hollow vs flat grinding thoughts

[Jan]

I would suggest a third category. This is the mild hollow grind of a larger grinding wheel. The spiritual ancestor of this group is the large, hand turned wet grinding wheel. By definition and Mr. Euclid of Alexandria, this kind of grinder also produces a hollow grind. For lack of a more scientific term, I would call this a "barely hollow grind".

Ken

Does this grinding wheel correspond with your understanding of a "barely hollow grind"? 



Jan

[Ken S]

Great, post, Jan.

That's it!

Ken

[Rob]

Now that's a real water wheel!

[Ken S]

Jan,

Your last post reminds me of something I remember from being a student in the Leica School thirty years ago. The topic was Leica filters. We presumed they were ground flat. The instructor corrected us. They were ground to a radius. I remember the radius as forty five kilometers, although it may have been forty five meters. Either way, it seemed flat to me.

Ken

[Herman Trivilino]

My shop floor appears flat, but it's actually hollow ground to a radius of 6000 km. 

[Ken S]

Is that to keep the ball bearing parts you drop in the center?

[Jan]

Ones I was looking up the meaning of the phrase "nose to the grindstone" and have found the following explanation:



A large waterwheel powered grindstone. The user would lie on the plank above the grindstone while grinding metal items, giving rise to the phrase nose to the grindstone. (http://en.wikipedia.org/wiki/Grinds)

Jan

[Ken S]

Another very iinteresting post, Jan.

Ken

[Jan]

Congrats, Ken, on exceeding 1500 posts this week! 
Keep us posted!

Jan

[Ken S]

Thanks, Jan. I remember when the first forum member passed the fifty post mark. (I was the second.)

Ken

[Herman Trivilino]

Is that to keep the ball bearing parts you drop in the center?

It's not a dip, Ken. It's a crown. A ball bearing stays anywhere you put it!

[Ken S]

Herman, I think the same mason got carried away with the crown in my garage floor. Instead of logically flowing toward a drain in the center, the crown diverts all the water melting off the car toward the side, which is used for misc. (junk) storage.

Ken

[Jan]

Ok theory set aside, let's assume someone brings me a chisel that is flat ground at a 25° bevel. After it is sharpened they want it to be just as "strong" as it is now. I plan to use the Tormek to form a hollow grind that covers the whole face of the chisel. Without trial and error methods and minimal steel removal, where should the Tormek wheel first come into contact with the flat ground bevel assuming the flat bevel is truly and squarely flat?

If you set the Angle Master to 25^o you will end up with a chisel that has more steel on the heel relative to the tip than it had when it was flat ground at 25^o. The angle at the tip will be 25^o when you're done. The angle at the tip was 25^o when it was flat ground. Theoretically that extra steel will make the chisel stronger and it should perform the same at the tip. It will not perform the same at the heel, though, as that extra steel on the hollow ground chisel may be a bother when paring.

But, to answer your question, you would have to set the Tormek Angle Master at a smaller angle. How much smaller? It depends on the thickness of the chisel. See the chart Jan posted earlier in this thread.

Elden's question was already answered by Herman. My belated remark concerns the second paragraph of his answer.

If you plan to form a micro bevel, by the way nicely described in reply #28, and you wish to have the angle of this micro-bevel 25 degrees, than you have to set the Angle Master at a smaller angle.

Assuming you are using grindstone with the diameter 10", then
for chisel thickness t = 1/8" you set the Angle Master at 23.5 degrees,
for chisel thickness t = 1/4" you set the Angle Master at 22.0 degrees,
for chisel thickness t = 3/8" you set the Angle Master at 20.5 degrees.

Assuming you are using grindstone with the diameter 8", then
for chisel thickness t = 1/8" you set the Angle Master at 23.0 degrees,
for chisel thickness t = 1/4" you set the Angle Master at 21.0 degrees,
for chisel thickness t = 3/8" you set the Angle Master at 19.5 degrees.

Jan