radial cam material choice

[petertha]

With my rather lengthy lathe repair issue finally behind me, I am back on the 5-cyl radial project. Thus far I've finished a cylinder mockup, crankcase, crankshaft, now working on the gear/cam business end.

I'm mulling over material type for the cam rings. My plan was O1 oil hardening tool steel. Now I'm wondering if I should consider air hardening. I've never used it before, only O1 on simple parts. In fact have done very little hardening, flame & dunk method.

My understanding of the knife blade crowd is they use air hardening & clamp between 2 aluminum plates to 'quench' in order to minimize distortion of thin blades. My cams are nominal 44mm (1.7") diameter but are kind of swiss cheesed with holes. I don't have grinding facilities. I could tolerate a teeny bit of warpage but not much. Any feedback or experience?

This link shows similar operation, except he used hardening compound. Maybe so as not to risk quenching distortion?
http://philsradial.blogspot.ca/#!/2012/09/cam-assembly.html

 

[Cogsy]

At least for bearing purposes, case hardening is often used so a harder surface with better wear characteristics can be used, whilst the soft inner core reduces overall brittleness of the bearing. For through hardening, the overall hardness cannot be matched without rendering the nearing to fragile to be used. Possibly this is why case hardening was used in this application.

The differing hardening methods is the main difference between Timken brand tapered roller bearings (case hardened) and most of the Japanese brands (through hardened). So if you have Timken wheel bearings fitted and they start to make a noise, they are perilously close to wearing through the case hardening and need to be replaced immediately before they disintegrate. If you have through hardened bearings, well a bit of noise never hurt anything, so just change them when you get around to it in the next 10 thousand miles or so...

 

[petertha]

Yes I should have mentioned (not shown in the CAD sketch), the cam followers are segments of ball profile ended shaft 3mm diameter, instructions say 'silver steel hardened'.

The cam is specified as '16MNCr5 hardened after manufacturing the cam outline'. German instructions, Ohrdorf design, quite abbreviated.

I guess if I want the sacrificial wear part to be the follower because its simpler to re-make if worn, that infers is should be slightly less hard than cam? That's what makes me think the surface hardening 'powder' treatment on the cam more finicky & possibly softer (also mentioned in the Phil link). But it seems the real risk is quenching, hence the idea about air hardening steel which is a slower process & clamped as mentioned. But targeting the same resultant hardness number