Sharpness Testing Machine

Has anyone else around here built one of the sharpness testing machines designed by Cliff Stamp and BassLakeDan? It's a pretty cool concept and allows for nice empirical data in at least one dimension measuring "point sharpness" meaning it measure in grams the force needed by a blade to rupture/cut a specific medium. Here's a picture of Sarah using ours today:



We're in the process of building a new machine which is much more automated and will allow us to program the style of cut to be performed on various media e.g. we will be able to specify push cutting vs a big range of slice/draw cutting options. With it, we can track initial sharpness of an edge against a specific media and how well that edge holds up over time. We'll be investigating edge geometry and finish on like blade samples to find optimum edge configurations for different things people want to cut.

Here's a sample graph of the kind of data we're currently collecting:

 

The whole idea of testing sharpness IMO isn't relevant for kitchen knives. They aren't used for shaving. And even a pretty dull knife would still cut well if it's thing behind the edge and has good geometry. That being said I don't see any practical reasons for pursuing ultimate sharpness on a tool that is probably going to be in contact with pretty dense things (cutting boards, seeds, hard root vegetables etc).

When sharpening my knives I usually slice some paper to get an idea of how consistent the sharpness is across the edge. And then I try cutting tomato and that's the best test for me.

 

I shave my arm hair or cut paper.

 

I have lot less empirical method , my left arm hair or
Cold potatoes

 

Your point is well taken. There are some pretty good reasons though for considering your finish that go to edge retention and also to quality of the food you prepare. For example, edge geometry and finish x might have the highest initial sharpness but degrades quickly whereas edge geometry and finish y has only slightly less initial sharpness and maintains a much higher sharpness average over time.

A fun study I did relates to shelf life of produce after being cut with knives with different edge preparation. The results were pretty dramatic:

The above sections of celery were cut from the same stalk with two identical knives with different edge preparations then sealed and refrigerated. The photo above shows them after day 2.

The image above is of the same test at day 9. Again, these sections were all cut from the same stalk of celery.

 

Clay , I should have elaborated bit with more about cold potatoes . In my opinion cold potatoes are the one of densest things a kitchen knife will cut and I have 10pound bag in my pantry any time . When a blade is finished , I start cutting a cold potato from tip to heel about 20-30 slices , then horizontal slices . All of them are push cut . If there is any area that is less sharp than ideal I can feel it because there is no extra weight of the handle to push trough

 

This test makes sense! It's repeatable and goes to exactly how you use the tool. Plus you probably get to make something good to eat afterward. What geometry/finish have you found to be the most successful in this test?

 

Highly asymmetric and not much polished but again it still depends on the preferences of the user , thin blade versus thick blade , tall versus short , low nose , high nose , pointy tip ... And the list goes on . There wouldn't be a perfect answer that applies to all

 

Asymmetric as in different angles or same angles but different sized bevels? The asymmetric majority of blades I've studied are 70/30 for bevel size with the same angles but that's not necessarily a good sample of what's out there, just what I've come across.

 

Same angle sharpened but more like 70/30 , another point is the food release , I wouldn't mind sacrificing some thinness or sharpness if it is going to make it is easier with the food release.

 

nothing worse than a cold refridgerated peeled potato soaking in water sticking to a blade when you have 10 gallons of them to dice for the friday chowder... But yes, cold potatoes are great. I like to use onions on the tip but I think I use the tip of my knife a lot more than the heel and middle.

 

A bit over the top, but pretty cool. I usually just cut some produce...Great illustration with the celery. Every cook here is likely cutting fresh every day if not every shift.

 

Thats a little much for me, like most I cut something for feel to see when I'm done rubbing metal on rocks.....

 

whether it's ultimately needed or not, research is always commendable in my book. cheers

 

So, what did you prepare with the 3 slices of 9 days old celery??
I guess youve discarded the other 3?

Good that someone here actually cuts food after sharpening

 

I too have a slight distaste for shaving and slicing paper after sharpening, to me they seem like not the best test of a kitchen knife.Funny I've never had either one on my prep list. Fiskar scissors will cut paper and disposable razors will shave...
For me I go to the thumbnail and maybe the three finger but not as much.

 

Yes, exactly.

One other thing is to quickly check if the knife is sharpened properly by using nail or TFT, and other again to check sharpness by immediately slicing half a dozen newspapers.

 

Man, that 3 finger test would get your totin chip pulled!

 

I'm personally working towards slicing a silk scarf in mid air. that's when i will know I'm good!

 

You are sure your nickname shouldnt be thedisbodyguarded? :cool1ump