Sunday, February 03, 2008

Sharpening Wood Turning Tools

There has been a discussion in progress over rec.crafts.woodturning dealing with some of the ins and outs of sharpening wood turning tools. I thought I would post a few of my views.

First of all, there is no definitive way to sharpen out tools and the same person will use different methods of sharpening say a skew versus a roughing gouge. I, for instance, would sharpen a skew free hand but use a jig for the roughing gouge, at least most of the time. A bowl gouge I would almost always sharpen with a jig for long wings but likely freehand for straight across but sometimes would reverse that. While I would like to give coherent reasons for doing so it probably depends more on mood than logic.

One of the problems that beginners have and continue having as they begin turning is the mastery not of sharpening, but of sharpening turning tools. Many turners begin their woodworking careers with flat work of some sort. There router bits and table saw blades are generally sent out for sharpening while chisels and plane irons are sharpened with an assortment of stones or sandpaper and possibly a few jigs. There also tends to be a fairly long interval between sharpenings. Not so with wood turning.

A wood lathe simply moves wood over the edge of the tool faster than does most other wood working methods. Wood turners also tend to use wood that is rougher than flat woodworkers and it may still have bark and grit in it. The edge of the tool simply does not last for very long under such circumstances.

Flat workers tend to use grinders to remove large amounts of metal under circumstances such as dents and nicks that call for a tool to be reshaped. A wood turner uses a grinder to quickly sharpen and get back to work. The fine edge of the wood plane simply disappears under the speed and fury of the lathe but the edge from the grinder lasts sufficiently well and cuts sufficiently well to be considered more than adequate for the job.

So a grinder should be thought of as a sharpener and only enough metal should be intended to be removed so as to leave a good cutting edge. For this reason some turners think a slow speed grinder is best for the job as it is cooler to work with and supposedly removes less metal. Others such as myself like a high speed grinder as with high speed steel heat is not an issue and I only intend to remove enough steel to leave a good edge. Enough is enough whether one uses a fast or slow grinder.

Over the next few days I will add some thoughts on free hand sharpening versus the jig.


Derek Andrews said...

The other advantage that I see to using a half-speed grinder (I assume you are talking here about half-speed grinders, not the very slow machines like the Tormek?) is that it gives you much more time to manipulate the tool in a controlled manner.

Darrell Feltmate said...

Right Derek, I mean the half-speed machines. I never have used the Tormek although I have a birthday coming up and one of those would be nice :-) The slow speed should give you more time to manipulate the tool under good control. On the other hand a light touch on the high speed can do the same thing. Notice that free hand sharpeners say that sharpening is the same motion as wood turning? This is true BUT how often wo we turn a 6" diameter log at 1750 let alone an 8"? or at 3500? Methinks I feel wordy and shall elaborate in a further blog.

Derek Andrews said...

Its not the same motion, but uses many of the same basic hand and eye skills which enable us to control and manipulate the tool.

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