Count me in as someone who has wondered about the mechanics involved with roller bearings. They make perfect sense from a continuous load-bearing point-of-view in an axial configuration, I.E. wrapped around a shaft, but are definitely a bit more problematic to consider used in a radial application, such as thrust bearings in a knife pivot, which is our subject here. They could be tapered in such a way that each roller would move the same number of rotations at both the inboard and outboard ends as they swept through their required arc of movement. This, of course, would require that the surfaces they interface with be milled to match their taper, which I do not believe to be the case with the inside of liner/underlay washer or the blade tang. As
Officer's Match
and
@Sharp & Fiery have noted, using cylindrical instead of conical rollers would require some sort of gliding or other accommodation in order to function.
I did a bit of math in order to wrap my head around this, as geometry has always been at the core of my approach to my carpentry, building, and sheetmetal fabrication vocations. (I think it's the German, mad scientist part of my DNA.
). Anyway, I used
"Havoc"
's very clear overhead shot of his digital caliper 5/8" measurement of the roller bearing race as a starting point, converting to mm's, printing the image, and scaling the dimensions of the various components--roller length, roller diameter, and the diameter of rotation both at the inboard and outboard edges of the rollers. Scaling a pic isn't all that accurate, but it's close enough in this case for argument and puts us in the right ballpark (or knife block).
Without breaking down all the numbers, figuring that the blade has to move about 180 degrees, or about a half-circle, to open or close, I calculated that the inboard edge of the rollers in the race in question have to spin about 4.125 rotations in their travel and the outboard edge needs rotate about 5.374 times to cover that greater distance. Clearly a conflict and one that seems to indicate the need for some "gliding" as has been mentioned earlier.
The thing to consider here, though, is that the bearing races holding the rollers are not themselves fixed. I think what is happening in the pivot is that the rollers both spin and the bearing races rotate somewhat according to the difference in travel required at the inboard and outboard ends of the rollers. There are probably some physical complications in this that could better be calculated by an engineer, the product of these being some increased friction within the assemblies as the rollers still may glide somewhat over blade and washer surfaces as well as bind somewhat within the races.
This could account for Havoc's observations about the blade with SRRBs not free-dropping like in the MRBS incarnation of his F3. I can see where the knife would feel much more "solid" with the rollers than the BBs, as that's the point of the different bearing system anyway, isn't it? Not sure about the "opening faster" part as my SRBs F95T seems to open faster than my MRBS F95R, the former with less contact area and the latter with more. The MRBS does feel more solid, though, and smoother too. I wonder if Havoc's F3R with MRRBS feels smoother.
Well that's certainly a wall of text. Hope it doesn't put y'all to sleep halfway through.