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Thread: Machine tuning - bushings don't fit

  1. #1

    Default Machine tuning - bushings don't fit

    I have a early 20th century bowlback mandolin that I am working on getting into playable condition. The machine tuning pegs were bent and difficult to tune so I decided to replace them. The new ones seem to fit except for a few things. The bushings do not fit. The pegs seem to line up but once they are in, they are clearly not straight. I believe the previous ones were bent because of the pressure applied during tuning. My thought is to clearance from on top of the holes to fit in the bushings. Will this be enough or will the holes need redrilled? I have pictures of the mandolin at the links below.

    Pictures of mandolin: https://imgur.com/gallery/jdA9XWQ

    Pictures of machine tuning pegs: http://imgur.com/gallery/IGH0Htf

  2. #2
    Registered User Tavy's Avatar
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    Default Re: Machine tuning - bushings don't fit

    I'm afraid that's not going to work: these old instruments do not have the same tuner post spacing as modern instruments, so wherever possible you should try to restore the old machine heads. I realise that the post holes get worn over time and may need some work, but the result is likely to look a lot better than fitting modern hardware.

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    Default Re: Machine tuning - bushings don't fit

    What I have done in the past to use tuners that don't fit is cut the tuner plate at the screw mounting holes. The cuts will let the tuner fit your mandolin. The screws will still hold the tuners on just fine. I feel I would rather modify the new tuners than the old mandolin. Have had the tuners on my Gibson now for decades with this same mod, there were none to buy back then. You could buy new tuners, or use the ones you have.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  4. #4
    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    Tuners are measure by the spacing from center of the post to the center of the post. You may or may not be able to find this size post spacing. The first thing you need to do is to measure it.

    After that you have pretty much two choices for sizes. Stewmac makes a set that is spaced for Gibson A style mandolins up until about 1924. They are the only one making that spacing. They are here. Scroll to the bottom of the page for the specs. The post spacing is .931" or 23.6 mm.

    The second choice is the modern spacing. You have lots of choices with this spacing. I'll show the Stewmac again. It is here. The post spacing is .906" or 23.0 mm.

    It would appear that yours aren't either of these. Get the post measurements and there is a minuscule chance that someone makes an off sized tuner that might fit but without having that measurement everything is just a guess.

    Tavy's statement about restoring the original tuners is true. Hopefully they are intact and complete.

    The size of the bushing can be fixed by enlarging the holes but if the holes aren't in the right place it's not going to matter.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  5. #5

    Default Re: Machine tuning - bushings don't fit

    Thank you everyone for replying. Unfortunately we do not have the original machine heads. The ones I removed from the mandolin were identical to the modern ones I purchased, the only difference is they were warped and bent to the point of the metal between the posts was breaking due to continued strain at being bent. No idea how long they had been that way as I purchased it that way about 2-months ago.

    I measured them with a ruler which wasn't super accurate, my husband has a device for getting exact readings I'll try to see if I can find a set with that reading. If I can't find an exact set that will fit, any suggestions? I wondered if I could even purchase individual posts to use instead of 4 connected posts?

    Unfortunately, I don't know enough about this to know if that would even work. I can also take it to a luthier if needs be, I just live in a rural area and recognize they aren't common here so I'll have to travel.

  6. #6
    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    There are individual mini tuners used mostly for guitars, just make sure you get the right orientation. They are usually sold in sets of 6, 3 on each side so you might have to buy two sets to get 8 or or you could use the method pops1 describes. Get the measurements with a digital caliper if possible. The other thing you can do since it's not going to be original anyway is to plug the holes and have them re-drilled to fit a standard set of tuners. Before you do any of that get the spacing measurements so we can at least see if there is a better option.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  7. #7

    Default Re: Machine tuning - bushings don't fit

    I’m guessing that you are in luck - that the previous owner didn’t know about the original spacing and just put on the wrong (later) on; a mistake that could have been decades ago.
    So, to measure what you really need, you are going to have to measure from the center of one hole to another: not an easy thing to do accurately, especially if the holes are worn egg-shaped. This is how:
    The backside (tuner side) holes should be less deformed than the topside, so think of them as more accurate.
    If you can put some 1/4 dowels in hole one and hole 4, and mark their centers (by eye should work), measuring from one to the other will be pretty close.
    Do this on both bass and treble side of the peghead, and also perhaps make some intermediate measurements just to see if the original holes are equally spaced. Or also get measurements from the topside.
    Divide that 1-4 measurement by 3, and compare with the numbers Mike gave above. If the spacing comes out more than say, 0.010” different from both those numbers, you really have something different, and go to plan B.
    Just FYI, I bought some tuners on ebay and found that the advertised spacings can be wrong, and also that the cheapest ones are just no good, but you don’t have to go far in the expensive direction.
    Bushings: old mandolins mostly didn’t have them, which after many years resulted in the holes deforming a little. So the original holes are just a loose fit on the posts, and if you’re staying with the original look, omit the bushings. Bushings are an improvement because they’re not likely to wear, but also are quite critical and unforgiving in placement, and must be drilled for accurately, which also isn’t easy on an old, deformed hole without jigs and tools.
    What it all means: The top surface of the peghead is really a contact point for the string posts, which form a shaft going to the second contact in a hole in the metal plate, or sometimes at the point the little gear touches the spiral (worm) gear. The strings pull the top in one direction - towards the instrument body - and if that little post has misalignment due to wrong tuner type, wear on the wood, or sloppy installation, it will be tilted. Too much? This is when there’s little or too much hard contact between the gear and the worm; in the one, high friction and wear, in the other, backlash (slop) in tuning. Primitive? Yes, but it does work.
    And: there are a few other issues to consider on that fragile old piece of wood before it gets back in circulation, so if you know, or can find a skilled luthier or a player, by all means let them look it over for structural issues and make suggestions. Bear in mind that bowl backs, even ancient ones, are usually not valuable in the marketplace, and not “worth” the cost of repairs, but ....so what?

  8. #8
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    Default Re: Machine tuning - bushings don't fit

    Worst case scenario is you plug the existing tuner holes and drill ones for your replacement tuners.

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  10. #9

    Default Re: Machine tuning - bushings don't fit

    Thank you for the great information. The smallest dowel I could find last night was 1/3 inch. I will pick one up tonight on the way home to try, or I will whittle the 1/3 down a bit tonight if I get a bit more time.

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    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    If you are planning on filling the holes and re-drilling it would make more sense to get a matched drill bit and dowel set that would allow you to enlarge the hole and have the correct sized dowel to fill it. That may be more work than you want to do but if the fit isn't right when it's glued you're going to have issues. Were you able to measure the distance between the centers of the holes?
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  12. #11

    Default Re: Machine tuning - bushings don't fit

    Alright, I was able to get quarter inch dowels and measure with an electronic caliper.

    On the back side left (anterior right)
    Top: 23.51 mm
    Middle: 24.05 mm
    Bottom: 23.80 mm
    Average: 23.78 mm

    Back right (anterior left)
    Top: 23.17 mm
    Middle: 23.74 mm
    Bottom: 23.78 mm
    Average: 23.56 mm

    Front side left
    Top: 22.45 mm
    Middle: 23.41 mm
    Bottom: 22.88 mm
    Average: 22.91 mm

    Front right side
    Top: 22.18 mm
    Middle: 22.23 mm
    Bottom: 22.57 mm
    Average: 22.32 mm

    Between posts horizontally
    First set: 35.48 mm
    Second: 35.49 mm
    Third: 33.26 mm
    Fourth: 27.57 mm

    Would I be correct in thinking the 23.65 mm would be my best fit of what's been mentioned so far?

    I edited because I lost the measurements one and was afraid of it happening a second time since I'm on my phone. I did find someone I can have look the mandolin over, and they know a luthier if needed. There is a crack on the mandolin front that I'll need to repair although it did sound playable when I got it.

    My husband and I seem to have a knack for rescuing old instruments. We have two 30s era trumpets as well as a trombone we saved from a scrap yard. We also have a century old piano that can't hold a tune. This mandolin is the first I can play as I can't seem to get the knack of the brass mouthpiece. I just have interest in pouring a bit of love into an instrument that hasn't seen love in a while. We bought it from a pawnshop where it was covered thick in dust. I know it's playable as it sounded ok before I removed the old strings and tuners; I was a little so worried they would break in play or tuning they were in such poor condition though. If this ends up unplayable for some reason, it still has value and will be beautiful in our home.
    Last edited by dasx; Jan-16-2021 at 8:49pm. Reason: Wanted to get information saved

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    Default Re: Machine tuning - bushings don't fit


  14. #13
    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    Those are the tuners I linked to above and could be the closest to what you have. Look at this diagram. That is the dimension you need to be checking.
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    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  15. #14

    Default Re: Machine tuning - bushings don't fit

    That's what I checked, I will get them ordered. I'll double check with my husband to make sure before I do so though.

  16. #15
    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    Those will be the dimensions of the tuners. If they match up with your post holes center to center it should work. Mark the middle of each hole and verify you are close to that dimension on each hole in reference to the next. I can see what you wrote, it just doesn't make a whole lot of sense. You're working too hard.

    If you measure the distance from the center of the hole closest to the top of the headstock to the center of the hole closest to the fingerboard it should be 70.8mm. If that number is off by any great amount these tuners won't work.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  17. #16

    Default Re: Machine tuning - bushings don't fit

    Quote Originally Posted by MikeEdgerton View Post

    If you measure the distance from the center of the hole closest to the top of the headstock to the center of the hole closest to the fingerboard it should be 70.8mm. If that number is off by any great amount these tuners won't work.
    So the OP missed that suggestion, no big deal. As an ex-Fellow at what was the National Bureau of Standards, I often think the cultural inability of Americans to either understand measurement or get weaned early from English units is a main source of economic rot and global non-competitiveness.
    That, and of course, an uncoordinated, expensive and silly approach to education in general.

  18. #17

    Default Re: Machine tuning - bushings don't fit

    Richard500, you make a large assumption about my ability to read and filter information based on whether it meets my needs. My need is not to determine if these specific tuners will work but to find a set that will if these do not. I can see that I switched gears without making that need known so I recognize the confusion started with my lack of clarity. Measuring the distance as suggested by Mike would indeed tell me these tuners don't work, but I already suspect they don't work hence the reason I'm here. The pictures I included clearly showed bowed tuning heads which seemed wrong. My need is to find tuners that work which I have been able to do with the suggestions provided. By measuring the post holes I now understand what I need. Let's be clear I did that in metric so I'm not entirely certain what the purpose of your post is besides filling the room with the unnecessary sound of your voice.

    Mike: if I did work too hard it was effort well spent as I have a very good mental model of why the tuners I bought didn't look right and how I determine what tuners will work best. I hope to buy a flat back mandolin and this mental model will help if I ever find need to replace tuners in the future.

    Thank you all for your help.

  19. #18
    Moderator MikeEdgerton's Avatar
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    Default Re: Machine tuning - bushings don't fit

    Quote Originally Posted by dasx View Post
    Mike: if I did work too hard it was effort well spent as I have a very good mental model of why the tuners I bought didn't look right and how I determine what tuners will work best. I hope to buy a flat back mandolin and this mental model will help if I ever find need to replace tuners in the future.

    Thank you all for your help.
    Best of luck, let us know how it comes out.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

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