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Thread: Pls critique this nut work

  1. #1
    Registered User mandolin breeze's Avatar
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    Default Pls critique this nut work

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    I have been trying to improve the nut on my F5. Before, all the strings were filed below the top of the nut. The distance to the first fret is good, so I don't want to alter that. All I really have done is file down the nut height to where it's at now in the photos. In looking at many Collings for reference, it looks like a good portion of the string sits above the top of the nut. Is there standard reference, 1/2 or a 1/3rd of the string above the nut, etc?

    Another aspect I'd like your feedback on: The strings are sticking quite badly when tuning. I have not used any graphite or other lube. I'm assuming that even with a perfect nut cut, there is going to be some sticking without graphite - correct / incorrect? I have the little round nut files and lightly ran them thru the slots (without going deeper). Would it help to go slightly larger with the file size, i.e. 40 string / 42 file, 26/28, 15/17, 11/13. Anyone found a better lube to use than pencil lead?

    Sorry for the multiple questions, and thanks for your feedback, advice or sharing in advance.

    PHOTOS OF NUT https://photos.app.goo.gl/fJAa8GWydM8iYZfX8

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    Last edited by mandolin breeze; Feb-09-2020 at 11:44am.

  2. #2
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    Default Re: Pls critique this nut work

    They are most likely sticking on the sides. I would do one of two things. File the top of the nut down so that the string sits at least 1/2 or 1/3 of the diameter of the string above the nut. If you don't want to do that on your mandolin a down and dirty way to do the same thing is to take a larger file, say a 52 for a 40 slot, and file so the top half of the slot is wider and the string can't rub on it. Leave as smooth a surface on the bottom as you can. I also like to file down at the end of the nut toward the tuners where the string angles to the tuners so it doesn't have a sharp edge for the string to move across. If the string bends to get to a tuner then I want to take some of the same edge on the side of the slot so the string doesn't rub on the side while moving. I wouldn't at this point try to get the E and A strings 1/3 of the diameter of the string, they can pop out when playing hard. I would widen the top half of that slot with a larger file, leaving the string to sit in a shallow trough of the proper diameter.
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  3. #3

    Default Re: Pls critique this nut work

    Your nut looks great. But looks/cosmetic refinement is the last step when adjusting a nut after everything else has been done. As a professional tech, I find that refining the adjustment of the nut is the singular biggest bang for the buck that I can perform on any stringed instrument. It takes patience, skill, and good tools. It also has risk involved because when you achieve the optimal adjustment, you're only one or two file strokes from totally ruining the nut and starting all over with a new nut blank.

    There shouldn't be any resistance to tuning. If there is, it will typically result in tuning instability as the tension on either side of the nut balances out while you're playing.

    Slot depth can be as little as 50% but 60% to 100% is okay. At any given moment, only up to 50% of the string can be in contact with the nut material. It follows that any part of the nut slot that is not in contact with the string is not necessary because it has no function. But this is not completely true if the player is very aggressive. At 50%, a .010 string has only a .005" slot depth and it doesn't take a lot of lateral force for the string to pop out of the slot. Also, the 50% minimum depth is a 50% depth that is in-line with the downward force of the string so if tuning post is offset from the major length of the string, the slot depth is at an angle.

    Even after doing this for 20 years I still have problems. All you can do is the best you can. The slot needs to be like a water-slide with no bends for the flow of the string. Its all about minimizing drag while achieving a clean definitive break off point. I want a 1/8" long rounded curve to bear the force of the string with no point in that length having more force applied to it than the average.

    Optimally the slot needs to be .002 to .004 wider than the string but these sort of measurements are impossible to routinely achieve with accuracy.

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  5. #4

    Default Re: Pls critique this nut work

    I’m sure that this has been covered in detail for a very long time, but maybe it’s still news that a wound string is a file; very high friction on any material that’s softer. The change in angle at the nut maximizes the downforce, and the contact area is small. The nut material, even bone, is softer than the string, so the question is really what the actual friction is providing that the material can’t actually be sheared. A problem best addressed by experiment, because the important details are specific to this particular arrangement. The spec is high shear strength, low friction. And something called lubricity. Lignum Vitae is one natural example, although historical.
    Now if the nut is as hard or harder than the string, less deformation, less net friction. E.G. a zero fret should work well. The zero is good because it separates string location from support, so no jamming.
    Our imaginary engineer might suggest little roller sheaves. Our imaginary watchmaker, sapphire. I suggest thinking about something else.

  6. #5
    Confused... or?
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    Default Re: Pls critique this nut work

    Quote Originally Posted by Richard500 View Post
    ... Our imaginary engineer might suggest little roller sheaves...
    I think Mr. Imaginary worked at Fender 20 or so years ago. Something about nut friction upsetting tuning when locking-tremolo bridges went into "dive-bomb" mode, maybe?
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    Registered User amowry's Avatar
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    Default Re: Pls critique this nut work

    I try to seat wound strings 50% and plain strings 100%. I use nut files that are a few thousandths wider than the strings, and don't use any lubrication in the slots. I would say if your strings are sticking the culprit is using a file the same width as the strings.

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  9. #7
    Registered User amowry's Avatar
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    Default Re: Pls critique this nut work

    One thing I notice in your photo is that it looks like the A and E strings bear at the front of the but not the back, in other words there doesn't appear to be a break angle where the strings exit the back (headstock side) of the nut. That can result in a sitar sound because the strings may be able to vibrate in the nut slot. It's hard to tell in the photo if that's actually the case. I try to have the slots bisect the headstock angle, so the strings bear on both the front and back edges of the nut, which also distributes the load and the resulting wear.

    I realize you didn't cut the original slots, so it's not your fault I just thought I'd mention it.

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  11. #8
    Registered User mandolin breeze's Avatar
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    Default Re: Pls critique this nut work

    Hi amowry & others,

    There is a link to a few photos of the nut from different angles in my original post.

    Here it is again if you'd like to evaluate. Thanks so much. https://photos.app.goo.gl/fJAa8GWydM8iYZfX8

  12. #9
    Adrian Minarovic
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    Default Re: Pls critique this nut work

    Quote Originally Posted by amowry View Post
    One thing I notice in your photo is that it looks like the A and E strings bear at the front of the but not the back...
    Think that the bearing point will take most of the force and will slowly abrade lower over time. I noticed this especially on pearl - unwound strings - player with agressive sweat combination where the sweat accumulates in the string slot slowly eroding the pearl and string that becomes somewhat gritty and saws down or sometimes the leading edge will chip away (or the technician has to clean/smooth out the slot with few strokes of file later). Best approach, IMO, is when the nut slot gradually changes from parallel to string to parallel to exit direction. That keeps the load of string over the length of slot more even.
    Adrian

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  14. #10
    Registered User mandolin breeze's Avatar
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    Default Re: Pls critique this nut work

    Just wanted to follow up . . . 1) Filed down the top of the nut to rest the strings with about 1/2 of the string above the nut. 2) added a bit more relief off the back side of the nut with about 1/8" flat in the front where the strings rest 3) I did refile (without going deeper) the width of the string slots by about .04 bigger than the string. 4) I scrapped some pencil graphite into the slots. All of that resulted in a great improvement - the strings don't hang up with tuning anymore. I'm sure there was friction on the sides with strings sitting too deep and too tight on the sides. It is satisfying to make genuine improvements by yourself with the help from the members. Thx

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    Last edited by mandolin breeze; Feb-19-2020 at 3:04pm.

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