Greetings Jon and Jim,
I have been trying, with a carbide scraper, to scrape a little. I have
read that book about machine tool rebuilding by Connely. But it seems
to take a lot of force. I do have bad wrists so maybe it is not as
hard as I think. I have looked at one page about scraping that has
been posted several times here but it doesn't tell me enough. Could be
that I'm just dense.

The Connelly book is too old and not terribly specific about the
tools available now. As for force, it should not take much force
to scrape cast iron. I scraped in the Michael Morgan straightedge,
and it took a long time, my wrists DID get tired, but not very
quickly. I could scrape for 3 hours at a stretch before I was sore.

I am now scraping a lathe cross slide that is cast steel, and was
flame sprayed with hard Chrome. The scraper blade literaly could
not even scratch the Chrome, but it scrapes the steel pretty nicely
now that I've rubbed the Chrome off with a Cratex grinding wheel.
(I had to remove the Chrome because the flame spraying operation
warped the part!) I can only scrape this part about an hour at a time,
it takes more force than cast iron.

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. 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.

And, if you are trying to hand scrape a steel part, you certainly want
to anneal it first!

Let us know a little more about what you are trying to so, and maybe
we can offer more specific help.

Jon