Todays Project - What did you do today?

[awemawson]

I've had an occasional failure to index properly on the tool turret of my cnc lathe. The 'curvic coupling' doesn't quite seat properly. Now there are 45 kgs of tooling on the tool disk so it has got quite a task to position properly, and the tools need to be carefully balanced so the weight isn't lopsided. Now the same servo motor that rotates the tool disk also drives the powered tooling, and I'd thought that I'd noticed an anomaly between commanded speed and actual speed measured with a reflective meter. So today's task was to go chasing and find what's happening.

OK reflective tab on an ER32 collet chuck nut - 100 rpm gave 350, 200 rpm gave about 400, 1000 rpm gave approx 1600 - what the heck?

Then, in a flash of inspiration I wrapped brown insulation round the collet nut, and stuck the reflective tab onto that. Guess what:
100 =100, 200 =200 etc etc up to 2000 rpm - absolutely spot on all the way through the range. But this itself is rather peculiar, as I've been fiddling with the Tacho scaling pot so I'd not expect it to have been so accurate.

So I wrote a diddy program to exercise the turret and try and bring on the fault. The intention being to give it long and short moves in both directions. It selects tools in this sequence 1,12,2,11,3,10,4,9,5,8,6,7,6,8,5,9,4,10,3,11,2,12 and then it cycles back ad infinitum

https://www.youtube.com/watch?v=e5bHWOefifQ

Left it running for ages and of course it never failed !!!