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- Jan 9, 2006
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- 9,684
With a pivot bushing, the hole in the tang of the blade is larger diameter than the female part of the pivot, and the bushing takes up the "windage" between the two. Here's a bali blade with pivot bushings:
With knives like Bose, he makes them by hand and can tune them any way he wishes. They also cost $2000+, so rightfully so. Spyderco can't afford to do that on every knife they made. The PM2 has a cool pivot, but the one's that aren't right just don't have nice action. So it's not really comparable to the CRK pivot bushing. It's an extra part and extra work that probably doesn't seem worth it, especially when a majority of knife users likely aren't on BladeForums.
Washers (phosphor bronze) make the biggest difference to me. CRK has very expensive equipment and a lot invested in making a few patterns to very tight specs. Benchmade or Spyderco can't offer the diversity in models that they do and afford to have such refined equipment. I've seen a production factory where they have machinery like that. Each machine costs easily $250K to $500K, some even more.
My guess is that few manufacturers use them because (until recently) knives are Primitive tools.
As the manufacturers catch up with popular demand there will be many more knives touting pivot bushings (IMHO)
You all keep stating production costs...
What cost? Where?
These bushings are approx 12 bucks a pound (or thousand).
What production cost to take an extra 1 second, and drop a bushing over the pivot pin?
You have to make a larger hole in the blade?
Wait until you re-tool your machine, and add a larger bit!
No disrespect to Mr Bose but his knives are NOT 2 grand because of a bushing that costs a fraction of a penny.
Neither is it due to the extra 1 second it takes to install.
My guess is that few manufacturers use them because (until recently) knives are Primitive tools.
As the manufacturers catch up with popular demand there will be many more knives touting pivot bushings (IMHO)
Your understanding of the issue is limited to your knowledge of making things. The tighter the tolerances, the more expensive the tool and the facilities to use that tool.
That is to say, a machine capable of maintaining .0002in on a diameter is going to have premium construction itself.
You can't hold .0002 on a diameter consistently then the environment changes radically because parts change with temperature.
Make sense?
With all respect sir...
I don't think many parts on the now retired Space Shuttles were made to 0.002".
However your point is completely valid,
To expand on that point, makers that do NOT have that type of tooling should NOT be in the premium knife market. Stick to the 200.00 buck range, and put out the occasional 3 grand "hand made, and tuned" models.
If it all about the tooling than you are actually only as good as your tools.
I didn't say Bose knives cost two grand because he uses a bushing. Production cost includes time and labor. To hand tune a knife that it is as smooth as Bose or a CRK requires a competitive, living salary for every person working on that knife. It isn't as if CRKs are just spit off some magical assembly like in perfect order. They get tuned so they operate that way. Watch his factory videos and compare them to the Spyderco factory videos. Or just ask Sal how much more money his knives would cost to cover production cost increases if he decided to turn Golden into a factory like CRK's... Sal is very transparent and he will probably tell you.
As far as bushings costing 12 bucks a pound... Those bushings aren't CRK tolerance bushings. CRK makes all their own parts in house, as far as I know, and the only thing they outsource is the pocket clip. The machine Chris bought to make pivots doesn't produce $12/lb bushings...
most charge what the market will bear despite what our feelings are
I'm no engineer. But I've worked on plenty of machinery that uses, and doesn't use, bushings at pivot points. My guess is that knife manufacturers don't see a bushing as necessary, without enough return on investment. One of the advantages of using a bushing would be the ability to economically repair worn components in the pivot area. With a knife pivot, the two surfaces are of similar hardness, and operate at relatively slow speeds and relatively few cycles. Two surfaces of equal hardness, well finished and well lubricated should operate with little friction and little wear. In a folding knife, the blade is likely (slightly) harder than the pivot screw, so the wear would eventually occur on the screw, a relatively inexpensive replacement part. And, the wear would happen much slower than if one surface was a soft bushing. A soft bushing may also require more attention to lubrication. A sintered bushing could be made "self lubrcating." But I'm not sure if a certain amount of heat may be needed for the sintered metal to "release" the lubricant.
As has been said, another advantage of the bushing would be that blade side clearance would be set by the dimension of the bushing, relative to the thickness of the blade. This would require very close manufacturing tolerances, rather than allowing the side clearance to be tuned during assembly.
Most pivot points in firearms don't use bushings, and they are, arguably, subjected to higher loads, higher speeds, and potentially more cycles than a typical knife pivot.
One area that I'ma big fan of brass bushings is in motorcycle clutch and brake levers. But, those are dissimilar metals, and the brass bushing can be made much more wear resistant than the aluminum lever, slowing down wear. I don't think that a new, lubricated, unbushed aluminum lever is inherently less smooth than a brass bushed one. But the unbushed aluminum lever will "wallow" out much quicker.
Heaven help me, but I must ask. Why does any (not all) knife use them if they add so much cost? I read the "pros" at the beginning and either don't get it or don't buy it. Is the action REALLY so very much more smooth? I've tried sebenzas and, of course, they are fine knives but I've never found them worth the price (I know, to each his own); 30 years ago, very much so, but now? I get all (well maybe not ALL) the technical jargon, what I don't get is why. So, if someone would (without too much ridicule) tell me what is so wonderful about them, I would truly appreciate it. Thank you (I hope-ducking now).