Rozen-guy, you are a man after my own heart! Show me someone who grinds his
own HSS tools and I'll show you a craftsman.

Bob Swinney
"jim rozen" wrote in message
...
In article Eddkb.586100$cF.255267@rwcrnsc53, Bob Swinney says...

Be careful not to confuse rake with relief.

Indeed. I like to form turning tools from HSS
blanks using three grinds only:

First grind forms front relief and front
cutting angle, and is done on the front of the
blank.

The second grind is done on the side of the
tool, and forms only side relief. This grind
has its axis exactly parallel to the tool
blank's axis, and is done so that the edge of
the grind exactly intersects the side corner
of the tool blank, as nearly as possible.

Stopping at this point turns the tool into
a brass-turning tool: No side rake at all,
it has a flat top, formed by the factory
top surface.

But for turning steel, there's a third grind:
the one that forms the side rake. That grind
is likewise done parallel to the tool's long
axis, and likewise is done so that it terminates
at the very corner of the factory square shape.
(once again, this edge is the corner between
the top surface, and the left surface of the
tool, for a tool that cuts towards the headstock)

If this grind is done with back angle, then the
cutting tool has both side, and back rake as
well. Many folks feel that back rake is essential
to good cutting, I've never found that to be true.

The advantage to grinding lathe tools this way
is easy to understand - the cross section of the
cutting tool does not vary as one moves back from
the working edge. The tool can be sharpened by
simply doing a new front grind, and the geometry
and more importantly, the *height* of the cutting
edge is nearly unchanged. [1]

Honestly this is not as good as using insert cutting
tools, but for the home shop type, it's nice to be
able to do a quick touchup on the tool in the middle
of the project, and have the height and geometery
stay almost exactly the same.

Jim

[1] getting the formed cutting edge to be exactly
coincident with the factory corner of the tool requires
two things: a grinding wheel that is dressed quite
flat, and a steady hand to sneak up on the corner.

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