Thread Milling
Threads are usually created by a tap for small internal threads or a die for small external threads. Taps work well for small (usually under 1 inch) holes, but when the thread diameters are larger the cost of the tap becomes prohibitive and the required torque on the tapping spindle may exceed the machine tool's capability. The same is true for cutting external threads with dies.
Because of the high cutting torque required to drive a large tap, the risk of breaking the tool in the part is increased. If the tap is broken in a part, it is very difficult to remove without damaging the part. Thread Milling is one solution to these problems. Thread Milling uses a special type of milling cutter that profile mills the thread using either single or multiple flute thread cutting tool. Thread milling is a finishing operation for machining threads that have large diameters.
Thread Milling Considerations
The following limitations should be considered when using Thread Milling:
Selection of thread features is currently not available. You must select the cylindrical face associated with the thread feature. Each cylindrical face has only one associated thread feature.
A single deselect cannot be performed when Select All has been used. You can deselect geometry using Remove/Remove All in the Edit mode.
You should not Rename or Copy an operation in the Operation Navigator. This limitation is because Thread Milling is implemented as a User Defined Operations.
If you are using the Circle option, the diameter of the circle will be compared with the diameters in the thread table file. There are two default thread table files, one for English unit threads and one for metric unit threads are supported. The environment variables UGII_ENGLISH_THREADS and UGII_METRIC_THREADS are used to identify these thread table files, respectively. If the diameter is not available in the table file, the closest diameter available is selected for machining. If the tables that we provide are not the standard that your company uses, you can modify the tables as required.
You should exercise caution when using helical/linear engages and retracts. Gouge checking is not performed during these motions.
The insert length of the tool should be such that the number of teeth available on the tool should be greater than the number of teeth. The number of teeth can be computed as per the formula below:
Number of teeth = Insert length/tool pitch
The thread features cannot be selected using Name. There is no selection mask.
Accessing Thread Milling
Thread Milling is implemented as a User Defined Operation. To create a Thread Milling operation, set Type to mill_planar or drill and select THREAD_MILLING Subtype in the Create Operation dialog.