Polished vs Non Polished Edges Cutting Results

[Ankerson]

During the rope cutting testing we started to see something that has been known, but never really shown in cutting results data wise here.

Part of what I was doing when I did the reviews on the 2 Phil Wilson knives was seeing what the difference in performance is between Polished and Non Polished edges and record the differences. Phil thought that the scratches in the non polished edges were stress points that cause the edges to break down faster so we put it to the test.

The testing Process was as follows:

Cutting 5/8" Manila rope on a Scale with wood to cut on. The scale was calibrated for the weight of the wood. Making 3 to 4 slicing cuts from back to tip using the least amount of down force needed to get the starting down force. Once that was established 20 cuts were made then down force was tested again and that continued until 20 LBS was reached. Edges were at 32 degrees inclusive.

The testing method is accurate to + or - 10 cuts and + or - 1 LB as was verified doing a blind test of blades of unknown hardness until they were tested after. 2 blades of the same hardness and steel, sharpened the same and same model of knife.

M390 (62)

Starting Down force Non Polished - 13 LBS

Starting Down force Polished - 12 LBS

Ending was 20 LBS for both edges and a difference of 80 cuts or 21% in favor of the Polished edge.

ELMAX (62)

Starting Down force Non Polished - 14 LBS

Starting Force Polished - 12 LBS

Ending was 20 LBS for both edges and a difference of 60 cuts or 19% in favor of the Polished edge.

 

[singularity35]

Nice work Jim. Now we know what those mirror edges are good for except just looking good.

 

[Ankerson]

Nice work Jim. Now we know what those mirror edges are good for except just looking good.

Thanks, we wanted to use his knives so the differences would really show up more so than with production knives as in number of total cuts made.

 

[DennisStrickland]

jim this is a very accurate rest & the difference in only 2% between the 2 alloys validates 2 factors
1--the polished edge factor was verifiable as significant
2-- the fact 2 very different alloys tested showed only 2% variance substantiates the accuracy of the tests.
your efforts have been exhaustive & extremely through.thanks man
dennis--p.s. i believe unit & either so-lo or sodak did some tests also showing similar results between polished & un polished edges.

 

[singularity35]

How did you determine that sharpness of the polished and unpolished edges were close? Weren't the polished blades sharper to start with?

 

[Ankerson]

jim this is a very accurate rest & the difference in only 2% between the 2 alloys validates 2 factors
1--the polished edge factor was verifiable as significant
2-- the fact 2 very different alloys tested showed only 2% variance substantiates the accuracy of the tests.
your efforts have been exhaustive & extremely through.thanks man
dennis--p.s. i believe unit & either so-lo or sodak did some tests also showing similar results between polished & un polished edges.

Thanks Dennis.

Like I was saying this would be posted before the rest of the cutting data on the other steels putting them into categories by edge retention.

20% is really a huge difference, larger than I thought it would be, but this is how it worked out.

 

[Ankerson]

How did you determine that sharpness of the polished and unpolished edges were close?

The polished edges were tested by slicing TP clean, my standard of sharpness for testing all the knives with polished edges.

The non polished edges were tested by slicing phonebook paper as we know that a non polished edge won't slice though TP clean.

Starting sharpness really doesn't matter for this test as we were testing edge stability and breakdown differences between the edges.

The polished edges will lose that TP slicing edge quick then stabilizes over the course of the cutting while the non polished edge stabilizes faster before it starts to break down.

The sharpness of the edges will equal out within the 1st 30 cuts when the edges stabilize then towards the end the real differences really start to show up between the polished and non polished edges because it takes a lot longer for the polished edge to break down.

 

[singularity35]

Starting sharpness really doesn't matter for this test as we were testing edge stability and breakdown differences between the edges.

I didn't really understand this part but when you, Dennis Strickland, and Phil Wilson say so, I tend to take your word for it. :thumbup:

 

[Ankerson]

I didn't really understand this part but when you, Dennis Strickland, and Phil Wilson say so, I tend to take your word for it. :thumbup:

Thats because the edges will stabilize very quickly in the 1st 30 cuts or so or settle down as I say to the same level of sharpness. This is before breakdown of the edges even starts, this is also why some assume that the polished edge isn't really good over a non polished edge.

It's something you would have to see and experience looking at the cutting data of a lot of different steels. There is a pattern that develops and is consistant.

 

[singularity35]

Thats because the edges will stabilize very quickly in the 1st 30 cuts or so or settle down as I say to the same level of sharpness. This is before breakdown of the edges even starts, this is also why some assume that the polished edge isn't really good over a non polished edge.

It's something you would have to see and experience looking at the cutting data of a lot of different steels. There is a pattern that develops and is consistant.

I understand that better, thanks. Thanks to you and guys like you, i just need to read about what you have found out.

 

[gunmike1]

Great test with a huge amount of time and effort put into it. I can't wait to see how the rest of the tests with the different steels turned out. I am wondering how geometry factors into this, as Phil Wilson's knives are extremely thin and thicker factory knives might effect how easy it is for the polished edge to just drop right through the rope, but I'm sure your other testing will answer that question. I know with a very sharp coarse edge that tree tops arm hair and push cuts newsprint easily (usually DMT coarse) the knife really bites into thick rope when using a slicing motion better than a polished edge for me. Then again, when it is properly sharpened the polished edge starts out slicing pretty good (though not as good as the coarse edge for me), and it push cuts WAY better than a coarse edge. Also, once that polished edge initiates the cut on a slice, it starts to glide through the rope easier than a coarse edge, so I can see where the total force to cut the rope initially is less than with the coarse edge even if the starting force to initiate the cut may possibly be a bit higher. The coarse edge just feels much sharper to me initially because of the slicing aggression.

My CPM M4 Mule has done very well with a polished edge in processing a 400 lb. pig that I shot. I was wishing it had a coarse edge before we started cutting up the hog, but at the end it was still cutting like a champ, and maybe if I would have left it with a very sharp coarse edge it would have started getting to the point where it had trouble making clean cuts like the polished edge was still doing towards the middle and end of processing that boar. I do know that as you said that a wickedly sharp polished edge's ability to easily whittle hair goes away after the first couple cuts, but as you described it settles into an edge that keeps on cutting. Maybe the mind trick I have as far as the coarse edge staying sharper longer for slicing is that you don't have nearly as steep of a drop in sharpness as you do with the polished edge so I figured it is better for slicing for long periods.

One thing that would be interesting is to see if the mega carbide, mega Vanadium steels like S90V, S110V, and 10V do better with a polished edge than a coarse edge. They don't take a polish nearly as well as something like 13C26 or CPM M4, and at least for me S90V takes a great coarse edge and holds it for a really long time. I have come to just leaving my S90V Manix 2 with a coarser edge because it was real quick and easy and the knife seems to slice longer than when I take the time to really polish it out, but again that may just be a mind trick.

Again, great test and thanks for the effort.

Mike

 

[unit]

-p.s. i believe unit & either so-lo or sodak did some tests also showing similar results between polished & un polished edges.

I did something along these lines.

Perhaps my most popular videos...some day perhaps I will get back to making videos?

Regardless, there should be little doubt that a polished edge (and bevels) will offer less resistance to cutting...and the thicker the substrate, the more pronounced the reduction in resistance becomes.

Another (fairly obvious) note is that with very thick substrate, the overall thickness of the blade factors in heavily.

As always, thanks for the effort. A lot of people like to glance at this stuff and occasionally some wonderful soul will lodge complaints or even attacks...the truth is, this stuff takes a BUNCH of time, thought, and work to do in a meaningful manner. Props to all those who do it and share!

 

[miro44]

Very interesting, thanks for the test.
I' m quite surprised that it' s actually about 20% better with the polished edge, I expected alot less, something barely noticable

 

[Ankerson]

Very interesting, thanks for the test.
I' m quite surprised that it' s actually about 20% better with the polished edge, I expected alot less, something barely noticable

That's the same thing a lot of people thought because the coarse edge feels sharper to them because it's rough, but cut with them and keep cutting the differences really show up.

I have had people tell me that one of my polished edges was dull...

I was like OK bud.......

 

[unit]

That's the same thing a lot of people thought because the coarse edge feels sharper to them because it's rough, but cut with them and keep cutting the differences really show up.

I have had people tell me that one of my polished edges was dull...

I was like OK bud.......

That is funny! I had a similar experience that ended with the guy cutting himself. The look on his face was worth a million words. Polished edges do not "bite" they skip that unnecessary step and go straight into "media separation".

 

[Ankerson]

That is funny! I had a similar experience that ended with the guy cutting himself. The look on his face was worth a million words. Polished edges do not "bite" they skip that unnecessary step and go straight into "media separation".

Yeah I know what you mean.

 

[knarfeng]

Thanks for posting this. I look forward for to your further reports. I'd say more but Mike already said most of what I was thinking. I am not sure I understand what happens when an alloy that is dependent on abrasion resistant carbide chunks for its edge retention gets polished so that those carbides are fractured away and aren't as available to do their job. I'll be interested to find out.

One thing that may make your testing more complicated:
I noticed in my recent testing that even though the Gayle Bradley CPM M4 and the 710 M390 were equally sharp under the lens, the Gayle Bradley felt to me as if it took less force to cut. This was true from start to finish. I was cutting rope so that the blade shape should have had minimal impact. I have no explanation. Just an observation that may complicate your force measurements.

 

[Ankerson]

Thanks for posting this. I look forward for to your further reports. I'd say more but Mike already said most of what I was thinking. I am not sure I understand what happens when an alloy that is dependent on abrasion resistant carbide chunks for its edge retention gets polished so that those carbides are fractured away and aren't as available to do their job. I'll be interested to find out.

One thing that may make your testing more complicated:
I noticed in my recent testing that even though the Gayle Bradley CPM M4 and the 710 M390 were equally sharp under the lens, the Gayle Bradley felt to me as if it took less force to cut. This was true from start to finish. I was cutting rope so that the blade shape should have had minimal impact. I have no explanation. Just an observation that may complicate your force measurements.

Just got done with the GB, it cut well, I reprofiled it to 30 inclusive and polished the edge.

 

[hardheart]

I have been wondering about primary grinds and any effects on rope cutting. Since the rope is cut as individual strands, not even the full thickness at the top of the edge bevel would have an effect on the downward force of the cut. But depending on how the rope is held, there would be some compression of the rope that is in contact with the surface of the primary grind. The thinner/more acute the primary grind, the less of the downward cutting force would be translated to a force perpendicular to the blade surface, and a compression normal to that.

Something else that can affect perception of coarse edges is that the velocity of the blade as it moves in a slicing motion increases cutting ability and reduces effort in the cut. If you have a tendency to slice with coarse edges, then you may think it is the edge finish helping things out when it is also the slicing action itself also providing some benefit. But coarse edges also provide deeper cuts with less downward force in a pure slicing action, and polished edges cut more easily in a true push cut.

 

[arty]

Perhaps I looked through the thread too quickly and missed it, but how did you polish the edges?