What would you consider perfect action in a folder?

Q

Quinn406

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Nov 6, 2021
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Hello everyone, this is my first post here. I consider myself a maker of various things, mostly rc helicopters. I have a cnc mill turn machine that i designed and built mostly for the purpose of manufacturing rc helicopter airframes and upgrades. If anyone is familiar with rc helis, i designed and built the Q700. During the last 5 years or so of learning cnc, i watched a lot of videos from John Saunders and John Grimsmo and kept up with Business of Machining podcast, so im very familiar with grimsmo knives and a lot of what goes into manufacturing them. Even though i got started in machining for rc helis, ive always been interested in pocket knives and wanted to design/build one. I like to come up with unique designs that dont follow the average way of doing things as i did with my rc heli airframe which i believe was pretty successful. There is demand for my airframe, but the hobby is not large enough for me to take that path seriously.
At this point i think id like to take a crack at a folding knife design, whether it someday be sold or just for fun. I already have most of whats required to build myself a knife. My machine is a bridge style mill with a servo driven bt30 spindle as well as a servo driven horizontal turning spindle which can handle both turning and 4 axis machining. Great for parts that need both milling and turning like custom screws, pivots, bearing parts, standoffs, etc. as well as plently of table space for fixture plates. Some of the other stuff i would need are things i have also needed for many rc heli parts i would like to start making, specifically a hardening setup, cnc grinding additions to my machine, belt grinder, etc.
For the last couple months ive been throwing some ideas around in my head, somewhat unique bearing arrangements and lock mechanisms. I feel there are ways to get the ultimate friction free smoothness with absolutely zero slop and max rigidity. It seems that even the smoothest bearing pivot folders have sources of friction and slop here and there. For example the Norseman is bearing supported axially but still just a bushing type pivot which has not much but a little bit of friction radially. Also part of the action has the detent ball dragging on the blade. Ive never held a Norseman so i dont know what the action feels like, but there has to be at least some amount of clearance around the pivot which will create slop. This slop may only be a few tenths and maybe not (probably not) felt or heard in the action, but what if you had a truly slop free friction free action? This means no sliding surfaces, only bearing support in both radial and axial with some amount of preload to eliminate all slop. The closing detent can also be done in a way that it does not drag before closing, or at least only drag the last couple degrees. The question is, can it be too smooth? What if you could hold your knife out horizontally spine up, flip the blade out and it was able to pendulum back and forth for some amount of time while still being absolutely slop free and 100% rigid when locked? Is this too much? What about the drag from detent ball before closing all the way? Do we want it there, or is it better off eliminated?
Before i try to design the perfect folder, id like to hear some opinions on what the perfect action really is. I realize that many prefer the reliability of a none bearing knife that is less sensitive to dirt, even though a washer style will have more drag, but this will lean more towards a mechanically impressive knife with an emphasis on smoothness and ease of deployment. Somewhat of a fidgeters knife but still extremely reliable and handles abuse.
 
For me it's about smooth and solid not fast. I have bearing flippers from various companies,and love the flick-pop action. Well made ones are smooth and have minimal side play.cheaper ones can feel a bit "gritty"
I love my Classic 21 Sebenza with the bushing system, does not pop open but is butter smooth and as close to zero play as production folder is likely to get.
So my vote is focus on smooth and solid.
Auto's, flippers,assisted are nice,fun, love to fidget flip, but fast is not my concern.
One handed is important, but if I want super fast attack capability, then I'll join the Airforce or somethin.
I look foward to seeing what you come up with, most knife pivots and locks are pretty simple.
 
I'm on the "Smooth and Solid" Bandwagon also....Shirogorov and Chris Reeve have set pretty high benchmarks. To find out what you're up against you need to handle these knives to really know what Smooth and Solid feel like.
 
Great input guys. I agree the focus should be smooth and solid, maybe replace fast with effortless, but not so effortless that you dont have control over it. For a knife that is truly 100% solid with a smooth somewhat effortless action, its going to require all motion to be supported by preloaded bearings. To build such a thing with already produced bearings that are assembled into the knife, it would be difficult to fit it into a nice package that isnt large in the pivot area. The bearing components will be integrated. Similar to grimsmo, the only part of this knife i wont be machining/grinding myself is the ceramic balls. Tolerances will be very important for such an assembly. Possibly need a preload adjustment to get it just right. Im curious if such a knife is out there, zero movement other than rolling of preloaded balls. A pivot with a couple tenths of slop in it will bounce around a bit when locking. I want to eliminate any source of that. A really nice solid single microsecond thud when the knife locks into place. The difference between slight slop and actual preload is only a couple tenths and i think its something our hands and ears can pick up on.

Busto, i think youre right, i definitely need to get some of these nicer knives into my hands to really get a feel for whats out there. Ill have to at least find a place that will let me play with a couple knives, possibly buy a couple.

As for the axis lock, its one of the best options out there i would say, but the goal here is to do something unique in as many aspects as possible. I think i will start by building my pivot bearing assembly and test it for smoothness, rigidity, strength, point of failure, mode of failure etc. Once i have something i like there i will move outwards to the stops, lock, detent, etc. Obviously all these things will be competing for space and need to be worked together but i want to test some general concepts first.

Once again, great input guys, keep it coming.
 
Pivots don’t have a couple tenths of clearance in them. Generally it’s a couple thousandths at most. Pivots I use combine with reaming should be around one thousandth or less. The pivots I use have between 3-7 ten thousandths of clearance from pivot hole size.
 
Quinn406 said:
A pivot with a couple tenths of slop in it will bounce around a bit when locking.
Click to expand...

There are two places where a typical good folder (for me) has been hand-adjusted by the maker:

- Pivot: you start with a Pivot that's a little to large and sand it down with 800" paper until it fits perfectly (lapping).
- The lock geometry for framelocks

By the way, all my favorite folders have 1/4" pivots. And if you want to distinguish yourself from all the Chinese Ti knife makers, again, I suggest to use PB washers, not bearings.
 
ferider said:
There are two places where a typical good folder (for me) has been hand-adjusted by the maker:

- Pivot: you start with a Pivot that's a little to large and sand it down with 800" paper until it fits perfectly (lapping).
- The lock geometry for framelocks

By the way, all my favorite folders have 1/4" pivots.
Click to expand...
just picked up some .25" hardware from Alpha Knife Supply Alpha Knife Supply . It's really nice stuff. Haven't made a folder yet, but the first one will be pretty oversized with .25 pivot and stop pin. It'll be like a folders for dummies project. I think I'll need a proper surface gauge before I get started, because my feeling is that if I don't start with a perfect flat surface, I won't have a perfectly perpendicular pivot hole and it'll be all downhill from there
 
Lorien said:
just picked up some .25" hardware from Alpha Knife Supply Alpha Knife Supply . It's really nice stuff. Haven't made a folder yet, but the first one will be pretty oversized with .25 pivot and stop pin. It'll be like a folders for dummies project. I think I'll need a proper surface gauge before I get started, because my feeling is that if I don't start with a perfect flat surface, I won't have a perfectly perpendicular pivot hole and it'll be all downhill from there
Click to expand...

I'm not a knifemaker by far, Lorien, but I've lapped a couple of pivots myself, because I wanted Torx hardware on some of my Hinderers.

These are from TiConnector - 1/4" SS pivots with Ti screws, come as kits in different lengths. I simply put the new pivot in a drill and used fine sandpaper (on a flat surface) until the pivot fit - it doesn't take much. Then I ground it to length.

i-sHdQ3zT-X2.jpg
 
Daniel Carraher said:
Pivots don’t have a couple tenths of clearance in them. Generally it’s a couple thousandths at most. Pivots I use combine with reaming should be around one thousandth or less. The pivots I use have between 3-7 ten thousandths of clearance from pivot hole size.
Click to expand...
When i say tenths, i mean ten thousandths. A couple thou is much more. I want there to be none as well as no friction, preloaded bearings that have support in both axial and radial direction.
I realize that a thou or 2 clearance around a pivot is going to give low friction rotation and maybe not noticeable slop, but i want to go the next step, zero slop anywhere which can be done with a radial/axial preloaded bearing system.
 
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