Feeding Rate Calculation
Because of the circular motion of the cutter as it forms a thread the actual feed rate at the cutting edge will be different from that which is programmed at the center of the tool. For an internal thread, the feed rate at the edge increases when the cutter diameter increases. For an external thread, the feed rate at the edge decreases when the cutter diameter increases. It can be shown as a direct relation between the size of the circle of cutter moves around, and size of the circle cut.
The actual feed rate is calculated by using the standard formula: F = (RPM) X (Chip load) X (No. of teeth)
The simplest way to produce a thread form using an Advent Thread Mill is as follows:
1. center of the hole being the X-Y zero point. Moving the cutter to the center of the hole, then to the thread depth demanded.
2. Move the cutter over a short distance (usually about .02” towards the three-o’clock position) to call up your cutter compensation.
3. The machine in a counter-clockwise direction generating a 1/2 circle and ending at full thread depth at the nine-o’clock position. Simultaneously moving 1/2 pitch at the Z direction. The direction of the Z movement will decide the handedness of the thread.
4. Producing your thread by generating 1 full circle (counter-clockwise) around the center, when moving 1 full pitch in the Z direction.
5. After the full form has been machined, return back to your starting position near the center of the hole. This is done by generating another 1/2 circle (counter-clockwise) combined with a 1/2 pitch move at Z direction.
6. Return back to your hole center, and exit the hole.