the 8th fret. Didn’t you just create a hump that would cause fret buzz. Yes if you have too much relief…Won’t we now not have enough bow/relief between the 7th fret and the end of the fretboard? Maybe we don’t have a problem because shorter strings do not move as great a distance when they vibrate as longer strings. My whole point is that your explanation of the “geometry” of the fretboard is obvious. It only took me about 3 builds (fighting the misapplication of this obvious fact) caused by a template/router base combined error of about .5 degree in the neck pocket for me to figure it out. Oh, and more than once I have had to build a temp template late in the build to cut the pocket just a little deeper after fitting a new bridge…or usually not being careful enough measuring the depth of my original routing of the pocket or my neck was just a tiny bit thicker that one inch. It took me all this to say thank for taking the time to explain this “obvious” relationship between the fretboard and the bridge.

Now that you have shown us the geometry between a Fender tele/strat zero angled neck and those other guitars with a 3 degree angle or so. Why would we ever want to have an angled neck …. in order to accommodate a badly designed bridge maybe… Leo must have gotten it right, right?

I didn't go into the details of what happens when you put tension on the strings - I did talk about that in a different thread on setup (go to post #28 on page 2)

But I'll repeat a bit of it here. We know that string tension wants to pull a bit of bow into the neck, and that is good. The combination of a bit of bow (relief) combined with the fact that action is higher at the saddle end than the nut means that the envelope of the strings vibration has some clearance to the next frets. The ideal situation would be uniform parabolic shaped relief from the nut to the end of the fretboard, but that would require a uniformly homogeneous neck which we don't have. Most necks get really stiff from the heel to the end and so your relief ends up looking more like

You are correct that the neck to body joint often results in a buzz point - you can see why from the little sketch. There are some things that can be done to help - running the minimum amount of relief (which requires perfect frets). I will sometimes dress those frets at the joint very slightly to give a little more clearance. And the second on the neck from the joint to the end of the f/b can be given a very slight relief when it is made.

The problem is less common on electrics but can be a big issue on acoustics with their greater string tension and higher relief settings.

Anyway, the idea of this thread was to talk about those basic geometry decisions that we make at the design stage to result in a guitar that hopefully we can make playable when it is done.

#### Freeman Keller

##### Doctor of Teleocity
Now that you have shown us the geometry between a Fender tele/strat zero angled neck and those other guitars with a 3 degree angle or so. Why would we ever want to have an angled neck …. in order to accommodate a badly designed bridge maybe… Leo must have gotten it right, right?

I don't think one is better than the other, just different and depending on which kind of guitar we are building, we need to be aware of the differences. Remember that the two designs come from very different back grounds and philosophies - Gibson electrics harken to the beautiful arch topped guitars from their golden days, Leo was trying to make it as cheap and simple as possible. Almost every guitar other than Fender has some angle to the neck - acoustic "flat top" guitars are not flat on top.

I don't necessarily think the Gibson bridge design is bad - the ToM is based on the floating arch top bridges and they work wonderfully.

I build both kinds of guitars but personally I prefer the beauty and elegance of a carved top with nicely angled neck. Milage will vary......

##### Tele-Afflicted
I don't think one is better than the other, just different and depending on which kind of guitar we are building, we need to be aware of the differences. Remember that the two designs come from very different back grounds and philosophies - Gibson electrics harken to the beautiful arch topped guitars from their golden days, Leo was trying to make it as cheap and simple as possible. Almost every guitar other than Fender has some angle to the neck - acoustic "flat top" guitars are not flat on top.

I don't necessarily think the Gibson bridge design is bad - the ToM is based on the floating arch top bridges and they work wonderfully.

I build both kinds of guitars but personally I prefer the beauty and elegance of a carved top with nicely angled neck. Milage will vary......

I am sure you can tell I was being facetious. Thanks for taking the time to do this valuable posting.

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#### s_tones

##### Tele-Afflicted
Always an interesting topic.
These are issues that are thrust upon us pretty quickly when we start building.
A friend of mine built 3. None were functional! Despite my admonishments he just never took the time to look hard at the geometry required to make the things actually playable.

One thing the angled neck/high bridge does is make it a WHOLE lot easier to adjust the bridge to something that works (if you are off a little bit). Low bridges are unforgiving. High bridges also give you a little elevation of the strings which keeps you from scraping up the guitar top (if it's bare). They make single coil pickups a bit awkward as they look funny sticking up high (IMHO)

Lately I have taken GREAT pains to model in CAD every component to fractions of a mm so that I can build the thing and not have to worry about that final moment to find out that the bridge is too high or low. This is not only really helpful but FUN. It's pretty doggone hard to do actually.

.

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