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Thread: Top repair patch

  1. #1
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    Default Top repair patch

    Once again a router did me dirty. I was trimming the top flat with the sides and having successfully done all of the places where you are going against the grain, all that was left was the back, and don't yo know the router grabbed the grain and tore a notch out of the top. I did an initial repair with a patch and was not happy with the outcome so I am making a second attempt.I am just refacing the original patch since it is functionally good. I have it carved out on an angle, and a patch that lines the grain up reasonable well, but am wondering what kind of glue is best for not showing a glue line, and I am open for any other suggestions. Attached is a photo of the original patch, and the cut out for the new patch.Click image for larger version. 

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    Thanks a lot
    Bob Schmidt

  2. #2
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    Default Re: Top repair patch

    No glue line will be completely invisible on conifers. The best you can hope for is repair that will probably stick out like a sore thumb to you, but others will not be able to notice unless you direct their attention to it.

    Hide glue will probably give you the best results. Other glues will tend to show more color or penetrate into the surrounding wood, inhibiting the ability of the wood in the area to accept finish evenly. The better the fit, the less visible the repair will be.

    Me, I might flatten the angle and make a new, larger patch that will blend in at a less oblique angle. Look up the technique for making a violin "soundpost patch;" the two surfaces blend together rather than having a distinct looking joint. Make sure any grain run-out is in the same direction of that of the top. Sand the area extra well to make sure there is no glue left on the surface. A sunburst finish can help to hide the repair. And remember, the size of the repaired area will be reduced when you install binding.

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  4. #3
    Registered User sunburst's Avatar
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    Default Re: Top repair patch

    You can't hide that patch without "painting over it". That means a dark, sprayed sunburst or other dark sprayed color.
    Any difference in grain direction and especially run out in spruce will show up. Unless we have the scrap piece that was left when the top was cut out, and we use the adjacent section and align the grain lines perfectly we can forget about a spruce patch not showing up under varying light conditions.
    So, now that your expectations should be realistic, I recommend hot hide glue of a high clarity description, or perhaps Knox gelatin. Gelitin is very clear and will show up the least of anything you can use. Grain match and fit are all you have to work with to make the patch less visible, so spend as much time as you feel like you can afford making the piece fit, glue it in and move on.

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  6. #4
    Adrian Minarovic
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    Default Re: Top repair patch

    Quote Originally Posted by sunburst View Post
    You can't hide that patch without "painting over it". That means a dark, sprayed sunburst or other dark sprayed color.
    Any difference in grain direction and especially run out in spruce will show up. Unless we have the scrap piece that was left when the top was cut out, and we use the adjacent section and align the grain lines perfectly we can forget about a spruce patch not showing up under varying light conditions.
    So, now that your expectations should be realistic, I recommend hot hide glue of a high clarity description, or perhaps Knox gelatin. Gelitin is very clear and will show up the least of anything you can use. Grain match and fit are all you have to work with to make the patch less visible, so spend as much time as you feel like you can afford making the piece fit, glue it in and move on.
    I would add that what John said works for top grade professional work where perfect fit is norm and you don't want any visible staining of surrounding wood. If your fitting is not perfect, any gap filled with clear glue will show as dark/black line. For this reason I often recommend glue that dries opaque tan or whitish (like lower grade HHG or Titebond) that is easier to cover with some touchup after repair. Mask surounding areas to prevent glue stains in the wood (thay may show only during finishing).
    Just as a side note... top-tier violinmakers would approach this quite differently. Often this kind of patch on visible part is done one grain line at a time so you will match grain pattern perfectly and making sure the angle where the patch strip vanishes is not too small (30-45 degrees) so there is not a loooong vanishing glue line (or glue saturated wood) where the patch ends and not in straight line that would be more apparent. Each strip shoud end at slightly different lenght so the ends don't align to create one long ghost. Use thick glue with short gel time so it won't suck too deep. Clean any squeeze out with sharp edge, don't wash it with water or you will soak the wood with the glue.
    Adrian

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  8. #5

    Default Re: Top repair patch

    What Adrian suggests is similar to repairing a hardwood floor: replace linear elements, stagger the cut ends. Imagine what a floor with a patch going diagonally would look like. On the tiny scale, obviously a very time-consuming thing.
    I’m thinking, as someone who has also run into router tearout because cutter direction and grain can’t always be correct, that a reversible router and bi-directional bits could help, although probably non-existent. I have (again, I don’t build instruments) made simple cutters for use on my mill, which is reversible just to avoid this problem. It’s almost standard (manual mill) practice to upcut metals (properly) on roughing passes and reverse travel (not rotation) for a smoother final cut.

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  10. #6
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    Default Re: Top repair patch

    Thanks everyone for the responses, and setting my expectations more realistic. If worse comes to worse I can sunburst it, but the initial design was to keep it white with ebony binding and trim, and I am not sure how that would look with a sunburst finish. I suspect that switching to white plastic would be better.
    I do have the cutoff from that part of the top, but unfortunately it was too short to fill the patch. The piece I used on the first patch was close, but it was proud by a bit when I glued it in, and from the slope of the grain run out, the allignment shifted a bit as I sanded it down.
    I have another piece that is close that I will try next. Offsetting the glue line one grain at a time sounds like a skill worth learning. I will try that on a piece of scrap to see how well it hides the repair.
    So it sounds like a thick HHG is best to avoid penetration.
    Can anything be done between the grain lines using glue and spruce dust to break up the glue line or would that show with the finish?

    Thanks again everyone for the helpful suggestions
    Thanks a lot
    Bob Schmidt

  11. #7
    Adrian Minarovic
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    Default Re: Top repair patch

    Quote Originally Posted by irishmando View Post
    Can anything be done between the grain lines using glue and spruce dust to break up the glue line or would that show with the finish?
    Anything other than direct wood to wood contact with infinitesimal glue line will show. Even glue that penetrated at the joint can show.
    Another way to hide this tear out would be along the line If you cannot hide it, highlight it! You can do some funny inlay in the place like minion peeking from behind the binding to cover the spot...
    Adrian

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  13. #8
    Mando-Accumulator Jim Garber's Avatar
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    Default Re: Top repair patch

    Sunburst! save the blond for the next one.
    Jim

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  15. #9

    Default Re: Top repair patch

    OK, here's radical idea that might work..

    If you want a perfect match, very carefully cut out an area of the top slightly larger than the damaged area and level it all to the thickness of that damage. This now becomes the top or face section of the new patch. You simply graft in extra spruce on the back to re-create the original thickness, and fit it into the area you just cut if from as the new top patch.

    If this was done with "infinite care" as the instructions for seating an old violin bridge once said, you would have the grain match perfectly, the fit perfectly match (have to cut carefully!) and the grain be properly oriented. Use the smallest jeweler's saw blades available or perhaps cut it with a razor. If you glue it tight to the original section, you'll only have a difference of the saw blades width at the edge and you can sand that even.

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  17. #10
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    Default Re: Top repair patch

    It came out better this time, but It is still visible. It looks like it will be a good candidate for a sunburst. With that in view, the original design was going to be with ebony bindings. Does anyone have experience with black bindings under a sunburst? If so what colors might work?
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    Thanks a lot
    Bob Schmidt

  18. #11
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    Default Re: Top repair patch

    You can add a simple white (or other light colored) purfling strip between black binding and the top. That will set off the binding and it tends to have a nice "classy" look. Otherwise, a black binding will more or less blend into a dark 'burst. That can be a good look too, but it may not be what you had in mind.

    BTW, it looks like you still have to cut the binding channel. Besides working from the proper direction with a rotary tool, you might want to consider scoring with a gramil or purfling cutter before making the cut. That can help against chips going beyond the score line. If you don't have access to one, you can make a simple temporary one using bits of wood and an Xacto blade. Also, you can make several passes, each cutting a small amount. That lessens the chance of blow-out, but it offers more opportunities to make a mistake...

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  20. #12
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    Default Re: Top repair patch

    Thanks John,

    The white purfling sounds like a nice touch. I just came across a picture Steve Sorensen posted of a beautiful mandolin where it appears that is what he did.
    I do have a gramil, and will use it to scribe the bindings before routing.
    Thanks a lot
    Bob Schmidt

  21. #13
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    Default Re: Top repair patch

    I had to look up "gramil". Imagine my surprise to discover I already a pretty good one! Now I'll try to work it into conversation to help me remember it.

    From an amateur woodworker's perspective I am impressed with the patch, version 2.0. In my book that qualifies as a dang fine fix for a boo-boo.
    Clark Beavans

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  23. #14

    Default Re: Top repair patch

    That's a pretty good looking repair! You might be ablate get away with a amber top or a very light burst.

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  25. #15

    Default Re: Top repair patch

    I think your repair came out quite nice. Under an amber finish it may look like a cross grain scratch or gouge. You could even distress the finish on top of the "scratch" line to make it look more authentic. Sunbursting is a whole other art. Best of luck!

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