Umnumzaan Questions....

hotbossa

hotbossa

Joined
Mar 31, 2006
Messages
652
I have done a little research on this knife but I wanted to present some questions to get a better understanding.

From what I understand that lock bar has a small piece of ceramic that acts as the detent. Is that also where the lock rests on the tang of the blade when it is open? It seems to me that the entire lenght of the lockbar contacting the blade tang would me more robust (like the Sebenza). Any thoughts or issues with this set up?

Has anyone experienced the rubber washers on the lugs tearing or coming off?

Is the pivot the same as the sebenza as far as tightening?

THanks!
 
I don't own the Umnumzaan but AFAIK, the ceramic piece is actually the ball that fits in the detent on the tang of the blade but is also the part that fits under the tang when the knife is opened. When you open the knife, the lock bar acts the same way as any frame lock. The idea behind the ceramic ball is that it polishes the tang where it comes in contact with the blade to make opening and closing smoother.

This video might be able to answer some of your questions:

[youtube]ryou0sMRGNY[/youtube]
 
The Umnumzaan has a ceramic ball set into the end of the lockbar that is indeed where the tang of the blade rests when the knife is open. There is no pivot bushings like on the Sebenza so you actually set the tension and use loctite to secure it.
 
I'm not sure that having the entire lockbar face contacting the blade tang is any more robust than a very hard ceramic ball. If you think about the physics of it, the further away from the pivot point, the greater the distance traveled. When force is exerted to close the knife when in the open position, the point of greatest pressure will be at the point furthest from the pivot.

The ceramic ball localizes these forces to a single point on a very very hard material with a lot of surface area behind it. On the Sebenza lockbar, the heat-treated lockbar face has a lesser amount of surface area behind the point of contact.

Ceramics are extremely strong, but also very brittle; they can withstand extreme amounts of force as long as the energy is distributed over longer period of time.

In regards to the pivot bushing, I actually prefer more resistance when opening and closing on my knives, so I like that I can adjust the pivot.
 
Looks like others have answered most of your questions - I've had an Umnum since summer 2010 and the "O" rings on the thumb studs have not come off - there is actually a groove machined in each stud that the "O" ring sits in. The rings are actually a little tricky to get off the thumb studs. I can't see them tearing - they may wear out over a long period of time with a lot of opening and closing - but they are easily replaced. Note - the knife performs just as well if you remove the "O" rings, so the knife will not strand you.

As far as the ceramic ball and the lock-up - no problems with it. The lock up on mine is solid, with no blade play in any direction.

You will need to pick up a takedown kit - I think the one I got was around $13 - it includes the delrin takedown tools and some loc-tite. I've only taken mine apart once (out of curiosity) and didn't have a lot of problems re-assembling it. You do need to let the knife sit for a little bit to allow the loc-tite to set up - not that big of a deal for me.

For the record - I use mine and have carried it a lot since purchasing - it's one of my favorite knives. I do like the Umnum more than my large Sebenza.
 
By the way, the "rubber" O-rings aren't made of rubber, they are made of polyurethane.

http://en.wikipedia.org/wiki/Polyurethane

I'd like to see the person who could possibly use their knife "hard" enough to damage the O-rings.

Now, leave the knife sitting under banks of UV lights, and I could maybe see the O-rings degrade over time...
 
Nice guys, thanks for all the information. I have been bitten by the CRK bug big time. I have liquidated about 10 or so knives to buy a Large 21, Small 21, and Nyala. The Umnum is next!! (My bank account hates me!!!)
 
I just got my new Umnumzaan last week from knifeart.com and it hasn't left my pocket since! As others have stated the lock up as well as the tolerances are incredibly tight. The intention of the ceramic ball is to avoid wearing of the lock bar where it makes contact with the tang since ceramic is harder than the metal tang. It also keeps the deployment very smooth and quiet since the ball never leaves contact with the blade because it serves as the ball detent as well. BTW, mine has a birthdate of 2/23/11 with the S35VN blade and the Idaho stamp. Highly recommend it. Pictures don't do it justice. Awesome piece of engineering.
 
Cynic2701 said:
By the way, the "rubber" O-rings aren't made of rubber, they are made of polyurethane.

http://en.wikipedia.org/wiki/Polyurethane

I'd like to see the person who could possibly use their knife "hard" enough to damage the O-rings.

Now, leave the knife sitting under banks of UV lights, and I could maybe see the O-rings degrade over time...
Click to expand...

The o-rings on my Umnumzaan took about 6 months of being used every day to become loose and baggy. I now carry
the knife with out them but they are of course very easy to find and cheap to buy if I ever want to replace them. :thumbup:
 
The Umnum is solid.. buy it... use it.. love it.

It's a bit of a chunky knife for me, but the absolute smoothest action I've owned and 'user adjustable' on how tight it is. Very cool design.
 
Haze said:
The o-rings on my Umnumzaan took about 6 months of being used every day to become loose and baggy. I now carry
the knife with out them but they are of course very easy to find and cheap to buy if I ever want to replace them. :thumbup:
Click to expand...

Not that I'm disputing that it happened, but I'm a fairly obsessive "knifesturbator", and I probably cycle my Umnumzaan around a six or seven hundred times a day for the past five months and I have yet to detect any degradation of the O-rings.

Do your uses put the O-rings in an abrasive environment with a lot of strong daylight?
 
Cynic2701 said:
Not that I'm disputing that it happened, but I'm a fairly obsessive "knifesturbator", and I probably cycle my Umnumzaan around a six or seven hundred times a day for the past five months and I have yet to detect any degradation of the O-rings.

Do your uses put the O-rings in an abrasive environment with a lot of strong daylight?
Click to expand...

I live in Taiwan so it is very sunny and humid for a good part of the year. Being a sweaty foreigner in this land probably just adds to that equation. :p
 
I don't know about your location, but the neoprene o-rings are easy to find here, but not urethane. CRK can provide replacements, though.
 
edlex said:
. . .BTW, mine has a birthdate of 2/23/11 with the S35VN blade and the Idaho stamp. Highly recommend it. Pictures don't do it justice. Awesome piece of engineering.
Click to expand...
Hmmm, just received an email from Heather at CRK and as of this morning, "We have not yet begun producing the Umnumzaan in S35Vn". FWIW
 
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