Thread: Pressure Fitted pins

This will seem like blasphemy to some people and I have mental images of horn scales exploding and bone scales breaking and wood scales cracking and people crying and babies dying, but would it in theory be possible to forgo the whole washer thing and just pressure fit flush pins?

My plan is thus: drill a hole, say, 1/16". Take 1/16" pin material. Very very lightly sand or run over a finishing hone(to rough up the surface) Plunge in liquid N2. Insert through hole. Let warm. Pressure fit. Done!


Yes, I know very very cold can mess up the blade steel. HOWEVER... the heat loss would be equal to the weight of the pin times it's specific heat times the temp difference (m*c*dT) and so the razor blade would only be cooled by a little bit as its mass is much higher. AND you're cooling at the tang not the edge. AND heats dissipates through a piece of metal according to a sine funciton approximation- like a ripple. So by the time the heat sinking reaches the edge it will no longer be that significant. AND one could add a moderate heat source (match, fingers, warm water) at the shoulder to curb heat loss (cooling) at the edge.

only problem(as if) is; that is not how razor pivot pins work.

If i follow your technique, it would only serve to lock the razor in place

I assume you think the whole thing will be pressure fitted... but if the pin still has clearance on the blade, the razor will still open and close....

good idea questions is this. that pin should cool off then it will come to is it original size right? will get loose? or i am missing something?

1/16 pin, 1/16 tang hole- ah yes, you were not saying the tang hole should be 1/16.

how much would the pin contract?

Originally Posted by hi_bud_gl

good idea questions is this. that pin should cool off then it will come to is it original size right? will get loose? or i am missing something?

yeah, that too

NO... you dunk the pin in liquid N2 so it contracts. You then insert it. as it warms it grows slightly, which will then pressure it in place.
I said 1/16" as an example. One would have to figure out the hole sizes etc. On the converse, or at the same time, the scales could be heated and then they would shrink down on the pin, further pressure fitting it. Just to be clear, the pins would not fit in the hole in this scenario, unless they were shrunk or the holes enlarged. Thats the way a press fit works. And yes, exact hole sizes are press fits. Typically a 1/16" bit drills a "clearance" hole that is actually around .01 wider than the actual width to prevent press fits.

This may work but how much pin will shrink by cooling? do you think that amount will be good enough? i can't say .Someone needs to experiment this and let us know the result.

I think the interference fit of the pin would have more side ways splitting pressure on the scales than that of a washer pressing in from the side.


Charlie

Originally Posted by khaos

This will seem like blasphemy to some people and I have mental images of horn scales exploding and bone scales breaking and wood scales cracking and people crying and babies dying

I'm getting some liquid N2 from my dad this weekend and will be testing in my downtime in the evenings.

I suspect that an interference fit would cause cracking if the actual differential was say, .1". But I'm talking about .005". And yes, this is enough. I remember pressure fitting bearings on a catapult swing arm using a .003" press fit. Even something with an OD of x and something with an ID of the same x is considered a press fit in the engineering world.