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Thread: Bowlback tuner problem

  1. #1
    Registered User George Roberts's Avatar
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    Default Bowlback tuner problem

    This is an "American Conservatory" mandolin that hasn't been out of the case for many years. I took the tuners off to clean and lubricate them, but now when trying to string it up, the round gear is sliding up and off the stem. In the picture of the tuners, the second gear from the left, on the bass side, can be seen to be partially up. This also happened with the second from the right on the same set of tuners.
    I have never had this happen before.
    Any explanations and/or solutions would be greatly appreciated.Click image for larger version. 

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  2. #2

    Default Re: Bowlback tuner problem

    And cracked gears on both E strings too! I just checked both of my Conservatory bowlbacks: neither has these particular tuners. Someone will chime in. Anyway, if you are going to repair, I’ve had good luck just brazing those little cracked gears if steel; if brass, low temperature silver solder. If the gears are actually not removable, it becomes less easy.
    On Ford’s ‘Frets.com’ under luthiers, tuners, see “Cracked Cog” which details both of the problems you have. On the subject tuners, the gear is pressed onto the shaft. This is tricky to replicate as it requires some machining, and also easily cracks the gear. Ford’s solution is to drill and pin the gear to the shaft, which is also a delicate machine operation. Not having ever done this, I think the better part of valor is to remove the button to protect it, and actually solder the gear to the post, which has to be in place with a little clearance on the other side. Easier, but still requires skill and hard soldering experience.
    Of course, if you have access to a scrap tuner collection, replace the whole gear and post assembly if you can find one that’s close.
    Last edited by Richard500; Nov-10-2022 at 6:22pm.

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  4. #3
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    Thank you Richard. I had somehow mistaken the cracks for witness lines that had been used when cutting the gears. Three out of the four gears on that plate have them. I'll have to mull this over a bit. The shaft does not fit through the plate. The gears must have been pressed onto the shaft, when already in place on the plate. It seems as though I will have to pull the gears off the shaft, silver solder them (they are brass) and then re-press them onto the shaft. Hopefully they won't need to be pinned, as well. I have a little tool made for pulling hammers off the locks of muzzle-loading guns. It should be perfect for pulling off the gears.

  5. #4

    Default Re: Bowlback tuner problem

    The post must not come through the plate or the whole thing would come apart: a step on the post and the gear are what locate the thing. You don’t want to chance pulling the post through the plate or deforming the latter in extracting the gear, so if you have a small puller, make sure it can bear on the end of the post: if that won’t fit, clamp the post in the vise very firmly, right up to the plate, then use your puller.

    However, you may do less damage if you just use a little heat to expand the gear off the post end. Brass expands a lot. Use a very small torch, not a plumbing one. If you try this, torch in one hand and pliers in the other and feel if the gear is getting loose. (Post end still in the vise.) If you want to get a merit badge, you could even try to replace the gears with a calculated shrink fit and no solder, but the distance between loose and breaking the gear again is very small.

    Fortunately, tuners using worm and pinion are pretty low-precision devices, and are likely to work even if the tooth forms are damaged or worn, but if you solder up those gears, look closely afterward and clean up any related spillage and misalignments with small files, and run in the finished repair before putting strings on.

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  7. #5
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    Default Re: Bowlback tuner problem

    Quote Originally Posted by Richard500 View Post
    ... a step on the post and the gear are what locate the thing.
    Are you sure that the left and right plates are identical? And that all posts are identical? If you mixed posts to a plate w/ different size holes, that could be (part of) the issue.
    - Ed

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    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    Richard, thanks again for your very wise approach. I will let you know how it goes.
    Ed, I only had the one set of tuners off the mandolin, and there was only the one gear off the post, so I'm sure the posts and plates haven't been mixed up.
    This mandolin was a gift to me more than 50 years ago, and as I think back, the reason it has been in the case for about 50 years is because I started having trouble tuning it back then.

  9. #7
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    Well, I silver soldered the 3 cogs, and 2 of the 3 split again when pressed onto the posts. I checked Frank Ford's article "Nobody Wants A Cracked Cog" and the tuner he was repairing was from a 100 year old Washburn and looked identical to mine. (I believe the American Conservatory brand was a Washburn/ L&H product.)
    I have pinned the 3 cogs, but wonder if I will need to drill and tap the posts for screws to keep the cogs from lifting up.

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    Default Re: Bowlback tuner problem

    Quote Originally Posted by George Roberts View Post
    Well, I silver soldered the 3 cogs, and 2 of the 3 split again when pressed onto the posts. I checked Frank Ford's article "Nobody Wants A Cracked Cog" and the tuner he was repairing was from a 100 year old Washburn and looked identical to mine. (I believe the American Conservatory brand was a Washburn/ L&H product.)
    I have pinned the 3 cogs, but wonder if I will need to drill and tap the posts for screws to keep the cogs from lifting up.
    American Conservatory was a Lyon and Healy brand.
    Washburn was a Lyon and Healy brand.

    If all you want to do is make it playable then I would measure the post spacing center to center to see if it fits the early mandolin spacing. Honestly changing the tuners isn't going to affect the value. Being playable will affect the value.
    "It's comparable to playing a cheese slicer."
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    "Bargain instruments are no bargains if you can't play them"
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  12. #9

    Default Re: Bowlback tuner problem

    If you pinned them a la Ford, parallel to the axis, yes, nothing will prevent lifting. So I guess you didn’t leave clearance for a solder joint if you had to press them. Solder would have held. Fortunately neither of us can be criticized for near-neurotic little hobby challenges, so yes, you do need to hold the cogs on. One direction of the worm drives the gear upwards, possibly with some force.
    The good news is that if you were equipped to do the near-microscopic pinning, d&t will be easy. Easier, of course without the cogs because you could center in the lathe, but you dare not pull them again. Also, the post ends are crowned, so you need a punch center. I just checked: some of my ancient posts are brass, others, steel, but likely soft either way. Leave little clearance between the screw head and gear, which might be excessive due to the crown and post dimensions.
    As you know, tiny taps can be frustrating, so use best practices, and the largest size reasonable. A snapped tap can be a problem, and you’d have to just solder on a washer to recover. If the posts were steel, and I didn’t want to fuss, I’d use the spot welder instead of screws and just tack on a disc, but you may not have one handy.
    And don’t be tempted to convert that flintlock to piezo ignition.

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  14. #10
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    Again, thanks Richard. Some of the teeth of the cogs were already misshapen, but now with the silver solder added to the picture, the worm gear is not turning well for any of the three. Earlier on, before the splits were pointed out to me, I had tried valve grinding compound, with minimal success (probably because of the cracks). It is beginning to feel like a long run for a short slide.
    Richard, was the flintlock/piezo reference an analogy, as in keep it original? I actually make and shoot flintlock rifles.
    Mike, thanks for the advice. The posts are 3/16 inch diameter, with 7/8 inch center to center spacing. I have not been able to find anything comparable so far. Any suggestions?

  15. #11

    Default Re: Bowlback tuner problem

    See this recent thread. https://www.mandolincafe.com/forum/t...r-old-Gibson-A

    Seems that there are two general standards, but I just calipered half a dozen old and new ones, and got significant variations. Worse, my two ACs differ from each other, even though they both look like yours otherwise. One has covered, the other open, so re-measure more carefully. Nothing 7/8. I think there are more than two species out there.
    I’d say you have license to replace at this point! In case the SMs work but are too expensive, be careful looking at low cost Asian ones on Ebay - the descriptions are generic if provided at all, and can be dimensionally wrong, and I bought one set that was just too crappy to use.

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  17. #12
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    Default Re: Bowlback tuner problem

    Quote Originally Posted by George Roberts View Post
    ...Mike, thanks for the advice. The posts are 3/16 inch diameter, with 7/8 inch center to center spacing. I have not been able to find anything comparable so far. Any suggestions?
    If the math is right you are looking at 22.24 mm center to center. The early Gibson mandolin tuners were 23.60 mm. The modern tuners are 23.00 mm. A modern set might work, again if my math is right. I'd at least look at them.

    Stewmac sells these. You have the mandolin in your hands so you should be able to make a determination. The relic nickel might look right. Others make less expensive sets with different finishes.

    The differences in the post diameters shouldn't be an issue. The peghead bushings can cover some of the differences when you make room for the newer tuners and the plate in the back will hide anything there.

    Your originals appear to be worm under tuners and these will be worm over so the position of the buttons on the headstock might change a bit.

    Good luck.
    "It's comparable to playing a cheese slicer."
    --M. Stillion

    "Bargain instruments are no bargains if you can't play them"
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    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Bowlback tuner problem

    To add even more obscurity to the discussion, I just measured a Washburn and an AC bowl I have in my junkyard.

    Both come in a 7/8" spacing.

    The AC are inset tuners though.

    Finding a junker L+H mandolin to nab some tuners from shouldn't be too hard.

    I'd sell you these but I'm still fantasizing fixing the Washburn, though it has the dreaded top cave-in North of the soundhole.

    It was a fine mandolin, XL gauge strings and then suddenly it decided it wanted to give way.

    That was a sad morning.


    Mick
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  20. #14
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    I thought I had posted this already, but don't see it. I wanted to thank everyone for all the information and advice.
    My father was an expert on antique furniture, and he always stressed how important it was to keep things as original as possible. I tried with this mandolin, but to no avail. I ordered a new set of tuners from SM. Fortunately they were on sale, so it offset some of the shipping cost.
    George

  21. #15
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    OK, so the tuners arrived, and they are very high quality. The spacing of the posts was a little off, but that was manageable. On the other hand, the plates were way too long, as were the posts. I could (possibly) have taken all of the posts off and cut them down to the right length, and then turned them down to the right diameter, on my 1942 Logan lathe, and then re-drilled the holes for the strings. Once again, it seemed like a long run for a short slide. I sent the tuners back to SM. The mandolin will probably go back into the original case for another 50 years. Maybe the gears could be re-cut at that time using modern technology.
    Once again for all the help and. support.
    George

  22. #16

    Default Re: Bowlback tuner problem

    Coincidences. Just yesterday I finally got my two ACs usable. Both needed surgery, and initially, the fancier (44 rib) one sounded pretty bad. Those are other stories, one needing an added brace, the other, reglued braces (2) and a neck alteration, but I’m showing the tuners for the OPs information. As of last night, both seem stable and the less-fancy one sounds extremely pleasant. AC’s reputation vindicated. And use very light strings.
    Now about those tuners. The one bare set is almost certainly original, very simple, and 4” long, which seems about the limit. The post protrusion is only a scant 1/4”, which is really on the short side. Longer wouldn’t be noticeable or inappropriate. However, the closer to the wood that the last turn on the strings are, the less strain on the tuner because the wood is the fulcrum of a lever. Anyway, Pops1’s old fix of just cutting those plates is IMHO just fine, so get yourself any set, used or new, and chop off the ends and split the plate at least once if needed. Or advertise on this site for ‘wanted’, or visit any music shop that might have a junk drawer.
    Logan! Pictured is my nominal vintage 11 (nameplate missing). Like my very minimal Strad-o-lin, it is not a professional, i.e. high quality thing, but gets used all the time in a house where there are around 8 more, and better lathes. Almost a kitchen tool - with a few upgrades, like a decent chuck and an Aloris post, and recently, a separate fine feed drive. Even has an adapter to use larger collets as the spindle bore is tiny.
    Click image for larger version. 

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  23. #17
    Registered User George Roberts's Avatar
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    Default Re: Bowlback tuner problem

    Richard, Thanks for your reply. After my "I'm giving up!" post, I didn't check back until now. I contacted my old buddy, Marc Silber, in Berkeley. He had me put the tuners on a copy machine, and put a towel over them. The copy came out remarkably well, and I mailed it off to him. He's going to check through his stash of old tuners for me.
    My wife thought that your lathe looked a lot like mine, especially the decor. I never knew how much I needed a lathe, until I got one. We always had a wood lathe at home when I was a kid, and my dad was very creative in getting it to do what he needed. He would have had a ball with a metal lathe.
    Good to see that you got both AC mandolins playing again.

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