The Value Of Probing On Turn-Mills

Turn-mills are attractive because they can oftentimes carry out all the operations needed to complete complex components like the shaft shown on the following page. In this case, an M50 Millturn machine from WFL Millturn Technologies turns journals, mills gears, drills holes, broaches internal splines and hobs external splines to complete the part. (The video to the right demonstrates these various operations.)

However, there’s a twist: This shaft must be hardened. And that means two setups are required. Roughing operations are performed prior to heat treating rather than having the turn-mill (or “millturn” as WFL refers to it) machine the entire workpiece in a hardened state. The workpiece must then be finish-machined on the M50 Millturn after it’s hardened. Although heat treating brings the workpiece to the specified hardness, it also slightly “bananas” the shaft. As a result, the part must be carefully measured once it’s reinstalled in the machine so that the program can be tweaked to compensate for the twisting distortion.

Manual measurement combined with subsequent program adjustments can take many hours for parts like this shaft that have complex features. However, WFL has developed canned probing cycles for its machines to automatically measure such parts and update the NC code for the finishing operations. For this workpiece example, a touch probe measures specific points on the gear teeth in the center of the shaft. In doing so, the gear’s pitch diameter is determined as is the true position of the gear centerline. The true position of the gear centerline is really what’s important. That’s because the machining code is automatically updated so all shaft features are machined to the gear’s true (measured) centerline, not the machine’s centerline. This ensures precise feature-to-feature accuracy after finish machining.