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Thread: Mandolin neck repair: the final solution?

  1. #26

    Default Re: Mandolin neck repair: the final solution?

    I think you've gotten good advice already, but being a forum and all, I'll throw mine in as well. (Free of charge, which some might think is too high a price!)

    There are several problems with the CF rod as the primary source of reinforcement. Even though it's running the length of the neck, the part supporting the break is still relatively small. It's probably strong enough, but the glue area is still relatively small and my suspicion is that with that cross section it will subject to side forces that may compromise stability. It does little to strengthen the short grain break, which is the root cause of multiple failed repairs. Full disclosure - I am a mechanical engineer, not structural...

    My strong preference would be for the back strap type repair, already noted on frets.com. You'd remove the faceplate and reglue the headstock to set the alignment. Then you would thin the entire back of the headstock by the thickness of the backstrap. That would extend onto the neck shaft well past the break and be blended into the neck shape. A new faceplate would be installed, and the original logo (pearl I assume) reused. The larger glueing areas here would offer much greater support than the proposed permanent truss rod cover and short back inlay.

    I think this method would support a truss rod as in the original construction, but I could live without the truss rod too. Many instruments don't have one, and a mandolin will do fine without it. The CF rod would be be helpful here, though not as the main source of strength for the broken section. I am loath to argue with Will Kimble about mandolin construction, but other builders such as Paul Newson have built several fixed-reinforced necks with great success. It's part and parcel of old Martin guitars as well. You do have to be more careful with compression fretting and such, but once the relief is correct, it's likely to stay there.

    Summary - I could go either way on adjustable or fixed neck reinforcement, but believe the front and back strap repair has a far greater likelihood of success, near 100% if well executed.

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  3. #27
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by HoGo View Post
    Bernie's drawings are photo of the Siminoff drawings with lines added (I have no ide what program he used). I saved one of his, removed lines in Photoshop and drew in new curves in Photoshop as well. But for drawings I use combination of Photoshop and Illustrator or Rhino for 3D modelling.
    I just used PowerPoint which is a primarily presentation program with very limited graphics design tools -- I probably could have spent a little more time on it and rounded the strap out but I was merely trying portray a concept. Photoshop is a much more sophisticate drafting program and better to use for this purpose. I don't think I have a working copy anymore on any of my computers....
    Bernie
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  4. #28

    Default Re: Mandolin neck repair: the final solution?

    Can I just say what a useful, thoughtful and well-tempered collegiate discussion this has been. I don't currently have such a repair to do, but it has equipped me for success if I do in the future. Thank you all!

  5. #29
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by HoGo View Post
    I would keep the lines smooth and use bent piece of maple (straight grained). You can extend the backstrap all along the headstock to make its end less visible there (Frank Ford has such guitar repair on his site) That would be easiest to do if you have drum sander - just add shim at the end of headstock to keep taper (if present) and sand away 1/8" from rear of headstock and then smooth the transition into neck at least 2" past the break. Bend long piece of maple rib stock to fit the curve and glue it in place with strong fresh HHG and flexible cauls. Trim excess wood and done.
    Just to make sure we are on the same page here before any wood is carved.

    Would you envision the back strap to look like the first image just a rectangular piece the covers the break and protrudes into the head stock. First image, (Note: this mandolin has a volute that I would not plan to retain in order to make the job easier).

    Or do you see a back strap that includes the entire head stock width -- say up to the first tuner holes for example? For this I could cut a thin 1/8 to 3/61" "slice" off from the sugar maple block for example and attempt to bend that entire piece into place. (second image)

    PS you can see why I am note excited about putting a back strap on the beautiful maple neck!
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    Last edited by Bernie Daniel; Oct-03-2018 at 8:07pm.
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  6. #30

    Default Re: Mandolin neck repair: the final solution?

    Here's Frank Ford's page on the backstrap repair. It covers the entire back of the headstock, which is how I would do it. There's no advantage to making it smaller.

    http://www.frets.com/FretsPages/Luth...phoverlay.html

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  8. #31

    Default Re: Mandolin neck repair: the final solution?

    What Adrian said! If you have a spindle sander, set up a fence so you can feed the headstock between the spindle and the fence removing 1/8" from the back of the headstock. Go about 2 inches past the break. Go slow, so you sand the wood away, not burn it. Then bend a 1/8" thick piece of maple to fit the back of the headstock and glue it in place. Trim & touch up and it should be a very strong repair.

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  10. #32
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Buck View Post
    Here's Frank Ford's page on the backstrap repair. It covers the entire back of the headstock, which is how I would do it. There's no advantage to making it smaller.

    http://www.frets.com/FretsPages/Luth...phoverlay.html
    Thanks I intended to go look for that today!
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  11. #33
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Joe Mendel View Post
    What Adrian said! If you have a spindle sander, set up a fence so you can feed the headstock between the spindle and the fence removing 1/8" from the back of the headstock. Go about 2 inches past the break. Go slow, so you sand the wood away, not burn it. Then bend a 1/8" thick piece of maple to fit the back of the headstock and glue it in place. Trim & touch up and it should be a very strong repair.
    Thanks so basically you are saying make a "strap" (1/8" thick) the would look like the second image I presented in post #29?

    I don' t have a spindle sander but I might be able to remove the wood I need using a sander on a drum and then clean it up with a cabinet scraper?

    One other thought. If I remove 1/8" from the head stock and neck I think the strap might have to be a little thicker than 1/8" so as to allow for error when carving back to shape?
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  12. #34
    Adrian Minarovic
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    Default Re: Mandolin neck repair: the final solution?

    I would go for whole width of headstock (unless you have reason to fit it into channel like in first pic - that would work but it is infinitely easier to prepare flat surface across whole headstock), whether full length or not depends on your tools. With drum sander it is easy to thin the whole headstock, with handtools only I would go for 2-3" into headstock (full width). You want the surface be perfectly flat across and smooth bend along for best strength of glue joint (start with sanding blocksto create smooth bend along neck and finish with flat scraper to get perfectly flat surface across width).
    Also I'd prefer straight grained wood for strength. Perhaps you can find a piece that has small part with very little curl (1-2" which will be right at the break) and transition into nice curl to match the neck shaft... if you really want curly wood, use thicker overlay. Always count with some extra wood for safety. You can build up the volute with another piece on top of the backstrap if you wish (I've seen that on decorated old time banjos)...
    Last edited by HoGo; Oct-04-2018 at 3:47am.
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    Default Re: Mandolin neck repair: the final solution?

    I'd just use a 1/8" thick ebony veneer for the "backstrap". Just as if you we're building a new mando. Taper the veneer to a point past the crack. Use the CF rod as well.

    Lot easier than than you think. You're just putting veneer on the back of a mandolin. It would look much better than a maple piece stuck in there, in fact no one would know any different. You build mandos, this is nothing.

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  15. #36
    Adrian Minarovic
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    Default Re: Mandolin neck repair: the final solution?

    Ebony can be brittle and may crack when bending at that thickness or even worse invisible cracks form that can lead to failure in future. Also maple glues better to maple than ebony so simple hard maple is hard to beat in this case.
    Adrian

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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by HoGo View Post
    Ebony can be brittle and may crack when bending at that thickness or even worse invisible cracks form that can lead to failure in future. Also maple glues better to maple than ebony so simple hard maple is hard to beat in this case.
    Each round I learn more! Thanks to all!

    I think I have 3 or 4 thin panels (maybe 8" X 4"X1/16") of maple, with little curl. In fact I do not know what kind of maple it is but it is very plain looking essentially little figure. Does the repair have to be done with "hard" maple or would any quality maple wood work as well?

    Thinking about these panels makes me wonder if I could take 1/8" of wood off the back of the neck and head stock and then heat bend in 2 or 3 of these panels to the instrument -- gluing each separately to make a "maple plywood" back strap?

    They would be easier to bend and in theory would result in a tighter fit and, also in theory, be stronger because potential weak area one piece would likely be reinforced by the piece above or below?

    Then the thought occurs to me that it might actually end up being easier to run the back strap over the whole back of the head stock? becasue then I would not have to content with the doing a blend on the back of the head stock? (Although I have a bunch of ebony veneer (paper thin) that I could use to cover it).

    Always more questions! LOL
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Bernie Daniel View Post
    Each round I learn more! Thanks to all!

    I think I have 3 or 4 thin panels (maybe 8" X 4"X1/16") of maple, with little curl. In fact I do not know what kind of maple it is but it is very plain looking essentially little figure. Does the repair have to be done with "hard" maple or would any quality maple wood work as well?

    Thinking about these panels makes me wonder if I could take 1/8" of wood off the back of the neck and head stock and then heat bend in 2 or 3 of these panels to the instrument -- gluing each separately to make a "maple plywood" back strap?

    They would be easier to bend and in theory would result in a tighter fit and, also in theory, be stronger because potential weak area one piece would likely be reinforced by the piece above or below?

    Then the thought occurs to me that it might actually end up being easier to run the back strap over the whole back of the head stock? becasue then I would not have to content with the doing a blend on the back of the head stock? (Although I have a bunch of ebony veneer (paper thin) that I could use to cover it).

    Always more questions! LOL
    Any good clear defect free maple should do OK.
    I'd go for one thicker layer. It's not hard at all to bend it to such curve. You can wet it and heat it on clothes iron and clamp it against some curved object with similar radius to the neck transition. Then smooth the gluing surface on surfacing plate (I use large flat piece of plywood with rough sandpaper attached) to remove any kinks of the bend (likely to appear on curly maple)
    Thin layers would be easier to bend but applying glue to so many surfaces and trying to press excess glue out will make the whoe asssembly want to slide in every direction or in case of HHG the glue will gel before you manage to add all layers. You can glue layers separately, but that's more work and more glue soak into the grain - possible problems during finishing. And the layered strap would be more noticeable than carefully selected single piece.
    Use either shaped caul with layer of soft cork or "kerfed plastic (LDPE or such) caul" to clamp the strap in place and you'll get nice tight joint in one go.
    Whether to do the backstrap on the whole length of headstock is just your decision. With my toolbox it would be easier to cut less off the headstock and then trim/blend the end of backstrap. (I also always use layer of black veneer on back of mandolin headstocks) You may find it easier to cut the whole headstock and not have to deal with the transition on the headstock end of backstrap... Also remember that larger area means larger caul (ore more than one) and more clamps and thus time to get proper pressure meaning, more time that is precious when using HHG. But heating room and the wood before gluing will help with that.
    Adrian

  19. #39

    Default Re: Mandolin neck repair: the final solution?

    I wanted to add that while the repair is straightforward in theory, to get results like Frank Ford requires a lot of experience, IMHO.

    Plus, it's a guitar, so the pieces are slightly larger, FWIW.
    Last edited by Jeff Mando; Oct-04-2018 at 10:14pm.

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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Jeff Mando View Post
    I wanted to add that while the repair is straightforward in theory, to get results like Frank Ford requires a lot of experience, IMHO.

    Plus, it's a guitar, so the pieces are slightly larger, FWIW.
    I agree! I've looked at those Frank Ford pics about half a dozen times now......
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    Default Re: Mandolin neck repair: the final solution?

    Thinking of going with a 3/16" hard maple back strap?

    Have to experiment a little with bending a piece that thick though.
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    Default Re: Mandolin neck repair: the final solution?

    I find it interesting that by using bent wood instead of carving a thicker piece you end up with the compression and stretch of the repair wood opposite of the failure crack. I don’t know if this has and effect in strength but would reduce exposed endgrain.
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  25. #43
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Bernie Daniel View Post
    Thinking of going with a 3/16" hard maple back strap?

    Have to experiment a little with bending a piece that thick though.
    Thicker will add more strenght but will be trickier to glue as it will not conform to the glued surface as easily as thinner piece (using cork lined cauls). I would dampen it slightly wrap in plastic wrap and heat it in microvawe for bending. That would heat the wood evenly all the way through and help clean bending. claming against a form of some sort would be best for getting good smooth bend with thicker piece.
    Adrian

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  27. #44

    Default Re: Mandolin neck repair: the final solution?

    Thanks for this thread. I'm looking at the same situation, so this is useful. Thanks, everyone.

    M&M

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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by hank View Post
    I find it interesting that by using bent wood instead of carving a thicker piece you end up with the compression and stretch of the repair wood opposite of the failure crack. I don’t know if this has and effect in strength but would reduce exposed endgrain.
    Thanks for that thought! I have not been on this thread for a while but yes that thought occurred to me as well. I have been doing other things and will probably start the back strap next week.
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by HoGo View Post
    Thicker will add more strenght but will be trickier to glue as it will not conform to the glued surface as easily as thinner piece (using cork lined cauls). I would dampen it slightly wrap in plastic wrap and heat it in microvawe for bending. That would heat the wood evenly all the way through and help clean bending. claming against a form of some sort would be best for getting good smooth bend with thicker piece.
    Thanks I really like that idea!

    I could remove the wood from the neck until I got where I wanted it to be then measure that angle between the head stock to the neck. Then I could cut the same angle in a piece of 2X4 and use that as a form to clamp the hot maple (forcing the bend) into place until it cools?

    I wonder how long one might microwave the wood or better what temperature one might take the piece of maple to?
    Bernie
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  31. #47
    Registered User j. condino's Avatar
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    Default Re: Mandolin neck repair: the final solution?

    All of that work and mental anguish and time spent on the worldwide waste of time....

    A new neck would take less effort and we'd all agree that it was solid......

  32. #48

    Default Re: Mandolin neck repair: the final solution?

    Jerry Rosa has a Rosa Strings Workshop YouTube video where he cuts out the broken part altogether and scarf joints a new piece to bridge the gap. I believe he has one for guitar too. Interesting stuff there.
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    Default Re: Mandolin neck repair: the final solution?

    Quote Originally Posted by Br1ck View Post
    Jerry Rosa has a Rosa Strings Workshop YouTube video where he cuts out the broken part altogether and scarf joints a new piece to bridge the gap. I believe he has one for guitar too. Interesting stuff there.
    Yes thanks I watched those -- the two on the mandolin repair are both about 1 hour long so they are perfect for my WiFi tablet when I am on the treadmill at the fitness center! I think I watched both of them twice. Really great videos!
    Last edited by Bernie Daniel; Nov-18-2018 at 6:00pm.
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    Default Re: Mandolin neck repair: the final solution?

    Regardless of what method you use to bend the wood for the backstrap,there will always be residual stress in the strap after bending. That's why we often see instrument sides coming adrift. So,unless there's a way of 'stress relieving' the strap prior to fitting it,then carving it to fit the 'bend' is IMHO,the way to do it. At least the strap won't be imposing any stresses right from the off,& as long as the strap is strong enough,it should be fine.
    I found this on the 'net :-

    " When a piece of wood is bent, it is stretched, or in tension, along the outer (convex) side of the bend and compressed along the inner (concave) side. Its convex side is thus longer than its concave side. This distortion is accompanied by stresses that tend to bring the bent piece back to its original straightness. The purpose of softening wood with moisture and heat or plasticizing chemicals is to restrict the development of these stresses.".

    Note that it says ''restrict'' NOT remove any stress development,
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