Geometry and Steel HELP!!! --- ...---

Shane Wink

Shane Wink

Well-Known Member
Some topics or questions are just so hard to ask in a forum but here is one that has been bugging me for a while, How to know how steep to grind the bevels and how to setup the edge geometry for different steel. In my case O1 for an outdoor knife. The reason I ask about this today is that I was reading www.cliffstamp.com/knives/reviews/blade_materials.html#C_52100 and on the site there was mentioned many times about improper angles for the steel being used that caused failure or premature dulling from the metal fracturing or shearing off.

I want to do the best job that I can and am very OCD about knowing things are done correctly and this is just bugging me to no end. Honestly I have never given much thought about how steep the bevels are, nor was I told it mattered. All I do is flat grind to .015 then convex the edge and finish up on the strop. The blades cut well but how do I go about figuring out the best geometry for a given purpose and steel to get better cutting results?

I have entered a makers challenge and knew going into it that I would step out of my comfort zone and it would be a good learning process also I am sure I will make the rest of the guys that entered look real good! What I did not know was that when I buckled down and started designing a knife for the tasks that the blade will be subjected too was how much I took for granted on optimum geometry and how much I just dont know :sad:

If someone is willing to take the time and post some information or wants to exchange emails or phone calls on my dime I promise it wont be wasted. I am not looking for someone to design anything either I will do my own work, just want to know how to attack it and why.

Thanks
shane
 
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It is the honorable thing to do the best you can, and also to ask if you don't know. From my experience it is more a matter of what the knife is being used for rather than
the steel type. For instance, the angle of filleting and kitchen knives could be okay with a 10 or 12 degree angle as compared to hunting or heavy duty camp knives, which
should have a steeper angle like 16degrees and more if the knife is used for limb cutting etc, and extemely cold temperatures may also be a factor for the steeper angle.
 
Shane,
I didn't read that gentleman's post because I don't have to, Nothing against him, Don't know him? and he may have good things to say?

Making knives and testing to destruction is the way I and most makers that want to learn for themselves & really understand what is going on do it!

Hers is what I recommend and what I did when I started,

Take a favorite knife that you respect,of the kind you wish to make and analyze every aspect of it.

Them built a knife with what you feel are improvements.
Then work the blade to death! Analyze what happens and when and then incorporate that knowledge into your next knife.

Then repeat the process.

You can read what someone else say's about all the aspects of making the perfect knife? Or you can do it until you understand what it takes to make what you feel is the perfect knife?

Laurence

www.rhinoknives.com
 
Thanks guys, Charlie those angles are general guides that are passed around but each steel has its own characteristics that allow the angles to be as steep or obtuse as they are. Choosing the steel to meet the task then choosing the right angles for that steel would yield better performance I would think. An example would be say cpm 3v and 5160. If you gave 5160 the same thin edge you would give cpm 3v on a chopper the 5160 edge would likely fail as cpm 3v . Of course this too is subjective as well when considering at what RC the blades are as well but it was a simplistic attempt of an example. I am talking this from my experience with both steels and it may also be error on my part in geometry that caused the above results.

Laurence, thanks as well. You are right and I have 2 identical blade profiles on the bench but of different thickness for the first run of test and I will be placing an order with aldo soon for more, however I had hoped there would be an easy answer lol even though I knew there was not. I also have the exact same profiles in 3v and will be doing a side by side comparison. I have more experience with 3v and am more comfortable with its geometry than the other steel but its not cheap :)
 
I think that you can see that steel selection is only one aspect of choosing an angle for a finished blade. Yes O1 might need a different secondary bevel than, lets say, 1095 but it will also depend on how it was heat treated. O1 that has been heat treated by preheating and then holding at 1450-1475° will behave differently than O1 that was austinized with a torch. The thickness of the steel also comes into play as well as the intended purpose. You would undoubtedly choose a different angle for the secondary bevel for a chopper made from 1/4" stock than you would for a caping knife knife made from 1/8" stock. Also the shape of the secondary bevel comes into play. A convex secondary bevel will be stronger than a flat secondary bevel, all else being equal, but it might not be as good a slicer for some applications. Remember that form follow function.

Doug
 
Shane, I wrote this a few months back (come to think of it, about a year ago) to help calculate your angles. As for finding the correct angle per your steel choice, it depends on a number of factors; namely purpose and heat treat. I have O1 kitchen knives at about 62ish HRC with 10* inclusive angles that do great in the kitchen but would fail horribly anywhere else. For my choppers, I love 1084FG from Aldo as it can take some punishment and is very affordable. I've tested more knives to destruction this past year than I sold and have learned quite a bit about geometry, heat treat and purposing a steel per the job to be performed. Not that these is only one steel per application but this is what worked for me.

https://docs.google.com/spreadsheet/ccc?key=0AhJg7rJKBKEvdGNMcTRtTGdtTmdtMXNCVmVGYmRaWkE#gid=0
 
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Shane, I am glad you decided to post about this. Geometry is talked about a lot but I feel the discussions that I have seen, ( I do not exactly go looking for them or have done a search ) lack reasoning and "data" that proves why an improper angle was the reason behind something. There are a lot of different aspects when it comes to proper working blades, geometry only being one of them.

I hope we could take the time and talk about it and see how it progresses...
 
Hey Doug I am sry I did not respond to you but you are absolutely hitting on all cylinders. I will be using a baseline heat treat during the testing. For O1 I will be following the information listed on Kevin's website utilizing the lower austinizing temp and doing a 7 second interuppted quench to manage plate martensite formation and stress relief with the auto tempering effect.

There are so many variables to control having as few wild cards as possible is key in interpreting the results. In any case I knew going into the contest I would learn far more than by not entering.
 
Laurence said:
Shane
All quality materials have there cost. I started my Rhino Vegetable knife out of 440C with a RC of 58 because it was a bit less expensive and a little easier for home Chefs to sharpen. After a decade of getting feedback from customers and making small improvements in angle of handle, finger cutouts, adding relief holes to keep food from sticking, modifying the tip,dropping the steel thickness from .125 of a inch to 0.98 etc and then moving to CPM-154 and increasing the RC to 60.

This current version is well received and I don't see anymore refinements in the near future but I am always taking in feedback and getting to examine my knives as they comeback in for sharpening & tune up's.

My point here is for me, I will always be searching for those improvements that I can make and will never say that I am done and won't make anymore changes.

If it makes it work better, than I will do it and refuse to let my ego say it's now perfect.

Have fun and enjoy your work!

Laurence

www.rhinoknives.com
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