Since this came up in another topic, and it comes up time to time - this idea that hollow grinds create chipping edges instead of what's happening at the edge itself is a great example of "thinking" of a a reason for something and never following up on it.
Then thinking long enough about it, repeating it, getting consensus without anyone ever following up. How long would it take to test the theory? the first silica laden piece of wood you can find and an A/B test in 10 minutes.
The reality is that if a hollow creates a weak edge, the damage will go past the edge into the hollow, but that's still supposition. The proof is trying to find an instance where you can make a microbevel below a hollow grind fail when a flat grind won't (and in some situation that would actually occur - like a 20-25 degree grind and then a microbevel).
Last year, I tested plane irons (I usually grind with a 6" grinder, but will use anything in front of me, flat by hand, belt grinder, whatever - if it's quicker at the moment).
one of the pieces of wood (hard maple) had a mineral inclusion - like tiny pieces of sand. The damage was immediate, I was testing 6 different irons, so instead of stopping, i ran all of them through it (the test would need to be restarted, anyway) to see if any would hold up. None did. about 1/8th to 1/6th of the edge took nicks like this and unless keeping this nicking out of the cut, the plane would not take a thick smoother shaving (any reasonable thickness - I was testing at 3 thousandth, but increasing the thickness didn't help). The damage was all in one spot on each iron, so I took pictures of it. you could easily see it on the edge of the iron with the naked eye. I expected *large* damage.
This is a picture of one of the irons (the others all look similar -the harder an iron was the less deep the dents or chips, but they all stopped planing).
The height of the picture is 0.019". That would put these dents at about 2 thousandths of an inch. Significant because you cannot plane with them in the iron. The argument that "well, they could be deeper than that". Maybe in a jack plane, but you can still feel the dullness.
How large is the final bevel. It's at least several hundredths. Does what's going on 10 times farther away really affect this? No. But, we can play games and round over the tip of the iron and see if that stops failure. I didn't do this at the time, because I later figured out how to modify the edge.
But later, I planed a piece of cocobolo laden with silca. Predictable results. It dented the edge. I buffed the tip of the iron that I was using (didn't even bother to refine the back further than medium oilstone) and then planed about 75 feet, and the entire iron was damage free.
(the slightly higher brightness at the tip of the plane is just burnishing from cocobolo rubbing over the edge)
Please don't peddle the old wives tale to people starting out that they'll have weak edges if they use a hollow grind, and if you suppose a problem with any kind of method, follow up on it and spend 10 minutes seeing if you can prove it.
Then thinking long enough about it, repeating it, getting consensus without anyone ever following up. How long would it take to test the theory? the first silica laden piece of wood you can find and an A/B test in 10 minutes.
The reality is that if a hollow creates a weak edge, the damage will go past the edge into the hollow, but that's still supposition. The proof is trying to find an instance where you can make a microbevel below a hollow grind fail when a flat grind won't (and in some situation that would actually occur - like a 20-25 degree grind and then a microbevel).
Last year, I tested plane irons (I usually grind with a 6" grinder, but will use anything in front of me, flat by hand, belt grinder, whatever - if it's quicker at the moment).
one of the pieces of wood (hard maple) had a mineral inclusion - like tiny pieces of sand. The damage was immediate, I was testing 6 different irons, so instead of stopping, i ran all of them through it (the test would need to be restarted, anyway) to see if any would hold up. None did. about 1/8th to 1/6th of the edge took nicks like this and unless keeping this nicking out of the cut, the plane would not take a thick smoother shaving (any reasonable thickness - I was testing at 3 thousandth, but increasing the thickness didn't help). The damage was all in one spot on each iron, so I took pictures of it. you could easily see it on the edge of the iron with the naked eye. I expected *large* damage.
This is a picture of one of the irons (the others all look similar -the harder an iron was the less deep the dents or chips, but they all stopped planing).
The height of the picture is 0.019". That would put these dents at about 2 thousandths of an inch. Significant because you cannot plane with them in the iron. The argument that "well, they could be deeper than that". Maybe in a jack plane, but you can still feel the dullness.
How large is the final bevel. It's at least several hundredths. Does what's going on 10 times farther away really affect this? No. But, we can play games and round over the tip of the iron and see if that stops failure. I didn't do this at the time, because I later figured out how to modify the edge.
But later, I planed a piece of cocobolo laden with silca. Predictable results. It dented the edge. I buffed the tip of the iron that I was using (didn't even bother to refine the back further than medium oilstone) and then planed about 75 feet, and the entire iron was damage free.
(the slightly higher brightness at the tip of the plane is just burnishing from cocobolo rubbing over the edge)
Please don't peddle the old wives tale to people starting out that they'll have weak edges if they use a hollow grind, and if you suppose a problem with any kind of method, follow up on it and spend 10 minutes seeing if you can prove it.
