Sebenza Blade Centering - Measurements & Observations

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hondahirny

hondahirny

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Just want to start out by saying I like both my Sebenzas very much and intend to keep them. This is not meant to be a CRK whine and cheese thread, but rather some info to the CRK community on possible causes to any blade centering issue found on a Sebenza. It certainly seems my experience is not unique, so this may apply to other blades as well.

Short version of the paragraphs below - the blades are not straight on either of my Sebbies. Read below for how I got to that conclusion.

Having read a few threads recently, a few folks commented about their new Sebbie's blade being off-center. I own two Sebenzas, both from April 2012. My large Insingo was bought new from a dealer, while the small micarta Insingo was purchased LNIB from a BF member. Both knives were received with blades biased towards the lock bar. Both have been cleaned and lubed a few times now, so things are better broken in. By following the published CRK procedure for cleaning and reassembly, I was unable to produce any visually noticeable difference in centering. In a way, this tells me that the tolerances of the assembled are such that reassembly is a very repeatable process.

I used a Mitutoyo digital caliper for all measurements, model 500-192-20. A fine knife deserves a fine tool to be measured with :D I measured the Ti scale spacing to be 0.1530". This puts a centered blade at 0.0765" from one of the scales. On my Sebbie, my blade tip measured 0.0650" from the lock side. This puts the blade at 0.0115" off center. Visually, the blade looks center from the spine side of the knife, but looks slightly off when looked at from the other side. Can't figure out why, but that's what I see, vs what I measured. For reference, the plastic card stock used for credit and debit cards is 0.030". So, my large Sebbie is off center by 1/3 the thickness of a credit card.

On my small Sebenza, my scale spacing was measured to be 0.1440". That puts a centered blade at 0.072" from the scale. My small Sebbie measured only 0.0555" from the lock bar side, or 0.0165" off center. To me, that extra few thousands is far more visually obvious on the knife.

Ok, so my blades are off center. Next thing was to find out why. I was able to devise a simple fixture where i could hold the blade pivot area on a flat surface and scratch a block of aluminum with the tip of the blade. I was then able to flip the blade and mark the aluminum block again. A "perfect" blade should produce the scratch in the same spot from either side. In the case of both my blades, that didn't happen. The better centered large blade produced scratches about 10 thousands apart, while the small blade (the worse one) was about 20 thousands apart. The absolute values of these measurements may not be right on, but visually, there was a clear difference in the scratch spacing between the two blades.

Next steps were to take a straight edge to the flat portions of the blade and see if I can find any bowing. I found that on my small Sebbie blade I saw lots more light in the gap on one side of the blade than the other.

To me, the amazing thing is how consistently my Sebbies go together. While they're not perfect in every way, the tolerances are most definitely better than any knife i've ever owned. It appears that with some Sebenzas, the blades themselves are not perfectly straight. This would also imply that given proper assembly, centering the blade will not be normally possible. If the scales are straight and the washers uniformly thick, there's no reason why a straight blade would not be centered. A slightly bowed blade however does not stand a chance. That seems to be the case with my two Sebbies.

I'm debating if I want to send them in. I like using them both and don't really want to let them out of my sight. Anywho, just a bit of info for fellow CRK owners. I'm not saying all blade centering issues mean a bent blade, but it seems to be the case for me.
 
I would send them in to be inspected and made right if found to be manufacturing defects. But that's just me. Maybe they will find that a certain batch was affected. People should speak up and contact CRK directly to discuss these issues.
 
Interesting measurements and methods to determine centering. (Also very picky, but let's just call it being a "discerning" customer.) :)

I would never have suspected a slightly bowed blade, and I wonder what causes that in manufacturing. Then I wonder if it also is the reason for other blades being off center in other knife makers...

Either way, I think something that minor, you'll learn to live with. I just checked the centering on my two sebenzas. My small is visually perfect (not sure what would happen if I used calipers). But my large turns out to be biased to the non-locking side. I've owned it for over a year and never really noticed...other than maybe in the honeymoon stage in the beginning.
 
It would be interesting to know how these measurements compare with similar knives. Also, do you think my $20 digital calipers would be acurate enough for me to try your method?
 
Not to be confrontational, but I think blade centering as a quality metric for a working tool is over-rated. While there's cause for concern if the centering interferes with function, I just can't embrace the whole blade centering controversy as a means to be alarmed, especially if at some angles it looks centered to the naked eye.

We all have our own perceptional on what's acceptable (for any product) and therefore, what may be of concern to me may not be of concern to others and vice versa; so, one size clearly doesn't fit all and that's ok too. It's just that if we resort to dissecting working tools with precision instruments of measure, I think we'll find measurable data in tolerances that wouldn't otherwise be prevalent to such a punctilious degree.

I liken this to tool marks. With a naked eye, we may not notice much, as the product appears aesthetically pleasing. But, under a macro lens, it's a completely different story; much like a blade edge under a microscope. Just my observation folks. I want an aesthetically pleasing tool that function 100% of the time and is guaranteed for life to just that, if they pass the microscope test, well then, that's just a bonus.
 
I'm not suggesting people go out and call CRK to tell them their blade is a few thousands off-center. My large is close enough to where I'll probably leave it alone. My small is bugging me a bit, so I'll call CRK about it.

On knives with looser tolerances, you can often bias the scales and make a blade centered. I've been able to do this often, so never really looked for blade straightness much. In the case of the Sebenza, the knife is so precise, that there isn't much one can do, short of blade replacement or somehow straightening the blade. I'm certainly not taking a hammer to my Seb. I'll let CRK do that :)

In terms of performance, I'd say it has zero effect. If it's not rubbing the liners, there should be minimal impact in usage.

It comes down to customer expectations. Generally, more expensive products call for greater expectations. It's a large gray area. Some folks are more picky than others.

BTW, I heard the heat treating process can cause blade warpage. It may be the reason for the slight bend in my small Insingo.
 
Just got off the phone with CRK. I will ship my small Insingo to them for evaluation. I'll be sure to update you guys once I get it back.

Their customer service really is excellent thus far for me.
 
hondahirny said:
I'm not suggesting people go out and call CRK to tell them their blade is a few thousands off-center. It comes down to customer expectations. Generally, more expensive products call for greater expectations. It's a large gray area. Some folks are more picky than others.
Click to expand...
I totally agree with the fact that it boils down to individual customer satisfaction; especially when you're paying a premium price for a premium product. Hope my previous post didn't come across as a negative towards folks who feel as though their product expectations weren't met. I'm actually looking forward to your resolution report.;)
 
Highly doubt you have a warped blade. I think the most likely cause of the slightly off centered blade is from any sort of grinding imperfections. You grind off a little more steel on one side compared to the other side and now you have what looks like an off centered blade. Your scratch test proves this theory imo. You also have to consider that the lockbar side cannot be perfectly straight because it is being pressed in to the detent hole so it may look like there is more space on the non locking side. I've measured the centering with cheapo calipers on every single sebenza/umnumzaan that has passed through my hands and the centering was never 100% perfect when you get down to that many decimals (not possible really) but it was always just barely off like you showed. This bothered me until I measured my other knives that I considered dead balls centered to my eyes and under magnification. For example my Sage 2 and even my SNG looked absolutely dead centered to me and more centered than my large sebenza so I measured it with calipers. What do you know, the Sage 2 and SNG were considerably more off centered than my Sebenza. The gap between the blade and scales of a CRK folder is so tiny that even smallest variation in blade centering looks more off centered than a folder with a much larger gap like the Sage 2 or Strider SNG. Kind of like an optical illusion or something. Honestly I would not have sent in your small sebenza because it really is ridiculous if you think about it but I dont blame you for being that picky. Just seems like NO other mid tech production company has to deal with caliper wielding, psychopathic, OCD customers like the ones you find on this forum :) (myself included).
 
I find this discussion interesting. Its true that expectations for centering, etc is directly tied to how much I've spent for a knife. And the sebenza I recently purchased is the most I've spent in my short knife collecting experience, so I guess I was expecting 'perfection' like those I'd held and seen online, but mine too was off center. I played around with it for a few weeks and finally decided to send it back to CRK and see if they can make it any better. We'll see how that plays out.

BFC07EED-1CF2-414A-AEFB-141F9958089D-10464-00000A67E74006E1-1.jpg
 
THAT is off centered by anyones standard and I've actually never seen any CRK that off centered before. I assure you that the off centering issues you are reading about in this thread are nearly imperceptible at a glance. We're talking decimal points off centered. You should be upset and I'm positive CRK will fix that for you.
 
From a purely manufacturing aspect- What are the tolerances for the various parts? I wonder what's measured and spec'd out for the blade? I'd love to see the Design Drawings :D

From the few I've seen they appear very consistent so that speaks of good process control. The one above Not so.
 
I think CRK has the pickiest customers. I guess that is what they get though for pricing their knives to the point where you expect THOUSANDS of an inch perfection. I wouldn't send mine in. I own three sebs and all seem perfectly center to me but I'm blind as a bat.
 
Did my best to keep the perspective as straight as possible. While the blade tip is clearly off center, it does not affect function of the knife:

offcenter.jpg


I redid my measurement on the computer, using Photoshop. I got pretty much the same measurement, with the blade tip being 15 mils off center. You guys like that better? Mils? How about MILS! Maybe it's an acronym that means My Insingo Lacks Sentering (I know, a bit of a stretch, spelling-wise). Now when you choose to marginalize my opinion, you won't have to type nearly as many capital letters. :D

The point was to educate folks a bit about my experience. I've been on here for a while and it seems every time anyone says something possibly construed as negative about a CRK product, the fanboys have to chime in and pound the offender into submission. During my time here, I recall people commenting/complaining about the following thing on their Sebenzas:

-Off center blades.
-Stiff opening.
-Off center screws (the hex hole being off center).
-Handle inserts too small (can see shiny metal past the Micarta or whetever material they used).
-Lock rock and lock bar issues.

From the five items above, my small Insingo qualifies for 4 of the 5. Aside from no lock bar issues (don't expect any), my one knife has or had the first four items. Aside from the already discussed blade centering, the blade was crazy stiff unless I made the pivot screw almost completely loose. All three of the screws are off center on the non lockbar side. The ones they machine themselves are fine. All three of my Micarta inserts are slightly short, so I can see shiny metal from where the handle was milled. I hadn't complained about any of those issues on my knife. I'm not really all too worried about those items, but may mention them when I send the knife in. It's still a very nice knife.

I bought a Sebenza because people like to talk about how perfect they are. Well, I know they're not perfect and I realize that getting absolute perfection is seriously expensive. However, when you buy a knife from a company that has been the quality leader in the industry, I think it's fair to evaluate the knives with a bit greater detail. Yup, I dared to take a caliper to a Sebenza. I can quantify my statements this way, vs. providing qualitative information only. I'm an engineer and just can't help it I guess. It's what I do.

I will send it in, as I said, and we'll see what CRK does. I'll let you folks know.
 

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I just checked three Sebbies and my Umnumzaan (again). They appear perfectly centered, which is what I expect from CRK.
I'll check a fourth Sebbie when it arrives tomorrow. They are SMOOOOTH.
p.s. I never expected to own a CRK. Then I got my Zaan. Now, I've added four large Sebbies, traded off a small collector's Seb. I think I need a job.

Although I have a nice dial micrometer, have a math and physics background, and enjoy playing with numbers, I don't mess with my CRK's unless the centering would be visually uncentered. My eyes have seen the glory...so I quit right there.

Sonnydaze
 
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