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Carbide tool steel When to use it instead of HSS

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mickri

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#1
My lathe came with a half dozen or so pieces of 1/4" square by 2" long carbide tool steel. What in general would I use this for instead of HSS. I know that's an open ended it all depends question. I am looking general knowledge. I don't have anything specific in mind. My lathe also came with several right hand tool bits with a carbide tip. And last but not least 10 or 12 tool bits with a 60 degree carbide tip that look to be for threading.

Just looking for general knowledge as to when I should consider using the carbide instead of HSS
 

JimDawson

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#2
Not sure that I have ever heard of ''carbide tool steel''. Maybe cobalt tool steel (M42)? But in any case, assuming it is tougher and has higher heat resistance than standard M2 tool steel, then it would probably work well on stainless or other nickel/chrome bearing alloys.

Yes, a 60 degree can be used for threading, and general turning if you like. In general, you use the tool bit shape that will reach the surface that your are machining and have clearance for those surfaces that you don't want to touch or will be done in another operation. In some cases I have used 3 or 4 different bit shapes on a single setup to be able to machine all of the surfaces.

Normally you can turn faster with carbide tools and machine harder materials, other than that they are pretty much interchangeable.
 

mikey

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#3
Good question. I have no experience grinding a square carbide tool bit. Cobalt, yes, but not carbide. I would think that they would be used in a tool holder of some kind but I'm not sure.

The brazed carbide tools can be honed with a diamond stone to be quite sharp. I suggest honing a very tiny nose radius at the tip and hone the top flat. Be sure to follow the relief angles when you hone them to provide as much clearance as you can. If you want to grind them, a green silicone carbide grinding wheel is recommended. I don't use these much but when I do, I use Micro 100 bits. I think you might be surprised at how well they work on a small lathe. They cut quite well, although they won't take a micro-cut as well as HSS.
 

mickri

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#4
Oops. I made a mistake. I just went and looked at the 1/4" x 2" pieces and they do say cobalt on them. The packages for the others in my OP all say carbide.
 

Ulma Doctor

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carbide tooling will cut most of the stuff you can't cut with HSS, Cobalt HSS, & High Carbon Tool Steels
you will need either Green, Diamond or CBN grinding wheels to shape the tools for use.

beware: carbide can be quite brittle, especially on interrupted cuts.

most small lathes will not be able to use carbide tooling to the maximum potential due to lack of rigidity and/or low spindle speeds.
not to say that carbide can't be used, but HSS is superior for a lot of things on smaller machines
 
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