Threading Nitronic 60

[SpaciouS]

Hi,

Background:
We have bushings and "extremely fine" (M3 x 0.2 mm pitch) adjuster-set screws used in kinematic mirror mounts for some of or optical systems. The bushings are made of brass and the adjuster screws are made of 303 stainless steel. We have some design concerns and one of them is the brass bushing and its wear characteristics. So I'm wondering if I could make a bushing made of Nitronic 60 instead of brass.

Question:
Does anyone know if you can thread a pitch as fine as 0.2 mm, within a diameter range of 3 mm to 5 mm (M3 x 0.2 - M5 x 0.2)?


Thanks,
Sean

 

[dgallup]

I can't say I've tried it first hand but Nitronic 60 is quite tough to machine and those are some seriously small threads. I think it would lead to a lot of broken taps and gnashing of teeth. If you do try to tap the Nitronic 60 I would keep the tap drill to the high side to minimize the depth of cut the tap has to make. Generally, with these highly work-hardening alloys you want to be pretty aggressive with the speeds and feeds. Going at them slowly just hardens the work piece. However, I'm sure you can not get very aggressive with an M3 x 0.2 tap.

I would be more likely to try an electroless plating process such as nickel or nickel-cobalt, possibly with a bake (heat treatment) to give the brass surface better wear properties. How often do these screws get turned? 303 does not have very good wear properties either.



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[SpaciouS]

dgallup thanks for replying,

First to answer your question, "How often do these screws get turned?"
These screws are not adjusted all that much when compared to a typical environment. However they do get adjustments when calibrating the optical sensor and the challenge for us is our sensors measure "marks" on a wafer at the nanometer level. So when we say we have "wobbly screw" issues, it's not on a common scale.

Because of our level of alignment specs, cost often takes a back seat (just fyi).

For Nitronic 60, have you considered alternative thread techniques other than using a tap?
Maybe “sinlge point” threading?
or
Maybe” thread ground”?




Thanks,
Sean

 

[MikeHalloran]

There's brass, and then there's brass.
Start at copper.org and see if you can find something that's available from your bushing supplier's bar supplier, and more in keeping with your requirements.



Mike Halloran
Pembroke Pines, FL, USA