Sharpening – Club discussion and Class on Jan 19th, 2008

As usual the information breadth and depth was excellent, with good insights provided by David, Jim, John, Clarence, and Tom. The topic of sharpening wood turning tools takes on much less mystique. As a novice in training, I have seen most of the videos, been to several classes, but the bits of learning I was able to obtain here was excellent.

A quick summary of the ideas is my focus here, ideas perhaps not found in documents as found elsewhere, such as DeHeer’s article on Sharpening in AWA Winter 2006.There are clearly as many ways to sharpen tools as there are ways to setup the three sides of a triangle, for that is most of what one has to figure out how to do. With gouges, the angles of the side cut, and the tool face or front are also set in several ways. Clarence’s presentation was about a system that relies on setting the angle of the tool holder arm and fixing the distance from the pivot arm to the base in both x and y dimensions. Ask him for a diagram if you need one.

Other approaches can use a sample tool profile of a known good profile, and set the angle of the front and side by iteration of two adjustments. The examination of this given known tool profile (available from Craft Supplies) and the setting of the distance away from the grinding wheel along with the angle of the holder, can lead to a good setup, with iteration necessary. In any event there are many ways to pursue the end goal of a sharp tool. The important thing I learned in these discussions is that it is quite easy to grind and not sharpen tools.

So here goes on a quick summary of the bits of experience I collected, and I must say after I tried my approach with these ideas, I have seen a marked improvement in the tool appearance and feeling of sharpness. Any of these thoughts here certainly are open to critique and correction, and I request this input. I will publish in a later newsletter any such corrections.

Wheels: J or K hardness, running slow speed (around 1780rpm), well balanced and dressed, and 8in if possible.

Grit used for tools used for fine work is 120, or 80 or above. Rough cutting can use 40 to 60 grit, as John Jordan and Mahoney advise. To reduce sanding and make very smooth cuts in bowls, use the finer grits after the tool is shaped. In cutting exotic woods, one wants a sharp, smooth edge possible with the finer grits. Roughing cuts can get by with larger grits used in tool sharpening.

Balancing: dressing the wheels aids in this process greatly, once the wheel is tightened on the grinder. Even taking the wheel off and repositioning will require dressing with a diamond tool. Balancing is complete if a tool does not bounce at all if a tool end and not tip is casually placed freehand on the rotating wheel. Even finer balancing can be done with a wheel balancing system such as made by OneWay.

Tool holders: Wolverine older and newer, and TruGrind. The TruGrind holder is the most versatile, as it accommodates the most tool-types and tightens well on tools with flute transitions at the tightening point. Grind tip of a holder that pivots in a Wolverine base - grind to a point to insure smooth rotation. Distance of tool tip in holder:2 in is what most use in this club. Fix this dimension and set it consistently. Angle of holder arm: ranges from something close to 23 degrees from horizontal or tool to something around 45 degrees. In some setups this angle is fixed, and in others it varies. Decide for yourself what approach works best for you. The advantage of the constant angle approach is that it is perhaps quicker.

Angle of tool tip: bevel edges for scrapers at 55 – 70 degrees, skews at 25 degrees, roughing at 45, gouges from 40 to perhaps over 60.The latter would be used for more finishing cuts inside a bowl, by some. Side-cut profile – side view: is not concave in any event. The longer swept back grinds the top profile is either flat (more aggressive) or slightly convex. Concave is not advised. Side-cut profile – top view: looking down on the flute. Is variable, but it seems that for a gouge one does not want too large an “ears”, or too thin an edge of the side cutting surface. Making the side wall steeper will reduce the size of the ears as the tool transitions to the tool tip. It seems key in this consideration what bevel riding one wants and in what cutting situation it is applied. See the signature series of tools to examine what variations exist. Also the tool samples mentioned above are good references. Tool-tip profile: as seen from the side - is generally flat but can be tailored. For long tool tips edges, grinding this edge to more round than flat can give some options in wood cutting, but requires more tool control. A flat edge gives consistent bevel riding during cutting. A shortened bevel on the tip and even sides of the tool can give less compression damage on some cuts and better control of the transition cut at the bottom of a bowl, but requires very good tool control.

Sharpening: requires an idea of the above profiles, and how to control, once the tool is setup in the holder. A gentle holding of the tool, with one hand nearer the top of the handle rather the end of the handle, is preferred for finer control. The amount of sparks flying gives some indication of the amount of grinding versus sharpening. A smooth transition of the tool bevels on the side and tip is a concern. Not having dips or flat spots in the profile or bevel is a must to avoid catching during turning.

Cutting edge: will vary with tool and how it is used. With a bowl cut, shear scraping for instance, is done perhaps nearer the tip for more aggressive cuts, or nearer the flute for more strength and control. I am certain there are many ways to do this cut and as many good opinions.

There are many good sources of information as to how to sharpen. The videos published by AAW, DVD’s in the library, classes at Woodcraft, and others exist. The best source of information available that I have seen thus far, is the expertise in the club.  Terry Gannon