Ask Dale
Ask Dale is a regular column featured in Woodturning Design. Listed below are the questions and Dale's answers from Issue 29.
I belong to a woodworking club and have noticed that woodcarvers usually hone their tools after using the wheel to shape or restore an edge, while woodturners usually go from the wheel to the lathe and continue with the turning process without honing. Why the difference in sharpening technique, since they all cut wood?
It is true that carvers and turners all are cutting wood, but the difference is the amount of wood going past the cutting edge at any given amount of time. Years ago, Richard Raffan was turning in my shop and I noticed he went directly to the work from the wheel. I had read that honing makes the tools sharper and was curious why he did not hone his tools, so I asked him. I mentioned that honing tools makes them sharper. He replied, “Honing makes them sharper, but the honed tools will stay sharper for about five seconds. And anyway, sharpening is not my hobby, I am a woodturner.”

 Sharper tools are not really the question here, but rather the amount of wood going past the chisel is critical. A carver’s chisel will not remove wood quickly, because it is hand-driven and only a small amount can be removed during the cut. Woodturning is a different problem. The wood is power-driven, so heavier cuts may be made; the wood can be quite soft or very hard, so the amount of wood removed varies greatly. For example, a turner turning an 8" bowl will probably set his lathe speed at around 750 rpm. This is a good, safe speed. Multiply the rim speed by the diameter in inches and this bowl will be turning at 18,850 inches/minute; 1571 feet/ minute; 94,248 feet/ hour; or at 17.85 miles per hour. Compare the amount of wood a carver will cut in the same amount of time, and it is obvious the comparison will favor the woodturner by hundreds of times.

The key to sharpness and edge-holding ability on turning tools is the steel, not whether tools are honed or not. Most turning tools made for woodturning are high-speed steel, tempered to hardness around 63 to 65. Whether a tool is M2, M3, Kryo-treated, powdered metallurgy, or otherwise, it doesn’t make much difference to the average woodturner hobbyist. Practice and experience are of more benefit to the turner, rather than whether or not the tools are hard.
I’ve read posts and articles about moisture meters for checking dryness of rough turnings, but they are somewhat expensive and I hate to spend the money foolishly. Also, some have pins on the ends that I think would damage the surfaces of the bowls. Are moisture meters really worth buying or are there easier, more accurate ways to determine if a rough-turned bowl is ready to turn?

Most rough turnings do not require a precise moisture measurement prior to finish-turning, so I do not use a moisture meter to check the dryness of rough-turned bowls. Moisture meters are quite expensive, starting at about $75.00 for a basic one. When roughing out, most bowl turners will leave a rough wall thickness of at least 10% of the diameter, which allows for the finished bowl to be turned to final dimension without getting the piece too thin. After the work is roughed out, there are several options, depending on your experience.

Wall Thickness:
Roughed-out bowls will warp during the drying process, so the wall thickness must be adequate to accommodate warping. Wall thickness depends on a number of factors: moisture content of the wood, density, figure, species, shape, finished thickness desired, and open or closed grain, etc. However, the standard recommendation is that the wall thickness be uniform and about 10% of the diameter of the blank, or a minimum of about 3/4". For example, a 10" diameter blank would have a wall thickness of about 1". A 12" diameter blank would have a wall thickness of about 1-1/4". Smaller bowls will have a wall thickness of about 3/4". These thicknesses will allow a finished wall thickness of 1/4" to 3/8".

Drying Roughed-Out Bowl Blanks:
It is difficult to ascertain a definite way to dry roughed-out bowls, because so many variables may determine procedure or success. Some of the variables are air temperature, humidity, wood stability, moisture content of wood, figure or grain (such as crotch, stump, or burl), open or closed grain, density or weight, sapwood or heartwood, plain sawed or quarter-sawed, tension wood, etc.

It is not the intention of this column to deal with these in detail; however, here are a few conclusions based on years of working or turning green wood.

  1. Partially seasoned wood (below 35% moisture content) is easier to dry than freshly cut, very wet wood. Dead-standing trees are usually at about 35%.
  2. Quarter-sawed wood is more stable and less likely to warp than plain or flat-sawed wood.
  3. Open-grain woods are easier to dry than dense, closed-grain woods.
  4. Fruitwoods are difficult to dry, and the sapwood needs to be removed during the roughing-out process.
  5. Don’t turn or try to dry blanks that have the heart center in them, as they will crack or check most of the time.
  6. Burls are much easier to dry.
  7. Crotch wood or stump wood is more difficult to dry than plain or quarter-sawed wood from another part of the tree.
  8. The harder and denser the wood, the slower it must dry and more care must be taken in the drying process.
  9. Direct sunlight causes more problems than heat or low humidity.
Once the bowl is roughed out, it must be taken care of or it will probably crack. Treatment of roughed-out bowls may be accomplished in a number of ways, but the objective is to slow down the moisture evaporation from the wood, particularly in the end-grain areas, so that the inside wood dries at about the same rate as the outside wood.

Treatment Options:
Roughed-out unseasoned bowls should be kept in a cool area—on the floor if possible, and away from the heat or sunlight. These precautions will help greatly to reduce or eliminate most problems with cracking. Some partially dry, open-grain woods may be dried without further treatment.

Other Treatment Choices:

  1. Coat the bowl inside and out with green wood sealer, such as Anchorseal.
  2. Coat the end-grain areas with the green wood sealer, and leave the flat-grain area uncoated.
  3. Coat the end-grain area with paste wax and leave the flat-grain area uncoated.
  4. Put the bowl in a box and cover it with shavings from the rough-out.
  5. Place the bowl in a plastic bag, and every two or three days take it out and let the surface moisture evaporate. Turn the bag inside out and put the bowl back in it. Repeat every two or three days until moisture no longer collects inside the bag, and then leave the bowl out to finish drying. This method is usually necessary for dense, hardwoods that are difficult to dry.
I built a steady rest as per one of the articles in this magazine. I used roller scooter wheels from Walmart that look just like roller blade wheels. On most woods they seem to work fine, but I made a large hickory vessel last week, and even though I kept it wet, it still made small check marks that were almost impossible to sand out. Most people would probably not notice them, but I can see where the wheels turned around the piece. Are some wheels better than others, or do you have any ideas about how to keep these marks from appearing?
Steady rests for a lathe should be made with “soft wheels,” which will steady the work without leaving marks on the work. Wheel pressure on the work should be minimal. Too much pressure on the work will partially crush the fibers where the wheels run, and the crushed fibers will allow the finish to penetrate differently, at least enough difference to show a line where the wheels have contacted the work. Keeping the work wet probably made the marking problem worse, as the fibers crushed a bit more where the wheels ran and this would show up more when the piece is finished. Next time, use less pressure on the steady rest.
I recently started to turn vessels that are about 10" in diameter with a 5" opening. My 4-jawed chuck is too small to span the opening in order for me to reverse the bowl to turn the bottom. I’ve been turning a wooden jam chuck to fit the opening, but I’d like to know if there is a chuck or some other method that I could use that wouldn’t necessitate making a new jam chuck to use with each new vessel.
As you have been turning bowls with a 5" opening, there are several options other than jam chucking. However, jam chucking is an inexpensive and effective way to go. You already have a 4-jawed chuck and it’s likely you could purchase a set of auxiliary jaws from your tool supplier. These jaws are available to fit Vicmarc, Oneway, and Nova chucks. Large jaws, such as Cole jaws, will hold work from 4" to 10-1/2" in diameter and Vicmarc Adjusta-jaws will extend from 4-1/2" to 19-1/2".

 Another option is to fasten wooden jaws to the chuck jaws to extend the range of sizes your chuck can handle. In the end, jam chucking is the least expensive way to go, but the versatility of the expanding chuck is lost.
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