Benefits of needle thrust bearings? | BladeForums.com
Jun. 16, 2025
Benefits of needle thrust bearings? | BladeForums.com
You could also mail RJ Martin a $10 knife with washers that is ultra smooth.
If you must have bearings, needle bearings make more sense. But only if it makes any sense at all to use bearings on something as simple and hopefully trouble free as a knife. The engineering argument for bearings doesn't make a lot of sense when most of the bearing knives don't have hardened races - like any real bearing system would. The smoothness argument is nice, except when you have washer systems that are seemingly as smooth.
How is at relavent? This isnt about if bearings are better or worse than washers. But since you went there.
In most cases knives arent seeing the lateral stresses that would require a hardened race to begin with. but for those like you who say these things you should know that all true ikbs system knives have work hardened races made from intentionally cold rolling the race into the titanium. This race is work hardened and completely adequate for its purpose. And for the knives with bearings riding on titanium without those forced races the only thing that is going to happen is that those races will form and the wear will cease. But you should also know that the majority of bearing knife manufacturers do in fact use hardened steel inserts for the bearings to ride on. In fact i only know of a single production company who hasnt adopted the practice. And if i had to guess why they havent is because in the numerous years these knives have been out an actual "problem" never arose. The wear starts a race forms and the wear ceases. And you are also assuming that everyone buys bearing equipped knives for smoothness. I know i dont.
Some of the Sebenzas have washers with holes in them to reduce surface area to decrease friction.
Purple, please explain what the purpose of a bearing system would be if not "smoothness" (decreased friction)?
And I really don't understand this titanium work hardening thing. That's usually what results in galling.
I choose bearings because in my case i am not concerned in the slightest about damage from lateral force. It just doesnt present itself as a problem in my daily activities. And the reason i prefer them is because i despise most pivot assemblies. Bearings are much less sensitive to pinching. the design is much more forgiving to increased torque being applied by the pivot. They have a much larger sweet spot for adjusting pivot tension.
Also i feel you are confusing decreasing friction with increasing smoothness and reducing resistance. They are separate things. The perceived smoothness of a knife is mostly felt in the detent ball, not the actual pivot. The ability for that ball to glide along the tang is affected by many things none of which have to do with the pivot. The smoothest pivot in the world can be completly overshadowed by a detent ball digging into the blade. Smooth is how the blade feels as its moving. When considering that a sebenza can be just as smooth feeling as a bearing equipped knife. But the sebenza will have more stiction and resistance to get that blade moving. If you can reduce the friction you can reduce the amount of torque needed to get that blade moving. But if you choose to still apply that same amount of torque to a knife with bearings regardelss it will have the same smoothness but the speed will be increased.
The last term is resistance. I call it stiction. I personally dont like it. Some like to take a sebenza and polish the washers to get it "smoother". Maybe as the blade is moving but i find two completely polished surfaces pushed up against each other and any space between them being taken up by grease actually makes those surfaces stick together. It requires more force to get them moving because the washers are acting like suction cups. get them moving and they slip fine but i prefer washers to be turned as there will be less microscopic surface areas coming together and the turned surface of a washer will carry lubricant where a polished washer will push it out leaving only enough to create a vacuum with the surface its being stuck to. But even with resistance and friction a pivot will feel smooth as its gliding.
Now dont get me wrong a bearing system is not on any way going to give you a cutting performance advantage. My desire for them is very similar to my infatuation with automatic knives. Its not a need but a want based on my likes. And i find them much easier to dial in to my liking.
On to work hardening. Work hardening is not galling. That is when to surfaces wear by actually sticking. In the case of work hardening you are intentionally crushing the titanium, increasing the surface hardness of the material bu crushing it. I dont know all the intricacies of how or why it happens but you can understand the concept with a paperclip.
If you take a paperclip and yield (permanantly bend) the metal back and forth it heats up, and if you bend in that same spot enough times the material becomes stiff and harder to manipulate. Keep doing it long enough and you will harden the material so much by cold working it that it will actually beome brittle and break in half but not before you have increased the hardness at the point where you were flexing it. When a hard beari g rides on titanium it is not removing metal but crushing it. Pushing it down and compressing it. Gradually the bearings push deeper and deeper. The titanium at that point is pushing back on the bearing and hardening in the process. As the balls go deeper it is becoming harder and harder to do so because the ti is not only getting stro ger but the surface contact is oncreasing and the race is now cupping and cradling the ball and supporting it rather than just having the acute bottom of the ball digging in a localized area.
In other words the balls only crush the titanium so much before it is too hard and supports the bearing to well for it to have any negative effects. Flavio ikoma, terry guinn and other makers intentionally force that race into the titanium and ito this day i have never seen a single report of a failure in regardes to bearings wearing on titanium.
Thrust Bearings to Reduce Friction and Support Axial Loads
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