Saturday, February 27, 2010

Finish Preparation

It's hard to get out in the garage in the cold, so there hasn't been much work done on Clark's Zebrawood cutaway OM.  But one milder days when I get crank the heaters up a few hours ahead of time, I can get the temp around the workbench into the low to mid 60's and do some work.

I started sanding the back and sides a few weeks ago, but then stopped.  I had noticed that the rosewood binding on the top cutaway was really thin, and, after deciding that I could live with it, decided one night that I couldn't.  It's going out with my name on it, and while I don't expect perfection in my workmanship, I don't want to settle for something going out there that I know can be better with some more work.

So I ordered some more rosewood binding and some b/w/b purfling from LMI, and in the meantime removed the offending binding.  I used heat from an iron to loosen the glue and the peeled it off with a chisel.  I sanded down to bare wood in the binding channel since Tite-Bond doesn't not adhere well to dried glue. 

When the bindings arrived I got out the blow torch and bending pipes and bent the binding.  I've posted before about this process; you can go here if you missed it.

The side purfling and binding went on pretty well, and I was back to sanding.  I start with the back and sides, beginning with 100 grit, then moving to 150 and finishing with 220 grit.  This is a really important step, because a finish won't hide scratches, it will actually magnify them and draw attention.  Here are the basic tools:  sandpaper, a felt block, and a lamp positioned at a low angle to the surface.  (I also wrap the sandpaper around a 1" diameter dowel to reach the curved parts like the cutaway and waist.)

By raking the light across the surface at a low angel, defects suddenly appear that are invisible otherwise.  I move the light constantly as I'm sanding.  I really only do this when I'm sanding with 100 grit.  After that I'm just removing the sanding marks left by previous grit.  Like I said, I sand the back and sides to 220, but the top gets sanded to 320.  I go across the grain to remove scratches and defects, but then sand with the grain to achieve a nice smooth surface.

That doesn't include the neck, however.  We've decided to finish the neck with an oil finish instead of the glossy finish that will be used on the body.  If your hand gets a little sweaty it will sometimes get a little sticky on a neck with a high gloss finish.  Actually, "sticky" is probably overstating things, but your thumb, instead of sliding easily up and down the neck, feels like it is grabbing the back of the neck.  This doesn't happen with a nice oil finish.

The thing with the oil finish is that, instead of the finish providing a smooth surface and feel, the wood itself must be practically polished.  So I move from 320 grit to 400 and finally 600 grit sandpaper for the neck and headstock.

After the sanding, there is still a lot of work to be done before applying the finish.  In order to build up a finish, all gaps and pores must be filled.  Invariably there are going to be gaps around the binding; they are unavoidable.  Most of the gaps are very small and can be filled with a medium or heavy viscosity superglue.  Put some in the gap, level it with a razor, spritz it with accelerant, sand it level, and it's invisible.

However, there is one place on the binding that I just replaced where the gap is huge:

So I sliced off a sliver of rosewood binding, wedged it in there, wicked some super glue around it.  When it was dry I leveled the splice with a chisel and sandpaper, and here's the result:

Nice, huh?

When I finish filling all the gaps, I'll move to filling the pores of the Zebrawood.  More on that soon.  Hopefully soon.

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