A Look at Failure and Reassessment – Jack Ruddat

Last week I tried my hand at machining the base of my monstrance out of 2″ thick aluminum round stock. Because the stock is over 6″ long, both a chuck and a tailstock with a dead center are needed to support both ends so that the pressure of the cutting tool does not cause the part to deflect from its axis of rotation. Although the machining was done on a CNC lathe, the parts labeled on the manual metal lathe below still apply.

Image result for lathe parts chuck and tailstock

Near the end of the machining process, I had forgotten to omit the part of my program that faces off or flattens the very end of the part. This was my first time using a tailstock, and so it had never crossed my mind until it was too late. The lathes insert ended up cutting into the dead center just as the program was set to make its final pass on the desired profile. With this I was left with a part that is 0.02″ larger than it should be diametrically. Although the part does not require such tight tolerances, the quality of the surface finish is less than what I could be which would be desired for the purposes of reflecting light and adding sheen. The solution is simply to trim the part of the programed toolpath that interferes with the tailstock and instead run the machine again over the same surface, this time using with a single finishing pass to clean up the geometry and tool marks left from the roughing passes. It will require careful calibration of tool and part positions so that it traces over the same path as before.

Setup before use of tailstock
Pilot hole drilled with a center drill for use the dead center on the tailstock
Setup with use of tailstock as support during the machining process

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