First results

[Ken S]

A couple years ago I tried regrinding the bevel on one of my chisels from twenty five to thirty degrees. I use this chisel for rough work and wanted to find a way to reduce the nicks. I originally planned to reshape the entire length of the bevel, but wisely stopped halfway through. I had inadvertently stumbled upon the chisel equivalent of making chef's knives into paring knives with a sandstone wet wheel.

The Tormek makes quick work of sharpening an existing bevel. Changing entire bevel angles can make quick work of reducing chisels to mini chisels with large handles. I believe there is room in Tormek technique for micro bevels.

Ken

[Elden]

And now comes the insight!
Only the edge is riding on the stone. That means the angle setting of the WM 200 is always correct. Hollow grinding doesn't lead to a decreasing angle, it produces an increasing angle!

Rolf (Hatchcanyon),
   Thank you for the well done pictorial and verbal presentation of your journey to the culmination of your thought process!

[Hatchcanyon]

More work on hollow grinding. As shown in an earlier posting the WM-200 gives a correct setup and the edge of the iron touches the stone first.


The edge touches first

But what happens if the iron is set to contact the stone at first in the middle of the bevel?


First stone contact of the bevel at its middle

Clearly visible - the edge and the upper end of the bevel are not contacting the stone. That means the stone will work itself into the middle of the bevel first. How about the resulting angle?

Lets ask the WM-200:


Reading is about 22°

The value corresponds nicely to Leonard Lee's formula. (6° reduction for an angle of 28°, an iron thickness of 12,8 mm and a wheel diameter of 250 mm) The bevel angle will be reduced of that amount on the edge and the same amount will be added on the farther end.

Now lets go extreme and position the iron to contact the wheel at first with the upper end of the bevel.


First wheel contact on the far end of the bevel


WM-200 reads 15°

This is a further doubling of angle reduction due to hollow grinding but is was expectable by Lee's formula. The edge would be weakened to 15° or by 12-13° On the other hand the bevel angle will increase the same amount with the first setting where the edge touches first (up to 40-41°). With a relatively thick iron this might not be desirable too. Grinding such long bevels only partially seems to be the solution.

With other words: The complete modification in angles is double the value Lee's formula predicts. The user decides how to distribute the modification, but it always will be there with the same value.

Result. The WM-200 AngleMaster can also tell about hollow grinding angles. I like the tool! 

Rolf