Results 1 to 13 of 13

Thread: Tips for repairing bowlback cracks?

  1. #1
    Likes quaint instruments poul hansen's Avatar
    Join Date
    Jun 2020
    Location
    Danmark
    Posts
    278

    Default Tips for repairing bowlback cracks?

    How do you fasten a bowlback on the worktable and how do you close cracks between the staves?
    I'm not collecting, not collecting, not........OUMM.....
    Kentucky KM-805
    Hora: M1086 Portuguese II; M1088 Mandola; M1087 Octave
    Richmond RMA-110-VS
    Noname (German?) mandolin
    Mandoline Pochette by Franz Janisch Wien; Unknown Pocket Mandolin
    Mandolinetto Neapolitane
    Johs Møller 1945;
    Marma Seashell back
    Crafton(in the car)

  2. #2

    Default Re: Tips for repairing bowlback cracks?

    I guess the primary issue is not how to do it, but how to get it done, since I read here over and over that due to unpopularity and low resale value of bowl backs, luthiers are not eager to mess with them. Having just done a stave repair on one, and seeking no approval, and therefore not describing the method, I did get to think about some of the issues. First, we’re in luck because we have a soundhole for internal access, which is helpful. On the other side, the shape can require customizing clamps, the internal surface is often covered in paper or fabric that might interfere with glue, and the real possibility that a crack reflects an overall change of shape of the bowl that could be extremely difficult to fix without a complete teardown. A warped or cracked top would be a clue.
    At this point I’ve got around a dozen of these; most are not sonically impressive, but a couple are, so some care is needed as the bowl part is definitely a vibrating element. (Use a stethoscope or fingertips to verify). So a massive or stiff reinforcement could be a bad idea.
    Overstepping here, I think a simple minimal separation without misalignment of the edges, is a glue job, but warpage, broken wood, etc. is the complex issue.

  3. The following members say thank you to Richard500 for this post:


  4. #3
    Likes quaint instruments poul hansen's Avatar
    Join Date
    Jun 2020
    Location
    Danmark
    Posts
    278

    Default Re: Tips for repairing bowlback cracks?

    Quote Originally Posted by Richard500 View Post
    IHaving just done a stave repair on one, and seeking no approval, and therefore not describing the method,
    Hmm ?? Why not?

    The one I just got has a "Florida" so not much access through the sound hole but I really don't want to remove the top
    I'm not collecting, not collecting, not........OUMM.....
    Kentucky KM-805
    Hora: M1086 Portuguese II; M1088 Mandola; M1087 Octave
    Richmond RMA-110-VS
    Noname (German?) mandolin
    Mandoline Pochette by Franz Janisch Wien; Unknown Pocket Mandolin
    Mandolinetto Neapolitane
    Johs Møller 1945;
    Marma Seashell back
    Crafton(in the car)

  5. #4
    Registered User
    Join Date
    Jan 2009
    Location
    S.W. Wisconsin
    Posts
    6,270

    Default Re: Tips for repairing bowlback cracks?

    You could put it face down and clamp the neck to the bench. If you have a wooden faced vice with leather over the wood you could clamp the neck in the vice. Since you won't be using clamps on the rounded back you won't be adding weight so the vice will work here. To clamp the large rubber bands work well, glue the crack, align and wrap. A friend of mine years ago didn't have any large rubber bands so he glued it and had someone wrap string around his hands while he held the crack shut and walked around for hours with the mandolin in his hands tied up to let the glue set. Not what I am advising by any means, but a good story.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  6. The following members say thank you to pops1 for this post:


  7. #5

    Default Re: Tips for repairing bowlback cracks?

    Why not? Cause I ain’t no luthier, just a hacker and have great respect for the professionals. Reversibility of a repair is their credo, as well as maintaining originality if possible. I also don’t have a particularly good ear.
    Can you photograph or describe the issue you have, and also if there’s market value involved? Somebody will chime in.
    Forgot to mention: also frequently noted here is the fact that a neck repair can be a fatal problem on one of these,

  8. The following members say thank you to Richard500 for this post:


  9. #6
    Registered User Simon DS's Avatar
    Join Date
    Feb 2016
    Location
    South of France
    Posts
    1,372

    Default Re: Tips for repairing bowlback cracks?

    Face down on a block of wood that’s slightly larger than the face with four or five bicycle inner tube straps?

  10. The following members say thank you to Simon DS for this post:


  11. #7
    Likes quaint instruments poul hansen's Avatar
    Join Date
    Jun 2020
    Location
    Danmark
    Posts
    278

    Default Re: Tips for repairing bowlback cracks?

    It's not VERY valuable but is made by a known luthier, Johs. Møller 1945, so worth keeping fit.

    The big crack has a "repair" which I am trying to remove.

    I do have a lot of old bicyle tubes I use but it looks very difficult to get any kind of pressure across the rear end.

    Do you use extra humidification, before trying to close the gaps?


    I might just have to loosen the white strip and realign it and then fill in the gap and colour it in.

    Click image for larger version. 

Name:	20210923_154301.jpg 
Views:	32 
Size:	274.5 KB 
ID:	196446Click image for larger version. 

Name:	20210923_154251.jpg 
Views:	22 
Size:	213.0 KB 
ID:	196447
    I'm not collecting, not collecting, not........OUMM.....
    Kentucky KM-805
    Hora: M1086 Portuguese II; M1088 Mandola; M1087 Octave
    Richmond RMA-110-VS
    Noname (German?) mandolin
    Mandoline Pochette by Franz Janisch Wien; Unknown Pocket Mandolin
    Mandolinetto Neapolitane
    Johs Møller 1945;
    Marma Seashell back
    Crafton(in the car)

  12. #8

    Default Re: Tips for repairing bowlback cracks?

    Not too bad, except for the prior ‘repair’. I would still inspect the inside just in case something got glued in, and also to clean up for glue and see if the white strips are plain or T-shaped. Attaching pix of homebrew tools. I’ve attached large and small (60mm and 25 mm) mirrors to bendable but heavy copper electrical wire to offer better access than the usual dental mirror. The wire also can be used for figuring out the shape of a custom clamp if needed. The black snake is the working end of a cheap endoscope (10m long!) that works with a smart phone through Bluetooth and is semi-rigid. The double screw and turnbuckle is not needed here and is sized for fore-and-aft pressure. Clumsy, but needed once.
    Whether or not you need to squeeze the bowl a little is a judgement call.
    To get both staves level with each other at all points is tricky, but after you clean out the old glue (hand held scroll-saw blade useful), you’ll know better and with luck, a little leverage with a thin blade may be good enough. Alternatively, there are hardware solutions, and internal and external clampls.
    Finishing nicely is fairly easy, since all the staves have different shades, so if you can’t match color exactly, it won’t show, as long as you do the whole stave. I don’t have, but have been thinking about getting a set of different stains. The purple shoe polish on the old repair may have to be sanded to the wood if it penetrated.
    Click image for larger version. 

Name:	E14A2598-D82D-4772-B139-6731A14682E2.jpg 
Views:	11 
Size:	846.0 KB 
ID:	196452

  13. The following members say thank you to Richard500 for this post:


  14. #9
    Registered User DavidKOS's Avatar
    Join Date
    Oct 2014
    Location
    North CA
    Posts
    4,471

    Default Re: Tips for repairing bowlback cracks?

    A hurdy gurdy maker I know uses Superglue to close cracks on mandolin backs...but never on the soundboard!

  15. The following members say thank you to DavidKOS for this post:


  16. #10
    Likes quaint instruments poul hansen's Avatar
    Join Date
    Jun 2020
    Location
    Danmark
    Posts
    278

    Default Re: Tips for repairing bowlback cracks?

    The purple shoe polish on the old repair may have to be sanded to the wood if it penetrated.
    That colour is only in the photo, actually the french polish is just missing there.

    never on the soundboard!
    Why not?

    thinking about getting a set of different stains
    I have some repair markers with woodcolour
    I'm not collecting, not collecting, not........OUMM.....
    Kentucky KM-805
    Hora: M1086 Portuguese II; M1088 Mandola; M1087 Octave
    Richmond RMA-110-VS
    Noname (German?) mandolin
    Mandoline Pochette by Franz Janisch Wien; Unknown Pocket Mandolin
    Mandolinetto Neapolitane
    Johs Møller 1945;
    Marma Seashell back
    Crafton(in the car)

  17. #11
    Teacher, luthier
    Join Date
    Oct 2017
    Location
    Southeast Tennessee
    Posts
    2,553

    Default Re: Tips for repairing bowlback cracks?

    If it requires a lot of force to close it, it will either open up again or develop a new crack in a different spot.
    I found this out the hard way, although it wasn't on a bowl back.
    I recommend that you install splints and line things up the best that you can.

  18. The Following 2 Users Say Thank You to rcc56 For This Useful Post:


  19. #12
    Likes quaint instruments poul hansen's Avatar
    Join Date
    Jun 2020
    Location
    Danmark
    Posts
    278

    Default Re: Tips for repairing bowlback cracks?

    Quote Originally Posted by rcc56 View Post
    If it requires a lot of force to close it, it will either open up again or develop a new crack in a different spot.
    I found this out the hard way, although it wasn't on a bowl back.
    I recommend that you install splints and line things up the best that you can.
    Yes that's why I was contemplating humidification.
    I'm not collecting, not collecting, not........OUMM.....
    Kentucky KM-805
    Hora: M1086 Portuguese II; M1088 Mandola; M1087 Octave
    Richmond RMA-110-VS
    Noname (German?) mandolin
    Mandoline Pochette by Franz Janisch Wien; Unknown Pocket Mandolin
    Mandolinetto Neapolitane
    Johs Møller 1945;
    Marma Seashell back
    Crafton(in the car)

  20. #13
    Teacher, luthier
    Join Date
    Oct 2017
    Location
    Southeast Tennessee
    Posts
    2,553

    Default Re: Tips for repairing bowlback cracks?

    You can humidify it, but then you must let it sit for at least a couple of weeks to let it find equilibrium. After that, if the cracks still won't close with a minimum of pressure, you will have to splint. If you try to force them closed with high humidity, and then glue it in its very humid state, it will crack again after the instrument has returned to a "normal" moisture level. This is what I found out the hard way.
    Last edited by rcc56; Sep-23-2021 at 3:38pm.

  21. The following members say thank you to rcc56 for this post:


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •