Thread: Pressure Fitted pins

Isn't a blind rivet sort of what I was thinking of? Expanding metal into the scale? Correct me if I'm wrong, but putting the male end into a female end spreads the female end, creating a press fit right?

That seems cur tand argumentative, but I am really curious about flush pins... which is why I started this thread.

And what if instead of flexing scales you had friction washers at the hinge? I know this need s aspecial straight not tapered tang, but worth it?

Not the whole rivet just the flanged end fit to the thickness of the scale one on each scale pressed into each hole then pinned with a normal brass or NiAg rod but the peen will be more contained in the flanged part of the rivet....

I hope that makes sense

Originally Posted by gssixgun

Not the whole rivet just the flanged end fit to the thickness of the scale one on each scale pressed into each hole then pinned with a normal brass or NiAg rod but the peen will be more contained in the flanged part of the rivet....

I hope that makes sense

A pop rivet? well, two used without the original pin, essentially making them washers.

Originally Posted by khaos

it does in fact place shear on the pin... the compressive/tensile forces due to flexing are lateral in the scale, which is normal to the pin, which is shearing. Trust me. I am at college for mechanical engineering. I know my mechanics of solids....

I guess I just dont understand how it is not tension on the pin when the scales flex apart. If you were to press fit with just enough force to hold the scales tight against the tang with the blade open, then close the razor. The scales will spread when the wider portion of the tang is encountered, and pull away from the tang.

these scales have very very little flex, but they are peened very tightly against the tang which flexes the scales open to some degree, also I installed/glued the wedge in first which created a wide spread at the pin, but the scales are shaped to help them bend in the right places to create a path for the tang. there are no bushings or washers. there is a small countersink in the scale pivot and were peened flush as Ignaz recently described.

Glen can you please elaborate this is very interesting but I'm not quite following...

KevinT- Just because it is in tension (which you are correct that it is) doesn't mean there are not other forces acting on it.

Later when I am home again I will post some drawing I did with regard to the forces I believe are in the scales, and please can people comment on that time? I'm really curious about this. (Note: the shearing force creates a bending moment, which could explain bent pins on old razors....)

Also, guys who know about press fits, Hypothetically, if I were to insert metal bracers (1/8" nickel zinc alloys)into the scales (like someone's diagram earlier), and finish the whole thing with epoxy, would a press fit be more feasible? IN THEORY? I know everyone's opinion, just please play devil's advocate. Would it work? Work, but loosen? Loosen slower than without the bracer? Lets assume that I can take a pair of calipers and measure my rods/pins, and that I use a 1/32" end mill to CNC mill holes that are teh right width for a press fit (which I may be able to do if I can justify it/ volunteer enough in the lab).

Admittedly I haven't read every post in this thread, but the question keeps arising for me...

Why bother?

There are easier, safer, and cheaper ways to acheive the exact same end result in terms of aesthetics. I can't see a mechanical improvement by using this method either.

Can you suggest the safer cheaper alternatives? I know there's no mechnical benefit. I'm looking for the flush pin aesthetic.

I'd be interested to hear speculations on the disadvantages of the way I described. I used a larger than 1/16 pin of annealed copper. larger because with smaller dia. copper it is too easy to bend (pins are bent in peening not from shear of open/close). I like copper more than brass btw

It's softer and easier to spread into the counter sink. I have also had to remove these same pins and I can say the swell from peening extends quite a ways, there is no danger of it coming off even with substantial filing for flush fit. I see no advantage to sleeving or use of flush washers. These increase the potential for splitting natural materials like wood, bone. horn

There is no hard finish to maintain so you can just restore when adjustments need to be made. I have many unfinished wood items that I have lived with for many years. There are advantages and disadvantages to everything- degradation and wood movement are not serious issues with proper care and appropriate compromises. Stabilized wood and, or hard finishes are not a necessity for razor scales

So I have been fiddling around all afternoon with this thermal press fit idea. Please keep in mind I am in rural Missouri on a Farm with antiquated tools and not at Cornell right now.

Few disclaimers- different pin materials had to be used based on different materials and availabilities and stuff. See the results for a sample by sample explanation.

I have not been able to test all the materials I wanted to for various reasons. I will post results for materials I am confident either WILL work, or WILL NOT work. If it almost worked and was a matter of the hole being oval, or the material being only 1/32 thick, etc, I just threw it out and might test with a better sample tomorrow.

Procedure:
1. Drill hole in sample small than pin material and use a round file to widen it some.
2. Immerse pin material in nitrogen till boiling stops (temperature equilibrated)
3. Insert. If it doesn't fit, reimmerse pin while filing hole a little bigger. If fit is not very very close, drill another hole and start over.
4. Let warm to room temp NATURALLY. (samples that I heated to speed up if over heated in certain materials overexpanded and loosened the overall fit)
5. Test fit with pliers
6. Test fit by hanging a 5lb weight. (pin material bent to act as a hook)
7. Walk away. Come back, check if weight is still hanging or pin has fallen out.

Results:
-Osage Orange (dried in barn for about 1 year 2 months- sample was taken from logs cut from trees when we cleared brush in June last year, the logs have been drying for fenceposts) I sanded the area to test pin to about 1/8" thickness (scale thickness) and bored a 1/8" hole. A nail with thickness 1/8" fit, but fell out when heavily loaded, so I cut a sample of fecning wire, and bored out the hole a little. (took three tries to get it right). Weight is still hanging after two hours. I can't pull it out with pliers, no matter what force I use. Have tested heating it, won't loosen when too hot to touch, have suberged whole sample in nitrogen, fit is still good when it warms. Did NOT crack. It can rotate a little bit with a lot of force (only using 15" long pliers, and only if you grip the bent part, you can't rotate it by the part still in line with the pin part)

-3/32 shatterproof Lexan hole bored was 1/8". At first, nail was snug fit (not loose, but not tight enough). Thinking that I may be able to tighten the lexan thermally I bored the hole at high speed (vs. low speed I used first time). Lexan was hot to touch, hole seems to have tightened up. The same 1/8" nail was inserted frozen, and is still there after 2 hours hanging. Same deal as the Osage Orange. Resubmersion is fine. Heating is fine. Can't pull it out with pliers. Can't rotate it.

-Steel thrown out (corrugated steel- material too thin, more deformation than is worth)

-Oak thrown out, tried to make a custom hole 3 times (for the fencing wire), gave up. Seems a very good candidate though, if one could bore a good hole. I will post results if I make it work.

-Copper/Nickel alloy and Zinc thrown out (reason not disclosed) due to inability to drill a clean hole with my samples. I think they will work fine if one has the correct bit/width of pinning material.

-Pine is too soft. Fit is good but loosens.

-Cedar is too soft. see pine.

-Sycamore is too soft. I was using a not-completely dry sample though (from a brush pile that has been outside (so not fully dry conditions) cut in April (so not a whole year)

-I had stated I would test horn, bone and tusk. I am unwilling to use the horns we have for experiments. I apologise. I don't have a bone right now, though will probably have one tomorrow or the day after. Tusk (from a warthog, but similar to ivory) will have to wait until I get permission from my father, but I should be able to test one.

I will take pictures of the Osage Orange and Lexan (and possibly others) if they pass the test of hanging a 5ish pound weight overnight. So people can see proof. My bet is on Lexan though. It is working wonderfully.