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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

7075 aluminum

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sb327:
Interesting.

A single cylinder of this?

Dave

JuryRigger:
I seem to recall reading somewhere that the single biggest factor that would make-or-break  a plain bearing was the difference in hardness between the shaft and the journal-had to be at least so many points on one of the hardness scales difference.. Can't remember what those numbers were, and they'd be absolutely meaningless to me and likely you as well, but the concept stuck in my head  :)
In other words, the same material on the same material at the same hardness will result in quick wearing, and or galling of the mating surfaces...
I believe there is an exception to the rule once you get hard enough, something about the necessary difference growing smaller as the general hardness level went up?.... Some precision lathe spindles were made with a hardened spindle running in a hardened bush, and last a very long time...
Dunno, too much packed into my brain-attic, and the filing system is atrocious...  ;)

Might have something to do with it, also seems to me that 6061 feels 'slicker' than 7075, so there's that, I suppose...
Jesse

sb327:
You are spot on. You should always design a softer/harder bearing surface interface. Obviously the softer being your sacrificial side (inserts in an engine).

It has been studied quite a bit

https://www.bing.com/search?q=hardness+difference+to+prevent+galling&form=APIPH1&PC=APPL

Dave

KWK:

--- Quote from: sb327 on February 24, 2023, 07:22:33 PM ---Interesting.

A single cylinder of this?

Dave

--- End quote ---
I made a very similar single cylinder rotary valve engine like that when I was 14. The exhaust came out through the center of the crankshaft. I still have parts from it out in my shop. I made a better version when I was 15 but lost it in my early 20's.
Here is a wobbler type engine that runs real nice

sb327:
I’ve made a few myself. A  couple wobblers and a dual acting standard (I run it real slow on an aquarium pump).

My favorite I built is a vacuum ( flame eater).

Dave

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