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Sanding figured maple - scalloped finish problem

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Sanding figured maple - scalloped finish problem

Postby Brian Evans » Tue Mar 27, 2018 3:43 pm

I'm doing final sanding before finish on some figured maple - one is quilted with some curl, the other birdseye with some curl. In both cases I feel like I have a wavy, kind of scalloped feel where the wood is not coming quite level from the curly bits. It feels like the figure results in harder and softer transitions in the wood which respond differently to sanding. I can't see it or measure it, I can only feel it so it might be my imagination. Anyone else experience this, is it just a fact of life, or is there some technique I might try? Currently my best idea has been 400 grit paper with a quite hard backing pad, but all the surfaces are curved so this might not work all that well.

Thanks, Brian
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Re: Sanding figured maple - scalloped finish problem

Postby Peter Wilcox » Tue Mar 27, 2018 5:04 pm

I've noticed this at some time in the past, but can't really remember if it was real or not. (I think it just may be a difference you feel in texture, especially if you're using a hard backing to sand which would obviate any digging out of the soft areas.) After applying the finish and sanding flat, I don't remember any problem, so if it was real it wasn't deep enough that the finish couldn't fill it.
Maybe I can't fix it, but I can fix it so no one can fix it
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Re: Sanding figured maple - scalloped finish problem

Postby David King » Wed Mar 28, 2018 1:00 pm

I see it all the time. Are you dampening the wood between sandings to raise the grain? If you don't do that now it will happen on it's own over time and under the finish. I use a really sharp paper like Norton 3X 400grit (the blue stuff). On complex curves you can stick it to a thin steel ruler or a thin stick of clear grain wood to fair the surfaces. Don't push hard just less the ruler flex and dust the high spots. You might just be feeling the changes in grain orientation...
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Re: Sanding figured maple - scalloped finish problem

Postby Alan Carruth » Wed Mar 28, 2018 2:01 pm

Grain figure like that is caused by changes in run out. The sandpaper takes a bit more wood off when the grain is parallel to the surface than when it's even a little end on, so you end up with waves. The only solution is blocking, which is difficult on a curved surface, as you say.

OTOH, I don't find that look particularly unattractive: it just looks like wood. Also, keep in mind, that the wood will move after you've got the finish on, and take on that wavy look anyway. The only way to avoid that is to use a really thick, hard finish, which is not what you want on an instrument.
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Re: Sanding figured maple - scalloped finish problem

Postby Brian Evans » Wed Mar 28, 2018 2:50 pm

Thanks. They are archtops, so really nothing flat anywhere. I won't stress about it. :) I do find that the visual and tactile changes as end grain becomes more or less exposed along the arch can really throw me for a loop. I can't count the number of times I have been sanding out "scratches" only to put the opti-visor on and find out I've been polishing the heck out of grain figures...

Brian
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