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TOPIC: Sharpness Testing Jig

Sharpness Testing Jig 1 year 3 weeks ago #13237

  • wickededge
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PhilipPasteur wrote:
Clay,
Thanks for the link to the weight set. It looks like it would be easier to manipulate than the fishing weights, especially with the second beam in place.

I tried looking closely at the pictures, but I could not figure it out. How did you attach the second beam to the main arm? Maybe some rubber tubing just taped in place ??

I am getting interested...
:)

I took an 1/8" rod and taped it to the clamp with friction tape, though any tape would do. I added a spacer (two washers and a nut) at the extreme end to give the weights enough room to slide on the rod. I might add the third rod to make the whole system even more accurate. I think another change to make would be to balance the beam (and drill the hole at the fulcrum) with just one set of weights (250g) at the end of the bar. It would (I think) give me finer incremental adjustments when sliding the second weight set along the beam. To do it again, I might just use something heavy, right around 1/2 lb for the balance and then employ the two sets of slotted weight hangers on separate beams. The first set would add an amount of force not quite enough to cut the material, maybe 50%-75% of what's needed, and the second set would continue to add weight in fine increments to increase the accuracy. I've found that the quality of the slotted weight sets isn't critical, so I'd opt for 2-3 sets of the cheapest ones. I do like the flexibility of being able to add/remove weights as light as 5 grams from the sets.
--Clay Allison
Last Edit: 1 year 3 weeks ago by wickededge.
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Sharpness Testing Jig 1 year 3 weeks ago #13238

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I'm already starting to build some data and seeing some trends. At first blush, it looks like a blade sharpened at 15 degrees and finished w/ 14um strops is significantly sharper than a blade sharpened at 20 degrees and finished with .25um strops/. Go figure... :) I also noticed an impressive deterioration in the sharpness with progressive testings, due I imagine to the repeated force applied to the edge in each successive testing. It should be fairly simple to conduct some durability/edge retention tests using the methods Dan describes on his site. This is really fun!
--Clay Allison
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Sharpness Testing Jig 1 year 3 weeks ago #13239

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I added the third beam and it makes a big difference! I'm able to easily increase the weight by 1 gram at a time with no fears of going over by moving the weight too far.
--Clay Allison
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Sharpness Testing Jig 1 year 3 weeks ago #13243

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Continuing to have fun with this machine, thanks again Dan! I've starting to establish baseline values for different grits at the same angle:

Blade: Utility Blade
Angle: 15 degrees
Finish: 1600# ceramic
Strokes: 60+ per side till I hit point of diminishing returns
Grams of force needed to cut the media: AVG 200g

Once I've established a baseline for all the stones, I can start to experiment with different strops, angles of stropping etc... All of a sudden the possibilities of things to explore and test are gigantic and slightly overwhelming, in the best of ways possible.
--Clay Allison
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Sharpness Testing Jig 1 year 3 weeks ago #13248

  • LeoBarr
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Wow that will turn into some very useful data it is probable going to necessitate an awfully lot of testing and then there are all the different types materials & Rockwell Hardness to consider .

I think for the WE user this will be incredibly valuable information.

I think the angle is absolutely in hand with sharpness we know that more acute angles are used on blades for chopping and general abuse and suit softer steels whereas the really low angles like a razor blade 12Ëšor less are suited to slicing and have a high Rockwell hardness.

How many cooks and chefs love to use Japanese knives but use them incorrectly for chopping and often are nor disciplined enough to even cut on the right materials - too many sadly ! Still they generate business both for the manufactures and for us so it is all good.

I have found that since I have got into sharpening knives I almost have sympathy pains for these poor abused blades.

I like the testing device it looks cheap to make some real old school design went into that I imagine it gives very consistent results.
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Sharpness Testing Jig 1 year 3 weeks ago #13249

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Some more preliminary results, all at 15 degrees:

Superfine 1600# = 200g
Microfine 0.6um = 185g
14um Strops 10 strokes = 175g
14um Strops 20 strokes = 195g
14um Strops 30 strokes = 220g

These are quick results, not well documented yet as I'm still just getting a feel for the testing methodology, the data collection, the machine etc...

Still, it's fascinating to see the rapid improvement from just a little light stropping, at a much coarser grit and then see the edge degrade rapidly with additional strokes. What I've seen so far gives me some ideas for setting up a few tests to see if this preliminary data holds up and then maybe we can come up with some theories to further test. I already have some educated guesses about the strops but will hold off any judgement until we have enough data to be confident.
--Clay Allison
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Sharpness Testing Jig 1 year 3 weeks ago #13251

  • razoredgeknives
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Definitely following this thread w/ interest!! Nice job btw Clay on the build! I really need to build one myself...

Ok, so who's going to start the data entry and create some neat looking graphs? lol

So what test media to degrade the edge and test edge retention (in the future of course) will you use Clay? Something that is consistant but not too abrasive...hmmmm

I am really interested in if this will be able to be used at some point in the future to rate the slicing ability of any given edge...

Good work again!! Thanks for investing the time, the Lord knows I don't have any extra right now lol
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Sharpness Testing Jig 1 year 3 weeks ago #13256

  • BassLakeDan
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wickededge wrote:
I'm already starting to build some data and seeing some trends. ... I also noticed an impressive deterioration in the sharpness with progressive testings, due I imagine to the repeated force applied to the edge in each successive testing. It should be fairly simple to conduct some durability/edge retention tests...

Yes, this is a common observation when one begins testing blades with the jig. Since the jig is very much more sensitive than non numeric testing methods (paper slicing, hair whittling, etc..) it surprises and hits everyone over the head when you see that (and realize) that sharply apexed steel is actually a very very delicate item and deforms and degrades very rapidly with initial use. The slope of the curve of degradation is extremely rapid. Of course, this is counter intuitve, as we build bridges and freeway overpasses out of steel, so in any form it is strong and permanate?, or so we think. All our understanding of steel works for us in everyday life, until we use it at its extreme application: cutting edges where apex edges are measured in microns.

using the scotch tape media to do this type of testing is described in detail on the jig tester site. Excel spreadsheet templates are provided to record and graph this type of testing: http://www.howsharpisit.com/Edge_Retention_Tests/Template_Degradation_Testing.xls
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Sharpness Testing Jig 1 year 3 weeks ago #13264

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It is interesting to note that extremely low sharpening angles do not retain their sharpness for long.
Yet we know that a descent thinning bevel before the primary cutting bevel makes for a perceptibly keener edge .
What I would be really interesting to see is the effect of compound bevels so a thinning bevel with a fine cutting bevel topped by an acute micro bevel .
I brought this up elsewhere in the forum - Japanese Knife Imports posted a video on this a couple of years ago so what they say some of the top-line Japanese knife manufactures are doing is on top of the normal cutting bevel of 15-16Ëš they are putting a micro-micro bevel nearing 40Ëš on top of this thus beefing up the blade edge whilst retaining the characteristics of the low angle bevel. It seems to make absolute sense to me and it would be interesting to see repeated sharpness tests to either prove or dis-prove this method. I suspect that these Japanese knife manufactures know what they are doing since they are some of the best blade-smiths in the world . It would however be very interesting to see if this holds as an acceptable finishing to maintain an edge for longer. I include a link to the video showing this albeit done on water-stones.
Last Edit: 1 year 3 weeks ago by LeoBarr. Reason: spelling
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Sharpness Testing Jig 1 year 3 weeks ago #13269

  • mark76
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Really nice job! And very interesting results... Looks like I've got a project to do :cheer:
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