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Target neck geometry on electrics
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10123&t=48449		 Page 1 of 1
Author:  Freeman [ Sun Oct 23, 2016 8:43 pm ]
Post subject:  Target neck geometry on electrics
I'm mostly an acoustic builder and always follow the idea that the fret plane should just hit the top of the bridge, that allows about 1/8 inch of saddle and good action. While I'm building an acoustic I'll continuously check the angle - slide the neck in its pocket or the dovetail, put a straightedge on the frets and make sure the end is the right height off the top at the bridge (usually 3/8 inch).

As I've started building electrics I discover that I don't have a similar target for my neck angle. Yes I know that Gibson necks are usually 3 to 4 degrees and yes I know that Fender necks stand proud of the body by 3/8 or so, but is there some way to calculate the neck angle based on the height of the bridge I want to use.

On several of my set neck guitars with ToM bridges I have set the neck so the fret plane just hits the bridge at its lowest adjustment. Here is the neck clamped in the pocket with the fretted board on top, straight edge pointed to a ToM bridge sitting on two little piece of wood the thickness of the studs and adjusters.

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My logic is that is the lowest I would ever want to go so I have enough adjustment to get there. I know that I'll want action of somewhere between 0.060 and 0.090 or so - that means the bridge will have to go up twice that, or roughly 1/8 inch. I also know that the nut and relief will add a little "action" and on the four set neck guitars I've built I've been able to adjust the action acceptably.

I'm now building an archtop with a dovetail joint. I want to use the ToM style bridge with archtop feet - StewMac says it is adjustable from 7/8 to 1-1/4. I'm assuming then that if I make the fret plane 7/8 to 1 inch I should be OK. Since this involves both the angle of the neck and the amount it stands proud I need have a target.

I've never seen this spelled out so I'm curious how you'all do it.
Author:  Mattia Valente [ Wed Oct 26, 2016 2:56 pm ]
Post subject:  Re: Target neck geometry on electrics
It's basic trigonometry. Draw out the triangle, with the bridge and fret height taken into account, and the trajectory of the string as you want it. Aim for a little bit above the fretboard surface, remembering that to raise your string by 1/16" of an inch at the 12th fret, you'll need to raise the bridge height by 1/8". Assume ridiculously low (unrealistic) string clearance, and plan to raise it a little.
Author:  Joe Beaver [ Thu Oct 27, 2016 11:32 pm ]
Post subject:  Re: Target neck geometry on electrics
I also am an accoustic builder but I have been helping a friend build an electric base. (A first for both of use) Like you I am unsure what normal setup geometry is. And to make it even more interesting it is a fretless base.
I'll be watching this thread
Author:  William Bustard [ Fri Oct 28, 2016 1:10 pm ]
Post subject:  Re: Target neck geometry on electrics
If I remember rightly, 1 1/8th" off the SB worked when I built a few archtops years ago.
I had a diagram but The bridge base height has some play as does the bridge height adjustment.
It is better to err on the side of too high absolutley as the whole structure will compress initially and somewhat over time
Maybe go with the neck angle of something like 4-4.5 degrees?
Adjust the neck height with the thickness of the fingerboard extension to get it(fret plane) around 1 1/8th" off the SB.
good luck.
Author:  Freeman [ Fri Oct 28, 2016 9:01 pm ]
Post subject:  Re: Target neck geometry on electrics
OK, here are some pictures of the actual guitar. While I agree with Mattia that it should be simple trigonometry it really isn't - the top of the guitar is arched, the fretboard and bridge are radiused and the neck both moves up and down in the dovetail and the angle changes. Here is the guitar right now - the neck is set but not flossed, the fretboard is clamped to the neck and I've put a stack of five business cards (0.050", roughly the same as the frets) on the board.

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The end of the straightedge is just a hair below the saddle with the bridge adjusted as low as it will go. The saddle and fretboard are the same radius - 12 inches.

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I know that the nut will raise the strings maybe 0.015 or so and I know that I'll have a few thousands of relief (which will further raise things a hair). My target action at the 12th fret will be somewhere between 0.060 and 0.100 - that means the bridge will be an 1/8 or a little more that it is in the picture.

So my question is, is the neck angle OK? When it is fretted and glued in will I have enough adjustment at the bridge to get a reasonable action and have enough adjustment that as the guitar ages I can take the bridge down (until I finally need to reset the neck). I know I can sand the bridge feet if I have to and I know there is a lot of adjustment in the thumb screws, but is this a good starting point? If so, or if not, how do you determine this?
Author:  rlrhett [ Sat Oct 29, 2016 4:48 pm ]
Post subject:  Re: Target neck geometry on electrics
I believe that with an archtop you are looking at the wrong measurement for confirming the neck angle.

IMO what matters is the break angle over the bridge. With the bridge set one inch above the soundboard I laid a ruler on the tail and saddle. I want my fret plane to match 6-8 degrees from that line (don't remember where I got that number, Benedetto? Alan Carrouth?)

Since I more or less build the same archtop over and over, it has standardized for me at 4.5 degree neck angle to the body with the fret plane elevated 3/4" above the sound board as measured at the body join. I don't measure the break anymore after dialing it in on the prototype.


Sent from my iPhone using Tapatalk
Author:  Freeman [ Sun Oct 30, 2016 1:11 pm ]
Post subject:  Re: Target neck geometry on electrics
rlrhett wrote:
I believe that with an archtop you are looking at the wrong measurement for confirming the neck angle.

IMO what matters is the break angle over the bridge. With the bridge set one inch above the soundboard I laid a ruler on the tail and saddle. I want my fret plane to match 6-8 degrees from that line (don't remember where I got that number, Benedetto? Alan Carrouth?)


This really isn't an archtop - it has a pressed laminated top and fairly heavy internal bracing to support the pickups and bridge. The top isn't intended to vibrate (much). It could have either a stop tailpiece (in which case the break angle is adjustable), a conventional tailpiece or even a Bigsby style vibrato - but I would also think that designing back from the tailpiece break angle to get the neck geometry would be a nightmare.

Anyway, thanks to those who have responded. I'm pretty comfortable that this will work - it has before - I just wondered how others did it.
Author:  Ken McKay [ Sun Nov 06, 2016 11:05 pm ]
Post subject:  Re: Target neck geometry on electrics
You did it right Freeman! Your angle will be OK. I usually put the straightedge on top of the saddle though, and I can't tell if yours is or on the TOM top. Anyway that is a small amount and you have enough adjustability by either sanding the feet and or raising the wheels.

Since you asked what others do, I have a jig that is just a straight edge beam of beach that stays straight in all weather and it sits on the frets and projects to the bridge spot on the top. One end of the beam is flush with the nut and at the other end, which is the distance of the scale length, 24.75 inch, I have a dowel that protrudes 0.5 inches. This works for all guitars, either archtop or flat top that are using a TOM. I adjust the neck angle to have a slight gap between the dowel end and the guitar top. The actual angle is not necessary to know! But usually for a TOM sitting on an arched plate at max 1/2 inch or so height, falls about 4.5 to 5 degrees. A flat top guitar with a TOM is around 2.5 to 3 degrees.

Another consideration is what I call the "overstand" which is a violin term. This is how far the fingerboard, sitting on the neck, is above the plate. On your nice archtop there, it looks as if your fingerboard is about as far down as it can sit. In other words the neck cannot go much deeper into the body. However that mortise on the neck (or dovetail) could have been cut so it would sit higher. This will of course raise the projection (bridge height) without altering the angle. Straight up down. You probably should consider filling that gap with a wedge of mahogany after you glue the neck.

As long as we are on the subject, consider a LP arching with a TOM. The fingerboard is actually sitting on the top of the guitar arching. so in this case the precision must be built into the arching. The arching of the guitar top lengthwise needs to be the correct angle so that with the fingerboard sitting above it, the straight edge would project 1/2 inch where the TOM sits.

Same with some other guitars that Gibson makes. Some flat top solid body electrics have an angled body under the fingerboard.

And in an acoustic guitar the angle of the top plate, under the fingerboard IS the angle that projects to the correct distance above the bridge/saddle in most cases. All set in advance so that the bridge/saddle height is standardized to a reasonable dimension.
Author:  Freeman [ Mon Nov 07, 2016 11:26 am ]
Post subject:  Re: Target neck geometry on electrics
Thank you very much, Ken, that is extremely helpful. I'm pretty comfortable with the angle, the "overstand" and the set of the neck but it seems like a lot of it was just futzing around with the fitment until I got it where I wanted it. I was curious how others approached it and appreciate your incite.

I have made a little wedge - that in itself was an exercise in multi dimensional frustration LOL. It has to fit the curve of the top (asymmetrical, of course), the plane of the neck as well as the sides of the fretboard and side of the cutaway, and the top of the dovetail. Just a simple little wedge of mahogany.....

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