How hard ?

[Coomba]

The last couple of weeks I have been working on my first model engine. It's a Webster. Some parts have been a bit of a challenge, but with a little research I have been able to figure it out. One thing that I have not been able to find, the the drawings says to polish, harden, and to temper the wrist pin, crankshaft, etc. but is does not say how hard to make it. I will be using 01 drill rod for these parts. So what does everyone else do? Thanks guys

 

[bazmak]

Heat to cherry red and quench.Polish,heat to straw/light blue
and quench quickly.Will usually suffice for most things
Regards barry

 

[Cogsy]

Whenever I've hardened drill rod I've only ever heated and quenched once, then tempered it in the oven at about 200 C for an hour, then left it to cool slowly in the oven. Always been plenty hard and not too brittle, although I've only ever hardened for tools, not engine pieces.

 

[Coomba]

Heat to cherry red and quench.Polish,heat to straw/light blue
and quench quickly.Will usually suffice for most things
Regards barry

Should it be hardened, before it's polished, then tempered? Seems it would be easier to polish then harden?

 

[chucketn]

Polishing usually comes between hardening and tempering, to allow you to see the color change when tempering via torch. If you are tempering to a specific temp point, as in an oven, it doesn't matter when it's polished except for desired finish and appearance. Both hardening and tempering will discolor the metal.

Chuck

 

[Coomba]

Polishing usually comes between hardening and tempering, to allow you to see the color change when tempering via torch. If you are tempering to a specific temp point, as in an oven, it doesn't matter when it's polished except for desired finish and appearance. Both hardening and tempering will discolor the metal.

Chuck

I have used a torch for hardening, but not for tempering. I have always, polished, hardened, cleaned, and then put parts in my lead pot for about an hour. This gives the 01 about a RC 57-60. I'm afraid with my old eyes I could not distinguish the lighter colors.

 

[Coomba]

I have used a torch for hardening, but not for tempering. I have always, polished, hardened, cleaned, and then put parts in my lead pot for about an hour. This gives the 01 about a RC 57-60. I'm afraid with my old eyes I could not distinguish the lighter colors.

Ok then, I'm assuming that my way would be acceptable, and that RC 57-60 is plenty hard.

 

[kquiggle]

I've got a related post up - a question about polishing bronze bushings (and the pins/axles that go in them).

With respect the this particular post, since this piece of the Webster (wrist pin) is essentially the axle on one end of the crank, my assumption is that both the pin and related bushing (unless you are using a ball bearing) need to be polished as a final step to reduce wear and friction.

My intention for the wrist pin was to heat to red heat, quench, and then temper in an oven. The only reason to polish between the quench and temper is so that you can observe the color change, but if you are using an oven there is no need for that (I find that quenching in a toaster oven at maximum setting for 1 hour does the trick). I plan to make the pin diameter (prior to hardening) just slightly larger (.001" - .0005") than the finished diameter, so final polishing with abrasive cloth won't require much material removal, and abrasive cloth should work even after hardening. Well - that's my plan, anyway.

Now to figure out how to polish the bronze bushing.

 

[mcostello]

There are 2 processes that come to mind, ballizing and roller burnishing, just for the record.

 

[kquiggle]

mcostello - Doesn't seem to me that that ballizing or roller burnishing are the right way to go for this particular application - I would think that lapping is probably closer to what the designer had in mind.

 

[kquiggle]

Well I finished my wrist pin. I ended up polishing (lapping) the bushing very briefly with 1200 grit paper. I polished the hardened and tempered wrist pin with 600 grit paper - just enough to remove the scale, and then continued with 1200 grit paper until I got a good fit in the bushing. Here's a picture of the completed pin and con-rod. For more pictures and more details, visit the link below the picture.

https://sites.google.com/site/lagad...lathes-mills-etc/build---webster-engine?pli=1