Here is a brief description of how I sand my bowls.
I first began using soft disc sanding when I was introduced to it in a workshop on stack laminated furniture around 1983 with Doug Sigler. Then about 1985 I took a workshop with David Ellsworth and he extolled disc sanding virtues even further. We're talking rpm's. Sanding while the bowl is stationary allows you to deal with voids, the natural edges, out-of-round bowls, and end grain. Over the years I have refined various aspects of the soft disc sanding and have ending up with a system that works fairly well. We all wish there was a way to sand faster, if not eliminate altogether, but that's not in the cards.
The backbone of my sanding is the Makita GV5000 sander/polisher. It is light and compact, allowing me to hold it close to the head, reducing arm fatigue. You can lock it on so you don't have to keep holding the trigger. It runs at 4000 rpm, way too fast for the foam or sandpaper, so I rigged up a standard household dimmer switch ganged to a duplex outlet and am able to dial in the preferred speed at will: faster with coarser grits, slower for the fine. No more wearing out the switch triggering it on and off to slow the sander down. The dimmer does not seem to harm the sander at all, witness I am still using the old 1984 one daily. I added a second duplex outlet to my dimmer switch, and now can switch back and forth between grits quickly as I work my way through sanding a piece. I believe my general speed is around 2,500 rpm. Some years back I got worried Makita might discontinue the model, and as I had not found anything comparable, I bought a second….and a few year later a third. Rather than being redundant, they are integral as a group.
If you have two sanders you can alternate which one you switch to a finer grit,
leap-frogging your way to the finest. For example, sand a bowl with 80 grit,
move to the second sander for 120 grit, and if you come across a spot you missed
pick up the 80 grit to fix it and then go back over with 120 grit. Now pull
off the 80 and put on 220. Sand the whole bowl, and again, if you find a spot
of 80 swirls you didn't quite get off, pick up the 120 and get rid of it. The
220 is pretty good at showing off scratches. Now replace the 120 with 320 and
sand all over with that. Again, you are easily able to pick up the 220 if there
is a spot the 320 can't easily work out. It has been my experience that a light
touch with the sander will leave the paper sharper longer and increase the
surface you are able to sand. It is all too easy to bear down on one spot to
get a scratch out, but as the wood and paper heat up the grit is quickly glazed
and the cutting action becomes polishing.
Commensurate with the hand-held sander is a braking system on the lathe. When I had a variable speed DC motor I found it acted as a brake in the opposite direction it was set to run. This helped hold the bowl in place as I was sanding. When I switched to variable speed AC motor I lost this feature. But then I passed a length of 3/8" O.D. rubber gas line from the auto parts store around the 4" drive pulley, and voila, a slip brake in both directions, easy to nudge forward with a hand but firm enough to resist the torque of sanding. I upgraded to a triple drive pulley so a groove is always available to drop the rubber over for sanding. A real advantage to this system is it frees up both hands to hold the sander. This greatly reduces the stress on the forearm that I found left me aching after a period of one-armed sanding. Plus, using two hands you are able to "float" the sander in your hands as you arc back and forth over the complex curves of a bowl, as well as gently sand around the top or the bowl to ease the sharp edges.
I use a
foam-backed leather-faced sanding system. I use the thinnest leather I can
find, 0.02"-0.04" thick (0.5 - 0.8 mm). Some pigskin I got from a
leather-working. A fine alternative to the Ester foam (as recommended in the
AAW article by Larry
Genender, fall 2005) may be bought from
http://www.foamorder.com/custom_cuts.php Go
to mattress foams, then conventional shapes, and choose rectangle: http://www.foamorder.com/custom_cuts.php?product=conventional&shape=1
It is easy to enter a size such as .75” x 24” x 24”, and get a list of types,
their prices, and descriptions. I tried 6 different types, and then re-ordered
two to make sure I had the right one. The best for my sanding purposes is the
DuraFlex D44, with a density of 2.25 lb/ft3, and ILD 40. It is blue, the only
blue one on the page, which makes it easy to identify. A 2’ square piece runs
$6.95 + shipping, way cheaper than the Ester foam, and they mail out in a timely
fashion. The 3M 90 does not degrade it, though it does slowly de-bond after
heavy use. But at that price, no problems. Just gluing on another piece when
it gets too loose.
I used to use 3M 77 to glue the foam to sander, leather to foam, but I find the 3M 90 considerably superior in ease of application, tenaciousness of grip, and in resistance to heat. It is well worth the extra dollars. Insist on it. Spray both sides and wait a minute or so until it is no longer wet but not altogether dry, and press together. I can use it after only a few more minutes, though it is better to give it half an hour. If the sander catches on an edge or in a crack and begins to rip loose, spray the 90 into the folded back leather, wait, and press to resume sanding. If it really works loose, simply peel it off and re-glue. When it comes time to replace the foam I take the time to sand the 3M 90 off the leather using a stationary belt sander, to keep the glue buildup from stiffening the leather. This is an older shot showing yellow foam.
I used to use full sheets of sandpaper. I used 3M Feathering Disc Adhesive Type II (part no. 08015), a liquid in a tube, or Norton Disc Adhesive, available in the auto store, and coated both the leather and the sandpaper. At higher speeds the discs would soften and fly off in most annoying fashion. Now I use 3M PSA discs, the U216 gold A weight available at auto finishing supply stores, and those discs never come off. I prime the leather with a thin film of the 3M Feathering Disc Adhesive which is good for weeks of sanding. If anything the grip is too strong, and you have to peel the paper off carefully to avoid damaging the leather/foam connection. Dusting the leather surface with the dust on your palms before putting on the next piece of sandpaper helps prevent too much stick. he PSA discs cost around 30 cents each, but the savings in time is enormous. I can usually sand two 14-16" bowls with one disc of each grit. I believed all those years I was using the only 3M Gold available, but I have recently learned about the 3M 255L Gold which may be superior in grit but has a mylar-like backing that I find a little too stiff. One place you may buy from is TCP Global see: http://www.tcpglobal.com/3mdepot/3m111-3.aspx Also AutoBodyToolmart see: http://www.autobodytoolmart.com/c-710-stikit-gold-disc-rolls.aspx
I I bolt on a 2.75" hard rubber sanding disc to the Makita shaft to which I glue a layer of denser foam (grey, closed cell, 3/8" thick) and then glue the blue foam to that. Each disc is larger ending up with leather around 4" diameter. I find the ideal sanding diameter 3 1/2 to 4". A large mouth canning jar band is a fine template but a little small. The small mouth will give you a 3" circle. Then I hold the spinning composition against a stationary belt sander and work it to about a 45 degree bevel. If all goes well it will run nice and true, but don't press too hard against the sander of the flex of the foam will lead to an oval disc.
I have just started using a new sander in place of the 500 grit on the Makita. Per the last AAW article on sanding, I have a Grex random orbital sander to which I have some blue foam attached by hook and loop, again with the leather upper surface. I put 500 grit on this, and find it does an excellent job of taking out 320 swirl marks without leaving any of it's own.
After stationary sanding to finest grit I like to hit the bowl with some of that white nylon scrubbing pad that you find in the grocery store. On a round bowl this is easy with the bowl spinning, but on a natural edge bowl you have to rub some parts by hand. Then I tried sticking some to a hook and loop disc and found it a great improvement. The soft foam 3" dia disc sold by Bruce Hoover of The Sanding Glove mounted on a high speed Sioux 45 deg. angle head drill makes a fine final polisher for any kind of bowl.
When I have a batch of bowls that have dried and are ready to have the bottoms flattened and signed, that wonderfully sanded surface is all rough from raised grain and has to be re-sanded before the final coat of finish can go on. Even using the Makita with the softest foam and finest grit can leave swirl marks at this stage, and my arm would ache after doing a dozen bowls in a row. So I bought a DeWalt DW423 random orbital sander, removed the dust hood and cut it down to 4" dia. This is hook and loop, so I glued a foam/leather system to a worn piece of hook and loop paper, stuck it on, and put on a piece of worn 400 grit paper. This sander is easy on the forearm because you can hold it right behind the foam. It cuts the raised grain without leaving much of a sanding mark. With really worn 500 or 600 grit it practically polishes. Such a system may be good for various other uses. After the DeWalt hook grew weak I sanded it off and glued the foam directly to it.
I use a stationary sander to flatten the bottom of bowls…..8" dia plywood disc glued to a pulley mounted to a vertical shaft, running at 1800 rpm. With 80 to 150 grit paper glued on it cuts the warped bottom flat. Those sanding marks are then removed with the flexible foam sanders.
Finally, although not a physically jolting as using the gouge, sanding can be quite hard on the joints and can make your arms ache. It is important to hold the sander as loosely as possible and to avoid tensing or hunching over the work. Having a sander that has a lock-on button is important, for it frees you up to hold the sander with both hands in the best way possible to loop freely over the rounded surface of the bowl using both arms and the whole body, not just one arm locked tight to the shoulder. My photo does not quite catch the effect, for I am not holding the trigger on though my finger is in the area. You can see the flex of the foam melding to the bowl in this older shot.
phone: 434-823-1882