Sebenza 25 construction flaw? (Nope, not a flaw, read inside)

[Moxy]

I'm sorry if I missed it, but where did anyone explain why the change from a press-fit pin to a double-screw pin was made? and where has it been opined that it was an improvement?

Why would Chris Reeve change the design if he didn't think it was an improvement? It's pretty easy to see that a fastener holding the pin in place is better than an interference fit. I was made aware of the change after watching a YouTube review of the 25. I can't remember the reviewers name, a few mention it actually.

 

[Muaddib1116]

Why would Chris Reeve change the design if he didn't think it was an improvement? It's pretty easy to see that a fastener holding the pin in place is better than an interference fit. I was made aware of the change after watching a YouTube review of the 25. I can't remember the reviewers name, a few mention it actually.

I know that some people here might not like to think so about CRK, but maybe it is just easier/cheaper. Please don't think I'm trying to be a smartass, but if it's easy for you to see that the new pin with 2 screws and the need for loctite (which has the chance of spinning and becoming a problem) is better than the interference fit pin (which nobody has complained about), can you explain it to me? Because honestly, I'm not seeing the improvement.

 

[Omega Leather Works]

Why would Chris Reeve change the design if he didn't think it was an improvement? It's pretty easy to see that a fastener holding the pin in place is better than an interference fit. I was made aware of the change after watching a YouTube review of the 25. I can't remember the reviewers name, a few mention it actually.

I'm not sure that I'd agree. I'm assuming that the change was made because it makes assembly easier at the factory, or it lowers cost, but that's no more an assumption than that it's an improvement on a flawed design.

Interference fit (or press fit) is something that CRK has been doing for, well, for as long as I can remember with their thumb studs.

Maybe press fitting into titanium presents a problem. That too would be a guess...

I guess the bottom line is, unless CRK tells us *why* they made the change (and they've made it clear that they won't) then any speculation is just that.

As far as I can tell it's a dead topic. Use the loc-tite that came with your knife and don't loosen that side. Or buy a 25 with a press fit pin. Those are your options.

 

[Moxy]

An interference fit should not be removed and replaced over and over. Otherwise, over time, the fit would come loose from wear and tear. Thumbstudes are never removed. But Chris himself encourages that his customers maintenance his products themselves. He includes tools, I love that. So a pin that relies only on tight tolerances will eventually become loose after a certain number of disassembly-reassembly cycles.

Thats just my opinion. I didn't meant to imply Chris is of the exact same opinion. Personally I'd rather have a fastened version.

 

[Officer's Match]

I still cannot fathom why the stop pin needed to be situated such that a clearance notch was necessary. It is easy to see what problem can arise should the pin rotate - what I don't get is what benefit arises from such an arrangement. Not saying Mr. Reeve doesn't have one, but I for one would like to know what it is?

 

[Muaddib1116]

An interference fit should not be removed and replaced over and over. Otherwise, over time, the fit would come loose from wear and tear. Thumbstudes are never removed. But Chris himself encourages that his customers maintenance his products themselves. He includes tools, I love that. So a pin that relies only on tight tolerances will eventually become loose after a certain number of disassembly-reassembly cycles.

Thats just my opinion. I didn't meant to imply Chris is of the exact same opinion. Personally I'd rather have a fastened version.

I'm not sure the interference fit pins do come out. I assumed that when one of the 25's with the older interference fit pins is disassembled the pin remains in the scale that it's pressed into. Can someone with the older models chime in on whether or not it can even be slid out of that scale?

 

[Mugen]

I remember watching one of the first Sebenza 25 disassembly videos(can't find the video anymore) and the owner of the knife could not get the scales to come apart because of the interference fit pin. I suppose this is the reason for the change in stop pin to being a non interference fit.

 

[Sam Dean]

I'm not sure the interference fit pins do come out. I assumed that when one of the 25's with the older interference fit pins is disassembled the pin remains in the scale that it's pressed into. Can someone with the older models chime in on whether or not it can even be slid out of that scale?

The stop pin is pressed in tight on mine - and I really like it this way. I'm not knocking the screw together stop pin because I haven't seen/used one; BUT, the pressed in stop pin is more "emotionally gratifying" to me.

Unless CRK can give us a little insight about the reason behind the change, I'll continue to think that way. Frankly, not wanting to say "why" because of the import knockoff market is kind of a cop-out. If the Chinese want to copy something, they'll buy one and reverse engineer it like they always do.

I really like CRK products because of the form-follows-function approach (and openness about WHY things are the way they are) they have had. Elegant simplicity at its finest! If I didn't care WHY some design element came about, I'd buy 4 or 5 Benchmades and forget about it....

Do they have to share all of this information? No, they certainly do not. Although if they want to continue getting my business they should.

 

[Officer's Match]

Press fit or screw retained, I still can't get my head around the need for a clearance notch in the stop pin. Like most other CRK lovers, I appreciate a useful tight tolerance. I don't understand this particular example of stop pin / pivot geometry. It seems to me to allow for much more potential trouble without any benefit I can imagine with my little pea brain.

 

[Muaddib1116]

Press fit or screw retained, I still can't get my head around the need for a clearance notch in the stop pin. Like most other CRK lovers, I appreciate a useful tight tolerance. I don't understand this particular example of stop pin / pivot geometry. It seems to me to allow for much more potential trouble without any benefit I can imagine with my little pea brain.

I have no actual experience, but I would guess that designing a frame-lock knife requires a balance in dimensions between the two sides of the tang that contact the stop pin (open & closed), the lock surface of the tang that contacts the lock-bar (the ceramic ball in this case), and the curve of the tang that rides on the ball detent (also the ceramic ball in this case) all while maintaining enough material around the stop pin to provide strength and enough surface area in contact with the washers to provide as solid a connection the the handle scales as possible.

I'm sure that they could have probably made the Sebenza 25 without this stop-pin clearance notch, but I'm sure they would have had to sacrifice something. Perhaps the stop pin diameter, the pivot diameter, or possibly the overall shape/dimensions of the knife/blade/handle. Personally I think it has to do with the large diameter stop pin and the larger diameter pivot of the Seb 25.

 

[Officer's Match]

I have no actual experience, but I would guess that designing a frame-lock knife requires a balance in dimensions between the two sides of the tang that contact the stop pin (open & closed), the lock surface of the tang that contacts the lock-bar (the ceramic ball in this case), and the curve of the tang that rides on the ball detent (also the ceramic ball in this case) all while maintaining enough material around the stop pin to provide strength and enough surface area in contact with the washers to provide as solid a connection the the handle scales as possible.

I'm sure that they could have probably made the Sebenza 25 without this stop-pin clearance notch, but I'm sure they would have had to sacrifice something. Perhaps the stop pin diameter, the pivot diameter, or possibly the overall shape/dimensions of the knife/blade/handle. Personally I think it has to do with the large diameter stop pin and the larger diameter pivot of the Seb 25.

Precisely my question - sacrifice what?

The downside of the design is easily apparent to me; I'd like to know the upside. Frankly, it would seem to me that moving the stop pin lower/closer to the center point of the pivot (and thus within the range of the tang) reduces the dimensional "timing" space where lockup occurs. I really don't get it, but would truly like to learn.

 

[Omega Leather Works]

I have no actual experience, but I would guess that designing a frame-lock knife requires a balance in dimensions between the two sides of the tang that contact the stop pin (open & closed), the lock surface of the tang that contacts the lock-bar (the ceramic ball in this case), and the curve of the tang that rides on the ball detent (also the ceramic ball in this case) all while maintaining enough material around the stop pin to provide strength and enough surface area in contact with the washers to provide as solid a connection the the handle scales as possible.

I'm sure that they could have probably made the Sebenza 25 without this stop-pin clearance notch, but I'm sure they would have had to sacrifice something. Perhaps the stop pin diameter, the pivot diameter, or possibly the overall shape/dimensions of the knife/blade/handle. Personally I think it has to do with the large diameter stop pin and the larger diameter pivot of the Seb 25.

I think that's a well written explanation.

Match-

It's not as simple as it may seem. There is a lot going on in a very small space. I can't re-engineer the knife to answer your question, and even if I had the technical mind to do so I probably wouldn't. Re-read the above a few times then start trying to figure out how to make a better design. Betcha can't.

As for the press fit pin... It's pressed into one side. It doesn't come out or move at all. You simply remove the fastener from one side and the pin stays with the other. Easy peasy and Imo, a better solution.

 

[Officer's Match]

I think that's a well written explanation.

Match-

It's not as simple as it may seem. There is a lot going on in a very small space. I can't re-engineer the knife to answer your question, and even if I had the technical mind to do so I probably wouldn't. Re-read the above a few times then start trying to figure out how to make a better design. Betcha can't.

As for the press fit pin... It's pressed into one side. It doesn't come out or move at all. You simply remove the fastener from one side and the pin stays with the other. Easy peasy and Imo, a better solution.

Well, I appreciate that input, I really do. I just don't see whereas either the pivot diameter (remember, we already are "giving up" the bushing) or the stop pin diameter is a reason that justifies a potential pivot action stopper. (anybody broken a 21 pivot and/or stop bar lately) I'll agree that I can't create a better design, but I think I know someone that (IMHO) already did.

 

[ToddM]

One possible reason from going away from the press fit is "user error". I've dealt with products that have high tolerance press fit alignment pins into one half of an assembly and invariably some users think to themselves "Well it comes out of one side so nice it MUST come out of the other too!" so they force it out, and the assembly is the same again. Another reason could be the tolerance range to get a press fit tight enough to stand the length of time (especially repeated blade opening impacts) but not so tight it damages parts when installed has to be miniscule and that increases production costs.

Just reducing the stop pin or the handle tang diameter seems an obvious solution, but lets face it, it was that easy it's safe to assume Mr. Reeve would have done it so I submit those are not viable options for whatever reasons. If you search on "broken stop pin" here or on google you quickly learn that stop pins almost never fail, of any size. A few no-name knock offs, and a brittle batch of Commander pins many years ago and that's about it.

I'm not an engineer or a knife maker but if I stayed in a holiday in express for a weekend my first idea would be to machine flats into the stop pin's interface with the handle slabs eliminating the possibility of it rotating, even if the screws fell out.

It looks like from various pics that there's enough room to do it, even a very small/shallow flat (especially with CRK tolerances) would keep it from rotating. It would certainly increase production time and cost though, and probably have a dozen other negative impacts I'm not smart enough to comprehend, which is why I'm not a knife maker

 

[Trabireiter]

Your user error idea might exactly be what it's all about. Somebody might think that when he cleans his knife than it's either completely or not at all. So the stop pin has do come out one way or another and then you are stuck.

 

[Omega Leather Works]

One possible reason from going away from the press fit is "user error". I've dealt with products that have high tolerance press fit alignment pins into one half of an assembly and invariably some users think to themselves "Well it comes out of one side so nice it MUST come out of the other too!" so they force it out, and the assembly is the same again. Another reason could be the tolerance range to get a press fit tight enough to stand the length of time (especially repeated blade opening impacts) but not so tight it damages parts when installed has to be miniscule and that increases production costs.

Just reducing the stop pin or the handle tang diameter seems an obvious solution, but lets face it, it was that easy it's safe to assume Mr. Reeve would have done it so I submit those are not viable options for whatever reasons. If you search on "broken stop pin" here or on google you quickly learn that stop pins almost never fail, of any size. A few no-name knock offs, and a brittle batch of Commander pins many years ago and that's about it.

I'm not an engineer or a knife maker but if I stayed in a holiday in express for a weekend my first idea would be to machine flats into the stop pin's interface with the handle slabs eliminating the possibility of it rotating, even if the screws fell out.

It looks like from various pics that there's enough room to do it, even a very small/shallow flat (especially with CRK tolerances) would keep it from rotating. It would certainly increase production time and cost though, and probably have a dozen other negative impacts I'm not smart enough to comprehend, which is why I'm not a knife maker

A couple of interesting points in there. I like the idea of a flat, similar to the flat many companies use on their pivots. Heck, the flat could go all the way across and be used for the clearance need too. Also interesting thought about repeated shock on the press fit pin.

I'm having trouble with imagining someone trying to force the pin out to clean it, but the other two points make plenty of sense.

When I first took mine apart I wondered why they hadn't used a flat on the pivot (ala Benchmade) but maybe there's an obvious reason and I'm just not seeing it. Doesn't matter because the pivot system seems to work fine.

 

[Sam Dean]

OK, (regarding the pressed in stop pin) I've been pondering this some. I think it has to do with several things:

1: Spa Treatment. How would they be able to re-blast the handle - and maintain the fit/finish of the SS stop pin - without removal. It just has to come out to do this properly.

2, 3 & 4: Graphics, Inlays & polished handle. Anyone who has watched the CRK shop video knows about how they do graphics & inlays. This would be impossible to do with a stop pin pressed in place because it projects slightly from the surface AND the stainless steel pin may prevent the titanium from being anodized properly (yes, I know it's only pressed into the locking side...). Also, how do you perfectly polish a handle slab (before inlay or after anodize) with a pin in the way?

Now, for the reason the stop pin has a relief cut into it - I am certain this was a calculated compromise in design, material selection and strength. Movement (relocation) of the stop pin also affects the shape of the blade tang, open & closed blade profile and range of movement. I see no reason at all why it should be any different, because any shift in position of the stop pin dictates other modifications which make the overall package not as appealing.

The only modification I could suggest (as already mentioned above) to the screw in stop pin would be a hex/square/flat or elliptical (anything not round) recess for the pin to seat into on the inside of one of the handle scales. This would assure proper orientation of the stop pin under any circumstance.

I really believe these changes were made because Chris is working on inlays/graphics for the 25. Now, that's something to get excited about!

 

[Omega Leather Works]

Good thinking speed freak.

One question regarding the Spa. When a knife blade goes in, how do they deal with the press fit thumb stud? I'm guessing they install a new one? Whatever they do, why couldn't they do the same with the pin?

Lastly, how is the dual thumbstud installed? Is it also some kind of interference fit? I'm wondering because if it isn't (and since dual is the only option on the 25) maybe they are doing away with interference fit everything...?

 

[Muaddib1116]

The thumbstud is a press fit also, and with the right tools it isn't hard to press out and in. The dual thumbstud is also press fit. I'm sure that during the spa treatment they could press out the stop pin to do any sort of finishing work they need on the scales.

 

[Omega Leather Works]

Interesting. I figured the dual studs were screwed together, but that's just because I can't figure out how they'd be pressed in.