Please discuss sanding for woodturning, that is, ways to avoid circular scratches under power which are hard to remove. — Gary Bashian
Dave Emerson replies: Turning well involves lots of practice, and so does sanding on the lathe. I use 80,120,180, 220, 280, cloth paper, an investment. I use the almost worn out pieces in between for each grit. Too much pressure results in scratches that are hard to remove. Maple is forgiving. Cherry is not. My results vary depending on how much I’ve been turning and have the feel of it.
Jon Siegel replies: There are two possible causes to your problem: 1. You are skipping grades. Try to take small steps as you work down to finer grades. For example do not try to work from 80 to 150 in one step, use 100 or 120 in between. However it is usually not necessary to take every step from 120, 150, 180, 220. Sometimes I go from 120 to 220 in one step, but it varies with different types of wood. 2. You are not inspecting well enough after each step. It is absolutely necessary to remove all the scratches from the preceding grade before moving on to the next one.
Mike Cyros replies: I use different methods depending on whether or not I am sanding spindle turnings or bowls. What they share in common is that I try to get a surface as smooth as possible off of the lathe tools before sanding. I never try to use sandpaper to “fine tune” the turning, but rather to take the tooled surfaces to a fine glass smooth finished surface. Also, I pay close attention to leave the sharp transitions of the turning such as cove and bead edges on a spindle, or a turned foot on a bowl.
Again, in both cases, I start with either 80 grit or 120 grit paper as the first sanding grit depending on how well I have completed the turning from the tools. I then progress through the grits from 80, 120, 180, 220, 320, 400 and sometimes even 600 grit depending on the finish I desire. What is most important is to be sure that you remove every scratch that you can see from the previous grit, and if you haven’t been able to, take a step backwards and go back a grit until that scratch is removed. Sounds tedious, but it is much quicker to do it this way, rather than to progress all the way through your sanding to your finest grit, only to see that you’ve enhanced and polished deeper scratches that you left from previous grits!
For spindle sanding, I prefer to reverse the direction of the lathe when possible for two primary reasons. The first is safety. When having the turning spin away from you (relative to the top surface of the turning), if you run into trouble with sand paper slipping, it will be pulled away from you out of your hand rather than the skinned knuckle (or worse) alternative if having the sandpaper wrap around the turning and pulling your finger in giving it a good sanding rather than your spindle.
The second is dust (another important safety topic). Note that with the lathe direction reversed, you are sanding on the top of the turning, and the dust is therefore projected mostly away from you rather than up and at your face. I always use a dust collector behind my lathe and this method of sanding actually directs the majority of the sanding dust directly into the dust collector.
Moving the sandpaper back and forth along the axis of the lathe also minimizes grooving.
In the case of bowl sanding, I use a right angle variable speed drill with a Velcro sanding pad attachment that takes either 2˝ or 3˝ sanding discs. I prefer the discs with the scalloped edges to avoid accidental ridging from the edge of the sand paper. As with spindles, I work my way through the grits as mentioned before, being sure not to progress to the next grit until I am sure that I have equalized all of the scratches. I run the lathe at a relatively low speed (well below 500 rpm), and keep my right angle drill/sander also running at a slower speed.
With bowl sanding, higher speeds quickly lead to heat which dramatically shortens the life of your sandpaper. I can speak from experience, sanding with faster RPMs does NOT make the sanding go any quicker, in fact, I’m convinced it slows you down! As with spindle sanding, I am moving the sanding point of contact back and forth to create an even and random scratch pattern that can be removed by the next grit.
Finally, a word about choice of sandpaper. To me, I think this is a simple case of “you get what you pay for”. Buy cheap paper, and you’ll go through a lot of it and frustrate yourself and your results. Buy quality paper, it will last much longer and you won’t be frustrated with the results. My absolute favorite paper for spindle sanding is the adhesive backed rolls by Carborundum Abrasives. They are available in 3˝ x 1 yd rolls in 80, 120, 180, 220 and 400 grit. I cut off a 4˝ length and fold it back on itself (it self sticks) to wind up with a two sided piece of sandpaper 2˝x3˝ which is perfect for smaller spindles. The resultant two sided paper can be flipped back and forth, and the double-sided grit means it doesn’t slip out of your fingers, and this paper lasts and lasts! It is available from Woodcraft among other retailers and online suppliers.
For bowl sanding, I prefer the green heavy cloth backed sandpaper with the scalloped edges. These are typically sold as “Green J-Flex Discs” or “Hi-Per Green Wave Discs” by the various turning supply catalogs. They are available in 80, 120, 180, 220, 320, 400 and 600 grits, and I use all of them.
Happy scratch-free sanding!