Sanding Tip -- longish *LINK*
Brad Vietje
>I've had an experience recently that I should share -- basically, it boils down to avoiding scratches by cleaning up between abrasive grits --a lesson from optical work.
I've been working with a newbie turner recently, who was having problems with scratches -- he'd sanded up through the grits, from 80 - 400, and still had scratches that were hard to sand out, especially in the end grain. BTW, as turners, we deal almost exclusively with end grain, and those things that are side grain are usually sanded sideways, which shows scratches pretty readily.
Turns out, he went from one abrasive to the next, to the next, then was surprised to find scratches. The key to avoiding this is to keep your abrasives separate, if possible, and especially, to clean the workpiece between grits. As we sand the wood, quite a few abrasive particles come off the surface of the sandpaper, (depending on the brand, paper vs cloth, wet or dry, etc...) Most of these little gritties go flying around the room, (remember that mask !) but some become embedded in the open pores of the wood.
If a few 180 grit particles decide to dis-lodge when you are really enjoying the developing sheen and cahtoyance at 400 or 600 or so, you will get nasty little scratches that tend to show up most in the end grain, where they require a reversal of grits, and a good deal of work, to remove.
To avoid this, use a compressor, compressed air canisters, or even a vacuum to clean the surface of the wood between grits. The more little grit particles you remove, the better your final finish will look. This is also true at the end of all sanding -- don't lock the grit and dust in those pores with your finish ! Fine grained woods like Maple, Boxwood or Hophornbeam have fewer problems with grit packing in the pores, while woods with open pores, such as Oak, Padauk, Walnut, and Ash are the most problematic. If you are trying for a high-gloss, mirror finish, this is especially important ! This is where the optical part comes in:
One of my other hobbies is Astronomy (no "L"), and telescope making, by which I mean grinding and polishing the glass optics by hand. We not only go for a "mirror-like" surface, we actually grind and polish a parabolic curved mirror, and one that is hundreds of times more precise than the one we look in when scrubing our teeth. The grits used in optical work are essentially the same as in woodworking, though optical grade abrasives are much more expensive because they are graded much more carefully for size. We use the same Silicon Carbide (carborundum), Aluminum Oxide, Emory, and, in some cases, Garnet.
The lesson from optical work is in cleanliness, and carefully cleaning up between 120 and 180 and 220, etc... Believe it or not, you can actually make a telescope by hand, in your basement, without fancy machines, that will easily out-perform all but the most expensive telescopes you can buy, if you can only master the cleanliness part. Just one little particle of 220 that dances across a mirror being polished to a tolerance of a few millionths of an inch, can create a real mess ! If this sounds somewhere between nuts and impossible, you might amuse yourself at one of my favorite web sites, the home page of the Springfield Telescope makers, below.
If you haven't taken the time to carefully blow off all traces of grit and dust between abrasives, "Try it -- you'll like it !" You'll save a lot of time, and get a nicer looking finish, too.
Safe Spinning,
Brad Vietje
Thetford, VT
Springfield Telescope Makers
