"Jon Elson" wrote in message
ervers.com...
Harold and Susan Vordos wrote:

I know about these, and I know they are totally inappropriate for most
home shop sized machines. With my smaller machines, I just don't even
THINK about negative rake. They can plow lots of material, but you need
lots of HP, and a very rigid setup. I was just trying to keep things
simple for the guy.

Jon



It was hard for me to understand that when you said:

"Pretty much all standard milling
cutters are set up for some positive rake. So, there shouldn't be any
concern
for rigidity and power when making the decision between the cutting
tool materials."

The negative rake insert shell mills I spoke of are included in the
group of
cutting tools that are considered *standard*. A general statement that
insert cutters are positive in nature simply isn't true. That was, and
is,
my point. You are wise to not try them on light duty machines, and, I
agree, the home shop is highly unlikely to have machines that can handle
such cutters, but some do.
Yup, I was just trying to simplify what can get quite complex, and went
overboard. I suspect you could use a cutter with 2 negative rake
inserts on a Bridgeport, but probably anything lighter than that would
have a problem with even two inserts on the cutter. The original poster
didn't describe his machine, so that makes it harder to recommend
anything. I know some Bridgeport owners have gotten a steal on a
big multi-insert shell mill, and ended up taking most of the inserts
out to keep the machine within its power and rigidity limits.

Jon


For 18 months, just prior to starting my own shop back in '67, I was
employed by a real nice job shop in Salt Lake City, United Precision. They
had a few Bridgeports on which they ran a small insert carbide cutter, but
I'll be damned if I can recall if they were positive or negative. I seem
to recall positive, though. I spent my entire tenure there on lathes, so I
didn't use them. At any rate, I think they had three inserts, and were
relatively small, maybe 1-1/2" diameter. It was about all a Bridgeport
could handle at that time, but remember they had only 1-1/2 horse motors.
The 2 horse models with vari-drive came along much later, something like
early '77 if I recall.

Your comment about great buys on large shell mills for light machines really
brings a smile to my face. In truth, what they really bought was a large,
expensive fly cutter. Before some of these things make sense, often a guy
must see how they are put to use properly. Only then will the novice come
to understand the huge differences in machines, and understand their
advantages and limitations. Large multi-toothed cutters require a huge
amount of power and rigidity in order to function anywhere near their
capacity. Anything less is a waste---particularly in tool life. Cutting
tools don't like to idle--it's tougher on tool life than making a cut.

Harold