Wednesday, October 10, 2007

Parting Tool Grinding

Honestly, one of my favorite activities is trying out new parting tool grinds. (Maybe I need to get out more!) There are a whole slew of them and my favorite tends to be the one that I'm using at the moment. The most important factor in parting tool grinding is of course frequency. I grind all the time. At this point I don't bother to hone my parting tool, I simply grind it and knock the burr off by dropping the tip into a block of soft wood and then get back to work.

Above is a photo of my technique for grinding the lower facet of the bevel. By grinding it on its side, the facet will curve (slightly) from side to side. Below is the grind that I use on the top facet. It imparts the curve from the toe to the heel of the bevel. By have the facets curve in different directions and meet at the tip, a slight spur is formed at the corners. The spurs help ensure a clean cut.

It is crucial that the grinding be done square to the axis of the tool. The diamond shape can make this tough to see. I like to look at the relationship of the bevel to the square edges at the top and bottom of the tool. Below is a picture of the (relatively) square grind.

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To function properly, the two bevels should meet and form a square line across the tip of the tool that seems to connect the widest part of the diamond. It is critical that the actual leading edge be square to the axis so that readings of the dimension of the workpiece not be thrown off by an angled surface. I don't have any absolutes as to the angle of the grind, I tend to freehand the top bevel on the wheel, and then get back to work. The lower bevel only gets ground when absolutely necessary because it takes a time consuming set up. Improving the performance of this tool may seem to be a waste of time, but I have come to see a smooth cut into the diameter of a fresh turning blank as gratifying as the final sweep with the skew.


DickL said...

OK Pete. It seems you have combined the usual grinding with that recommended by Oneway in their Wolverine HowTo video. Now I have two or three different grinds to try.

R Francis said...

Good to have you back in writing mode, however you sharpen it.