As usual, the forum community comes through with excellent information, and I thank you all once again. Here are 2 more questions that I am now at the point of dealing with:
1.) Suppose I want to route out a flat, level area that is in the shape of, say, a star, in flat material, and I want to have fairly sharp corners. I will use the offset tool set for a 1/8th inch end mill bit, which will give me satisfactorily sharp points on the star. But the star is large, and I don't want to have to route the whole thing with a 1/8th inch bit. How do I write the program to allow for a tool change to a, say, 1/2 inch end mill?
2.)I have used a 1/8th inch end mill to define a work area on my table by drilling down into the table with the bit at the 4 corners of the work rectangle. I have zeroed the xy to the lower left corner of that rectangle by setting the zeroes at the place where I drilled that hole. I then drew lines on the table that touch the outside edges of each 1/8th inch hole. Should I change the xy zero locations to account for the center of the bit being 1/16th of an inch from the line? Will the software know to offset from that 00 location when I change bit sizes?
Thanks again, and Happy Holidays to All,
Bob

Hood -

Yes, like you, my x axis homes between my front tool holder and my drill holder. Following your advice, all my drills are in holders and the tool offsets set so that selecting the tool, then Z0 and then X0 brings the tool to a position on the centreline and 5mm from the chuck.

I have done a similar thing with the cutting tools.

I finally decided on 5mm from the chuck as my Z0 because it allows a parting tool between it and the chuck, and it is an easy figure to remember when designing things.  Ball screws now - so had to go metric.

Bob -

Offsets for milling tools and diameter compensation have been covered many times, but the best one was by Graham Waterworth a few months ago, with diagrams as to which command to use depending on the way you were cutting. Try and look that up, becasue Graham is the man for that sort of thing.

I am not competant enough to advise, although - yes - you can use different sized cutters, and the same program, the compensation will automatically adjust for the width of the cutter. You have a problem with lead in and lead out.

I am wondering if it would be better just to design the star, using the bigger cutter, and writing the Code for the toolpath, then changing the tool and writing code for the toolpath to cut the sharp points, if you see what I mean, and make allowances in the code for the cutter width.

On your second query, your zeroing of the axis was not accurate, because the line you drew was outside the centre points of the bit so your actual 0.0 position is minus 1/16th on each axis, if you are lining up to the lines you drew.

I don't know how many stars you are cutting, but you can now see the benefit of "home" switches. If you can "home" your machine (and the actual position does not matter) then a simple offset G54 - G59 written into the program will always bring the table to the correct position for that program. You only have to set up once 

Ball screws now - so had to go metric.

Ha ha , well supppose you had to come into the modern world at some point in time
Hood