Lathe Motor Mount Improvements

[Paul Jones]

I used a free Android app to analyze the lathe vibration magnitudes and vibration frequencies before and after installing homemade motor mount pads on my 12” swing geared-head metal lathe. The pads were made from drilling ½ inch through hole in hard rubber furniture foot pads (from Home Depot) and machining Delrin shoulder washers for partially isolating the existing M10x1.25 motor mount bolts. The vibration improvement is dramatic and better than I expected but the phone app really captured the improvement. I included a photo of a machining sample of aluminum rod before and after making various lathe vibration improvements including: motor mounts; flexible drive belt; new change gears; and lathe leveling foot pads. However, adding the motor mount pads made a very significant improvement in the machining finish.

The download Android app is "FFT Vibration Analyzer". The app allows taking x, y and z axes readings and storing the analyses as "before" snapshots for reference benchmarks and then taking more snapshots of the vibration as needed after making the improvements. The app spectral snapshots are superimposed with the benchmark to allow before and after comparisons.

I attached photos of the motor mount improvement parts and installation. There is also a photo of the phone doing the analysis whereby the red bar measurements is before installing the lathe motor mounts and the yellow bars measurements is after adding the hard rubber and Delrin motor mounts. This analysis is for the lathe spindle running at 244 RPM and the graph shows a dominant frequency at 244 RPM/60 seconds = 4.07Hz. Most of the higher frequencies were eliminated with the motor mount improvement and the dominate 4Hz vibration was reduced with the new pads.

I also confirmed it was never the 60Hz causing the any motor vibration (this motor is a 120VAC, 60Hz, 1.5 HP motor). I measured the lathe spindle at several different RPMs and all showed significant vibration improvements (this is one reassure why I previously installed the lathe tachometer so I could accurately measure the RPM, see Homemade Metal Lathe Digital Tachometer). The smart phone was placed on the flat top of the lathe cross slide (app has a 5 second delay before measuring) and the spectral analysis was measured in the vertical z-axis direction.