"B.B." u wrote in message
news
In addition to my welding class I'm taking a machine shop class. Our
project involves a little piston air motor.
To make the cylinder for this we're instructed to drill & ream a
blind hole. I finished and reamed the hole, it's straight and clean,
except that it appears a chip wedged itself between the reamer and the
wall and scored the inside of the cylinder, making my piece scrap.
Is that just a danger of making a hole this way, or is there
something I can do to prevent such a problem? I did run the reamer a
bit faster than I was supposed to because the mill I was on had a broken
low range. Could that lead to this sort of thing?

Reamers, at best, are not a great tool for such things. As you progress,
you'll learn about boring. That's the preferred method of establishing a
hole that you want to be straight, round, and on location. Reamers are
notorious for cutting multi-sided holes and creating bell mouth in the
bargain.

When reaming, make sure you lubricate well, and take out less than .015".
Honing the cutting edge often pays dividends, but only if you know and
understand how a reamer cuts. You can render one useless very easily if you
don't know cutting theory.

The scoring you experienced is more likely from some chip welding on the
reamer. If you look closely at the reamer, where the chamfer is on the end,
you're likely to find one flute that has a chip firmly attached right at the
point of contact, the cutting surface. By taking lighter cuts and good
lubrication, plus clearing the reamer adequately, you can usually avoid that
condition. It also helps to not be machining mild steel, which is well
known for tearing.

Good luck!

Harold