Long subject, but here's some random brain droppings on it for you. Buffing is simply a means of applying an abrasive to a surface. The abrasive is carried on the wheels and the object is held relatively still, instead of the opposite as when sanding on the lathe. But it is still the abrasive action that produces results. Buffing abrasives vary in grit or coarseness just like sandpaper. Some, such as emory on a sisal wheel actually remove fairly significant amounts of material, while others like white diamond on a cotton flannel buff remove such a small amount that they only remove tiny scratches in an already smooth surface (called polishing).
Yes, you can turn a 3700 rpm grinder into a buffer. Is it the best solution? NO. One of the most important factors in buffing is the surface speed that the abrasive laden buff is moving past the object being polished at. This is a function of the rpm of the motor and the size of the buff. IE a 8 inch buff turning at 1750 rpm is buffing slower than a 6 inch buff at 5=3500 rpm. Lots of literature on the subject available on the net, but the bottom line is that for polishing wood or antler type items, a 6 inch buff at 3500 rpm is at the very top of the acceptable range, and this makes it tend to grab items and also makes it harder to get a smooth, wave free finish. It will work, just have to use a light touch. A better option is to get a couple of nice thick 8 inch buffs somewhere, and some half inch allthread, washers, and nuts and make yourself something to use mounted in your lathe, where you can control the speed.
Buffing will not fill in holes or low spots in a pen blank. It will polish the high spots and actually make the low spots more noticeable. A smooth, even blank with a uniform scratch pattern from a medium grit sandpaper like 400 or 600 is the best candidate for buffing. You can either buff on the mandrel, if you use one, or on a different buffing dowel. If you use the mandrel, try to avoid or minimize buffing the bushings, as this will drag grey metal residue onto your material. Also, loosen the nut to allow the blanks to spin. I have several dowels I turned out of scrap wood by my buffing lathe, labeled as to which blank they will just slip fit inside. I just use my thumbnail to hold the blank in the middle against the buff, but some people turn a slight bead in the dowel for that purpose either way you want the blank to spin slowly as you buff at an angle to the face of the buff. too close to a 90 degree angle and the blank spins too fast and doesn't get polished enough. Too close to parallel, and it doesn't spin enough and the polish is uneven. Easier to figure out while doing it than to explain it.
Keep your buffs clean! Dust from a sanding, turning ect drifting down onto the buff defeats the purpose of a uniform fine abrasive on the wheel. Shower caps make good buff covers if your using a center motor setup, grocery bags pulled down over the buffs work for a lathe mounted rig.
Get a buff rake and use it from time to time. With the fine abrasives and soft wheels we use it's not as big a deal as if your polishing chrome or stainless parts, but you still need to clean off the buffs occasionally. This will produce lots of really itchy and annoying fluff, so set up a shopvac or your DC inlet near the buff if possible.
Remember, most bar or stick abrasives like tripoli (abreviated EEE) or white diamond are held together by a synthetic wax, and this wax is deposited on the blank when you buff. Some finishes may work best if this wax coating is removed with acetone or DNA prior to finishing. I do not find it to interfere with application of my BLO/CA finish.
And lastly, as my brain runs dry, if you find that you are getting lines or blobs of white compound deposited on your blank, try adding more compound to the buff. Counterintuitive it may be, but more compound on the buff leaves a cleaner finished product. Up to a point of course. YMMV
Mostly it's a fun and quick way to get a nice finish without spending too much time hunched over the lathe breathing ca fumes, so have fun with it. The best part is that it is really very difficult to mess up something unrepairably with a buffing wheel, short of having the wheel grab it and throw it into the floor hard enought to crack it. DAMHIKT
