Notes used by Chuck Engstrom for his sharpening demo for Chesapeake Woodturners on December 14, 2012 at MD Hall woodturning room.
What do you want to achieve in sharpening your tools?
A good sharp edge, of course, a repeatable shape, and a quick and easy setup
How do you get this?
A shaky, out-of-balance/out-of-round grinder is just as hard to get good results out of as a shaky, out-of-balance lathe. Your tools will bounce off the wheel – very rapidly -- and you’ll have a hard time getting a smooth, repeatable grind that cuts the way you want it to, especially if you’re trying to grind freehand. Many of us have the Woodcraft 1725 rpm 8” grinder, as I do, and the Wolverine/Varigrind system from neway to help guide us, so I will base much of my discussion on that combination.
Grinder itself – check to see if the base is parallel to the shaft – I have one which isn’t, by a full quarter-inch, just discovered in preparation for this demo. It’s also nice to put a test set on the shaft each side to find out how much runout or eccentricity you have. Needless to say, less it better – your shaft should run true so that the wheel does too, and this is even more important if you are using a machined wheel like the CBN (cubic boron nitride) wheel that I’ll talk about later.
Setup – platform and accessories
Mount grinder on min. ¾ plywood, preferably two thicknesses glued together. Extra mass means more stability. Give plenty of length and width, about 16 x 24. A handle on each side can be useful if you plan to take it out on demos, etc.
Be sure to mount it at the proper height above the base (6-1/2”) specified in the Wolverine instructions. This usually requires a riser piece under the grinder’s own base. (the Woodcraft grinders are less than 6-1/2” but not all versions of it are the same height as time goes by, so you’ll have to measure). Oneway says to mount the grinder at the front edge of the deck but I haven’t found a good reason for that. T-nuts with 5/16” bolts may be best.You can set the riser piece back from the front edge of the base by the distance you want your gouge end to protrude from the Vari-Grind to give yourself a handy spot for setting it. Oneway recommends 1-3/4”, some favor a bit more at 2-1/8”, which is the length of the pocket on the Vee-Arm.
How high off the floor? I have found that having the grinder axle elbow-high is comfortable for me.
Be sure that the guides are mounted parallel to the face of the grinder wheels. Use T-nuts to mount the guides also;screws tend to come loose after a while and retightening them just degrades the screw holes. The Wolverine is predrilled for #10 screws.
Behind the middle of the grinder, mount a 2-1/2” cube of wood with 1/2” hole drilled in the center of one side, facing up. Screw this on from the bottom of the platform so you can move it around later if need be. This is to hold the base of a common swing-arm lamp.
You can also mount an empty coffee can with one screw straight through the bottom into the platform. The coffee can will then hold a smaller can inside it to hold some water to cool tools as you grind them. You can also screw an empty dog-food can onto the base of the grinder. Inside that, put an empty beer or soda can filled part-way with WD-40, and keep an old toothbrush hanging down into the can. Use the wet toothbrush to clear out moisture and gunk that has collected in the flute from green wood.
Wheels – Woodcraft/Craft Supply/etc Camel brand white is OK, pink a bit better, Norton blues (three types from Craft Supply) better yet, then on into CBN. Second in hardness to diamond but doesn’t react with iron. Available from d-waytools.com, in 80 or 180 grit, 6 or 8 inch, and from cuttermasters.com.
Several other advantages of CBN wheel:
Truing –The arbor washers supplied with Woodcraft grinders are stamped rather than machined, and as such they are not reliably perpendicular to the shaft – they may add a good bit of wobble to the irregularity already in the wheel itself. Better item is “outer clamp” for the blade on a Dewalt Sliding Compound Miter Saw, part number 151962-01, which does fit.
Balancing – The composition of wheels is rarely uniform enough for them to be wellbalanced out of the factory. If you are patient, you can hope to get some improvement by changing the rotational position of one wheel with respect to the other. Best to change the right-side wheel, whose threads are the usual righty-tighty. Leave the left one alone; it has the opposite thread so it won’t come loose in rotation. Trying to tighten the nut on one end by holding the nut on the other end will just loosen the one you think you’re holding firm.
Cleaning – Typical abrasive wheels capture a certain portion of the metal they are grinding off of tools. As this builds up, it fills in and glazes the grit that’s intended to be removing fresh metal for a sharpened edge. We usually remove this glaze by passing a diamond dresser across the wheel while running, and eventually, of course, the wheel is no longer its original size. The cloud of grit etc that comes off the wheel when you dress it is stuff you should avoid breathing.
David Ellsworth suggests filling the head of your diamond dresser, if it is the hollow type, with lead shot to give it more mass so it will not bounce so much off the rotating wheel. He fills this with epoxy. Loose lead.
Platforms: One of these comes with your Wolverine basic set. I found it useful to cover the upper surface with a scrap of Formica or similar; your tools slide more freely and you won’t ding a fresh edge as you might on the metal itself.
It’s helpful to get at least one additional platform, so you can leave one set up for skews and another for scrapers, for instance. Chasing after the perfect setting to duplicate what you did last time is a big way to loose time in the shop; better to just change out the platform in a couple of seconds. Oneway now makes a smaller size platform which is just as useful, especially when tools start to get short after years of use. There are guide devices for setting platforms.
Vari-Grind: This is a great help in sharpening bowl gouges and spindle gouges, but it took me quite a while to get a good understanding of how its various adjustments work together. Its range of adjustment offers endless possibilities for experimentation, but in the long run, it’s a good idea to settle on a couple of basic settings for quick repeatability. I’ll try to explain some of the variations you can experiment with once you’ve gotten the hang of it. There is a Vari-Grind 2 version I haven’t had a chance to try.
Setting the Vee-Arm at the same distance every time is easier if you cut a few pieces of scrap wood to use as guides. You can even glue a couple of pieces of different lengths together to combine them. Drill a hole in it, and hang it from a string so it doesn’t get lost and swept up and away amongst the shavings, but don’t let the string get caught on the grinder wheel.
Fundamental to understanding the Vari-Grind is the realization that you can grind precisely the same angle at the very, very tip end of your gouge by varying the length of protrusion, or the angle you set on the Vari-Grind, or the distance you set on the Vee-Arm, or any combination thereof. BUT once you start to swing the Vari-Grind through its arc, those changes will have a big effect on how the sides of the gouge end up. For bowl gouges, in recent months I have settled on using the #5 angle on the Vari-Grind and setting the Vee-Arm at a distance that yields a 60° angle at the leading edge of the gouge. Oneway talks of using a 65° angle; for that you would make bring the Vee-Arm out further at the same #5 angle on the Vari-Grind.
Mike Mahoney and Stewart Batty promote a 45° angle for bowl gouges and, I gather, most everything else.. If you try it and it works for you, that’s great. But keep in mind that with almost all the tools we use, a sharper angle is going to be more and more aggressive.
There is a growing trend to grind a second bevel on the bottom of your tool. This is easy to do with the Vari-Grind – just change the angle by a couple of notches and go back to the grinder. This second angle is less critical and needn’t be redone every time you touch up your edge.
Spindle gouges: I use #3 and a shorter distance on the Vee-Arm. This gives a sharper angle on the end of the gouge, about 45°. This seems to be a good choice for most spindle gouge cuts. You can go down toward 30° for a detail gouge but it will be a catchy tool. Skews and parting tools: I do a lot of spindle turning but use a square parting tool for most of it, rather than a skew. For both skew and square parting tool, though, I use the same angle at the end, around 45 - 50°. Lots of folks go for a sharper angle, maybe as low as 30°, but I’ve found this is a more aggressive angle than I’m comfortable with. If you go above 50° you’ll start to find that it’s not aggressive enough.
Scrapers: I have adopted the unorthodox technique of grinding scrapers face down, at about 80°. Yes, face down. My thinking is that this pulls a wire-edge down past the top of the tool as the grinder wheel rotates downward across the side of the scraper blade; the usual thinking seems to be that you’re going to drive a wire-edge up off the side of the scraper blade by having the grinder wheel rotate toward the top side of the scraper. I like the result I get, and it does yield a fine shaving off the wood. Doing scrapers face-down is one of the main reasons I put Formica on top of the platforms.
You can bring a scraper back to the grinder a couple of times to freshen the wire-edge, but every third time or so you should hone the top of the scraper with a fine or extra-fine hone to give a fresher surface for a new edge. It does pay to hone the tops of your scrapers before you use them, since none of the manufacturers seem to clean up their top surfaces – or their flutes, for that matter – as well as they advertise.
All tools, for that matter, are improved by honing the inside of the flute Its surface is one side of your cutting edge, and if it’s ragged in there, the whole edge is ragged no matter how sweetly you polish the outer side. Honing the inside of flutes calls for a round-edge stone or hone of some sort, and I have been using the Alan Lacer diamond hones he sells at http://stores.alanswoodturningstore.com/StoreFront.bok, though he seems to be out of stock at the moment. There is also a CBN 360/600 hone available from d-waytools.com.