CNC for CAD Users in One Easy Lesson.

I had to turn in a document as part of the group project on NC programming toolbar in Catia. As the machinist, I was considered to
have a "special" understanding. This is what I knocked out. (the two pictures didn't make the cut and past,
CNC for CAD Users in One Easy Lesson. 'pyotr filipivich'
Chapter 1     There is no such thing as “one easy lesson” when it comes to CNC.
Chapter 2
    The two things to remember when it comes to machining:         1) If the material moves but the tool doesn't, it is a lathe.         2) If the tool moves but the material doesn't, it is a mill.     Two other things to keep in mind: if you are not making chips, you aren't making money; and night shift coffee is not to be drunk by ordinary mortals.         “Tool life is the most important factor in a machining system,      so feeds and speeds cannot be selected as simple numbers, but      must be considered with respect to the many parameters that      influence tool life. The accuracy of the combined feed/speed      data presented is believed to be very high. However, machining      is a variable and complicated process and use of the feed and      speed tables require the user to follow the instructions      carefully to achieve good predictability. The results achieved,      therefore, may vary due to material condition, tool material,      machine setup and other factors, and cannot be guaranteed.” Pg.      994, Machinery's Handbook, 26th Ed , Industrial Press
    Feeds and Speeds, as implied, are a function of a number of variables, but to over simplify, it is to get the optimal chip load possible with a given cutting edge (usually less than .005” for roughing work, and between .001” and .002” for finish work), and how fast that edge can be forced through the material without failures. The more teeth the merrier (up to 4[1]), which is one reason most mills have four flutes, as it quadruples the chip production per revolution, increasing speed of the spindle in RPMs, and thus the possible feed rate of the tool through the material. If you are ever in a situation where the details are part of your job, you will become familiar not only with the Machining Operations section of The HandBook, but with every policy, procedure, practice and personal preference of the people you work for.
    One of these preferences will be in regard to Conventional vs Climb milling. Climb milling is so called because the cutting tool rotates in the same direction as the material travels, as if the tool is “climbing” the face of the material. The advantages of climbing milling is that the chips are tossed “behind”, the tool does not rub the material, (causing work hardness), and a smoother finish is left. A drawback is that it applies larger loads on the cutting tool which can be excessive if there is a backlash problem. [Backlash is the cumulative “play” in a mechanism when reversing direction of movement.]
    Conventional milling does not have the backlash problem, as the tool is rotating against the motion of the material. As can be seen below, the chip thickness begins at zero and grows to the full “chip thickness”. However, before the tool bites into the material, it rubs across the material, which can cause work hardening, and wear on the tool. Chips produced are tossed ahead of the cutter, thus conventional milling requires chip removal by flood coolant or air blast, as there is the risk of chip welding to either the material or the tool. Not good. Using conventional milling will usually produce an inferior finish than a climb cut with comparative feeds and speeds, generally speaking.     That said, there are times when the conventional wisdom needs to be set aside.
Chapter 3     There are a number of other issues to be aware of. Drilling is not Boring, the former uses “specialty” tool bits called drills to perforate a solid along the axis of the intended cavity, leaving a rough surface. Boring concerns itself with the sides of the cavity, and can be considered turning on the inside of a part, for putting rings inside a cylinder, or opening out a blind hole.
    Three Axis Vs. five axis machining. Three axis machining limits spindle motion to the X, Y and Z axis. With the right programming, you can get some very smooth curves, but all pockets will open in Z. With a 5Axis machine, the spindle head is able to rotate in two additional axis. The result is that rather than having to remove a part in order to mill on the side, the head can be rotated and what was formerly the “side” can now be treated as a “face”, and a pocket can be milled at an angle not otherwise possible. It can get very tricky, and you will know a whole lot more about it than I do before being turned loose to program any such tool paths.
[1] Joseph R Brown of Brown & Sharp began making “coarse” tooth cutters in the 1860s, Adolph L. De Leeuw of the Cincinnati Milling Machine Co demonstrated the science behind it in the 1920s. -- pyotr filipivich. Discussing the decline in the US's tech edge, James Niccol once wrote "It used to be that the USA was pretty good at producing stuff teenaged boys could lose a finger or two playing with."    
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typed in alt.machines.cnc the following:

    Yeah, I thought of that ... after I turned it in. On the other hand, I had in the back of my mind shaper tables. Where the material is held rigid while the tool moves. Which is backwards, and so shaper tables are "lathes".     And what with all the new fangled live tooling and multi-axis spindle heads - you can have both the tool and the metal moving. "Wasn't like this when I was a boy - dag-nab it!"
--
pyotr filipivich
Rock is Dead! --- Long live Paper & Scissors!
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