Umnum question

kamagong

kamagong

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Jan 13, 2001
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How dependent is the lock engagement on the hard rubber o-rings? I'm curious because all polymers deteriorate over time and am concerned that the lock-up of the Umnum may become compromised once that happens.
 
As I understand it the o ring is just for shock absorbtion and does not affect the lock up itself. I'd imagine that CR put alot of thought into the design if his name is on it.
 
kamagong said:
How dependent is the lock engagement on the hard rubber o-rings? I'm curious because all polymers deteriorate over time and am concerned that the lock-up of the Umnum may become compromised once that happens.
Click to expand...

Good question. It seems like the o-rings would affect the lockup (especially if missing) since they are lodged between the stop-pins/thumblugs and the frame when the knife is locked open. Maybe someone from the shop will chime in.
 
You mentioned “hard rubber” and ‘polymer’ in the same post. Hmm. They’re not rubber; they’re polyurethane, big difference.

You probably already know that, but I keep seeing people posting questions about the ‘rubber’ O-ring longevity issue.

Natural rubber is easily corrupted by ozone and many chemicals.
If CRK had put ‘rubber’ O-rings on the ‘zaan, I would say they had been drinking too much during the design phase.

Modern polyurethanes are very tough and long lasting.

I have no worries about the ones on my knife. I’m sure Chris did his homework on this part of the design and spec’ed the best he could find.
 
O-rings do not affect the lock up....the depth of the groove in the Thumbstud/bladestop does not allow the o-ring to compress enough to affect lock up nor will it allow the o-rings to wear.
 
bearcut,
Let me reassure you that we never drink to much when we design and make our knives. We very conscientiously drink exactly the right amount (which just happens to be a lot).

Of course, being a Mormon, I only drink Coke or water. However, I do have several coworkers who selflessly, regularly and even valiantly volunteer to be my Designated Drunkards.

Planned Failure: a device with moving parts will eventually fail in one or more of its parts. A smart designer will design that failure in, so that the part that fails is cheap and easily replaced with simple tools on hand and cheap labor.

The o-rings will wear out eventually, and when they do they can easily and cheaply be replaced by the customer. The only tools needed are fingers and opposable thumbs (which Chris does not take credit for . . . yet).
 
nifegrinder said:
bearcut,
Let me reassure you that we never drink to much when we design and make our knives. We very conscientiously drink exactly the right amount (which just happens to be a lot).

Of course, being a Mormon, I only drink Coke or water. However, I do have several coworkers who selflessly, regularly and even valiantly volunteer to be my Designated Drunkards.

Planned Failure: a device with moving parts will eventually fail in one or more of its parts. A smart designer will design that failure in, so that the part that fails is cheap and easily replaced with simple tools on hand and cheap labor.

The o-rings will wear out eventually, and when they do they can easily and cheaply be replaced by the customer. The only tools needed are fingers and opposable thumbs (which Chris does not take credit for . . . yet).
Click to expand...

So, getting back to the OP's actual question, do the o-rings (or lack there of) affect the lockup?
 
They don't affect lockup at all. The click at lockup is more audible with out them and I find it more assuring to hear it.
 
I imagine it's harder on the stop pin if you remove the o-rings as they absorb some of the impact it would normally take.
 
Hello all,

Sorry, I see this thread has been quiet for days now. Been playing around with my fresh out of the box from the factory Umnum now for an hour and was thinking about the role of the o-rings. I find opening the knife normally, not too hard, there is a "soft" feel and muted sound. I can then push back farther on the blade and watch the lock bar move farther over on the blade tang. The o-rings are compressible, and quite loose on the thumb stud/blade stop. When the blade is fully opened and seated I see metal to metal contact between the stops and handle, due to the fit of the rings in the grooves and their compressibility. I sadly must disagree with Bigmark, on my knife the o-rings do compress, and indeed must to allow a firm metal to metal lockup. Removing the o-rings would have no effect on the lockup, and yes, bring back that opening click like on my Sebbies.

Interesting design.

John B.
 
I played with one of these the other day and came away cold. Neat simplicity of design. Very few moving parts and all that jazz, but just not a knife that called out to me. The o-rings, btw, didn't appear to affect the lockup other than to provide some shock absorption. The scales need a little more relief, imo, to provide better thumb purchase when opening the blade. The "floating" lanyard bar was cool. Overall however, the 21 gets my vote. Now if the Um was marketed at an "entry level" pricepoint I think it would be a screaming success. They probably wouldn't be able to make them fast enough. But at it's current price, I don't see it as much of a threat to get the Seb discontinued.
 
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