In article , Jon Elson says...

The Connelly book is too old and not terribly specific about the
tools available now.

Yes. As I mentioned before, it does not do a very
good job of explaining the *real* basics of how to
take a stroke with a scraper, or how to sharpen one.

But, if your iron part is too hard to scrape, there must be something
wrong with your scraping blade. It should be flat and polished on the
wide sides, and have a very wide radius on the end.

This was really, really non-intuitive for me. I had tried
to make a small scraper blade from HSS toolbits before having
read Morgan's book, and it bore no resemblance at all to
what he showed they are supposed to look like. It was not
clear to me, either, that the correct blade would perform
at all in the way it should (but of course they do) from
a preliminary examination.

I guess what suprised me is that all of the hand scraper
operations are *negative* rake cuts. The rounded end
of the blade is is ground such that the cutting edge is
formed between the side of the blade, and the end surface
that the user grinds into it.

And that the end surface is really two two grinds that meet
along the centerline of the blades thickness, and the
actual cutting edge is slightly more than 90 degrees.
That, combined with the angle that the scraper makes
with the workpiece, gives a large negative rake angle on
the cut. And I was suprised at how well one can remove
metal with such a configuration.

You hold the
tool nearly flat to the work and push it in small strokes across the
surface. The first pass or two are harder, as there are lots of
hills to dig into. You approach the work from varying directions
each pass to prevent rows of hills from developing. Once the
surface begins to flatten out, it gets pretty easy to do the scraping,
and it shouldn't take much downforce to make the tool bite lightly
into the work. You don't want to take cuts like a lathe or shaper
tool! You should get dust mixed with the spotting dye, but never
curly chips, except on the first pass of a badly roughed piece.
If you need to make chips, do that work with a powered machine,
like a mill or shaper, and leave the last .001" or less for the
scraping.

That's right, Morgan makes it clear that one has to have the
surfaces within a thousanth or so by other means, before scraping.
Also that grinding is a very poor way to prepare a surface for
hand scraping, as it gives local hard spots. As you say,
milling is prefered.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================