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Sharpening a Skew


Sharpening a straight-edge skew. The skew is one of the more difficult tools to sharpen, because, ideally, both bevels should be perfectly flat.  Turners have developed a variety of ways to do it, and of course, strong opinions exist about which way is the easiest and best.  Not everyone, for example, even agrees that the bevels should be flat.


One method is to set the tool rest of the grinder at such an angle that the bevel matches the surface of the wheel. Then, with the body of the skew at an angle so that the cutting edge is square to the wheel, it is moved back and forth across the wheel to do the sharpening.  The other side is done by flipping it over and switching the angle of the tool on the rest.  


Some turners build a jig that slides back and forth on the rest to make it easier to keep the cutting edge square to the wheel.  The tool fits into a slot milled into the jig and is simply hand-held in the slot.  Two slots are required – one for each side.  The details of the rest dictate the design of the jig.  


This produces a bevel that is concave (hollow ground) because of the curvature of the wheel.  The next step is to flatten the bevel by stroking it on a stone, usually diamond.  Fortunately, not all the bevel has to be flattened.  In the photo, you can see that only the outer portion has been flattened to produce the D-shaped pattern that shows up in reflected light on an oval skew.

 


When you purchase a skew, it is almost certain to have a hollow grind as it comes from the store.  Therefore, the first thing you must do is sharpen it and flatten the bevels.  


Another method is to use a belt sander adapted to this purpose, or purchase a rig based on the same principle.  A sharpener of this type does not produce concave bevels and therefore eliminates one of the issues associated with a grinder.  


The photo shows a small (3 x 18”) belt sander that I mounted on a 1/2” plywood base so that it could be clamped to the edge of a work table.  A simple rest helps in holding the proper angle so the bevel is flat against the abrasive.  I use a 180-grit belt.  A 150 or 120 grit is a bit aggressive for my liking.


Note that the tool points in the direction the belt is moving so that the cutting edge is presented to the abrasive in trail.  This is critically important.  If you go in the other direction and aim the cutting edge directly at the oncoming abrasive, you are almost certain to get a dig in, and the result could be quite serious.


In my view, this is the best method for sharpening a skew, by a country mile.  You can buy fancy jigs that work with a grinder, but if you use a grinder, you are building in a problem (concave bevels) that you then have to solve.  The cost of a small belt sander is little if any more than that of a special jig, and mounting it upside down on a base is not a major issue.    


Hand sharpening.  A motor-driven sharpener is not required.  A skew can be stroked on a sharpening stone in exactly the same way a plane iron or chisel is sharpened.  All that’s required is the patience to do it.


How sharp should it be?  Some turners say a skew should be razor sharp.  Others are less demanding and use an edge comparable to that of a sharp gouge rather than to devote the extra time required develop a razor edge.  


Most experienced turners do not take the skew to the grinder very often.  Once the edge is formed, a few strokes with a diamond hone is all that is required to maintain it.  I am very protective of the cutting edge on my skews.  I never use them as scrapers because the scraping tends to take the edge off the tool.



Sharpening a radiused skew.  The method used by most turners is to set the rest of the grinder so the bevel matches the contour of the wheel, and then pivot the tool back and forth on the rest while lightly touching the bevel to the wheel.  This takes a bit of dexterity to do, but with a bit of practice, you can get pretty good at it.  Of course, once you finish the grinding, you then apply the hone, liberally, to flatten the bevels.


The belt sander makes the grinder seem crude by comparison.  It is a simple matter to press the bevel against the abrasive with a finger of one hand and then rotate or twist the handle with the other to roll the remainder of the bevel against the belt. I don’t even bother trying to use the rest – it’s not necessary.  Because the belt tends to produce flat bevels, a minor touching up with a hone is all that’s needed for it to be good to go.  


Two notes about honing:  (1) Frequently dipping the hone in a cup of water will help clear the metal particles and keep the hone from clogging.  I find it easier to prevent the clogging than to remove the buildup once it has been ground into the surface.


(2) When you hone, be careful to keep the bevel flat against the stone to avoid producing a convex curve right at the cutting edge. This rounding of the edge has a big effect.  


With a rounded edge, the tool will not cut when the bevel is flat on the wood, or nearly so, because the actual edge is above the surface.  To get it to cut, you have to rotate the tool more than normal, which brings the heel of the bevel well off the surface.  This makes the tool harder to control and will likely give a much rougher cut.  Further, because of the extra rotation, a runback is much more likely to occur.   


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Here are two articles on sharpening, by Jon Siegel.  He emphasizes the importance of flat bevels:  


http://www.bigtreetools.com/articles/sharpening1.html


http://www.bigtreeturnings.com/articles/sharpening2.html     

          

   


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