Reply To: Single Point Threading

[david pierce]

William,
Whenever I cut a thread the first thing I did was calculate the dimensions of the thread form. Much of this information can be found in MACHINERY’S HANDBOOK under threads. The thread you cut is called a 60 degree thread. This refers to what is called the included angle. The included angle is the angle between the two sides of the thread walls. One half of 60 is 30 so that is the angular path you want the cutter to follow when you are feeding the tool into the shaft. Your ATLAS LATHE and any true engine lathe has a compound axis that is to be set to 1/2 of the included angle of whatever thread form you are cutting. There are exceptions to this such as a Butress thread but don’t be concerned about that right now. Since the thread is a 60 degree thread, the cutting tool needs to be ground to that angle. The least expensive way to do this is to use at tool called a 60 degree center gage and a bench grinder. Enco sells these tools: 615-6300, 326-1096, 890-1357, 240-0228. They are inexpensive tools and are extremely helpful to grind and set up the thread cutting bit. The tool looks like and arrowhead with notches cut into it. The idea is to grind your tool bit and check the angle by putting the bit into the notch to make sure it matches. When this is done and your part is in the lathe, the tool is placed along side of the part and the bit is adjusted until it fits perfectly into the notch of the tool. once this is done, the tool is locked down. When cutting the thread, the tool is advanced into the work with the angled compound axis. The X axis is used only for positioning. For a simple screw or bolt, the thread depth can be checked with a nut. For more critical work, thread wires are used.
david