A truly sharp edge is formed when two flat planes (or an arc and a flat plane) meet perfectly with a good surface finish at the cutting edge. A good surface finish may be defined as a polish or near polish. Honing leaves a polished or near polished edge free of feather (or burr). In short, your spindle-turning tool should be razor sharp after honing.
There are two methods by which I hone lathe tools-whetstones and buffing. If at all possible, I buff because it’s the fastest, most effective method. I only resort to whetstones when absolutely necessary, such as when working in someone else’s shop. The one tool that is an exception is the skew chisel, which I always hone on whetstones. In fact, barring nicking the edge on a chuck or dropping it on a concrete floor, stones are the only way I sharpen a skew. This is because the skew works best with an absolutely flat bevel and must have a keen edge.
Whetstones As the name implies, whetstones are used with oil or water, which acts as a lubricant to prevent metal particles from bonding into the pores of the stone. Honing lathe tools requires polishing stones with very fine grit. Although I sharpen my skew chisels on the same stones that I use for plane irons and bench chisels, I have a collection of odd-shaped stones for the rest of my turning tools. These include small, tapered stones called slips and a variety of stones in triangular, round, and knife-edge designs. The latter are often sold in catalogs as files, but they are actually stones.
The trick to using flat stones to sharpen skew chisels is to keep the bevel absolutely flat on the stone. A honing jig can be of great help here. Most of the jigs that are used for honing plane blades and bench chisels can be adapted for honing a skew. The advantage to a jig is that you will obtain a flat bevel and a perfect edge If you do not have a jig, you will have to do it by feel. I have observed that most beginners place their hands far back on the tool, often holding chisels by the handle. Instead, you should place the tool down on the heel of the bevel and rock it forward until you feel the bevel go flat on the stone. In this position, you can lock your wrists and stroke in either a circular or a back-and-forth motion to maintain a flat bevel. Since the heel of the bevel is a fulcrum point, the shank of the tool is a lever arm. The farther back you grip, the longer the lever arm and the less you can feel the bevel. If possible, remove the tool handle because its weight throws off your sense of feel.
Whether you use circular motions or linear motions for the actual honing does not make much difference. The important thing is to maintain the bevel flat on the stone by locking your wrists and using your arms and upper body. Start with a sufficiently coarse stone that will remove enough metal to establish a new bevel along the entire cutting edge. Stop every so often and feel if you have rolled a burr along the back of the edge. This will be less or more pronounced depending on the grit of the stone. Work up to the next grade of stone, and keep progressing until you obtain a polish.
For the rest of the tools, it is typically easiest to hold the tool in one hand and the stone in the other. By looking sideways at the process, you can tell if you have placed the stone flat on the bevel (contacting at the edge and heel}. I often find it easier to brace the shank of the tool against the headstock or tailstock. This gives me both leverage and steadiness.
For the flute side of gouges, it is just a matter of finding a stone with a radius as close to the flute radius as possible and placing it flat down in the flute (see the illustration at right). Next, remove the burr and polish the edge with a rapid back-and-forth motion. I use plenty of water or oil, as required, during the entire process.
Honing is much easier with hollow-ground edges because the stone will touch at the very edge and the heel of the bevel. It takes a short time to bring up a polished edge. You can normally hone several times before having to go back to the grinder.
Buffers Buffing is the technique of using cloth or felt wheels, which revolve at high speed and are charged with abrasive compound, to improve the surface finish of metal. The abrasive compound is typically a wax/grease and abrasive mixture. Sold in stick form, it is crayoned on the revolving wheel. Many people make a buffer by simply mounting a cloth wheel in a bench grinder. I do not think a bench grinder makes a good buffer because the rest and guards get in the way.
One way to make a small buffer is to mount a buffing wheel in the lathe itself. Small arbors with a ¼ in. or 3/8 in. shank are sold for mounting a 4-in.-dia. buffing wheel in an electric drill. By mounting the arbor in a drill chuck in the headstock spindle of your lathe, you have an inexpensive (less than $20 including the compound) and effective buffer. I first latched onto this idea because I needed a buffer on the road when I do seminars and demonstrations.
In the long run, you will want to build another kind of buffer. Using a buffing wheel mounted in the lathe is inconvenient for tool sharpening because the work must be removed from the lathe every time you want to buff. Several companies manufacture inexpensive arbor heads for the purpose of building a buffer. These arbor heads have a ½ in. arbor, which fits readily available 6-in., 8-in.-, and 10-in.-dia. cloth wheels, and are best powered by a ¼ hp or 1/3 hp 1,725-rpm motor. Often a used motor can be found at a motor rewinder for a nominal price. To calculate the correct motor pulley diameter for 6-in. wheels and a 1 ,725-rpm motor, use the following formula:
Motor pulley diameter = 2,000 X Arbor head pulley diameter / 1,725
An rpm of 2 ,000 is needed to achieve 3,150 surface ft. per minute. For an 8-in.-dia. wheel, use 1,500 rpm instead of 2,000 rpm, and for a 1 0-in.-dia. wheel, use 1 ,200 rpm to achieve 3,150 surface ft. per minute. However, these bigger wheels can run even slower if pulley matching is a problem.
Wheels are available in two types: spiral sewn and cushion sewn. The descriptions denote how the layers of cloth that form the wheel are sewn together. As the name implies, the first type is stitched in a spiral starting at the center. The cushion-sewn wheel is stitched in concentric rings, making this type of wheel softer and fluffier. The spiral-sewn wheel is better for coarser compounds where aggressive cutting action is desired, while the cushion-sewn wheel is better for final polishing when gentle cutting action and a mirror finish is the goal.
Buffing compounds tend to be sold according to their final purpose buffing brass, steel, stainless steel, and so on. Sometimes a compound will do several jobs. For instance, stainless-steel compound is good for final buffing of steel or stainless steel and works well on brass.
For buffing lathe tools, I have found that a combination of two Dico compounds-E5 Emery and SCR Stainless-works well. Dico compounds and buffing wheels are made by Divine Brothers in Utica, N.Y., and are available in most good hardware stores. Equivalent compounds are made by Formax Company in Detroit, Mich., and are sold at all Sears stores. ES Emery is a fairly aggressive compound that will even remove rust from tools. It is great for initial buffing to remove grind marks and feather.
SCR Stainless is a great final compound to remove all traces of feather and bring the surface to a high polish. It is also good for touching up a slightly dull tool between grindings. I keep a spiral-sewn wheel charged with ES Emery on the left side of my buffing arbor and a cushion-sewn wheel charged with SCR Stainless on the right. After grinding, I lightly buff on the left wheel, then move to the right wheel for final finishing.
In grinding you always grind into the edge, but when buffing you must always buff off of the edge. Buffing into the edge could send you to the emergency room to have a tool removed from your leg. You must also touch the surface you wish to buff tangentially to the wheel (alternately the bevel and the back, or flute) until all feather is removed and a polish is created at the cutting edge. Most people make the mistake of sticking the tool straight into the wheel, which is counterproductive. The goal is to end up with a flat or slightly concave bevel leading to an edge that is free of feather. The key is to keep it light. Heavy buffing with any degree of pressure will round over the edge, requiring a return to the grinder.
For those using a Tormek grinder, honing is done by stropping. The machine comes with a flat strop much the size and shape of a buffing wheel. It is great for the outside of gouges, skew chisels, bedans, beading, and parting tools. For the inside of gouges, the optional profile leather honing wheel is necessary. The leather strops must be charged periodically with a chromium-oxide paste (a tube is supplied with the basic machine). A new strop will eat paste, but you can reduce this tendency by first covering the strops with a liberal amount of mineral oil, then applying the stropping paste.