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Frederick Skelly
03-26-2016, 9:42 PM
Does it hurt anything if, using my grinder, I strive for a 25* primary bevel but end up with something a little more or less than that? (I'm still having trouble setting my grinder to the precise angle, even with a pretty nice tool rest.) After grinding, I put the iron in my Veritas Mk-II and sharpened and honed to "exactly" 25*. It came out fine.

The backstory:
I bought a Rikon low speed dry grinder and a 120 grit Woodriver CBN wheel for changing the primary bevel or grinding back past chips at the same bevel angle. I like the tool a lot - the CBN combined with the 1700 rpm low speed really does give me plenty of working time without bluing the blade. I think it's going to take some practice to get good with the grinder, but with a bit of effort I get a square primary bevel that's ready to sharpen. I'm glad I bought it.

Rather than use a secondary bevel, I just sharpened and honed the primary bevel. The iron gets quite sharp. (New Buck Brothers 2" iron from the BORG, per a Jim K suggestion here months ago.)

What do you folks think? Is it ok to get close to 25* on the grinder and then work the cutting edge to exactly 25* on my diamond stones, until I get enough practice to get it exactly right, directly off the grinder?

Thank you!
Fred

Patrick Chase
03-26-2016, 10:30 PM
Does it hurt anything if, using my grinder, I strive for a 25* primary bevel but end up with something a little more or less than that? (I'm still having trouble setting my grinder to the precise angle, even with a pretty nice tool rest.) After grinding, I put the iron in my Veritas Mk-II and sharpened and honed to "exactly" 25*. It came out fine.

The backstory:
I bought a Rikon low speed dry grinder and a 120 grit Woodriver CBN wheel for changing the primary bevel or grinding back past chips at the same bevel angle. I like the tool a lot - the CBN combined with the 1700 rpm low speed really does give me plenty of working time without bluing the blade. I think it's going to take some practice to get good with the grinder, but with a bit of effort I get a square primary bevel that's ready to sharpen. I'm glad I bought it.

Rather than use a secondary bevel, I just sharpened and honed the primary bevel. The iron gets quite sharp. (New Buck Brothers 2" iron from the BORG, per a Jim K suggestion here months ago.)

What do you folks think? Is it ok to get close to 25* on the grinder and then work the cutting edge to exactly 25* on my diamond stones, until I get enough practice to get it exactly right, directly off the grinder?

Thank you!
Fred

I don't think it's a problem. Obviously a lot depends on how tall your secondary bevel is - if it's super-thin then at some point the edge will become fragile due to lack of support behind the tip, but I doubt that 25 vs 24 deg grinding angle will make or break you.

FWIW I use Charlseworth's approach:

1. Grind the face hollow at slightly less than the desired "primary" bevel. For example if I'm working on a BU blade where I want a 23 deg primary and 25 deg secondary, then I might grind the face at ~22.

2. Create a short primary bevel (extending maybe 1/4 of the way up the face to start) using a flat stone/disc/whatever. This would be 23 deg in the example I gave above.

3. Hone the secondary at the desired tip angle. This would be 25 deg in the example.

The idea here is that the secondary can be kept small and easy-to-hone, since we're not depending on it to provide support to the edge - the taller primary does that. When the secondary starts to get tall and hard to hone you can reduce it by working the primary. Doing so is easy because you only have to remove 1/4 (initially) as much material as you would if the primary extended all the way up the face. Finally, when the primary starts to extend far enough up the face that it's difficult to grind, you start over with a fresh hollow grind.

Obviously not everybody likes to be that "retentive" about their grounding/honing practices...

Frederick Skelly
03-26-2016, 10:49 PM
Thanks Patrick!
Fred

Edit: How do you get so accurate in setting your tool stand to exactly 23* ? With luck, Stewie's link will help me see it better. (Hope so.) But I found that even my Wixie Gauge just wasn't useful in setting the tool rest angle in this application. I'm wondering if the engineer in you HAS figured out how to use the Wixie?

Derek Cohen
03-27-2016, 2:22 AM
Hi Fred

The greatest value of a hollow grind is when you freehand on the hollow (using the sides of the hollow as a jig). This is what I do with BD plane blades and chisels. I do not use a honing guide and, therefore, there is no need for a secondary bevel.

The exception to free handing is honing a blade for a BU use where the bevel angle is high (generally 50 degrees). This will use a primer bevel of 25 degrees and a micro secondary of 50 degrees. I need a honing guide for that. This now takes me into your territory.

There is no need for accuracy for the primary bevel when using a honing guide. You want to be under the desired secondary bevel, not at the same angle you plan to end at, as Patrick noted. In the years when I used a honing guide, I ground bevels on a belt sander. The flat bevel was not better than a grinder, but a grinder was not specifically necessary for the honing guide. Plus it does not matter whether the primary is 1 or 5 degrees under the secondary - all that matters is the angle of the secondary. That is where the work lies in honing with a guide. The same applies if you freehand and lift the blade for a secondary bevel. Grinding angles only become important (and ball park is near enough) when freehand in on the hollow.

Regards from Perth

Derek

Stewie Simpson
03-27-2016, 6:31 AM
Fred. You may find the attached of some interest...

Stewie;

http://www3.telus.net/BrentBeach/Sharpen/grinder.html#calc

Frederick Skelly
03-27-2016, 6:40 AM
Hi Fred

The greatest value of a hollow grind is when you freehand on the hollow (using the sides of the hollow as a jig). This is what I do with BD plane blades and chisels. I do not use a honing guide and, therefore, there is no need for a secondary bevel.

The exception to free handing is honing a blade for a BU use where the bevel angle is high (generally 50 degrees). This will use a primer bevel of 25 degrees and a micro secondary of 50 degrees. I need a honing guide for that. This now takes me into your territory.

There is no need for accuracy for the primary bevel when using a honing guide. You want to be under the desired secondary bevel, not at the same angle you plan to end at, as Patrick noted. In the years when I used a honing guide, I ground bevels on a belt sander. The flat bevel was not better than a grinder, but a grinder was not specifically necessary for the honing guide. Plus it does not matter whether the primary is 1 or 5 degrees under the secondary - all that matters is the angle of the secondary. That is where the work lies in honing with a guide. The same applies if you freehand and lift the blade for a secondary bevel. Grinding angles only become important (and ball park is near enough) when freehand in on the hollow.

Regards from Perth

Derek

Thank you Derek! That all makes sense.

BTW, I bought that CBN wheel base on your comments and I really like it. Thanks for that tip too.

Best regards,
Fred

Frederick Skelly
03-27-2016, 6:46 AM
Fred. You may find the attached of some interest...

Stewie;

http://www3.telus.net/BrentBeach/Sharpen/grinder.html#calc

Thanks Stewie! I just scanned through that article and I think it will definitely help me. I'll read it in full detail later today.

Take care,
Fred

Tom M King
03-27-2016, 9:10 AM
I use the Stuart Batty gauges. If you want to hone to an accurate angle, it is much easier to grind to the exact bevel at first. I have stopped using micro bevels for a good while now, since I have started using fast cutting stones. It's so much faster overall if you keep it easy to reproduce accurate angles all the way through the process. See my thread with the jig setting gauges. They will only save you time if the tool has the right angle on it to start with. Even with a hollow grind to start with, the cutting edge and heel with get honed, and it will gradually take over the whole face in following honings.

Grinding is only done if an edge finds damage, which is very rare in the shop.

Don Jarvie
03-27-2016, 9:51 AM
25 to 30 degrees is fine. As Derek says when you hollow grind you don't need a honing guide. I don't use a secondary bevel. The primary works just fine.

FWIW, I hollow grind then use a medium oil stone then white Arkansas stone. My blades a plently sharp.

Daniel Rode
03-27-2016, 9:53 AM
Once the angle is initially set on a chisel, I eyeball the angle on the grinder. Essentially, I look to see if it's touching at about the center point of the bevel and, if necessary, adjust until it is. The angle it's not set at, works for all my standard chisels and irons, so I rarely have to adjust it. When I hone, I do not touch the back of the hollow at all. I'm a couple degrees, by feel, higher than the angle between the two edges of the hollow. I use the grinder to "remove" the secondary bevel when it starts to get too wide.

I have a handful of chisels with a 17* or 18* main bevel and a 20* working edge. These will slice cleanly through the softest pine end grain without tearing but the edge is not very durable. For these I have to change the angle I grind at but, again, I just eye the angle until it's at the center of the hollow.

Patrick Chase
03-27-2016, 11:11 AM
The greatest value of a hollow grind is when you freehand on the hollow (using the sides of the hollow as a jig). This is what I do with BD plane blades and chisels. I do not use a honing guide and, therefore, there is no need for a secondary bevel.

That's true IF you hone freehand. If you hone with a guide then being able to use the hollow as a jig has no value whatsoever. In that case the value of the hollow is that it reduces the amount of effort to work the primary and thereby keep the secondary small between grindings. That's what Charlesworth's method is all about. Charlesworth's method is also more conservative in that you only hollow the upper part of the bevel (i.e. the hollow never gets very close to the edge) though IMO some people make more of that than they should.

In general there is no single "best" or "correct" way to do things, whether it's grinding, stropping, or whatever.

Bill Houghton
03-27-2016, 12:26 PM
Just don't make the grind angle steeper than your desired angle, if you're using a jig. If you make it steeper, you won't be able to hone the edge.

If you're wondering how I know to mention that...

Jim Koepke
03-27-2016, 1:12 PM
It would be difficult for me to say what angle any of my chisel's bevels might be. I might be able to come close.

It isn't the angle so much as the edge in many cases.

For repeatability, some folks make gauges of metal cut on the grinder to make it easy to find the same angle repeatedly. Once the angle is where it is wanted, grind a hollow in a business card sized piece of flat metal. Make a few at different angels, cut a hollow in each end. Drill a hole so they can be kept on a nail near the grinder.

jtk

Pat Barry
03-27-2016, 4:27 PM
Thanks Jim, that's a great tip!

Frederick Skelly
03-27-2016, 5:55 PM
Tom, Don, Dan, Bill & Jim - thank you all for giving me your advice here!

Jim, I agree with Pat - that's a great tip. If one puts multiple angles on a single piece of metal, it reminds me of Batty Gauges that Tom suggested above.

Thanks again guys!
Fred