Steel hardness numbers

[Robin GrahamParticipant @robingraham42208]

[Robin GrahamParticipant @robingraham42208]

I might need to cut a bit off an MT arbor. I have a set of hardness testing files which go from HRC40 to HRC65 and (in my unskilled hands) it looks like the arbor steel is in the 45-50 range. Trouble is I have no real idea what these numbers mean other than 60-65 is kind of glassy and brittle.

Can anyone advise in practical terms – eg you can use a hacksaw/bandsaw up to this point, but then carbide, and above that a diamond disk?

Rob

[norman valentineParticipant @normanvalentine78682]

An angle grinder is the answer to your problems.

[Brian Sweeting 2Participant @briansweeting2]

As Norman says, an angle grinder does the business, certainly did for mine.

[HOWARDTParticipant @howardt]

60-65 Rc is grinding hard. 40Rc is tough but machinable with carbide. Neither is hacksaw country.

[MuzzerParticipant @muzzer]

You can machine hardened arbors using carbide tooling (I do) and possibly even with HSSCo if they are <50 HRC. With carbide, you need to run the lathe at top speed and take a half reasonable cut. Try it – you should get swarf coming off burning (take care!).

The process of machining hardened steel causes it to get very hot which softens it. Trying to machine it a slow speed would be problematic.

Murray

[Robin GrahamParticipant @robingraham42208]

Thanks – amazing thing t'internet, ask a question and get the answer within minutes! Angle grinder it'll be then. Reluctant to try a carbide parting tool, sounds like it might work but could cost me a new tool if it went horribly wrong.

Rob

[Anonymous]

The HRC scale is Rockwell scale C, which covers what we'd regard as hardened steel. It is arbitrarily based on the depth of impression made with a diamond tip under a load of, I think, 150kg. There is also a Rockwell B scale, which finishes where C starts. There are many other scales, eg, Brinell and VIckers, but they are all based on indentation of an anvil under a given load.

It is possible to machine hardened steel (>65Rc) with carbide inserts, but they look a bit sad afterwards. I don't think I'd want to try using a insert parting off tool. Using CBN inserts makes turning hardened steel a breeze, but they're expensive.

Andrew

[John ReeseParticipant @johnreese12848]

I have cut off the hardened shanks of straight shank ER collet chucks using a carbide insert parting tool. I have used both the self-grip and the Manchester style from Banggood. When cutting hardened steel the rigidity of the lathe and of your setup are really important. I also turn hardened material with carbide.

Muzzer recommeded keeping the speed low. I have better luck at a high surface speed and fairly light cuts. In parting off you need to feed hard enough to maintain continuous chip flow.

[Anonymous]

I read Muzzer's post as saying run fast?

Andrew

[John ReeseParticipant @johnreese12848]

Andrew,

You and Muzzer are right. I misread the post. Sorry.

[Author]

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