Tempering Screws for Polishing

[Steve CrowParticipant @stevecrow46066]

I have made and hardened around 80 M1.6 screws which I intend to black polish (or as near as I can get).

My question is, what temper to take them to?

G. Daniels recommends dark blue before polishing but a lot of components he refers too need a bit of "springiness" so that makes sense.

I would have thought that the harder the steel, the better its ability to take on a polish. I'm wondering if I might get better results with a light-straw temper or even none at all.

As my screws are for clock components and have no lateral load, it shouldn't matter if they are on the brittle side.

Cheers, Steve

[Steve CrowParticipant @stevecrow46066]

[Peter Cook 6Participant @petercook6]

Have consideration for future repair persons!

In 50-100 years when time, muck and corrosion have stuck the screws in firmly, really hard screws are more likely to break when being removed.

I don't think hardness has much bearing on the quality of the shine, in fact too hard might even prevent the polishing process from removing the imperfections. Think about the shine you can get on silver.

Go with Daniels you won't go far wrong!

[Tim StevensParticipant @timstevens64731]

I find it difficult to align the two words Black, and Polish, in relation to heat treating steel. It would help, too, to know what heat treatment has already been applied to the steel. If they need to be tough, it is likely that heating above the temperature at which the temper was drawn will reduce this toughness. And although modest heat does colour steel, the temperature required for a good black is well above normal tempering temperatures. But then we come to the polishing bit. This normally requires abrasion, with stages in which the fine-ness of the grit is reduced almost to nothing. The result, on steel, is a bright clean shiny surface like a mirror, a bit grey rather than silvery, but certainly not black. So, polish and then blacken. But the temperature for black will destroy the very shininess you have achieved. Once the tempering gets hotter than a dark purple, the corrosion (for that is what the colour is) becomes too deep to avoid destroying the flatness on which the polish depends.

Or have I got it completely wrong?

Cheers, Tim

[BizibilderParticipant @bizibilder]

"Black polishing" is nothing to do with hardening or tempering. It is just a case of getting such a "perfect" polish that the steel appears to be black. This is usually achieved by polishing as well as you can and then going one stage further with diamantine and oil. Clickspring does a demo here Video look at the finish about 2m 04s into the video. (Yes, he does harden first! but this is not necessary.). He uses arkansas stone dust to get his first polish and the diamantine to get the black reflective finish.

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