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Milling is a great way to create a thread. Recall from last month's column that we discussed advantages of thread milling. Some people might be concerned with programming issues when thread milling. Well, let's look at a sample. The following program is designed to thread mill a 2.625x14 TPI internal thread using a 1'' diameter multiple flute cutter with 3/4'' flute length.
The plan is to position the cutter to the lowest point of the thread and feed out of the part. Our program calls for the tool to use a 45° ramp-in move, complete a 360° rotation within the part and then finish with a 45° ramp-out move.
For this program we are using the center of the threaded hole as the datum. At this point, the coordinates are X0, Y0. The first thing to calculate is the cutter start point called the "pivot" point. This can be calculated as follows:
Pivot point =(part diameter-cutter diameter)÷2
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