For decades, CAM threading toolpaths were simple point-to-point toolpaths or canned cycles that required specific tooling for the threads to be cut.
Over the years, support for multi-start threads, tapered threads and cross centerline single-point threads were added, giving more control over complex threading processes. Thread milling is a revolution in threading operations.
Threading a hole with a traditional tap inherently puts a lot of force on the cutting edges.
Tool designers battle between keeping the tool rigid enough to handle these forces while minimizing the tool profile to allow for chip evacuation. Bottoming-style taps for blind holes suffer most from this design dilemma. Plug-style taps are designed to push the chips down, so designers can make these taps much more rigid—but the enormous forces on the cutting edges are still a concern. Unless there is a through-hole to thread, plug-style taps are seldom a viable option.
Thread milling reduces the cutting forces exponentially by reducing the area of the tool in contact with the material. This results in much higher stability for the threading process. Tool life for a traditional tap can be incredibly difficult to predict; thread milling tools wear more evenly, consistently and predictably. Thread milling can boost overall process efficiency—especially in gummy, difficult-to-machine materials such as stainless steels. These advantages are reflected in most modern CAM systems’ ability to create toolpaths for thread milling.
Chip evacuation is often important. Recutting chips will immediately result in decreased tool life or broken cutting edges. Another major problem with single-point threading in turning centers is “chip nesting,” which results in long, stringy chips wrapped around the cutting tool. This is especially true in ID threading—it prevents coolant from reaching the cutting edge. Programming fixes such as Sandvik’s OptiThreading targets the problem of chip evacuation and is a solution helpful for “lights-out” machining.
Newer machines can more accurately control acceleration/deceleration, while innovations in servo drives and processing hardware have allowed for smoother directional changes than ever before. For example, “orbital” machining is a process for single-point threading with a machining center that keeps the tool pointing toward the centerline (or away from in ID work) while using the XYZ axes to create the helical motion for threading.
Software advancements including Mastercam’s Custom Thread toolpath allow programmers to use a generic shaped tool to cut any shape or size thread the tool will physically fit into. This approach allows for machining of virtually any helical shaped pattern—square, rope, trapezoidal or custom thread profiles.
Fundamentals boosts efficiencies. For instance, through-tool coolant is a big tool life improvement. It keeps the cutting edge cool and lubricated, and chip recutting is greatly reduced.
Also, correct hole preparation can be easily overlooked when troubleshooting threading problems. The drilled/bored hole or turned diameter may not be inspected closely enough before the threading process is executed. Straight, round and properly sized diameters for the thread size and tolerance being machined will provide the best foundation on which to machine threads accurately and consistently.
Cutting tool distributors and CAM software technicians are a great resource. A quick chat by phone or email can be the difference between a profitable job or hours in a “whirl”wind.
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