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what material should I use for a new tailstock quill?

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Diamond
Joined
Sep 25, 2011
Location
Garbsen, Germany
I'm repairing a spare tailstock for my Studer RHU grinder, and need to make a new quill. Approximate dimensions are 32mm (1 1/4") diameter, 215mm (8.5") long, MT2 socket. I plan to rough turn it, rough turn the taper using the compound, finish the taper with an MT2 taper reamer, then put the quill onto my cylindrical grinder and touch up the OD.

What material you suggest for this? One choice would be 42CrMo4 (1.7225 or 4140 prehard). Or should I use another type of steel and take it to a hardening shop for nitriding or case hardening or carburising (after which I lap the MG2 socket and grind the OD)?
 
I made a new quill for my Monarch 10-EE out of LaSalle ETD-150 "Fatigue Proof" from McMaster. It is holding up well. It machines very nicely, because it is resulphurized. It has 130ksi min yield and HRC 32 min hardness. It is in the 41xx series of steels. It has little to no residual stress, and therefore doesn't warp when machined asymmetrically, like for a keyway.
 
Thanks for the helpful replies. What I have on hand in the right size is C45, 42MnCr4, and 16MnCr5 (1.7131, EC80, 5115). One of my friends has advised me that the 16MnCr5 (5115) would be a better choice than the 42MnCr4 (4140). Is that right?
 
Well, I don't have a specific recommendation but perhaps we could kick around the various issues that might suggest one direction or another.

In service, what challenges will the quill see? Is ultimate strength an issue? Is it subject to wear and if so what kind, abrasion impact or what? Another way of looking at what might shift a choice one direction or another is comparison with what those steels are most used for in industry. In automotive usage, the 4140 is often used for axles which might have a comparison to a quill. IIRC manganese additions to steel improve its impact resistance so would be used more often for edges of earthmoving equipment which doesn't seem relevant to a grinder component.

You also mentioned the prospect of hardening or case hardening. This might have a couple impacts. You note that it would be ground after heat treat. This could be advantageous for wear resistance but be more problematic for the internal taper unless you have good ID grinding capabilities. And wear resistance might also cut two ways. That is, if one component will wear more, you might prefer it to be the more easily replaceable one rather than a more expensive or difficult item. That last issue might suggest taking the hit on the quill rather than the grinder casting. Reducing wear around a grinder would seem like a natural advantage for case hardened 5115 but it might have less desirable consequences.

So I guess, all told, I'd choose the 4140 because you can control accuracy better (perhaps less warpage) and it would have less likelihood to shift wear to the adjacent, presumably more expensive component.
 








 
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