Bevels

[ken hatch]

I asked this question on another thread. What's with the multiple bevels, over the last couple or three weeks I keep seeing mention of primary, secondary, and even tertiary bevels. Most of the time Rob Cosman is also given credit as in "sharpened as Rob Cosman does". Why?

Is it a honing guide thing? Although if I remember correctly Cosman free hands.

I know, get the popcorn out but I'm curious as to the reason or reasons.

ken

[Tony Wilkins]

It’s what helps him make the large jump from 500/1000 to 16,000. He grinds, lifts up a little on the coarse stone/diamond plate, and then a little more on the polishing stone.

FWIW, Charlesworth (who uses a guide) also uses a tertiary bevel. I know he did in his articles a decade or so ago and I believe he does in his latest videos.

[mike stenson]

Yea, Rob does. Working from home, it's given me some ..ummm free time?? while waiting for jobs to run. So, he's running a primary and a secondary as I would. Then on his finest stone, he'll run a third bevel angle. Then the ruler trick. With that said, here's a link to a video where he's talking about doing exactly this. The first 3 minutes or so https://youtu.be/okLIEoz00v0

[David Bassett]

I'm not sure it's anything all that new in general. (Probably you have time on your hands these days and just noticed.) Perhaps some are coining new terms to distinguish specific variations?

To me, the concept seems sound & well known, though maybe not worth the trouble. If you reduce your primary bevel you can reduce wedging, but possibly create an edge that is too fragile in practice. With the secondary bevel you can strengthen the very edge, but keep the relief from wedging. (Rinse, repeat, you're at tertiary bevels. Or more.)

(It is also, to me, the same concept of knife sharpeners when they talk about thinning behind the edge. Different words, same basic concept. Possibly different details.)

On another forum David Weaver is going on about using a buffer with polishing compound to give a "micro-convex" edge. It seems, in his experiments, to improve edge longevity at very shallow bevel angles significantly. I'm have trouble imagining this is significantly different than the strop sharpeners get. Too much you dub the edge. Not enough you don't have any practical effect. It's conceptually close enough I won't get it figured out without hours of experimentation using equipment I don't have. (Probably won't, but....) BTW- I don't doubt their results. David's honest in his reporting, other's have tried and agree, plus a number of microscope photos show the different cutting edge profiles and different types of damage pretty well. I do doubt extra equipment, steps, and skills, is cost effective for me right now.

[ken hatch]

Yea, Rob does. Working from home, it's given me some ..ummm free time?? while waiting for jobs to run. So, he's running a primary and a secondary as I would. Then on his finest stone, he'll run a third bevel angle. Then the ruler trick. With that said, here's a link to a video where he's talking about doing exactly this. The first 3 minutes or so https://youtu.be/okLIEoz00v0

Mike,

I watched the video. Cosman is a good instructor and if you follow what he is selling you will have sharp cutters. That said, I think there are better ways to get there and there were a couple or three times he made statements that were like fingernails on a blackboard to me.

ken

[Steve Mathews]

Mike,

I watched the video. Cosman is a good instructor and if you follow what he is selling you will have sharp cutters. That said, I think there are better ways to get there and there were a couple or three times he made statements that were like fingernails on a blackboard to me.

ken

Inquiring minds want to know. Please elaborate.

[ken hatch]

Inquiring minds want to know. Please elaborate.

Steve,

Without watching again, his statements about cap irons, thick irons, and not letting the cutter over the edges of the stone. I'm sure there were several others but I'm old and forgetful. Bottom line, while doing it his way will result in a sharp cutter, as stated, I think there are better ways to get there.

ken

[ken hatch]

Steve,

I just wanted to add.

I've spent a good part of my adult life instructing. Even when "instructor' was not part of my job title I still did a lot of teaching. Cosman is very good at it, he is quite impressive having developed and broken down his method of getting to a working sharp cutter so that the average guy or gal can come off the street and learn to sharpen freehand in an hour or two. That part is pretty impressive. My hat is off to him.

ken

[Steve Mathews]

Steve,

I just wanted to add.

I've spent a good part of my adult life instructing. Even when "instructor' was not part of my job title I still did a lot of teaching. Cosman is very good at it, he is quite impressive having developed and broken down his method of getting to a working sharp cutter so that the average guy or gal can come off the street and learn to sharpen freehand in an hour or two. That part is pretty impressive. My hat is off to him.

ken

I agree Ken. His techniques may not be perfect and he has confessed to that but they work. As a relative beginner to woodworking I could do worse following someone with lesser experience. Besides, Rob is a charismatic sort of guy and entertaining to watch on YouTube. His efforts with the Purple Heart Project is a big plus for me.

[ken hatch]

I agree Ken. His techniques may not be perfect and he has confessed to that but they work. As a relative beginner to woodworking I could do worse following someone with lesser experience. Besides, Rob is a charismatic sort of guy and entertaining to watch on YouTube. His efforts with the Purple Heart Project is a big plus for me.

Steve,

Once you know what sharp is, loose the bevels. Learn to use the whole stone, I think it is Stan Covington that calls it "hang ten", and while you can get away with making that big jump in grits you will find it works better to put something in the middle. The problem with doing that using Cosman's technique you would need four bevels and pretty soon you would end up with a convex bevel and what you really want is a single flat bevel. Remember the process is grind (if needed and it almost always is), hone, and then polish. Most folks do not spend enough time on their polishing stone.

Just one more thought, shiny is not necessarily sharp. Some of the most prized finish stones will leave a hazy finish. That Shapton 16000 grit stone Cosman uses will shine so bright it can be blinding but when you look at the scratch pattern, it sucks.

Good luck,

ken

[Jim Koepke]

Mike,

I watched the video. Cosman is a good instructor and if you follow what he is selling you will have sharp cutters. That said, I think there are better ways to get there and there were a couple or three times he made statements that were like fingernails on a blackboard to me.

ken

Inquiring minds want to know. Please elaborate.

For me it is where he is demonstrating the ruler trick. At around 15 minutes in he states it saves one the trouble of having to flatten the whole back. What is wrong with holding only the 1/4 - 1/2" from the edge flat on one side of the stone and polishing it without a ruler?

Wouldn't this be the same as the ruler trick without the ruler?

Also like fingernails to me is recommending removing the burr only on the finest stone. Maybe this is fine with a very light burr when one is only using two stones. A heavy burr can leave some nasty scratches on a fine stone.

Maybe for folks who really hate spending time sharpening all of the different tricks to speed up a process are a God send. For me sharpening is a pleasant few moments of listening to music and restoring the edge on a tool for working wood.

Even when working on a project for commission or to sell, sharpening is not a big consumer of my time.

jtk

[J. Greg Jones]

For me it is where he is demonstrating the ruler trick. At around 15 minutes in he states it saves one the trouble of having to flatten the whole back. What is wrong with holding only the 1/4 - 1/2" from the edge flat on one side of the stone and polishing it without a ruler?

Wouldn't this be the same as the ruler trick without the ruler?

Seems like that could present a challenge as the blade wears. If you are moving it back ¼” on each sharpening, eventually there will be a bump to deal with. The ruler trick is so minuscule, less than a 1* bevel on the blade, and it maintains that 1* bevel with each sharpening.

Also like fingernails to me is recommending removing the burr only on the finest stone. Maybe this is fine with a very light burr when one is only using two stones. A heavy burr can leave some nasty scratches on a fine stone.

He is only using two stones, and with the ruler when the burr is removed, the edge of the blade is off the stone. The burr peels away as soon as it hits the edge of the stone.

[Erich Weidner]

Also like fingernails to me is recommending removing the burr only on the finest stone. Maybe this is fine with a very light burr when one is only using two stones. A heavy burr can leave some nasty scratches on a fine stone.
jtk

Hi Jim,
This comment made me take notice. Can you elaborate what you are doing/mean by this? I feel like I might be missing something important. (Since this thread has gotten a little "edgy" I want to point out there is no sarcasm here, genuine question).

I never tried the ruler trick/back bevel. I sharpen by first (new to me blade) flattening/polishing 2-3" of the back from the edge of the blade.
When sharpening the bevel, I progress up through the grits, feeling for a wire edge before progressing to next grit. (I use forward and back strokes). I can't really feel a wire edge after I get up to 6000 or so. But I can see the polish improve. My last grit is 10,000 water stone. After I get the polish from the stone on my micro bevel I pull the iron out of the honing guide and do 3-6 strokes flat on the back only keeping 2-3" on the stone. This last step I'm doing to remove the wire edge. (I'm just following a method that I read).

Are you doing something different between changing grits?

[steven c newman]

Sometimes, you can get a wire edge at EACH stone....and it is usually a good idea not to bring that wire edge to the next stone.

[ken hatch]

Sometimes, you can get a wire edge at EACH stone....and it is usually a good idea not to bring that wire edge to the next stone.

Steven,

How true.

Learning to sharpen free hand is not that difficult but it does take a little time on the stones to develop a feel for what is happening. That time is well spent, much more so than that spent on all the jigs, gadgets, and short cuts folks are selling.

ken