Unimat SL Lathe Headstock Alignment

[Paul Jones]

PJs,

Thank you for your follow-up information. I think your idea of a ground test bar with MT3 end placed in the lathe spindle is an excellent method. Room temperature and heating from work lights become an important factor when measuring in the 0.0001" ranges. I have a 12" ground test bar with a MT3 end. Send me a PM if you want to borrow it.

I used the 6061-T6 aluminum bar because it machines very accurately with a honed HSS cutting tool and has no visible shavings from the tool "spring" after three passes with the same locked cross slide dial setting. Also I wanted the test bar to directly mount on the headstock spindle so I can use it again after aligning the headstock and not always go through the machining and micrometer measurements. I measured the Unimat horizontal accuracy and it is very good and no shims are needed. The main reason I do the accuracy measurements is to understand the limits of my machine tools and to be able to work within these limiting factors and avoid surprises.

My 12" swing lathe with a D1-4 spindle with an internal MT5 taper in the spindle bore. I have a very accurate MT3 to MT5 adapter and a 12" hardened and ground straight steel test bar with a MT3 taper end (it is specified to be within 0.0002" from end-to-end). I had used the steel test bar to prove the 12" swing lathe spindle is both horizontally and vertically within a few tenths along the first 12" from the spindle (do this only after accurately leveling the lathe) and the lathe ways do not have a contributing factor. I am the third owner of this 12" swing lathe built in 1987 and it is in great shape despite needing new paint. I just wanted to know its TIR from the spindle so I can work around its limitations and not blame the machine tool for my mistakes.

Thanks for the information.

Paul