Dimension of secondary bevel on a full-flat

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Magicdrshoon

Joined
Jul 6, 2016
Messages
5
Hello!

I am planning on making myself a knife. I don't want to go into production, I just want to make a knife as best I can.

I want it to have a full-flat grind with a secondary bevel.

How big is the secondary bevel normally?

I am using M390, and the knife is going to be 4 mm x 50 mm x 250 mm in total.

I've guessed at it being 1 mm wide x 1.4 mm tall, making the angle of the secondary bevel at around 20° each side (40° in total).

Does this sound about right? What are they normally?

TIA
 
It will all vary depending on the application. What do you intend the knife for?
 
I like to start with an edge that is from .005"-010" thick on almost any knife with choppers being closer to .020". That will make a very small microbevel which is always my goal. (unless doing a fully convexed tip) Knives like this are easy to sharpen and the edge is more durable than you might think because of the knife just "wants" to cut through things.
 
Daniel Fairly Knives said:
I like to start with an edge that is from .005"-010" thick on almost any knife with choppers being closer to .020". That will make a very small microbevel which is always my goal. (unless doing a fully convexed tip) Knives like this are easy to sharpen and the edge is more durable than you might think because of the knife just "wants" to cut through things.
Click to expand...

That's half of what I guessed! I'm pleased I asked now!

The concern I have is that blade would be too thin over much of the depth.

My stock was going to be 4 mm thick, which would mean that 21.7 mm of the 50 mm blade depth would be less than 2 mm thick.

I'm sure it's just my inexperience. The steel is supposed to be good, and I've seen good reviews on the Lion Steel M4, so I think I'll just give it a go and see how it turns out!

Thanks for your help.
 
As another "newbie" to all of this, it's a bit difficult to get this stuff in your head & have it come out making sense. I was doing the wrong thing initially, making a blade which was "too thick" behind the edge. Some of my first blades ended up being almost 1mm thick behind the edge & they took a while to sharpen (with D2 steel at HRC 60, make that forever to sharpen!).

Something talked about here is that "geometry cuts" & the edge just wears due to the actual work & type of steel which is used. It's taken me a while to understand that simple concept, but it's starting to sink in now. Start with an edge which is about .33mm thick before sharpening, then run the actual bevel for the edge & you will have a good slicer. A blade with an initial thickness of .25mm or even less before sharpening, will cut like a laser with a 20 degree bevel per side & with a good steel & heat treat it will last a long time & stay sharp.

This is what I would try for, but be careful & take your time. If you can do this, you will have a new appreciation for some of the work you see here & the guys who are doing it. Best of luck & want to see some progress pictures when it's time!
 
Magicdrshoon said:
That's half of what I guessed! I'm pleased I asked now!

The concern I have is that blade would be too thin over much of the depth.

My stock was going to be 4 mm thick, which would mean that 21.7 mm of the 50 mm blade depth would be less than 2 mm thick.

I'm sure it's just my inexperience. The steel is supposed to be good, and I've seen good reviews on the Lion Steel M4, so I think I'll just give it a go and see how it turns out!

Thanks for your help.
Click to expand...

That will work nicely. I make a lot of blades that are 1.5 mm stock (1/16") to start and they have an aggressive "rolled back" high hollow grind... and are Titanium!

M4 will hold a great thin edge by the way.

A US penny is something like .040" thick for reference. I think .012" would be around 4 pieces of printer paper thick. There is not a lot of need to accurately check your edge thickness as a maker but it is a great reference to start from... maybe some inexpensive digital calipers would be handy but certainly not necessary.

Edge flex tests are somewhat handy... use them as a reference along with testing and edge thickness. Thumb behind the edge with a little pressure.. brass rod test, etc. Once i am seeing some flex I know the edge is very thin.

Cut an apple, potato, onion or the likes and see what you like.
 
Perhaps this will be helpful?

This is a drawing of a 1.25" wide blade with a full flat grind that is .125" at the spine, if you were to sharpen it to 20 DPS (40 INC), and how the various behind the edge thicknesses will effect the height of the secondary bevel.

N47Cve.png
 
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