Setting up end mills for CNC, and other things.

I'm working on my first program that will use two different end mills.
I don't really "need" two, I just want to use two as a learning
exercise. So I'm programming the machine to make one pass round the
profile with a 5/8" 4F hogging mill, followed by a 4F 3/4" end mill to
make a finish cut.

First an observation: I was interested to learn while playing with the
speeds and feeds calculator that within the constraints of surface
speed of the cutter (I happen to be using all HSS end mills) staying
constant, and number of flutes staying the same, when profiling around
a part, it is apparently faster to use the smallest end mill that can
safely make the required depth of cut.

Why is this I wondered? I constructed the following answer for
myself. The smaller mill makes more cuts per second at its given
surface speed because the cutter lips are closer together for the same
number of flutes, so it can be fed faster while carrying the same chip
load (say .002" per lip). I guess this shouldn't surprise me, I just
hadn't run into it before using a manual mill with an un calibrated
potentiometer setting the feed.

But I am straying away from my questions.

First: Using two tools, I need to pay attention to the differences in
offset for the two tools. To that end I'm working at learning the
Anilam's "tool" commands. I am having a bit of a problem with BobCAD
getting it to program corners correctly (move in an arc centered on
the corner, radius equal to cutter radius) on the part profile with
out using an offset path so that when I implement the offset in the
controller, it will cut where it is supposed to on corners that are
square or pointed. For example, if I set up an offset tool path it
will show the cutter centerline moving in a 90 degree arc with the
corner of the part at the center of the arc when it goes around a
corner. I'm not so sure I'm getting that except when I use the offset
function in BobCAD so I can see the path. Is there something special
I should be doing on corners, or should I just manually take the
cutter centerline past the edge by a cutter radius?

Second: Do you have any trick ways of setting up the vertical
offsets? My current plan is to go to the machine, install tool 1,
move it down to touch the top of the tooling fixture, read the "Z"
readout. Then do it again with tool 2, repeat for all tools needed.
Note the difference in "Z" readings form some "standard" and account
for that by manual programming. Is there an easier way?

Third: How do you go about measuring tools in holders so that it
isn't necessary to re-baseline the tool in the holder by installing it
and going to some place to touch it down? My number of tools is small
enough that touching it down to the top of a 1-2-3 block to find out
where it is relative to home isn't that big a deal, but it seems like
it would be better if I had a fixture I could put the end mill holder
in and measure the "Z" offset that was going to need to be in the
program.

Fitch
In So. Cal.

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