Compensated nut WIP

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donnyb
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Compensated nut WIP

Post by donnyb » Fri Dec 14, 2018 6:50 pm

https://i.imgur.com/nnhjIcf.jpg

Hi,

Im in the process of making a compensated nut for an Epiphone Dot, which is set up well overall, including minimum string clearances over the 2nd fret to help address some sharpness on all strings when fretted on the first 3-4 frets. Especially the 6th string (eg in an open G chord)

Due to this sharpness that's been put up with for a long time, I read Stephen Delft's great article on The Compensated Nut and have followed it closely today, except I'm using some small diameter WD40 spray tubing to initially map out the shape, instead of bone shims .

I'm surprised at the amount of compensation required on the 6th (approx. 5mm) , with the other strings requiring 1.5 -3 mm movement towards the bridge. The tubing has raised the string clearances slightly , so these measurements will come back a little.

Anyone else come across the necessity of such large shelf extensions to address sharpness in the first 1-4 frets ?

Regards,

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kiwigeo
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Re: Compensated nut WIP

Post by kiwigeo » Fri Dec 14, 2018 9:23 pm

Welcome to the forum,

A lot of factors will influence how much compensation is required at the nut. String action, neck relief, string properties, compensation at the saddle...and the list goes on. Trevor Gore covers the subject in great detail in his two book set co-authored with Gerard Gilet. Trevor also provides instruction on a number of methods to calculate nut compensation....with varying degrees of complexity and accuracy.
donnyb wrote:
Fri Dec 14, 2018 6:50 pm
https://i.imgur.com/nnhjIcf.jpg

Hi,

Im in the process of making a compensated nut for an Epiphone Dot, which is set up well overall, including minimum string clearances over the 2nd fret to help address some sharpness on all strings when fretted on the first 3-4 frets. Especially the 6th string (eg in an open G chord)

Due to this sharpness that's been put up with for a long time, I read Stephen Delft's great article on The Compensated Nut and have followed it closely today, except I'm using some small diameter WD40 spray tubing to initially map out the shape, instead of bone shims .

I'm surprised at the amount of compensation required on the 6th (approx. 5mm) , with the other strings requiring 1.5 -3 mm movement towards the bridge. The tubing has raised the string clearances slightly , so these measurements will come back a little.

Anyone else come across the necessity of such large shelf extensions to address sharpness in the first 1-4 frets ?

Regards,
Martin

donnyb
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Re: Compensated nut WIP

Post by donnyb » Fri Dec 14, 2018 9:47 pm

Thankyou Kiwigeo.
Ill see if I can find the book online.
Regards,

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kiwigeo
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Re: Compensated nut WIP

Post by kiwigeo » Fri Dec 14, 2018 9:56 pm

You can buy the books via Trevor's website and if you ask nicely Trevor will even sign them for you :) https://goreguitars.com.au/main/page_th ... _book.html

Trevor is also on this forum (see Trevor's subforum) so any questions on nut compensation can be directed to him and Im sure he'll respond with some very useful information.
donnyb wrote:
Fri Dec 14, 2018 9:47 pm
Thankyou Kiwigeo.
Ill see if I can find the book online.
Regards,
Martin

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nkforster
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Re: Compensated nut WIP

Post by nkforster » Sat Dec 15, 2018 9:17 am

Welcome Donny. Something is awry with your calculations, as 5mm forward on the bottom E is way too much. But the overall shape of the curve looks close.

You can make the calculations with an accurate tuner and a new set of strings. But the rest of the setup needs to be right first - the nut/zero fret height, neck relief and action.

The Peterson app seems pretty good compared to my Peterson tuner.

Trevor has written about it in his excellent books, Grey Byers and Mike Doolin both have articles online if you spend a bit of time on the web you'll find them.

donnyb
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Re: Compensated nut WIP

Post by donnyb » Sun Dec 16, 2018 9:50 am

Thanks for that reply. I see you're in Brisbane. I'm at north Gold Coast .

Yes, the guitar is my personal favourite (atm !) and is set up nicely, as I have all the gear for that part (Stew Mac love me), a precision based mechanical background, a lifetime of guitar playing in bands, but not a lifetime of guitar set up experience.

Due to the playing side of my experience, I had noticed annoying sharpness especially on the 6th string , 3rd fret (G) so I have to 'tread ' lightly there when playing hard.

When I was mapping out the rough profile to get that G sweet with the rest of the neck (which yes, does increase string clearance a bit over the fret to exacerbate things), I recognised that something surely is not right here with needing a 5mm projection. I'm thinking that this will come back to 3-4 mm with 6th string clearance over the 2nd fret (3rd capo'd) back to .006". But it still seems a lot !

What's the worst compensation projection dimensions you've seen on a guitar with everything else in order ?

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Re: Compensated nut WIP

Post by donnyb » Sun Dec 16, 2018 1:10 pm

More information which might be helpful .

Just rechecked all measurements. First the scale length.

Epiphone Dot Nominated Scale Length : 24.75 " (628.65mm)

Actual SL measured from 1st - 13th fret: 314.14mm x 2 = 628.28 mm = 24 47/64ths" = 24.735"

Actual SL measured from nut face - 12 fret : 313.50mm. x 2 = 627.0 mm = 24 11/16th "= 24.685"

So , Im concluding that the nut slot/end of fretboard is 1/16" to close towards the 12th fret. That's not what I was expecting. I was thinking based on the sharpness of the lower frets, that the distance would be longer. Am I correct in that reasoning ?

Second, I re- checked fret slot spacings by Stephen Delft's method , viz., by measuring 5 groups of frets x 1.0595. The result are differences ranging between .2mm and .5mm . Is that too big an error ?

As I type this, I'm wondering with a slight head ache emerging.... if a nut (not a compensated one) is set back ie away from the bridge 1/16", to make the scale length correct i.e. 24.75" (presumably what the fret slots were originally calculated to and cut)….. and the intonation to the 12th readjusted at the bridge saddles, will that ameliorate the sharpness issue I have in frets 1-4, or make it worse ?

donnyb
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Re: Compensated nut WIP

Post by donnyb » Sun Dec 16, 2018 5:56 pm

donnyb wrote:
Sun Dec 16, 2018 9:50 am

Thanks for that reply. I see you're in Brisbane. I'm at north Gold Coast .

Yes, the guitar is my personal favourite (atm !) and is set up nicely, as I have all the gear for that part (Stew Mac love me), a precision based mechanical background, a lifetime of guitar playing in bands, but not a lifetime of guitar set up experience.

Due to the playing side of my experience, I had noticed annoying sharpness especially on the 6th string , 3rd fret (G) so I have to 'tread ' lightly there when playing hard.

When I was mapping out the rough profile to get that G sweet with the rest of the neck (which yes, does increase string clearance a bit over the fret to exacerbate things), I recognised that something surely is not right here with needing a 5mm projection. I'm thinking that this will come back to 3-4 mm with 6th string clearance over the 2nd fret (3rd capo'd) back to .006". But it still seems a lot !

What's the worst compensation projection dimensions you've seen on a guitar with everything else in order ?
Further to my first reply to your post above, I have now also checked the bridge location, based on the nominal scale length of 24.75". The posts are around 3mm too close to the nut. I had noticed last week that to achieve perfect intonation, the saddles needed to be adjusted much closer towards the nut than what Id call normal, but was at that time thinking there was an issue at the other end or neck somewhere causing frets 1-4 sharpness on some notes.

Ive also vernier checked the fret spacings and these are good.

Anything ringing any bells for you here ?

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Re: Compensated nut WIP

Post by donnyb » Mon Dec 17, 2018 2:39 pm

At the risk of being a nuisance with multiple posts.... I decided to start again.
    Fitted another new set of strings 010-046 D'Darrio
      Fitted a new blank nut and filed slots to similar string heights of original nut
        Set up intonation from open to the 12th fret, not by the frets 1-13 method this time. Resultant saddles angle across bridge normal
          Checked for note sharpness in the 1-4 fret zone - its still there.
            Checked bridge posts location based on 24.75" scale length. Its not as bad as I thought . The bridge posts have a slight acoustic style compensation offset which I hadn't take into account.
              Started adding even smaller diameter clear plastic spray tubes to reduce gain in string heights over these, and to establish a profile
                With the new strings, the profile is similar but not a dead match to the previous profile SEE PHOTO
                  Found that the intonation to the 12th was now horrid
                    Adjusted intonation at the bridge with the 'tubes profile' nut in place, which produced an abnormal saddles angle across bridge
                    (SEE PHOTO)
                    Image, https://i.imgur.com/g6hfI8E.jpg
                    Image https://i.imgur.com/RA1bx8G.jpg

                    The guitar plays very sweet all over now, but there's not much room for further bridge saddle adjustment.

                    Uneducated question : in theory, in shaping the future compensated nut shelf.....if I moved that 'tube profile' in the above photo further away from the bridge, carving the 1st and 2nd profiles into the compensated nut, with the 3rd string profile becoming the front edge of the nut, so that the only protrusions over the fretboard are the 4th, 5th and 6th profiles, but now not projecting out as far....... its going to throw out the intonation severely (right ?).... but when I correct that at the saddles, I'm assuming the saddles will then take a more usual angle across the bridge ? Or at lease give more room for adjustment ?

                    Please remember this is my first attempt at a compensating nut, but by the playing result I got , I'm hopefully not too far off the track. I just struggle with the maths of it all.

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                    Trevor Gore
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                    Re: Compensated nut WIP

                    Post by Trevor Gore » Wed Dec 19, 2018 5:41 pm

                    Sorry it's taken me a while to get to this. My first thought when I read this a while back was that you need to figure out what scale length you are working with. Gibson/Epiphone are notorious for using weird scale lengths and fretboard divisions; some are 12th root of two and some are real rule of 18, depending on where/when it was built.

                    The best way I've found to figure out the theoretical scale length is to measure the distances between every fret and then compare the spacing with 12th root of 2 spacings computed from various scale lengths, and seeing which one matches best (i.e. the sum of the differences between measured and actual is a minimum; which can be done with an optimisation routine). Usually I ignore the nut to first fret spacing as that is the one that is frequently fiddled with. When you know the theoretical scale length used to divide the fretboard, you can figure out where the zero fret is supposed to be and calculate what (if any) nut compensation has already been applied and approximately where the saddle should be, allowing for a bit of traditional compensation. Expect one or two frets to be wrongly positioned. That's been the case with a number of guitars I've measured. At that point you will know whether the guitar has been put together anything like right with the fretboard, nut and saddle in more or less the right places. (A rogue fretboard (off a different model) may have been fitted. Stuff like that occasionally happens in factories).

                    If the guitar is put together correctly, using new strings, intonate it using the standard 12th fret, saddle-only compensation method. Now do a fretboard cents error mapping, but use something hard and fairly pointy (e.g. a worn flat head screwdriver) to fret the string exactly onto the top of the fret. The reason for doing this is that the string now takes a purely triangular path from nut to fret to saddle rather than from nut to fret(n-1) to finger to fret(n) to saddle. That extra path length is why nut compensation is needed. The proof of that is in Appendix 5 (2nd ed only). If your nut is in the zero fret position and the saddle is compensated to the 12th fret "rule" (when fretted with said screwdriver) all fretted (with the screwdriver) notes should play very close to in tune, at least on the frets that are in the right place. If they don't, there is a resonance coupling problem happening, where the strings are shifted in frequency by a body or neck resonance close in frequency to a played note frequency. On an Epiphone dot, this is more likely to be a neck resonance*, which can often be changed by changing the truss rod tension. It is usually best to have the neck just off dead straight, which in most cases will mean tightening the truss rod. That will change the action. Re-do the set-up to the 12th fret saddle-only compensation rule and map the fretboard again (fretting with the screwdriver) and see what you have. Hopefully it will be improved. Then try fretting with fingers and see if you can live with the difference. If you can't, some nut compensation will need to be applied. A quick and dirty way of doing that (that works pretty well) is to measure the saddle compensation added using the 12th fret saddle-only method (e.g. 3mm), divide the number by 2, (giving 1.5mm) then apply 1.5mm compensation to both the nut and saddle (i.e. take off 1.5mm of saddle compensation to bring you back to 1.5mm total saddle compensation and add 1.5mm of nut compensation, moving the nut toward fret 1). Do that for each string. That should get you reasonably close to accurate equal temperament (and hopefully your tuner is set up on equal temperament!)

                    * It could be a shift due to having the pick-ups too close to the strings, too, fixed by backing them off.

                    blackalex1952
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                    Re: Compensated nut WIP

                    Post by blackalex1952 » Wed Dec 19, 2018 9:23 pm

                    Thanks once again to Trevor for a concise and clear explanation!!! Awesome!!!
                    Cheers! Ross
                    "Everything I say on the topic is based solely upon inexperience and assumption!"

                    donnyb
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                    Re: Compensated nut WIP

                    Post by donnyb » Thu Dec 20, 2018 9:25 pm

                    Thankyou Trevor. Amazing stuff. I have a lot to digest and learn, but it keeps life interesting !

                    First up...re the scale length, where does the number 1.0595 fit with quote "12th root of two and some are real rule of 18" ?

                    I used the multiplier I quoted above (as stated by Stephen Delft in his article) when I measured out the groups of frets he stated in that article, "The Compensated Nut" to check scale length.

                    regards,
                    Don

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                    Trevor Gore
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                    Re: Compensated nut WIP

                    Post by Trevor Gore » Fri Dec 21, 2018 10:22 am

                    donnyb wrote:
                    Thu Dec 20, 2018 9:25 pm
                    First up...re the scale length, where does the number 1.0595 fit with quote "12th root of two and some are real rule of 18" ?
                    See Section 4.6.6, Design.

                    donnyb
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                    Re: Compensated nut WIP

                    Post by donnyb » Sat Dec 22, 2018 12:30 pm

                    Trevor,

                    Is that reference from one of your books ? Which one ?

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                    colburge
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                    Re: Compensated nut WIP

                    Post by colburge » Sat Dec 22, 2018 12:40 pm

                    It is a 2 volume set, one of them is the 'Design' volume and one of them is the "Build" volume.

                    Col

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                    Trevor Gore
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                    Re: Compensated nut WIP

                    Post by Trevor Gore » Sat Dec 22, 2018 4:48 pm

                    donnyb wrote:
                    Sat Dec 22, 2018 12:30 pm
                    Is that reference from one of your books ? Which one ?
                    Yes, the Design book as Col mentioned. Apologies, I jumped to the assumption that as you were messing with nut compensation you would already have them. There's a 25 page chapter on compensation and intonation (Section 4.7, Design) with a few different methods depending on how much maths you want to do.

                    I tend to reference the sections when there is maths involved, as forums are not the easiest places to write mathematical formulae (and it saves me a truck load of typing!)

                    donnyb
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                    Re: Compensated nut WIP

                    Post by donnyb » Sat Dec 22, 2018 5:43 pm

                    colburge wrote:
                    Sat Dec 22, 2018 12:40 pm
                    It is a 2 volume set, one of them is the 'Design' volume and one of them is the "Build" volume.

                    Col
                    Thanks Col.

                    donnyb
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                    Re: Compensated nut WIP

                    Post by donnyb » Sat Dec 22, 2018 5:55 pm

                    Trevor Gore wrote:
                    Sat Dec 22, 2018 4:48 pm

                    donnyb wrote:
                    Sat Dec 22, 2018 12:30 pm

                    Is that reference from one of your books ? Which one ?

                    Yes, the Design book as Col mentioned. Apologies, I jumped to the assumption that as you were messing with nut compensation you would already have them. There's a 25 page chapter on compensation and intonation (Section 4.7, Design) with a few different methods depending on how much maths you want to do.

                    I tend to reference the sections when there is maths involved, as forums are not the easiest places to write mathematical formulae (and it saves me a truck load of typing!)


                    Thanks Trevor. I will check out your website !

                    I have made several compensated saddles , including 12 string. And many standard nuts. However, the compensated nut is another matter altogether ! There's several luthiers on the web who say its not necessary at all, provided the fret positions etc etc are correct. They put a lot of weight on the string clearances over the frets near the nut and playing technique.

                    I run a clearance over the 2nd fret of .006" on the 6th string and .004" on the Ist, with the 3rd fret capo'd, and still get those sharp notes on some open chords. Should I take the clearances even lower before going further with the making of this compensated nut ?
                    regards,
                    Don

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                    Trevor Gore
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                    Re: Compensated nut WIP

                    Post by Trevor Gore » Sun Dec 23, 2018 9:29 am

                    donnyb wrote:
                    Sat Dec 22, 2018 5:55 pm
                    I run a clearance over the 2nd fret of .006" on the 6th string and .004" on the Ist, with the 3rd fret capo'd, and still get those sharp notes on some open chords. Should I take the clearances even lower before going further with the making of this compensated nut ?
                    I try to run the fret surfaces and the nut in the same plane, so fretted (or capo'd) at fret 3, the string just clears fret one. According to the analysis I mentioned before, the intonation error is more sensitive to fretting pressure than nut height.

                    donnyb
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                    Re: Compensated nut WIP

                    Post by donnyb » Sun Dec 23, 2018 10:03 am

                    I try to run the fret surfaces and the nut in the same plane, so fretted (or capo'd) at fret 3, the string just clears fret one. According to the analysis I mentioned before, the intonation error is more sensitive to fretting pressure than nut height.
                    [/quote]
                    [/i]

                    Thanks Trevor.

                    I have noticed that (re fretting pressure) using a tuner, as I started down this compensated nut path, as it was cited in some web articles . I wish I known that 52 years ago when I picked up that Maton Classical beginners guitar !
                    Its very hard now to compensate this 'yours truly' nut :roll:

                    I will report back later in January.

                    Happy Christmas !

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