Straightening a lathe feed rod

[Paul Jones]

I have a used lathe so I am not exactly sure how the feed rod for my 12” swing gear head lathe was bent. I used a dial indicator with an adjustable arm and magnetic base for measuring the rod runout. Measurements were mostly at 12” intervals and the runout measurement written on the rod with blue marker. Also, attaching the DI mag base to the side of the lathe tailstock and sliding the tailstock along the lathe ways greatly simplified the measurement process.

I discovered a maximum runout of 0.055” at about one third of the distance from the headstock and a gradual decrease in runout towards the headstock and tailstock. I had read about solving the runout problem by either removing the feed rod or working with it in place. I decided to do the work in place. I also watched several of the shaft straightening YouTube videos by Keith Fenner. Seeing Keith’s videos gave me confidence that the shaft has to be bent way beyond the 0.055” runout in the process of straightening the shaft.

I used a scissor jack and measured the upward vertical extension movement with a DI. It took almost 0.500” in movement in the opposite direction to the bend to eventually decrease the 0.055” runout. When you do this for the first time, and see the large bend in the feed rod, you think you going to ruin the feed rod. Upon slowly releasing the jack and measuring again, you realize it is going to work. Just work slowly and methodically, measuring and marking the improved runout corrections. Eventually, I corrected the runout to a maximum of 0.008" along the entire length.

However, after applying the bending corrections many times there comes a point when the runout begins to rotate (spiral) the along the axis of the feed rod. I think this is when it would be better to remove the feed rod and use a hydraulic press (or even spot heating method with a torch) and measure the corrections at the workbench. My significant improvement in the feed rod runout is okay for now. Eventually I plan to rebuild the gears and bearings in the feed power mechanism in the lathe carriage apron. This will be an opportunity to remove the feed rod and make the final corrections off the lathe.

Thank you for viewing this,

Paul Jones