Downsides to Pivot Bushings? Why don't all knives use them?

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:

 

Think of bushings like washers that go between the pivot and the blade instead of between the blade and the frame. They perform the same service: bearing surface.

 

Ah I see. So it's that tube with a head that only goes in one way, and a screw goes in the other end. Then, the only two knives I've dared to disassemble have had these.

 

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)

 

My point exactly sir.

As manufacturers see what customers are responding to they will begin to catch up with the "clique" knife makers.

Otherwise a knife has been a knife for what... a couple 20,000 years? maybe more?

 

Everyone is talking about the bushing existing between the pivot and blade tang. Well, that's obvious as it's the definition of a bushing. Isn't all the love for bushings over the fact that they act as a spacer between the handle halves. This allows one to fully tighten the pivot eliminating the need for loctite. If machined properly, the knife will stay tight and need no tweaking to keep things in order. The Para and Sebenza are both good examples. Neither is perfect and there exists both tight and loose models of each. Adjustments can be made by sanding washers or the bushing. Caution must be taken, but it's been done successfully by many. They shouldn't be called an expensive knife setup either. The para is bargain knife and Spyderco is doing it without having to do much machine work to the liners.

Zombie, people always demand fancier and more complex goods. We can't be pulled by horses and send messages with alternating length beeps forever. I don't think bushings are necessary, or even preferable, but neutral. I don't care what pivot it has so long as it works right.

 

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...

 

I do agree with everything you stated, and I know you are informed on what you post.

I am trying to keep it simplistic, and real.
There are hundreds of facilities in most states that can produce a knife of ANY quality you wish.
It only becomes an issue when mass production comes into play.

So really the bottom line is how much money do these guys want to make, and at what cost to customer concerns?

When does that cycle stop?

 

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'm a big fan of brass bushings is in motorcycle clutch, brake and shift 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.

 

Thank you sir... um Dude!
That's my bottom line right there.
The value for the goods received is not in tune with what it should actually be.
If you pay for the "love" then it's priceless. Pay for the pride of ownership... it's subjective.
Pay for what you actually have in your hand, and they should have Kryptonite blades with anti gravity bearings... A cheap arse bushing should be a given.

 

I may be slightly slow, and a bit dense but this is the best explanation I have seen so far.

So like I said in my first reply... They um do a twisty thing, sort of.

 

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).

 

Number 9's post above made a pretty fair argument for both sides of the discussion.

 

So, if you are an obsessive flipper (for example), then years later it would be cheaper to tighten your blade to the pivot by finding a new, perfectly matched pivot bushing? Seems like a poor investment to me. Just buy a new knife.

 

Tony uses a bushing that's readily available, but it's the hand fitting that makes his knives work so smooth. He sizes them .001 oversize and laps them to each knife he builds. It's actually more critical to get it right with a knife that doesn't have a screw type adjustable pivot. Handling a Bose enlightens every traditional knife lover. Lot's of custom makers use pivot bushings for slip joints, it's not rocket science but it's not like these things just drop in.

 

I have owned a few sebenzas, and based on the knife market, I felt their price was justified because of how well done the overall package is. Every little detail on that knife is considered. I don't own them anymore because I decided that $350 knives didn't match my finances and lifestyle, but if my income were more substantial then I may have felt differently. They don't cut any better than any other knife I've owned. But a Corvette doesn't get you to work any better than a Camry, really. Both will deliver you there. And the build quality of the Corvette's interior means it falls apart a lot quicker than the Camry's. Most places in this country don't have roads where you can really squeeze the performance out of a Corvette between home and work and get away with it every single day. And yet, listening to 1984 by Van Halen just doesn't feel the same in a Camry on a sunny afternoon when you're feeling fine, ya know?