Hi Dan;
I think what might have been said was to use "bar stock", which is any stock metal shape, as in square,
rectangular, flat, as well as round. What I'm getting at is, you don't have to limit yourself to using just
round shapes of metal to carve out your engine. The engine you see in my avatar picture is made from
bar stock metals that include brass, steel and aluminum.
The main reason to make your first engine, or your first few engines out of bar stock instead of castings
is, if you mess a piece of bar stock, you just go cut another piece and start again at the loss of usually
only a buck or two, where if you make a mistake on a casting, you have to buy a whole new piece from
the company you got the kit from, and that can get expensive. Also, castings often have no flat places
on them to help you find a starting point for that first critical cut. Bar stock is generally known to be
fairly flat, straight, or round, so you have a beginning reference.
A while back there was a thread here dedicated to designing a "first engine" for folks starting out in the
machining game. Here's a link to the original article, which contains a lot of discussion and some pics:
http://www.homemodelenginemachinist.com/index.php?topic=6259.0
Hopefully, this link will take you to the download section where you can copy the files for that engine
so you can look over the prints:
http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item218
That engine is pretty simple, and meant to help a guy get a running engine under his belt while getting
him some experience with his machines at the same time. There are a number of other engine plans
in the downloads section. You can find a link to it in the upper left hand of the forum page in the box
that says "Menu". There are also lots of books available. Checking through the downloads section will
get you started on something that can be made from bar stock without putting money out for a book
until you find a specific engine you would like to build.
Good luck!