July 20, 2011

Thread cutting on lathe 2.5 tpi

MINDLESS BORING: Thread cutting on any lathe can be a challenge, but cutting threads on a mini lathe can be frustrating. My 7x14 mini lathe from Big Dog Metalworks came with a 16 tpi lead screw and the corresponding change gears to cut threads 8 to 52 tpi threads. That being said in order to cut threads at any pitch other than these a conversion would have to be made if it is not a standard multiple of 16 or a even numbered ratio determined by the lathes gear change set.
Tool Bit Blanks, High-Speed Steel With the available lathe change gear set provided, a compromise would have made as far as tolerance of the finished thread was concerned. This compromise is a variation of the metric M10 pitch thread @ M9.9786 or 2.545 tpi with included error of 0.2143 % . These are the industry excepted corrections and this video I show you how it turns out. This is a square thread which place much more chip load on the machine than 60 degree single point threading and is a low rpm operation that probably would like a hand wheel attached to the outboard end of the spindle for best results.