How do you fasten a bowlback on the worktable and how do you close cracks between the staves?
Printable View
How do you fasten a bowlback on the worktable and how do you close cracks between the staves?
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.
Hmm ?? Why not?Quote:
Originally Posted by Richard500
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
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.
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,
Face down on a block of wood that’s slightly larger than the face with four or five bicycle inner tube straps? :)
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.
Attachment 196446Attachment 196447
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.
Attachment 196452
A hurdy gurdy maker I know uses Superglue to close cracks on mandolin backs...but never on the soundboard!
That colour is only in the photo, actually the french polish is just missing there.Quote:
The purple shoe polish on the old repair may have to be sanded to the wood if it penetrated.
Why not?Quote:
never on the soundboard!
I have some repair markers with woodcolourQuote:
thinking about getting a set of different stains
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.Quote:
Originally Posted by rcc56
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.