The prevailing way the scythe leading edge was formed (in continental Europe) for many generations is peening. Peening is cold hammering the cutting edge of the blade. Peening results in drawing out and thinning the steel at the edge. After peening the edge is finished and maintained with wheatstone.

From the metallurgical point of view peening is a mixture between work-hardening (cold working) and steel over-working. Peening is primarily a cold working process but I have observed some self-heating also*. Peening hardens the metal at the edge. Peening may induce desirable surface compressive stress, because cracks will not grow in a compressive environment. 

One study has shown that the surface hardness of a blade increased form HRC 46 for the core of the blade to HRC 53 in the hand hammered region. The test did not include the last 1mm zone which actually does the cutting and determines retention of keenness. So it is possible that the very edge is considerably harder.

I have never mastered the peening technique though I have inherited the equipment for it – a special stool with wide convex anvil and scythe hammer very similar to the one shown on the picture below.
   
From my childhood I remember well the characteristic ringing sound of the peening anvil and hammer which was an essential part of rural atmosphere. Reapers were peening their scythes each evening.
 
More info http://scythecymru.co.uk/scythes-for-sale/peening/
 
Jan

P.S.: * I have noticed that under hard hammer blow a blue oxide spot formed on the edge which means that the temperature locally increased by some 300°C (540°F).

As an old woodworker and newcomer to knives, the term "toothy" refering to edges is new to me. I don't ever recall it being applied to chisels or plane blades. 

I understand the concept of a toothy edge as it applies to cutting tomatoes with kitchen knives. I am not sure if it applies to everything cut with knives. Should knives always have toothy edges?

Ken

Mark, and anyone who coerces hot metal into shape,
I am trying to get my wish list together for my next phase of bladesmithing.

Could you recommend minimums on good tooling to get forging?  (overkill is good too)  

Anvils, size, weight, type
Hammers
Tongs
Ovens
Fuel types for those ovens
Gloves/safety equipment
All of the things I am not aware of

Any advice would be great!
(Well, not great for my wallet, but we ignore that as much as possible)

T.W.

I remember finding a statement by a sharpening source who, after testing, determined that, in his opinion, the ideal speed for a moving leather honing belt or wheel was approximately the speed of a Tormek.

I apologize for not being able to source this better; I have forgotten the name of the source. Perhaps someone on the forum can help out.

I am presently just beginning to test an 8" x 1" Duro Felt (hard grade) buffing wheel. I am using it on my Tormek T4, which uses eight inch (200mm) diameter grinding wheels. The felt wheel has a one inch bore opening. I have it mounted on a steel one inch to twelve mm reducing bushing.

I debated between the hard and rock hard grades. If the hard tests well, I may add a rock hard.

My initial problem has been slippage. 

My wife and grandchildren have awoken; I will return to this post.

Back.... The slippage issue is somewhat due to needing spacers to bring the one inch felt wheel to 40mm. 12mm fenders, readily available, should solve that. I remember they work better on one side of the grinding wheel. I don't remember whether that is the inside or outside. (50-50 chance of getting it right on the first attempt).

I would also like to glue the felt wheel to the steel bushing. Any glue suggestions?

Next issue will be choice of honing compound. 

I do not know if this will work well or not. Nothing ventured, nothing gained. Comments welcome.

Ken

In this thread, I would like to introduce this work of John Verhoeven, as the first subject of study for anyone interested in metallurgy as it applies specifically to anything related to knives.

Mr. Verhoeven's work is generally recognized as the most accurate and digestible writing specifically for knife enthusiasts, but still, without some formal background in metallurgy, it's not easy to digest much of it without discussion.

A search for John Verhoeven's writings will bring up at least four different studies. They encompass basic metallurgy, blade metallurgy and even one study specifically about Sharpening! 

I've tried to study this by myself, but TBH, some of it is beyond my pay grade. I have been able to take some specifics and apply them to my study of 52100, but Mr. Verhoeven's work encompases all aspects of blade steel.

Mr. Jan, I'm particularly interested in what you think of this. I'm pretty sure your background will come into play, as this does begin with atomic structures. From there, some familiarity of metallurgy would surely be helpful.

Everyone, please understand that this is meant to be a long term discussion. If there is enough interest, we will make it a sticky, because I don't expect this to be an everyday topic, but one in which we can casually meander through. If we can manage to do so, I believe it could become a discussion of significance for everyone. 

Since this is mainly a sharpening centered forum, if you would rather jump straight to Verhoeven's study on sharpening, I completely understand. It might help to take this quick overview of basic metallurgy first, but I leave everyone to their own designs, as one thought will surely lead to the next.

The floor is open! Please feel free to post all relevant discussion. 

Thank You!

A short time ago Max (The Knife) sent me a Lasting Cut 8” chef’s knife to test for sharpness.  Not only was I was impressed at how sharp it was for a $12.00 knife, but also by how wonderfully gnarly and toothy the edge was.  It was about perfect for a kitchen knife and would have no problems melting through tomato, broccoli stem or citrus skin.  So, I wanted to duplicate that edge finish.  This is the story of my first attempt.

Thank you Mr. pjwoolw for pointing me to Deerfos ceramic belts!  I believe Deer’s are my new favorite.  I love the way they cut; smooth as silk and aggressive, they create a very even grind with a wonderful “feel” whilst grinding.  I’m almost giddy.  For this attempt to duplicate the Lasting Cut edge, I decided to use a 1x42, DEER JS 997 Blue Ceramic J-Flex Cloth Belt, 180 grit. 

This knife is my victim for the experiment:


 
 This is the edge of the Lasting Cut blade I wanted to duplicate:


 
Keep in mind that I took the belt out of the box and had at it, so the belt is still pretty hot, fresh and gnarly.  I’m sure the results would be a bit different after the belt calms down from use.  Nonetheless, here’s what happened:
 
I threw the knife on the old Kally 1x42 and sharpened the blade producing a small, even burr.  It was a very thin burr and easy to crush, but very malleable.  It ended up being somewhat difficult to remove as it was very resistant to fracturing off due to fatigue.  It was easy to see with the naked eye.



I apologize that I did not spend much time getting the lighting just right on the following microscopy, but I think it’s good enough to tell the little story.

The next two images are taken at about 200X.  The two images are identical except that the first was with top lighting and the second image bottom lighting to avoid all the reflection from the burr.





I threw it on the PT50B and got 425g.  That was to be expected as I was mashing the test media against the burr crud covering the edge of the blade.
 
The following four sharpness measurements represent 20 strops each on my jeans on my thigh.  I’m counting one strop as (strop one side + strop other side) = 1 strop.
285g
305g
250g
245g
 
It was obvious that I had maxed out effectiveness of my thigh/jeans stropping but I was disappointed.  Thinking it should be sharper, I threw the blade under the microscope.



What a disgusting mess!  There are still piles of burr on the edge, and some has been simply smashed down over the side of the bevel.  Sadly, my thigh/jeans stropping was: FAIL! 

So I caved and threw a leather belt on the Kally, rough side out and stropped.  There was a very small amount of left over 1u-3u compound on the belt, but very, very little.  It took a good 10-15 light passes on each side before I could no longer see any burr.  Then I gave it 10 quick strops on my jeans to remove any bits of crap that came off the leather just to clean the edge up, and tested the sharpness.  This time:
 
155g

Perfect!  Exactly what I was going for.  But I was worried.  Did I obliterate the glorious toothy edge with all my stropping?  With trepidation, I threw it under the scope:
 


No! I did not ruin the toothy edge!   Still wonderfully aggressive and toothy!  Outstanding.  It melts through paper towel and cleanly cuts dry garlic skin laid flat on a cutting board without breaking or tearing it.  Of course it push cuts paper, etc.  
 
Now, compare that with the Lasting Cut edge shown at the start of this post.  I used a 180 grit belt for this test, and it looks to me that the Lasting Cut was ground with something more coarse, possible 120 grit?  But really, I don’t care!  I think this blade will probably perform very well, and I consider my duplication attempt a success.  I don’t think I need to go to a coarser grind, but I might give it a try just for grins.

So, how sharp is the knife?  I was removing the knife from a small vice I use to hold the knife solidly under the microscope when my finger ever so lightly brushed the tip of the blade.  I was instantly notified with that “special” feeling from my finger.  Upon examination, sure enough, epidermal leakage!!!  DOH! 

A customer of ours in the UK has ordered a PT50B and is interested in learning about benchmark sharpness levels for hand plane blades (irons) and chisels. We thought that this would be a great opportunity for our woodworking members and users to pitch in with their experiences with sharpening levels for these edges. We are certain that any and all information related to this sharpening area would be much appreciated.

Gotta love those how it's made videos!
https://youtu.be/e9PnTPIKd3g

My first forge has been serving me well for basic bladesmithing, but it really isn't big enough or hot enough to do the type of work I want to do now. Hence, I decided to build something that will keep me smiling for the foreseeable future. 

I figured I would need a sturdy tube about 18" in diameter by 3' long. I called the steel yard to see what that would cost, and it was about $150. I didn't think that was too bad, but they told me to come down and look through the scrap yard. Low and behold, I spotted a commercial water heater that looked about right, and payed the scrap price of $15. 

With the bottom cut out, and the top cut off, it was Exactly the size I wanted. It even has double thick reinforced ends. 

I cut the burner holes and welded the drilled and tapped burner mounts to the shell. After grinding a thick layer of water deposits out, I finished the inside with 2000*F primer and paint to get a good bond with the 3000*F mortar that holds all the 2800*F brick and insulation together.

There's a layer of 1-1/4" thick, 4-1/2" wide brick, under the 2-1/2"x 4-1/2"x 9" brick. This is the actual floor of the forge. After learning how Sairset works (which is dang slowly), I let it dry for about a week.




1 1/4" x6" x9" brick are fully mortared in, to make solid walls instead of Kaowool walls. Now you can see the "subfloor" layer better. This solid, bonded foundation is absolutely critical. 




The outside layer of 2" Kaowool is mortared to the shell. It's slightly asymmetrical so I have room for an extra layer of Kaowool on the right side, where the burners are aiming. This will create a swirl effect to help eliminate hot spots in the forge.




It's pretty tricky to get all the Kaowool mortared together and supported into a nice smooth arch before the mortar dries. I'm pretty happy with the results at this point. 

High temp brick is very soft and fragile before the mortar soaks in and drys. It was easy to rip the triangular pieces with an old blade on the tablesaw. These will be mortared into corners to facilitate smoother transitions for a cleaner laminar flow of the swirling gases.




While I was welding the burner tubes, I also welded short pieces of angle iron to the outside of the shell on all four corners for extra strong attachment points for the legs. They really came in handy whenever we needed to move this heavy, awkward  sucker. There really wasn't another way to grab it without messing up the insulation.

After a few days to dry, I started running thermal cycles to stabilize everything. 
If anyone is interested, I can show more to this build