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I noticed a comment you made about having a seven degree string break angle at the nut on Fenders and I thought perhaps this might make a good subject of conversation.

I developed these nuts to achieve several things. The first objective was to incorporate the broader objective of minimizing the degree of sharp breaks along the entire string path. The premise is that bending a string along radius is always going to be better than a hard angular break...as long as there are definite contact points that establish a clean, clear fulcrum.

Holding the radius of the fretboard and nut through cad/cam, and pressing in each fret with its own specifically radiused caul is not difficult so it occurred to me that green guitar setups would go much easier if the nut slots and top surface were pre-made...and a tool could be made to simply shave off the bottom of the nut at adjustable angles and depths. Doing so means that the nut slots, once cut on the cnc machine, are never touched again. All height adjustments are made on the bottom of the nut. This allows string grooves that are exactly .001" in diameter larger than the intended string. The string grooves perfectly harness and control the path of each string through the nut. There's a downside to this, of course. You can't play around with different string gauges...but this is an experiment.

The point is...I designed a two degree break angle and I've never had any kind of buzz associated with the nut. I've already made the nuts encompassing a wide range of string gauges for my next model of guitar. The nut shaving tool makes it simple to do a setup. Once the correct shave angle and depth are determined I can plop a nut of any gauge into the tool and quickly shave it (at least I will be able to do this with a minor modification). I can simply supply a customer with several nuts to accommodate a gauge above and below his or her preferred gauge.

So my theory is...the break angle is quite irrelevant as long as the fulcrum point is perfectly defined...and STAYS defined over years of use. What do you think?

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Hi Stuart!

I enjoyed reading about your process and innovative solution to creating production nuts that are closely optimized out-of-the-box. Nicely done and great thinking on your part!

My comment in the other thread regarding nut slots was to give the OP a starting point that is tried and true but of course not optimized. The 7ish degree angle comes from Frank Ford or more specifically Frank's guidance to take the typical headstock set-back angle (often around 14 degrees) and half it.

If you read the comment about Ravi Shankar (and his daughter....) and the sitar sound that invariably haunts new-nut-slot-cutters what I am addressing is a nut slot with too shallow an angle. What may result and often does when the angle is not great enough is the vibrating string vibrating in waves of course actually lifts above the shallow nut slot at the leading edge/face of the nut and does not properly terminate with a hard stop for some distance inward in the nut slot. Not only is a common occurrence the Ravi sound of a sitar but tuning stability issues can result as well since the "speaking length" of the string is now continuously variable.

Is two degrees at the face of your CNCed nuts a great enough angle? Don't know but if you are not getting the sitar sound or tuning stability issues you may have nailed it so-to-speak. I also agree with you on the better and more complete contact point of the curved slot provided that the remaining angle at the face of the slot is still great enough to properly terminate the speaking length of the string even with ham-fisted ax abusers...

From a production point of view your idea and process is pretty cool and again I appreciate you sharing it with us. Floyds too for all of time that there have been these miserable Floyd things on the market also address nut slot depth/height by augmenting the underside of the nut assembly with shims. I know you don't shim in favor of multiple nuts of various heights and for various string gauges.

Perhaps keep in mind that some day someone else will be servicing your very fine instruments and may not understand how the system was engineered to function and just possibly may take to the nut with individual files. Although not likely to cause any real harm beyond perhaps eliminating the gentle curves that you have engineered into the nut slots it's probably a good idea to consider what some hack might do to the thing down the road.

Even though you did not bring this up it's also on my mind, two things actually so bear with me here as I mention them.

Some nut materials suck and basically give way for the files but won't cut well. Nuts on many imports including some well made imports such as the PRS SE series use a rubbery nut material that moves out of the way of the files, in your case cutting tool, and then revert to their former state. When and if milling the slot .001" greater than string gauge I am bringing this up because these lesser materials may cut fine but may also close back up after being cut and may not actually be .001" greater than the string diameter. There is also the issue of quality control on various string sets - they are not always what they are labeled to be and a .001" tolerance may be too tight for some manufacturer's strings.

Lastly and related nut slot cutting is an art and it's been said many times that one has to do it at least 100 times (one hundred nuts, 600 slots...) to even begin to understand the nuances and how the entire string, nut, etc. system works together. I used to think that this was crap until I played instruments with very well cut slots - It's a noticeable difference and a very welcome one too in that the instrument is far easier to play.

With any system including bridges with adjustment points only at the ends it makes things unadjustable for the center strings. Nuts with the Floyd system have long suffered from this and instead of the ability to optimize the individual strings one has to accept compromises with the inset string since there is no individual adjustment.

On shredders with 9's I don't see any issue here but I would see some issues on acoustics with larger gauge strings already making the thing more difficult for those with less hand strength to play. Additionally on acoustics our volume does not come from a Marshall full stack set to "11" so we may hit the instrument harder for louder passages. This also makes the greater vibrational energy of the string more likely to go beyond the nut face on a shallow-cut slot.

One of our specialties one that I personally get off on is setting up guitars for folks with disabilities. This may include very young kids getting into it early as well. This is a place where that 5 - 10% improvement in playability may make the difference between not playing at all and enjoying how rewarding learning to play a guitar can be. It's also a place where a very skilled nut-slot-cutter can make a huge difference for a client.

For your market though in the high-end, custom electric world I don't that it will matter.

Again nice design, engineering and pretty innovative too!

Thank you, Hesh.

I've thought of the issue of servicing the instrument by others. There's not much that can be done except to amply inform the customer about these sorts of issues...and offer to consult with any repair person that gets their hands on it. I'm guessing it's going be only a small issue.

I think shimming would be less preferable than good solid contact of the bottom of the nut to the bottom of the nut slot....so adjusting with shims wouldn't work there.

On the newer nuts I've cut the string grooves bit deeper while maintaining the diameter control. Common sense says to do it although I've not had complaints or seen any issues myself. Theoretically the tiniest bit of a sidewall (.005") to the groove should keep it in place under any side load. Even so...no string has ever popped out of these half round grooves.

I think maybe tuning stability is enhanced by this design since the string has less tendency to bind at the nut. Without a sharp break, having accurately shaped grooves may facilitate a "slipping" action there...especially with wound strings..idk. The guitars made so far using this all hold tuning very well after the initial string stretching of a new set.

I wonder if you've noticed a linear relationship of the bottom of each string to the first fret? On a set of .009" - .042" I shoot for .015" off the fret on the the low E and .011" on the high E and let the four middle strings go for the ride. I'm not sure how other builders set them for electrics or whether .015" is high or low compared to others. I'm just curious if you've found that certain strings measure higher or lower than the expected position after a good setup.

So far...all I've used is Dupont Corian for nuts. I chose it after doing a lot of machining experiments with various stuff. I assume it meets with your approval for a material that will hold specifications when machining...it seems to work very well for nuts...and precise inlay work. Maybe it's a little brittle at worst but I take off all sharp edges and corners whenever possible to address this issue. The question is; how well it will hold up over time?

What do you think is the best nut material?

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

You are very welcome Stuart my friend.

Please know though that I am not an expert. I'm just a guy who started building acoustic guitars in my spare bathroom and built a number of them before it occurred to me that there may be Internet forums. Funny thing is that my second career that I spent several decades with was enterprise software. Why it never occurred to me that there were such things as Internet forums with the IT background that I have will give you some clue that I may not be the brightest bulb in the pack.... Just don't call me one of those fat-ass Al Gore CFL bulbs please....

Anyway much of what I have learned to date comes from David Collins who I apprenticed with for several years before hanging out my own shingle and diving into repair work and also selling my acoustic creations but never commissions, not into selling futures personally. More recently we opened Ann Arbor Guitars which is a three Luthier shop and one of the busiest in our neck of the woods. We fix everything from pre-war (WWII for Eric...) Martins, very-nearly-pre-civil-war Martins too to shredders, vintage arch tops, you name it.

I'm a reader and after a 10 hour day fixing Michigan's and Northern Ohio's axes I come home and play my strat or one of my acoustics and then start participating on forums, reading about Lutherie in what ever book is the currently in the library (bathroom.... but you have me interested in Emerson... ), etc.

OK, moving on: I think that amplifying your desire to support any servicing is indeed all that you can do. There are hacks out here though so beware. With the recent great recession and musical employment chairs lots of folks hung out shingles who did not have the benefit of a highly skilled mentor and are happy to mess up some of the nicest axes. We often see them after the damage is done and it's a crying shame.

Shimming is kind of sort of frowned upon except for the concept of "appropriate for the instrument." It's perfectly appropriate to shim a nut on say an acoustic that cost $229.95 at GC when the client budget is $80 and a new nut is $80 and the set-up is another $40. But for new instruments yeah shimming sucks in my view too.

Here is something to think about though. Don't know what you glue in your nuts with, we use CA, I use the slow CA giving my old self extra time to get the ends perfectly flush. Anyway it's pretty common when we work on guitars for the nuts to fall out or off. Invariably someone did use glue and it simply did not hold. What happens next is in order to get perfect contact with a now rough nut slot containing wood fibers, old glue, etc. the next step is the uber sharp chisel and cleaning out the slot. Many new instruments have uneven slots too or may have a hump or dip in the middle. So as you can see we have to remove a bit of material from the slot to true it up appropriately so that the reglued nut has complete contact everywhere. Once we remove a couple thou of material, well you can see where I am going with this. Reinstalling the original nut will make it less proud than it originally was. Very tight nut slot tolerances may result in the slots now being too low. Something to consider.

There are a lot of different views as to how low a nut slot should be cut. We subscribe to the thinking that this is the user interface to the instrument and very important in terms of the ease of playing of the guitar. So it's not uncommon for us to cut the slots pretty low. How low? Are you sitting down? For a high e we may cut it .001 or less from the crown of the first fret when fretting and holding between the second and third fret. Although there are no hard rules here for me I shoot for a space also while fretting and holding between the second and third fret of approx. half the diameter of the specific and individual string.

This is something that I was hinting at in my last post. So you can see depending on the individual string gauges in the set that every nut slot is different and every nut slot may benefit from being individually addressed. Again with 9's and a systematic approach with process controls such as your very cool system it may not matter.

A related topic is depth of nut slots. The idea that half the string should be proud of the nut slot we believe originated with Dan, Dan Earlywine. Is it necessary in my view - no. It looks cool though and is an indication of skill on the part of the Luthier but likely not something that would ever even be noticed by the players. Our nut slot depth is determined in how we make our nuts (bone and only bone, more on this in a min.). We make our nuts on the guitar cutting each individual slot as per above and when close to final depth I bring out my big, honking bastard file and file the nut's top and back angle until I destroy the set of strings used for the process. This makes our nut slot depth about the same as the string gauge. Final height is cut after the nut is highly polished on our nut buffer and firmly and correctly installed on the instrument. It can be a scary thing to watch for the uninitiated or ax owner in that we are filing away on their finished instrument. Kind of like watching the sausage making....

Corian is great stuff and often used in Lutherie school to make the student make their first 100 nuts with. Not kidding, there is a rite of passage thing here where it's also believed that you have to make 100 nuts before you know your nuts from a hole in the ground.... so-to-speak.... A typical scenario is the student makes his 41st nut, spends three hours doing so, it's near perfect and the student is pretty proud of it. The instructor is called over, he/she indicates that it not good enough without usually even looking and picks it up and throws it in the trash right in front of the student.... I've heard this story about this practice from a number of unrelated people but fortunately never had to endure it myself although I do personally see some value in repetition since I greatly benefit from doing things often and over and over.

Best nut material? Not sure that I would position decent quality, degreased, non-bleached bone as the best but we like it fine. In the acoustic world bone is considered an upgrade and in my own non-scientific testing I like bone on my own instruments over corian, rams horn, fossilized Mammoth, and some of the other materials that I have tried including wood, ebony and BRW. It lasts longer although not forever either and acoustically it seems to be less dampening than some of the other materials that I have tried. We won't use commercially available plastic nuts even upon request - we make a new custom bone nut or won't take on the job at all. The thinking being that one size never fits all in the repair world and once you manipulate and size a commercially available offering you have spent nearly as much time as it takes us to make a new bone nut from scratch sands raising the stinkin cow.... Besides some of our bone comes from an excellent meat market where I live that has fantastic filets...

Not sure if corian will hold up as well as bone, probably not but it certainly is WAY better than plastic and I would consider it an excellent nut material too.

I was going to suggest to you that you also contact Rick Turner who is on our other forum as well. He's a great guy but don't tell anyone because he likes to keep the gruff persona to ward off the mouth breathers. Anyway Rick has more experience with electric guitar production from a real Luthier standpoint than anyone else that I know. Like you he is also an innovator and has spent lots of time on the bleeding edge of Lutherie. Rick had a lot to do with me going the repair route in that he kind of shamed me into this endeavor and in the end he was absolutely right. I love what I do more so now than any of my other two previous careers. Anyway when it comes to materials science, process controls, and good old fashioned been there done that experience Rick is one of the best resources alive today. And did I mention that he is one hell of a great guy too!

Anyway I also wanted to compliment you on your approach to the market and your product development. I might not post much at times but I do read this forum every day and have watched with great interest your use of CNC and some of the other things that your instruments are pioneering. People seem to come and go with Lutherie forums and Lutherie in general but some of us hang in and it becomes our life. I have a strong suspicion that you are hooked, happy, and on your way!

@Stuart Gort, Thanks for bringing this topic up. I have always been curious about break angles at the nut and having done a number of them in my time I have sort of figured it out on my own from doing them wrong and ending up with a buzz or problems with tuning. For a number of years I just winged it and hoped for the best but now I have gotten pretty good at slotting a nut and having them work right. Hesh is quite correct that you can tell when they are set up correctly. I always do mine by eye trying to follow a smooth path from the frets to the tuners without any sharp breaks (you can usually tell when they are not right).

One question I have is about the horizontal angle of the slots. I see a lot of brand name guitars that cut the slots straight and I use to do it that way when replacing a nut but in the past few years I have started putting an angle on them. I have found that cutting the slot about half of the angle to the peg seem to work pretty well.

I think it is much more critical on acoustics than electrics. I have done a number of electrics and it seems they are much more forgiving (maybe because of they are amplified but I usually don't plug an electric in until after it is completely set up.

I always use bone because that is what I have always used but I have a Martin with a Corian that I have been tinking of swapping out for bone to see what the difference is. I have thought about trying it for new nuts but I have a pretty good supply of bone on hand so that is what I always grab.

Bob

I work the nut slot to a "slip" fit. It drops into the slot and I can slide it back and forth in, but only just barely. Once I finish the setup I glue the nut into place with two small drops of epoxy and clamp it. The nuts are machined flush to the finish...which is to say I design the neck width .02" narrower than the nut and assume about .01" finish. Then I sand it all flush and polish it after the epoxy cures. My new design uses a blind nut slot so the finishing issue is removed but in both cases the glue is used only to keep the nut from flying away. I'm striving for string pressure alone to create full contact....but then I'm cutting the nut slots and the nuts on the cnc so the bottom of the slot and the nut are always pretty well defined. Btw...I don't do repairs professionally now although I have in the past...but only for electrics...long ago. My overall guitar building experience is limited to about 70 necks and 35 bodies...but I have some depth with cad/cam/cnc and tool making.



The way I described doing it earlier I get close to the same result as the .001" you mentioned when the string is fretted between frets 2 and three. It's maybe .002" or .0025"...just enough to bind a little strip of legal paper...which is .003". I only ever check the outside strings and now I rarely even do that since the original measurements of a green setup and the subsequent working of the nut produce a pretty consistent result on the first attempt. The nut shaving tool works very well...if the measurements of the string from its bottom off the first fret are accurate. I use layered strips of paper as feeler gauges and find that I can really feel a slight obstruction with that.



You're probably right...so that's why you have to blow your own horn from time to time. I expect this design has some merit but no one will ever notice it unless I point to it on my web site...so I aim to do that, assuming that drawing attention to this level of design detail will, at worst, reflect positively on the rest of the instrument.



Thank you, Hesh. I've dreamed of building...since I was a kid. It wasn't until I had fairly mastered cad/cam/cnc that I started to realize I could actually build guitars without a massive learning curve. Of course, that was as wrong as Padma in a suit...but some learning curves are far more enjoyable than others.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I just put dots of glue on the end of the fingerboard. Never on the bottom of the slot. The glue holds the nut and is easily scraped of without taking any wood. I wish more folks did this. glue on the bottom of the slot does so much needless damage IMHO.

FWIW: in some experiments I did a few years ago, I found that a saddle break angle of 6 degrees was just just sufficient, and there's no reason a seven degree angle would not be fine at the nut. So long as the string remains in contact with the end point throughout it's full cycle of vibration, it will transfer all of the force to the nut or saddle, and a higher break angle won't do any more. Generally speaking, if the string is hopping off the end point, you'll know it by the sound.

Hi Stuart,
From several years of working with Corian and other solid surface materials I've found that some colors seem to be harder than others. Glacier white being one of the hardest. Corian is a filler material (aluminum hydroxide for the most part) in an acrylic resin and not nearly as hard as good quality bone. Easier to machine, but I don't think as long lasting. I still use corian for nuts and saddles on inexpensive instruments I build (stick dulcimers and such) but prefer bone or ivory for better quality stuff. I use mammoth ivory for the interesting colors it comes in and the nice polish it takes. It is reasonably hard although probably not as hard as bone.
If you are putting a lot of precision in the manufacture of the nut you may want to go to a material that will hold those tolerances longer.