Woodturning Design

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Ask Dale is a regular column featured in Woodturning Design. Listed below are the questions and Dale's answers from Issue 27.

Many of the new tools coming out seem to use carbide cutters. Being a lover of the old carbon steel, super-sharp tools, I would like to know if the advantages of the carbide tools outweigh the disadvantages—such as they cost more, cannot be resharpened, are not as sharp in the first place, etc. Are they really as good as the old tools?

Carbide tools may last longer, and will not need to be sharpened as often, but the particle sizes which make up the carbide will not allow it to ever be as sharp as carbon or high-speed steel tools. Carbide is a useful material for cutting steel, since it has the ability to withstand abrasion and a toughness that is more important than edge sharpness. Wood is a flexible material with a cellulose fiber that must be cut cleanly or be torn apart. A shearing cut, made by a properly sharpened gouge (either carbon or high-speed steel), is best accomplished with a tool sharper than it is possible to sharpen carbide. The typical turner cannot resharpen carbide, because the sharpening requires specialized equipment. However, carbide cutters on most tools on the market can be purchased from metal-working tool suppliers, such as Enco or MSC. These cutters are available in many shapes and sizes, but the most popular shapes are square, round, or diamond. When the cutter becomes dull, an Allen wrench is used to loosen the cutter so it can be rotated about a quarter turn to provide a new, sharp cutting area. A few woodturning tools, such as parting tools or tips on coring systems as in the McNaughton or Oneway, could use carbide tips, because the tools rely on a scraping action rather than a shearing cut. Another use for carbide tools is as a scraper for shaping hard or abrasive materials such as Corian, stone, or metal inlay materials that have been bonded with cyanoacrylate adhesives. This combination makes a cutting situation where carbide is a good choice, because the material is very abusive on the edge of the tool and a tough edge is needed rather than a sharp edge. Carbide is very useful in roughing-out wood blanks. The carbide inserts are many times more wear resistant than high-speed steel. It is common to turn more than ten bowls before changing an insert that costs only $6 to $10.

I’m somewhat new to woodturning and would like to turn a bowl with natural wood and stained wood on the same piece. The problem I’m having is trying to get a sharp edge where the two meet—the stain keeps migrating to the wood that I want to keep natural. Do you have any ideas that might work to keep the two from mingling?

When the term “stain” is used, the change in color can come from several sources: an oil stain, alcohol-based stain (spirit stain), a water stain, or a brown area which can be produced by “burning” a surface with pressure, such as a hard stick pressed against a spinning object. Colored wax can also be used to produce a stained appearance. Any time a colored area ends against an uncolored area, color will tend to transfer or “migrate” into the area which is uncolored, due to wood fibers (which are like miniature straws) “wicking” the colored solution to the other area. All stains that have a liquid form, no matter what the liquid is, will transfer color from a stained area to an unstained area if they are next to each other. To keep this from happening, it is necessary to prevent this wicking from taking place. One way to prevent this transfer is to mask off the areas that will remain unstained by applying tape securely to the surfaces to prevent the stain from wicking over. Then, apply a gel stain, only to the area to be stained, being careful to keep the gel stain off the masked areas. After the gel stain has been applied and set for a few minutes, gently wipe it off. When the gel stain is dry, spray the piece with lacquer to seal the stain. If the contrasting area to be stained is like a band around a bowl, determine where the band will be, and using the long point of a skew chisel, incise two lines defining the width of the band—the area in between will be stained. The incised line will cut the fibers and prevent the stain from wicking over to the unstained areas. This process will work best on close-grained woods, such as maple, box elder, or beech. These incised lines can also be burnt in with wire burners to give a clear line with an added finished effect to the band. This band could also be stained with a wax stain for precise control and a contrasting color. Properly applied, staining outside the band should not be a problem, because the wax is not a liquid and can be precisely controlled.

I recently joined a woodturning club and have acquired a box elder log about 11" in diameter by 7 or 8 feet long. I want to turn bowls for utility use, but where do I start?

Timber is very difficult to dry in thick pieces, such as logs, and if the log is over 6" in diameter, it probably won’t dry without cracking. Therefore, I would recommend cutting the log into sections and cutting out rough bowl blanks. I would cut the log into sections about 14" long and keep the sections in a covered area away from direct heat and sunlight. If the sections are to be stored for a week or longer, coat the ends of the log sections with green wood sealer. Another option would be to put each section in a plastic bag and tie the bag shut. If the weather is cool, the bag will keep the section wet, but don’t leave it in the bag too long or the section will mold. When ready, take the log section to the bandsaw, lay it down, and rip the log section into two pieces, cutting from heart center to heart center (see Fig. 1). You should now have two blanks with the pith visible on the cut face of each piece.

Measure across the flat face of the blank to find the maximum diameter. To use an example, it might measure 12".
2. Set the compass to lay out a circle about ½" less than the diameter—in this case, the compass would be set at 5-½".
Lay out a circle 11" in diameter out of a piece of thin plywood or cardboard, and mark the center point (see Fig. 2).
Cut out the circle on a bandsaw and drive a 1-½" nail through the center point of the plywood—just enough to hold it firmly in place.
Lay the blank on a flat surface and center the disk on the blank. Check to make sure the disk is centered. Drive the nail through the disk to secure the disk to the blank. Using the bandsaw and with the disk as a guideline, cut the blank into a circle (see Fig. 3). Remove the disk.
Turn the blank over and center the disk on the flat face. Drive in a nail to mark the center.
Drill a ¼" x ⅞" deep hole in the flat face of the blank.
Screw the screw center faceplate on the lathe.
Install the blank on the faceplate.
Set the lathe speed to about 600 rpm.
Turn the outside of the bowl to rough-shape.
Turn a tenon at the base of the bowl to fit your chuck without extending the jaws past the body of the chuck. A 5-½" chuck would need a tenon about 2-¾" diameter with a 5/16" beveled shoulder with a 10° inward bevel.
Install a chuck on the lathe (a faceplate screwed on would also work) and place the bowl blank in the chuck.
Rotate the blank, checking for security and balance.
Turn the inside of the bowl. The wall thickness should be about 1" (10% of the diameter). At this point, the bowl is roughed out. Date the bowl. Remove from the chuck, coat the bowl inside and out with green wood sealer, and set aside in a cool place away from heat and sunlight for 30 to 45 days. Now, it should be dry and ready to finish.


figure 1	figure 2	figure 3

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