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Are there any good tutorials on how to set the neck angle when sanding the sides before attaching the top? After 18 guitars I am still struggling to get my neck angles correct from the very beginning and spend way too much time trying to fit things later. (FYI - I am using a double bolt mortice and tenon setup with the necks created with a 1.5 degree angle.

When I was taught, I was told to radius dish the top rims and then go back and flat sand the area from the neck to the waist at the proper angle. I just read an article where it says that Martin flat sands the top rims and then does the neck angle sanding. I am reading that an angle of 1.3 degrees is what Martin (and some others) use. I have read that the goal is to have the flat neck relief angle from the neck block to the waist.

My math may be way off - but:
Given an 18.75" body length
6.5" center of waist of guitar from top of neck block

Would that mean to get a 1.3 degree angle from the neck block to the waist I need to put a .26" block under the tail block and sand until my pencil marks I make on the kerfed lining are gone to the waist?

I have attached a diagram I created to try to understand all this.

Am I way off - or is this correct?

Help is always appreciated.

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P A U L B U R N E R
Burner Guitars

Hesh has posted toots on this on the OLF.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Paul I believe you know about this toot, right? http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=25931

There is one other toot that is also important when using the flattening the upper bout method and that's in the toot's section too and it's about setting the neck angle.

There are things that will make your results or anyone's a bit different and the toots are offered as both a general guide and to describe a method that Martin has used for years.

Where folks in my experience answering questions about this method over the years tend to get confused is the notion that there is a magic neck angle number that will get us where we want to go. 1.5, 1.3 what ever these numbers will get us close but always the need for fitting will remain.

Necks have to be fitted, always and this method will get you close and got me right where I needed to go for dozens of guitars. If 1/4" for the shim works better for you use that number, please.

The other reason when on rare occasion someone is having trouble with the method as described is that they are doing something different from the prerequisites mentioned in the toot. An UTB with a radius beyond only the most minor radius will through off the numbers too. Non-standard bridge heights have also been an issue for one fellow that I can recall some years ago.

The top radius also is important as well more or less will skew what size shim works for ya.

If the issue is that material has to be removed from the neck heel and that the neck still needs to be fitted that's always going to be the case.

If you want to give me a call I'm always happy to help as you know my friend.

Here's a link to "Fitting a Neck."

http://www.luthiersforum.com/forum/viewtopic.php?f=10102&t=15022&p=214039&view=show#p214039

Thanks for the comments and links to the tutorial Hesh. I had forgotten where to find it.

This is is EXACTLY how I have been doing my upper bout area on my guitars - but I must not be quite high enough with my shim as I am getting a small gap a the end of my fingerboard extension where it should lay nice and flat against the top of the guitar.

I'll give you a call just so we can chat and catch up and think about my process. If I find something helpful for others I will post here.

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P A U L B U R N E R
Burner Guitars

Seems you are just a little off from the right path. Tipping the neck back away from the sound board about 1.3 degrees has become some what of a standard since it puts the fingerboard plane on a good trajectory with the bridge and saddle. What is important to remember is that the finger-board extension area on the sound board needs to match up and make a straight line (the waist curve has nothing to do with the angle that needs to be established) Now at the bridge location different factors can effect the measurement where the FB plane intersects the saddle. How much arch one puts in the SB bracing is one. But the fact is you can't tilt the neck one way or another to adjust to this height -- that screws up the nice straight no hump plane that has been established. To address this reality/variable the factories including Martin have an exquisitely simple solution -- they use bridges of slightly different thicknesses (Martin has four maybe more). I read over and over again about how builders obsess over this situation -- what often also gets over looked is that the saddle can vary a bit in height. Over the years I have found in my role as a trainer its far more important to teach the "Why am I doing this" before dwelling on the process itself. Seems you may have visited my article on the subject already if not check it out:
http://www.kennethmichaelguitars.com/neckangle.html

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Ken Cierp

http://www.kennethmichaelguitars.com/

Thanks Ken - yes I have checked out your website.

Appreciated the info.

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P A U L B U R N E R
Burner Guitars

Paul: Have not done the trig. so we assume your figures correct. It looks like your working with a flat top in your drawing but you say you are using a radius disc. The use of a radius disc will drop the tail block............most likely close to the difference between Hesh's block used in the tout and your own figure. I use a 30' radius and using Hesh's method things work out close in most cases. If not one can do small work arounds. As Ken suggests the neck and upper bout being co-planer is key along with being close to optimum height below that plane at the bridge location. I like that to be close to .100".

Tom
PS There is a write up in Trevor Gore's book about this. Not sure if you have the book or not but a worth while investment.

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A person who has never made a mistake has never made anything!!!

https://www.youtube.com/results?search_ ... tial+setup

https://www.youtube.com/watch?v=LrgRKKsxL-M


there are 2 links here one for the end result and the prepping to show the early stages

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

The one thing you always have to have in the back of your mind is what the box wil do under string tension. A perfect co-planer extension may become the dreaded rising extension strung up.
Your construction techniques and whether the extension is glued can be factors.

In some cases an upper bout angle that gives a little drop off unstrung may be fine.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Certainly I have seen this happen, but it is most likely with a rise in action height. A bit of a reset and all is well again. They seem to be all right then for the long haul. All of my guitars that I've kept for myself don't have the fingerboard extension glued. I have a couple that are at least 10 years old set up this way and all is OK. Mind you the rise of action at first may be partly as a result of not gluing but once that slight initial neck reset is done they become very stable. Just my experience, I'm sure others do things differently.
Tom

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A person who has never made a mistake has never made anything!!!

I think that is very true with an extension that is not glued to the top or some designs that are bolted on. I have used the Bourgeois type double tenon as described by Sylvan Wells and John Mayes and have seen exactly the same settling in and need for a minor neck set tweak early on in the first year or so of life. I also agree completely that they all seem very stable after that. I didn't see that issue with glued extensions.

I don't like the idea of sending a guitar out in the world knowing that it might need a little neck set tweak early on for optimal setup but love the flexibility of the double tenon bolt on neck so besides working on mods to make things more stable I usually angle the upper bout a little less than the neck angle and when all is strung up it usually results in the desired drop off and allows a little wiggle room for any further settling. I usually shoot for a fairly generous saddle height around 5/32-3/16 out of the gate for the same reason. I do make the customers aware that as with any new guitar some tweaking of the setup is inevitable in the first year or so.

Again this is for the Bourgeois style joint and others, especially those with glued or fully supported extensions will behave differently.

I think everyone needs to see what their guitars look like a couple of years down the road to get a handle on exactly what you want to do with the upper bout angle initially.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

My recurring issue is similar, and I'm hoping to get it worked out on my current project. Instead of a gap at the end of the fretboard, I have one at the joint itself. It's usually 1/32" or so.

My method of setting neck angle has been what I learned from the Mayes DVD: running a straight edge down an un-fretted fretboard until it just slides over the bridge. Using that method, my neck angle has been correct relative to the bridge, but evidently not for a seamless neck to body joint.

I don't know if this could be your problem Jim but if you use a tapered heel and the surface of the upper bout is radiused it'll never fit right out of the gate. There will always be a little high spot in the middle you have to deal with.

It took me several years of frustration to figure that out and I actually think I figured it out after reading something from Todd on this forum.

If you undercut the heel it is easy to floss out after you understand what is going on.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks, Terence. It sounds like you're describing the heel itself, and I do get a good fit there. My graphic skills are no where near as good as Paul's, but I'm getting my small gap where you see purple. It isn't as big as my graphic makes it seem. I usually have 1/32" of light between the fretboard and body at the joint, and it tapers to nothing over an inch or so. I've just lived with it, but I'd like to get the area seamless if I can.

This a pretty normal situation --- as mentioned above I think worrying a little too much about where a straight edge passes over the bridge simply messes with one's mind. Pretty common, I'd shave the heel the tiny amount necessary to get the complimentary angles to match perfectly. This of course will pitch the straight edge a tiny bit above the bridge --- the bridge thickness and the saddle height are important adjustable variables. As mentioned above either or both can be changed -- again the factories have a range of bridge thicknesses and saddle heights to cope with this issue.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Excellent. Thanks, Ken.



Tom, I have the books. Is it in Build or Design? Do you remember?

Section 4.6.12, Design.

One of these days I'll write a piece on all the issues around neck angle related to the different construction techniques. There are many ways to get it right and an infinity of ways to get it wrong. The majority of books don't cover it well (or there wouldn't be the level of confusion that exists). I did a search on one forum (can't remember which) on "neck angle" which delivered something like 19 pages of results, demonstrating how much confusion there is. Unless you really understand the basic geometry, mixing advice from different sources is likely to give you problems.

I wrote this on another forum, so I've just pasted it here, with minor edits for added clarity. It's a method that works well for outside mold/radius dish/bolt on neck construction (the method in the book), but the principles apply to any construction method provided they're properly applied. Don't forget about the relief issue, or you'll end up with a "ski jump" off the end of the fretboard. So....

"The best way to set the neck angle is...not to measure the angle!

You are primarily interested in two things - the string height above the twelfth fret (say 2.5mm for the 4th string) and the string height above the soundboard at the saddle position (say 14mm at the 4th string). However this knocks on into a whole stack of other things, like the doming of the top, bridge height, saddle protrusion, effect of relief on action, scale length, neck joint fret, etc. etc..

You don't have to do it this way, but many builders, including me, like to have the top of the neck coplanar with the upper bout, so you can glue a straight fretboard down flat. So, in fact, it is the longitudinal tangent to the upper bout projected over the saddle position that determines the neck angle, not any angle the neck assembly makes with the sides. That angle just needs to be fitted to suit. If one of the standard top domes is used, e.g. ~8m or ~10m you will end up with a string height above the soundboard that is too high (well, higher than the 14mm I use). So you need to flatten the upper bout (usually by reducing the curvature on the upper transverse brace) until the projection of the tangent over the upper bout comes out at ~2.5mm above the saddle position. Then when you add the fretboard, the frets and the strings at the right action you get to the target string height above the soundboard. Keeping to a tight target helps give you consistency in the sound.

If you prefer to play with a fair amount of relief in the neck, the relief effect normally adds to the action, so you have to take that into account. If you don't, and just add relief to a system that's been computed around straight lines, you will get either a higher action or lower string height at the saddle than you wanted. Further, if you drop the saddle height to get the right action [i.e. you rotate the string plane relative to the fretboard] this gives you a "ski-jump" effect on the end of the fretboard, which you then have to remove if you're looking for outstanding playability.

Classicals are a different story altogether!

Most books don't explain any of this stuff or how to do it "properly"."

All the detailed geometry, with diagrams, calculations etc. is explained in Section 4.6.12.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Exactly -- Which in fact is what Martin does at the factory, they and many builders including myself choose to use 1.3 degrees upper bout pitch in relation to the neck heel at the rim. There's about 200 plus Martin guitars per day made this way so it does work just fine.

Here's the machine that sands the rim top edge flat -- then tilts to sand the 1.3 degree upper bout slope. Jim Olson and Charlie Hoffman use a router to shave the slope.

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Ken Cierp

http://www.kennethmichaelguitars.com/

... which illustrates some of the causes of confusion.

The OP is using a radius dish...
As far as I can see, the Martin technique can only work if they are flat sanding, i.e. no radius (or a very large radius) on the dish. They are creating a lengthwise "pseudo arch" by tilting the sanding plane.

If a "standard" top dome (28' or 33') is sanded on both upper and lower bouts first and then a flat 1.3 degree tilt is sanded on the upper bout, the projection of a longitudinal tangent to the upper bout increases the clearance over the saddle position, leaving you with way too much neck angle. If one of the usual top radius domes is used, the arch on the upper transverse brace has to be reduced (which makes the upper bout flatter, but does not change the rim profile) to get the right clearance, i.e. to decrease the clearance of the projection of the tangent to the upper bout over the saddle position.

This is why it is important to know all the parameters surrounding a particular technique... ...and why
The Martin technique obviously works*, like many can, but it's really important to know all the ins and outs of that particular process. Of course, life isn't made any easier by the many published incorrect processes which a new builder has no way of recognizing.

* But Martin also use a variety of bridge heights to compensate for the fact that this technique cannot repeatably deliver sufficient accuracy. The height of the strings above the soundboard at the saddle position should be an inviolate design parameter (because it affects the torque on the sound board and all the consequences that go with that), not something that is compromised because they can't set the necks accurately enough. But that's one of the compromises that gets made in a factory situation.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Correct the contour on their main braces is 52' --- The sanding disk on the machine is flat

Could not agree more --- I know that Martins are just factory made guitars but we (KMG) strive to provide tooling, fixtures, kits and processes that help to closely emulate what's done in their facility.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Just enjoyed another hour in the books... Started in Design and went through Build.


Sent from my iPhone using Tapatalk

There is an important distinction between how Martin uses their own method and how we might and I do.

True Martin has several bridge heights that they draw from when need be and this is because they don't do the fitting process to the extent that we do. Or in other words using the Martin method that Frank Finiccihio teaches, Kevn Gallagher used to teach RIP, and a host of us do and use we fit the neck to our specific bridge making multiple bridge heights moot since we don't try to match a neck angle to a "range" of bridge heights.

Instead we match the neck angle to THE bridge height and again all necks have to be fitted unless you have multiple bridge heights but even still you will have to get the neck angle in range for the bridge choice possibilities.

Most builders have a target string height and corresponding bridge and saddle heights that we want to see when all is said and done.

Regarding if the method would work without either flattening the upper bout or using a very minor radius I would agree that flattening or a minor radius is key to the Martin method working. Flattening the upper bout has the added dividend besides helping with neck angle and fall-away of permitting the fret board to sit flat on the upper bout. If there is much of a radius there one has to hollow out under the fret board extension to match and who wants to do that....

Of all the operations that we might do to build a guitar getting the neck angle right is likely the very most critical with little room for error. That's why whatever method one uses it's important to follow that method to the letter or use a different method or develop your own method. Lots of things that we do in the commercial repair shop were developed by us including tooling. Just in my own struggles to get comfortable with my building you encounter light bulb moments that in time become how you approach the work in the future. Maybe soon someone will be 3D printing a Somogyi.... Maybe not.....

Amen to that!


As a side bar -- in a recent conversation I had with a Martin factory Engineer (we were actually discussing finger board slope and radius) some how neck fitting came up, I suppose this should not be a surprise, a comment was made that indicated that until the dawn of the cut-way models in the factory line up -- the neck fitting process was mainly a cosmetic concern play-ability above the 12th fret and tonal considerations were not a big issue. Think about that -- yet makers around the world are trying to duplicate the look and sound of those broad/mystery specification pre-cutaway guitars.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Here's some show and tell that I wanted to do.

Not only is neck angle critical to builders for those of us in the biz taking in guitars every day it's always super important to us to set the expectations of folks correctly. Not a bad thing to do in most pursuits I'll add.

When stuff comes in we need to be able to know for sure what the possibilities for the value that we might provide actually are. We also are not interested in either hurting ourselves by over promising or being wrong about something and even more important to us is that client expectation that is "critical to quality" in Six Sigma speak for the customer experience.

Both Dave and I can eyeball a neck and tell at once if the angle is to be a limiting factor, if it needs a reset, etc. But Dave made this tool so that we can know to what degree something is off AND give a visual indication with an accompanying narrative so that the client can see that they need a neck reset, or their guitar does.....

It's also critical for simple set-ups too to know if the neck angle is appropriate so that a set-up will improve things and to what degree. Again this permits us to set expectations correctly.

Don't mind the guitar in the pic or the tape. The tape is necessary so the jig stays in place for the pic. The guitar is some abandoned thing with some cracks in it that I am fixing up because, well guitars are people too.