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Posted by Black Dragon on June 1, 2008, 8:55 am
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John2005 wrote:
> Tool steel at RC 60 would be plenty strong. What type of cutter and
> feed rates are needed to machine tool steel this hard ? I didn't think
> anything would really cut tool steel that hard, let alone do it cost
> effectively. EDM may be a way to go as well, but I'm not sure
> expensive it is for two prototype pieces to test.
Again. What's the application? What tolerances do you need to hold? Why
do you need pre-hard material, are you trying to avoid the cost of heat
treat you may be able to do yourself if you select the proper material?
> I think most tool steel at around 52-55 RC would have a yield around
> 300,000 PSI which would be plenty strong (280,000 PSI compressive
> yield strength would be enough for me) . A2 or S7 would probably be
> ideal, but I don't know if their available in pre-hard, or at these
> hardness levels. Generally I had thought that anything at these
> hardness levels pretty much had to be ground.
A2 and S7 are typically very stable in heat treat when done by
commercial heat treaters that service the mold industry. You can expect
growth of approx .0008" per inch after heat treat and very minimal
warpage and distortion. S7 is tough steel which will bend before it
breaks and can be hardened up to approx RC 57. A2 steel is used in wear
applications and can be hardened up to approx RC 62. I've never seen those
materials purchased in a pre-hard condition. Also, S7 machines much
better than A2 at the same hardness, any steel designed for wear
resistance is going to be more difficult to machine.
Once again, without knowing what your application is it is difficult to
recommend the best material.
Anything to around RC 55ish is readily machinable (mill or turn, forget
drilling at that hardness, if you have to thread - mill bore with an
endmill then thread mill) with good TIALN coated carbide and a rigid
spindle. If you're thinking about machining stuff like this in a
Bridgeport you're destined for a colossal headache.
> I've drilled and countersunk pre-hard 4140 (I think it was 27-32 RC).
> I just used a new HSS bit and I was surprised how easy it cut but I
> had always thought machining tool steel in the 55-60 RC range was out
> of the question.
The Viscount 44 I mentioned is RC 42/46 and it can be drilled and tapped
with HSS tools.
--
Black Dragon
Todays title:
Creative Violence in Sexual Relationships
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> feed rates are needed to machine tool steel this hard ? I didn't think
> anything would really cut tool steel that hard, let alone do it cost
> effectively. EDM may be a way to go as well, but I'm not sure
> expensive it is for two prototype pieces to test.