Replies

1. 
   ErnieConover | Apr 19, 2006 06:12pm | #1

   We use shop built sanding mandrels that King Heiple (who also teaches here at Conover Workshops) came up with. His drawing for this mandrel is attached. This is a hook and loop (Velcro) type system and we use contact cement intended for holding down plastic laminate. It holds up well but will separate with excessive heat. If you get excessive heat you are not sanding properly or using the wrong type of sandpaper.

   The inertia type are what I call the autogyro (In honor of this type of plane) sander and unlike the plane are practically worthless. The best tool is Kings mandrel held in a electric drill. The faster the drill runs the better!

   Sanding makes or breaks a bowl and it is one of the most misunderstood parts of the turning process. Unfortunately, it also a dusty, dirty and time-consuming operation so is often given short shrift. It will generally take about as long to properly sand your bowl as it did to turn it. The bad news is that as your gouge work improves your turning time will improve, but the sanding time will stay about the same. The good news is that there are lots of tricks to sanding and proper technique pays big dividends.

   I use power sanding equipment for coarser grades and then move to different techniques with my power sander, as well as, hand sanding for finer grades. Let us start our discussion with the most overlooked part of the equation?sandpaper itself. Good sandpaper is like a razor sharp plane while the wrong kind is like using a garden hoe.

   Sandpaper is made with either cloth or paper backing. The thickness and stiffness of the backing material affects how the abrasive grit acts. Thick heavy backing makes the particles dig in deeper and cut more aggressively. Cloth backing tends to be stiffer and heavier than paper and its superior strength make it better for power sanding. Cloth backing comes in two weights X and its lighter, thinner brother J weight. Paper backings come in A, B, C, D, E and F with A being the lightest and F being the heaviest. While I used to use cloth X papers for initial power sanding and A, B or C papers for final sanding I now only use paper.

   The second quality of sandpaper than makes worlds of difference is the type of abrasive material and how it is bonded to the backing sheet. The four commonly available types of abrasive material are aluminum oxide, silicon carbide, ceramics and garnet. For sanding bowls aluminum oxide or garnet are best, especially for the finer grades above 120 grit. The abrasive is applied to the backing material in a closed or, much better for wood, an open coat. Open coat means that there is space between the particles so that swarf (the shavings created by the cutting action of the paper) has a place to go.
   The best paper for sanding bowls is stearated. A coating of zinc stearate, a lubricant, is applied to the finished sheet. Wood resins and finishes do not stick as readily to a stearated paper which is a big plus in bowl work, especially when sanding wet wood.

   Finally, sandpaper made in North America is graded under the Coated Abrasives Manufacturers Institute (CAMI) while European papers are rated under the P scale dictated by the Federation of European Producers Association (FEPA). The later always has a P in front of the grit number so is easy to tell. A grit size in one system does not exactly equal a grit size in the other, except at 180 grit where they cross. There is also a third system which gives the particle size in microns. It bears no resemblance to the other two systems but is easy to identify because of the Greek letter ? after the particle size in microns. The chart at the right will help you to sort out the three systems. All of my grit recommendations are in the P system.

   Whether machine or hand sanding, the biggest mistake a beginning bowl turner makes is not starting with coarse enough abrasive. There is always tearout where you were forced to cut against the grain in faceplate work and you must sand though this to achieve a really good surface finish. It is tempting to start with 120 grit. If you do, big white spots in the areas of tearout are the result when you apply finish? ugly! I like to start with 50 or 60 grit paper and I sand at this grit for much longer than I think I need to. This removes all traces of tearout. The second mistake is to jump grits rather than working up in an orderly fashion. I start with 50 or 60 grit, then sand progressively 80, 120, 150, 180 and 220. Skipping a grit wastes time and sandpaper.

   How fine of a grit you sand to is an important consideration. For a working bowl that is going to see kitchen life sanding much beyond 150 grit is counterproductive. If it?s Christmas Eve stop at 120 grit, your mother will still love the bowl on Christmas morning. Even better, she will use it every day rather than putting on a hollowed shelf with your graduation photo. If you want a "gallery" finish sand to about 220.

   The best bang for the buck I have found is Klingspor PS33 (available from The Sanding Catalogue). It is available in 3" rounds which fits King's sanding mandrel nicely. It is an open coat, stearated, aluminum oxide paper.

   I hand sand all grits above 150 as I think aligning the scratch marks in the same direction makes for a better look. I apply oil finish starting at 180. I then hand sand wet, even applying more finish to keep it wet. I apply more still finish, let it dry for about ten minutes and wipe clean with paper towel. After drying overnight I sand in the next coat of finish with 220, wipe the excess and let dry again. The same for 320 and 400. I see no improvement at grades finer that 400. It takes about four to six coats to get a really first rate finish. Be sure to dispose of all the sandpaper, cloth, paper towel and shavings that have become soaked with oil. Oil finish is very prone to spontaneous combustion and will start fires if left inappropriately.

   Send a photo of your results once you get everything sorted out.

   With best regards,
   Ernie Conover

   
1. 
   Austen | Apr 19, 2006 07:04pm | #2

   Ernie,

   Thanks so much for all the information and the diagram of the disk holder.  I've printed  out your comments and need to go over it a few times until it all sinks in!

   Thanks again

   Loran

    

1. 
   ErnieConover | Apr 19, 2006 07:10pm | #3

   You are welcome. Have fun and work safe.Regards,
   Ernie Conover