What is the advantage of hollow grinding chisel and plane blades?

[Ron Kanter]

Here is my question: why is it faster to sharpen a hollow ground blade?
Don't you still have to move the blade over the stone the same number of times? Clearly, there is less metal to remove, but the energy required is all about the number of strokes or the time devoted to sharpening.
I can't understand how the effort is really any different when moving 1/8" or even 1/4" of steel over the stones versus moving two 1/16" ridges with a hollow ground space between them over the stones. I hope my description makes sense.
Another way of picturing the blade to be sharpened is to think of it as one relatively thick line of steel versus two thin parallel lines of steel with a narrow, empty space between them. Would the two narrow lines get sharp faster? If so, why is that so?

If I am wrong, I hope you can help me understand what I am missing.

I can understand that less steel would offer less resistance when slicing wood, and there may be some small reduction in wear on the stones, but my question is about the ease of sharpening. Thanks for your thoughts.

Regards from Philadelphia,
Ron

[ken hatch]

Here is my question: why is it faster to sharpen a hollow ground blade?
Don't you still have to move the blade over the stone the same number of times? Clearly, there is less metal to remove, but the energy required is all about the number of strokes or the time devoted to sharpening.
I can't understand how the effort is really any different when moving 1/8" or even 1/4" of steel over the stones versus moving two 1/16" ridges with a hollow ground space between them over the stones. I hope my description makes sense.
Another way of picturing the blade to be sharpened is to think of it as one relatively thick line of steel versus two thin parallel lines of steel with a narrow, empty space between them. Would the two narrow lines get sharp faster? If so, why is that so?

If I am wrong, I hope you can help me understand what I am missing.

I can understand that less steel would offer less resistance when slicing wood, and there may be some small reduction in wear on the stones, but my question is about the ease of sharpening. Thanks for your thoughts.

Regards from Philadelphia,
Ron

Ron

You really know how to step in it.

Bottom line it isn't the number of strokes on the stone but how much metal needs to be removed. Hollow grind will need less metal removed by the stone.

ken, where is my popcorn when needed.

[Carl Baker]

I'll start by saying that I cant answer your question. BUT whether you know it or not, you've started a sharpening thread! That means we all get to weigh in! Like most of them, it will probably go a whole lot of different directions before it comes back to a question of how you work and the best way for you to stay sharp.
I see the logic in having less area to hone and I can imagine it would be quicker but i can't see it saving THAT much time. I have been reluctant to hollow grind simply because, and ironically because, I don't want to take the time to hollow grind the blade in the first place. I also use a hand crank grinding wheel for "heavy" work. If I spent the money on a nice machine, I would probably change my tune... if nothing else, just to get my money's worth! I also want to believe that less steel equals less strength... but that may just be me further justifying my own opinion.

[Stanley Covington]

Ron

You really know how to step in it.

Bottom line it isn't the number of strokes on the stone but how much metal needs to be removed. Hollow grind will need less metal removed by the stone.

ken, where is my popcorn when needed.

Ken:

Do you have the popcorn concession for SMC? (ツ）

Ron:

Ken has it right. It takes time, and effort, and worn-out stones to remove the metal. A hollow-ground blade has less metal to remove, so the job gets done sooner and at less cost.

A second important point is flatness. If you really pay attention, you will will notice that working a chisel or plane blade's flat over a stone to sharpen it almost always tends to make the flat curved instead of flat. This makes it harder to keep the area directly at the flat's extreme edge in contact with the stone. Until this area is sharpened its full width, the blade is not as sharp as it can be. Once again, wasted time, effort, and stones, and too often, a ratty cutting edge.

The hollow makes it much easier to keep the flat in a single plane (or close to it), at least the flat defined as the lands around the hollow, one of which is right at the cutting edge. Its just a better design. But a lot of people have lesser standards for sharpeness, or don't notice these small details. How small is your cutting edge's width, Ron?

Stan

[Derek Cohen]

It is all about surface area. The hollow grind has significantly less than the flat bevel.

Regards from Perth

Derek

[John C Cox]

The simplest answer is this.....

Hollow grinding ensures there isn't a hump in the middle of the back you will have to battle when setting up the chisel... Simple as that. As a result - you are flattening the cutting edge and sides sooner....

When you have a hump (or humps) in the back somewhere - you spend eons of time flattening out the hump before the sharpening process finally makes it to the edge.... I battled this out with a new set of Two Cherries chisels Friday evening... I finally broke down, dug out my surface plate and roll of 100 grit PSA and I made war...

Patrick has pointed this out - but it appears that most manufacturers are now grinding before heat treatment to save manufacturing time - which means you will have to deal with some warp... Some have sorted out how to do it right so you aren't grinding the backs for 4 hours on Friday night... Some have not...

It was worth it for the Two Cherries - as I was rewarded with fantastic steel that sharpens beautifully and holds an edge really well... Other chisels have not gone so well.

[ken hatch]

The simplest answer is this.....

Hollow grinding ensures there isn't a hump in the middle of the back you will have to battle when setting up the chisel... Simple as that. As a result - you are flattening the cutting edge and sides sooner....

When you have a hump (or humps) in the back somewhere - you spend eons of time flattening out the hump before the sharpening process finally makes it to the edge.... I battled this out with a new set of Two Cherries chisels Friday evening... I finally broke down, dug out my surface plate and roll of 100 grit PSA and I made war...

Patrick has pointed this out - but it appears that most manufacturers are now grinding before heat treatment to save manufacturing time - which means you will have to deal with some warp... Some have sorted out how to do it right so you aren't grinding the backs for 4 hours on Friday night... Some have not...

It was worth it for the Two Cherries - as I was rewarded with fantastic steel that sharpens beautifully and holds an edge really well... Other chisels have not gone so well.

John,

One modern maker (that I know of) still hammer forges their chisels and after heat treating looks for the "hollow" before grinding the bevels. Ashley Iles chisels are fair priced and really good chisels with a flat to hollow back. Now as to the hollow grinding I think you are thinking about the wrong side of the chisel.

ken

[Robert Engel]

You essentially get a secondary bevel with one effort.

I sharpen freehand and it helps me register the angle.

Now here's something to consider [with a mouthful of poplcorn LOL] -- a reduced wedging effect when chiselling.

[John C Cox]

John,

One modern maker (that I know of) still hammer forges their chisels and after heat treating looks for the "hollow" before grinding the bevels. Ashley Iles chisels are fair priced and really good chisels with a flat to hollow back. Now as to the hollow grinding I think you are thinking about the wrong side of the chisel.

ken

Nobody said anything about the bevel... The back is really where I want to see a bit of a hollow grind..... Not only for initial setup - but ongoing maintenance is easier as well..,,

The only reason I hollow grind the bevel is if I need to remove a lot of steel for some reason or another. It allows the Dremel to do the majority of the work without as much risk of drawing the temper or otherwise gouging the edge and ruining the edge geometry.. Chipped, rounded, or badly skewed from the factory is where I end up pulling out the grinder when I need to battle the initial setup as it comes to me... Just Saturday I hollow ground a badly chipped thrift store Stanley iron....

But if you like to hollow grind your bevel as a normal part of your use - have at it...

[Jim Koepke]

Here is my question: why is it faster to sharpen a hollow ground blade?

As said above, in theory there is less metal being removed. Creating a secondary bevel could possibly match this for the fast factor.

A hollow grind is created when the outside, curved surface of an abrasive wheel is used to remove metal. When using freehand sharpening, the hollow ground blade actually "clicks" into place on a stone. One of my books somewhere states in times of old it was not only an embarrassment to have a convex grind on an edged tool it was considered a sign of poor practice. So it became standard practice to 'hollow grind' every edged cutting tool in order to avoid having a product that didn't meet the expected standard. Since abrasive wheels were a standard item, this went on for a few centuries.

As times changed so did methods. There isn't an electric bench grinder in my shop. My electric sharpening system is a disk style machine from Veritas. It produces a flat bevel. It works fine for me. Touching up a flat bevel is not a horrendous task. Some folks make it even quicker with a micro bevel.

In my opinion bench grinders are often over used and shorten the life of many good tools by removing more metal than necessary.

For me, simple often works best. No worries about micro bevels, hollow grinds or many other "tricks of the trade" to distract me from enjoying time in the shop.

As per usual, a reminder... YMMV!!!.png

jtk

[Patrick Chase]

Patrick has pointed this out - but it appears that most manufacturers are now grinding before heat treatment to save manufacturing time - which means you will have to deal with some warp... Some have sorted out how to do it right so you aren't grinding the backs for 4 hours on Friday night... Some have not...

A lot depends on the HT process. Narex are well regarded despite doing that, because they use a fairly exotic HT process that inherently produces lower warp than conventional quenching. This enables them to skip post-machining without aggravating customers for any but their longest (paring) chisels. Some other (lower end) makers seem to use any old HT process and skip the post machining, with fairly disastrous results.

One modern maker (that I know of) still hammer forges their chisels and after heat treating looks for the "hollow" before grinding the bevels. Ashley Iles chisels are fair priced and really good chisels with a flat to hollow back. Now as to the hollow grinding I think you are thinking about the wrong side of the chisel.

The breakpoint between post-machined and not seems to be around $25/chisel right now. AI is north of that, and makes a quality post-machined product.

$70/chisel or so gets you a dead flat post-machined and then lapped back with perfectly machined side bevels extending all the way to the sole :-)

[Stanley Covington]

Here is my question: why is it faster to sharpen a hollow ground blade?
Don't you still have to move the blade over the stone the same number of times? Clearly, there is less metal to remove, but the energy required is all about the number of strokes or the time devoted to sharpening.
I can't understand how the effort is really any different when moving 1/8" or even 1/4" of steel over the stones versus moving two 1/16" ridges with a hollow ground space between them over the stones. I hope my description makes sense.
Another way of picturing the blade to be sharpened is to think of it as one relatively thick line of steel versus two thin parallel lines of steel with a narrow, empty space between them. Would the two narrow lines get sharp faster? If so, why is that so?

If I am wrong, I hope you can help me understand what I am missing.

I can understand that less steel would offer less resistance when slicing wood, and there may be some small reduction in wear on the stones, but my question is about the ease of sharpening. Thanks for your thoughts.

Regards from Philadelphia,
Ron

I guess I am confused. Are you talking about a concave grind on the cutting edge's bevel? Or a hollow grind on the blade's flat?

If a hollow flat, then my answer above is good.

If a concave bevel, then I think it is simple expediency. I don't use this technique on blades worth owning.

[ken hatch]

I guess I am confused. Are you talking about a concave grind on the cutting edge's bevel? Or a hollow grind on the blade's flat?

If a hollow flat, then my answer above is good.

If a concave bevel, then I think it is simple expediency. I don't use this technique on blades worth owning.

Stan,

Join the club. If I read the OP's post correctly he is asking about hollow grinding the bevel, some of the answers are about hollow grinding the back. But then I'm only fluent in Texan, never did figure out English.

ken

[Patrick Chase]

Join the club. If I read the OP's post correctly he is asking about hollow grinding the bevel, some of the answers are about hollow grinding the back. But then I'm only fluent in Texan, never did figure out English.

Y'all're incomprehensible! :-)

[Stanley Covington]

Your English maybe not plum but pert near.