Addendum to Will York's "Carson Mod 4" post

Bronco

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In the aftermath of Will York's recent excellent review here of his Carson large Model 4 folder, Will contacted me privately soliciting my opinions on Kit's 420V (S90V) blade steel versus other blade steels in my experience. I gladly gave it my best shot, and Will subsequently asked me to consider posting my response here on the Review forum as it may contain some information that could be of use to other fellow forumites.

So, without further ado, and in it's entirety, my response to Will:


Hi Will,
Nothing would please me more than an opportunity to wax eloquent with respect to the properties of Kit's 420V blades.

1) Cutting efficiency- To point out the obvious first, I think there are several aspects of Kit's overall design of the Mod 4 blade that lend themselves well to efficient cutting, most notably the generous width of the blade, and the deep hollow grind. That having been said, I actually found the out-of-the-box edge on my blade to be a bit on the obtuse side. Don't get me wrong, the blade was extremely sharp, but I estimated the original edge bevel to be at an included angle of approximately 50 degrees. In this configuration, the blade easily handled everything I threw at it. Now I'd be lying if I said I use my folders in the same way I use fixed blades, but I did spiritedly attack some hardwood (maple, mahogany) scraps just to get a feel for the durability of the edge at this angle, and as is probably no surprise, I encountered no chipping, rolling or indentations of any type.

Kit has obviously earned this reputation for making hard use folders and I considered at the time that this initial edge geometry was likely something of an insurance policy against those overly enthusiastic customers who might want to aggressively determine if their knife is in fact worthy of this reputation. That's just speculation on my part, and largely a moot point, because the blade performed so well out-of-the-box as it was, but in any case, I soon became interested in finding out how the blade would perform if I thinned out the edge a little bit. I sent Kit an email and asked for his opinion regarding how he felt the 420V would be able to stand up to a thinner profile. Here's a portion of his response from May of last year which I can't imagine he'd mind me sharing with you:

<font face="Verdana, Arial" size="2">"I do sometimes put a thicker (usually between .020 and .025) edge on my blades. There is no problem with you fine tuning it down to what you are comfortable with. I'd like the feedback and may need to do that on the 420V blades.</font>

So I set to work to do a little thinning out. This turned out to be one of the first blades I reprofiled with my then new Edge Pro Apex sharpener. Using the color coded edge angle scale on the Apex, I began reprofiling the blade to arrive at what I thought would be a new included edge of approximately 40 degrees. What I didn't realize at the time, but have since figured out, is that the angle scale on the Apex is only accurate for blades that lie flat on the support table (i.e. when the centerline of the blade remains perfectly parallel with the top of the support table). This seems pretty obvious now, but honestly escaped me back then.
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Because the Mod 4's hollow ground blade is already at an angle when first set on the support table, I actually ended up putting a new edge bevel on the blade at an included angle of what is probably closer to 22 degrees. Here's a bit of my response to Kit describing the performance of the new edge angle (which included my unfortunate angle miscalculations):

<font face="Verdana, Arial" size="2">"Somehow, I'm even more excited about carrying this knife around with me now, than I was before. I wouldn't have thought that possible. Based on the Apex' color coded marking system, the final included bevel angle is right around 42 degrees. I guess only time will tell, but I think this angle is going to be just fine with the 420V. I used it a little bit this weekend on a woodworking project to clean up some rabbit and dados cuts. Nothing too strenuous, but the work was done exclusively on hard maple and did include some occasional sideways pressure on the blade edge. Bottom line- the performance was great. The blade went through the maple as if it were pine and there was no discernible loss of sharpness whatsoever. I'll be sure to let you know of any significant future developments either good or bad."</font>

So, while I have made some progress in the interim telling the difference between a 25 degree edge angle and a 40 degree edge angle
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, even at the actual included angle of 20 to 25 degrees I was getting some excellent performance in terms of durability initially. Overall cutting efficiency, as you might imagine, increased significantly. But, even though I have maintained that edge geometry on my Mod 4 ever since, I would not now be inclined to recommend a bevel angle that terribly acute for Kit's 420V. Last fall I was helping a buddy set up for a backyard party. While hanging up a pinata for the kids I was cutting through some ratty old, dirt encrusted 3/4" polypro rope. I evidently impacted something hard that was embedded inbetween the strands of the rope and ended up chipping a small portion of the blade near the tip. The chip wasn't deep, but did span several millimeters of the edge. In all fairness, this damage did occur in an area near the tip where, due to the nature of my sharpening technique with the Apex, the bevel angle was even slightly less than the aforementioned 20 to 25 degrees. But, be that as it may, I would think at this point that a true included bevel angle of approximately 30 to 35 degrees would provide you with just about the optimal balance between good cutting efficiency, and reliable durability for a the widest range of tasks commonly encountered.

2) Edge aggressiveness- I've experimented with both 3000 grit mirror polished edges as well as somewhat rough 220 grit edges and found that Kit's 420V accommodates both very well. In the high polish mode I can get edges as sharp as I've ever gotten with any other steel. As long as you take your time, resist the urge to use too much elbow grease, and allow the stones to cut through the vanadium carbides rather than break them off, your efforts will be rewarded with very, very sharp edges. (I'm suddenly struck by the utter absurdity of this situation in which I'm giving Will York advice on how to sharpen blades with high vanadium carbide contents
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) In addition, I think you'll be impressed with your blade's ability to resist dulling when finished with a 220 grit edge, should you ever have the need for an edge biased heavily toward pull cutting efficiency.

3) Edge holding- I have yet to do any Cliff Stamp-like controlled testing which could put a figure on this in absolute terms, but suffice it to say that the edge holding properties of Kit's 420V are excellent. In my experience thus far, I've seen wear resistance characteristics for 420V that put it on a par with CPM-3V. Due to the chipping that I encountered (under admittedly extreme circumstances) I would have to give the nod to 3V in terms of actual edge holding, but assuming you don't make the same rookie sharpening mistakes I did, I think you'll be quite pleased with 420V in this regard.

4) Resistance to chipping and rolling- Based on the anecdotal evidence presented above, I think we'd be fairly safe in concluding that 420V is more likely to chip out cleanly than roll and deform. Again, we must recognize that this occured at a somewhat extreme edge angle, but I suppose it is telling nonetheless. If forced to make a comparison I would probably rate the toughness of 420V at, or slightly below, that of Paul Bos heat treated ATS-34. Assessments of this sort are extremely subjective, however, and influenced by a great number of variables, so please take what I say here with a large grain of salt.

5) Rust resistance- I may not be the best one to provide any meaningful comparisons here, simply because of the climate in which I live. The humidity is relatively low and it's fairly rare that one of my folders will be subjected to a thorough sweat soaking. Likewise, it's not often that the salt air coming off the ocean spans the mile separating my house from the beach. Still, it's probably worth mentioning that it's been three or four months since I've treated the blade of my Mod 4 with lubricants of any kind, and there's not even a hint of rust developing. It appears to my eye that, however Kit beadblasts his blades, the result is an extremely even and much smoother (almost frosted) finish than I'm accustomed to seeing on other beadblasted knives. I wouldn't be surprised if this afforded his blades more corrosion resistance than is normally encountered on your typical beadblasted blade.

So, to (finally) bottom line this thing, I'd have to say that 420V is probably my favorite folder blade steel of all at the current time. I have blades made with steels that can certainly endure more abuse than 420V, but none that are demonstrably better in terms of taking a razor sharp edge, or holding that edge for a long time. Also, though you're probably already aware of this fact, it bears repeating that Kit couldn't care less how many owners one of his blades has had in the past. If you ever need anything adjusted or repaired on your folder, just send it to him and he'll take care of the rest. Hope that helps a little and hope you have a great weekend.
s, Bill

In closing, it should be noted that I have maintained that same 20 to 25 degree edge bevel since the reported chipping incident and have experienced no additional chipping of any kind.
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------------------
Semper Fi

-Bill
 
Joined
Jan 21, 2000
Messages
8,888
Now THAT's a review!

It's not often we get that kind of detailed feedback on long-term use from someone who knows what to do with a blade.

Thanks, pard.

-w
 
Joined
Jan 21, 2000
Messages
8,888
For anyone using an Edge Pro system, a close look at Bronco's remarks above can be a big help in accurately re-profiling a blade. I have the system but have used it only to restore edges--I've done all reprofiling to date on a belt grinder. However, I intend to use the system to reprofile a couple of high-dollar, one-of-a-kind blades in the near future, to avoid taking away any more steel than is absolutely necessary. If I hadn't been aware of the pitfall of miscalculating the edge bevel angle, which Bronco illustrates so well above, I'm sure I'd have made the same error he did. This would have resulted not only in taking off more steel than I intended, but would have required another reprofiling job to correct the problem, meaning even more steel loss.

Thanks again, Bill.

-w
 

Bronco

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Joined
Feb 25, 2000
Messages
7,546
Will,
I'm glad the Edge Pro tip helped out a bit. It's a minor consideration, but a potentially important one. The payoff will come, though, when you see the perfect edge bevels that result from reprofiling with this excellent sharpener.

------------------
Semper Fi

-Bill
 
Joined
Jun 13, 2000
Messages
736
Bronco,

I have to agree with your assemment of Kits bead blasting. I don't know how he does it or what he uses...but it is very fine. It almost looks like a super fine tumbling job. I might have to put the scope on this....
 
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