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Thread: Top Crack Weymann Keystone Bowlback, How to draw together

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    Default Top Crack Weymann Keystone Bowlback, How to draw together

    How do I properly repair this top crack?

    Somehow I need to draw it together, but its fairly happy in its current position and doesn't want to come together. I tried using light pressure from a clamp but doesn't move. Is there a trick (short of removing top) that I could apply to draw this crack tight?

    Its been displayed on the wall for years, currently I am hydrating it in a sealed bag with a wet spronge (not touching wood)....

    I am a handy person, but novice on mando repair.
    Some pics below.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    If you canít get it to close with humidity or clamps, it probably isnít going to close, short of removing the entire top, taking off the braving, glueing and clamping, then re-attaching the bracing. The much simpler way would be to fill it with a splint. Find a similar piece of wood, cut an appropriately sized shaving with a plane, and glue that into the crack ice and tight. Let glue cure, then carefully cut it down flush, or nearly so, finishing up with sandpaper. Touch up finish to match and youíre done.
    Don

    2016 Weber Custom Bitterroot F
    2011 Weber Bitterroot A
    1974 Martin Style A
    Fender Octave Mandolin c.2004-2008

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    On "open" cracks of this sort, it will probably be necessary for you to fit a spruce splint into the crack. Leave it high and scrape it level to the surface after the glue has set with a cabinet scraper that has most of the cutting surface masked off with tape. See "razor blade scraping" in the "items for luthiers" section of frets.com.

    If a shaving from a plane is not thick enough, you can split out a section of spruce between two grain lines, and carefully work it down to size. If you taper it from top to bottom [or outside to inside], it will be easier to insert snugly. If there is a brace in the way, you might have to notch it. Cut a couple of extras. It's easy to mess one up.

    When it is level, it can be touched up with a tiny bit of shellac or violin varnish.
    If it came to my shop, that is the most likely way I would want to handle it.

    If you do not do this, there is a risk that the crack may open up again, or a new one may develop next to it. This is true even if humidification closes the crack most of the way.

    It might be possible to close the crack by loosening the top adjacent to the crack, but that is tricky work for an experienced repairman, and it is harder to do on a bowl-back. It is not a job for a novice luthier.

    Good luck.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Quote Originally Posted by rcc56 View Post
    On "open" cracks of this sort, it will probably be necessary for you to fit a spruce splint into the crack. Leave it high and scrape it level to the surface after the glue has set with a cabinet scraper that has most of the cutting surface masked off with tape. See "razor blade scraping" in the "items for luthiers" section of frets.com. When it is level, it can be touched up with a tiny bit of shellac or violin varnish.

    If you do not do this, there is a risk that the crack may open up again, or a new one may develop next to it. This is true even if humidification closes the crack most of the way.
    I should have re-read this again (haha) because I was struggling with how to split a tiny shaving.
    Came up with a razor shave (as you suggested, see pics), even had an old soundhole spruce plug that is likely same wood.

    But now the issue. The crack has closed somewhat after humidifying and the shaving doesn't want to go in very easy (dry fit). Thinking to let the mandolin sit out for a few days in normal humidity. Any tricks to get it in. Should I also cleat it? Would this avoid a new parallel crack??

    Thinking of clamping with bicycle inner tube wrap. What thoughts on clamping?

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    Last edited by scstill; May-27-2020 at 3:08pm.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    I usually dry fit them, insert dry, and then use hot hide glue.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Pops, I assume you meant "fit dry, remove, apply glue, and insert" . . . ?

    It might help if you can smooth out the inside edges of the crack a little bit, perhaps with an X-acto blade, or a very thin piece of metal with 220 or 320 sandpaper glued to it.

    Taper your splint slightly so it is a wedge fit. Gently fit your splint, remove, then glue it in. Hot hide glue is the best for crack repair in spruce. Push it in snugly, but not so hard that you break the splint. If you handle it right, clamping is not necessary.

    It might go in easier after you apply the glue-- wet glue is slippery.

    You can cleat it if you want. If you do, keep the cleats small. I generally do not cleat splinted cracks, some others do.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Some cracks are simply a shaving and you couldn't get it in the crack with glue. The glue seems to wick in the thin plane shaving. A larger splint would definitely need the glue first.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    So after humidifying in a bag with wet sponge for about a week, the crack got noticably closer.
    Tight enough that the splint would not fit in.
    I left the mandolin out for a few days and the crack expanded again.

    Do you recommend that I repair after it has settled in its normal environment with a splint?
    Rather than just gluing after humidying, thinking it might open a new parallel crack.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Quote Originally Posted by scstill View Post

    Do you recommend that I repair after it has settled in its normal environment with a splint?
    Rather than just gluing after humidying, thinking it might open a new parallel crack.

    Yes, that's the best way.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    So I have dry fitted the spruce splints as show. They fit really good.

    But the new challenge is how to properly clamp for gluing.

    The main issue I have is at the end (by the tailpiece) the top has lifted from the body and is the main spot for the gluing to get the top flat. Once this end is down the top seems flat. It would be a real project to build a special clamping caul around this corner.
    So I was wondering if you think it would be sufficient to use painters tape to hold the top down in this area?

    So the next question is...
    Will the flat top over the crack need a clamp along the splint since the two sides seem to match up. It would be tough to get an inside caul proper set through the little sound hole

    Then is it ok to "slobber" the liquid hide glue into the crack and then wipe off the top?
    Or is the finish sensitive to the glue?

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    I would glue and secure the loose top first. You can glue the splint in later, either after the top is secure but before the glue has set; or you can let the joint set and glue the splint the following day.

    If you use masking tape, use the low-tack blue masking tape and stick it to your jeans a couple of times to reduce the tack further. Otherwise, it might pull finish off when you try to remove it. You might try a dry run with the brown low tack masking paper instead of tape. It is less likely to damage the finish when you pull it off.

    When you glue down the top, try to be sparing on the glue in the area directly under where the splint will go. You may have to clean any excess glue that gets in the area where the splint will go.

    When you glue the splint, just rub some glue in the crack and on the splint, insert the splint as close to flush as it will go, and wipe off any excess glue with a damp [not soaked] rag. If the fit is snug, there is no need to clamp. If you're not satisfied with the top closure near the splint, now is the time to rub a little more glue in there and secure it the best you can.

    If the splint projects above the top after it is dry, you can glue some sandpaper to a small block of wood, stick 2 layers of blue tape to all but the center of the sanding block, and work the splint down with that. When you can't get the top of the splint any lower by using the block, mask off a small scraper or razor blade in the same manner to finish the job. See frets.com "razor blade scraping" for an illustration of the concept. You can mask off portions of sanding blocks, scrapers, and even chisels when you need to level a small surface without damaging adjoining areas.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    The end is repaired using tape to clamp it down. Pics showing the progress.

    But now I've discovered the two sides of the crack are not even
    So I'm thinking I need to clamp across the two sides of the crack.
    In order to do that I will need a caul inside to get over the two braces.
    Soooo....
    How do you get a wooden caul inside and hold it in place while tighening a deep throat c clamp? Thinking of glueing the caul to the clamp end. How would you do it?
    Or is there an alternative way?

    Remember I have a splint that is going in the crack. It is two pieces
    I could not remove the one showing from dry fit.
    So How would you get the glue into the dry stuck splint?
    Thinking to use suction cups to vacuum it in....

    There is also a slight hump in the lower part of the top.
    It moves up from the tailpiece
    Thinking I have to live with that??

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    If you put a 60 watt incandescent light bulb in a bench light and keep it about a foot above the top it will dry the area out so you can remove the splint. It may take a few hours to a day, I use this method for stuck violin pegs and it works great. Rare earth magnets, one inside one outside, will place a cleat or small caul where you want it easily. If you are using a clamp a small amount of glue or double stick tape on the clamp will hold the caul. Just reread and sounds like your caul will be too big for the magnets.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    You can use magnets to hold the caul in place. Glue a couple of magnets to the underside of the caul. Put it in place and hold it in place with two more magnets. The neo magnets can be pretty strong

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    After I removed the stuck splint (hairdryer) the sides of the crack were fairly level.
    So I decided to go without the clamp, not to bad. Will remember the magnet trick.
    Pictures of the process below. Taped each side with narrow sanding block got it pretty smooth. Fresh tape about 5 times.

    Now the issue is how to match the splint to the rest of the top.
    Thinking of using a violin varnish from international violin (from thread on stave replacement). Maybe get a of 2oz amber bottle, maybe a next shade darker as well. What do you think? Other ideas?

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Before you varnish, smooth it out some more by making a sanding block about 1" long and 3/4" wide. Secure some fine sandpaper to the block and then place a piece of tape directly over the sandpaper itself on one side of the block. Repeat on the other side, leaving only a narrow strip of sandpaper exposed. Again, visit frets.com and read the article on "razor blade scraping." You will be using the same principle here, but with a sanding block instead of a razor blade. If you have a miniature cabinet scraper, you can do the same thing with it also.

    Yes, violin varnish or shellac. Oil varnish is more forgiving for this sort of touchup because of its slow drying time. Or you can make up some spirit varnish by mixing 2 parts alcohol to one part shellac flakes, and add maybe 10% to 15% sandarac. Keep your color light. The first coat might not show any color at all. The color will tend to become visible with the next couple of coats. Use a test board to experiment with the color before you go to work on the instrument.

    Touch up is one of the most difficult aspects of instrument repair, and most of us [including me] are not very good at it. If you get anywhere near the original color, you will have done very well.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Quote Originally Posted by rcc56 View Post
    Before you varnish, smooth it out some more by making a sanding block about 1" long and 3/4" wide. Secure some fine sandpaper to the block and then place a piece of tape directly over the sandpaper itself on one side of the block. Repeat on the other side, leaving only a narrow strip of sandpaper exposed. Again, visit frets.com and read the article on "razor blade scraping." You will be using the same principle here, but with a sanding block instead of a razor blade. If you have a miniature cabinet scraper, you can do the same thing with it also.
    Yes I have read the razor scraping article. Very informative.
    But with this technique won't I mar the original finish? (trying to avoid that)
    That was my intention with the tape (super thin yellow frog tape) and narrow sand block.
    There also is a tiny offset across the crack (cause I didn't clamp) :-(

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Try it on a piece of scrap to get a better idea of how it works. The tape lifts the sandpaper surface above the areas adjacent to the splint. I usually use blue masking tape for the job-- it is fairly durable and has a fairly slick outer surface.

    You can double the tape if necessary, and check it every minute or two to make sure the sandpaper is not cutting through the tape. And yes, I also will often mask the instrument itself when I'm doing the initial work.

    When the splint is very close to level, I will finish up by removing the masking from the instrument and using a masked block or scraper alone to complete the final levelling process. And yes, you have to use a lot more care at this point in the process. For very precise work, you can sometimes switch to one or two layers of mylar Scotch Magic tape, but you have to be extra careful with it because the tape will wear through quite quickly.

    As far as the offset is concerned, just do the best you can to work with it. If you do a good job, the only person who will notice the flaws in the work will be you.

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    Quote Originally Posted by rcc56 View Post
    Try it on a piece of scrap to get a better idea of how it works. The tape lifts the sandpaper surface above the areas adjacent to the splint. I usually use blue masking tape for the job-- it is fairly durable and has a fairly slick outer surface.

    You can double the tape if necessary, and check it every minute or two to make sure the sandpaper is not cutting through the tape. And yes, I also will often mask the instrument itself when I'm doing the initial work.

    When the splint is very close to level, I will finish up by removing the masking from the instrument and using a masked block or scraper alone to complete the final levelling process. And yes, you have to use a lot more care at this point in the process. For very precise work, you can sometimes switch to one or two layers of mylar Scotch Magic tape, but you have to be extra careful with it because the tape will wear through quite quickly.

    As far as the offset is concerned, just do the best you can to work with it. If you do a good job, the only person who will notice the flaws in the work will be you.
    I plan to try this approach
    How does wrapping the sandblock with tape differ from just taping the instrument?

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    Default Re: Top Crack Weymann Keystone Bowlback, How to draw together

    It's easier to control the work.

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