ACRA Transmission Rebuild

by Conn on October 31, 2012

Mark, Patrick, and I originally met at Laney College in Oakland through their Machine Technology program. It’s a fantastic program and the instructors, Louis Quindlin and Peter Brown are both excellent machinists, but more importantly, fantastic teachers. We owe them quite a bit for all they’ve done for us and, like most academic departments these days, they’re understaffed and under a tight budget so we help out the shop when we can. There always seems to be a steady stream of broken tools and damaged machines (that’s just part of the learning process).

This was a pretty good one. Their guess is that a student accidentally rammed one of the gear selectors with a cart, which bent the gear selection forks in the transmission and allowed two gears to be engaged at the same time. Never a good thing. This was the result:

There were a few other gears that were damaged, along with some bearings that needed replacement, but you get the jist.

Lathe transmissions are pretty amazing. Seen below, the large gear on the left drives the input shaft and there are two output shafts on the right. The top shaft drives the lead screw which is used for threading while the center shaft controls feed rates. It’s an amazingly complex system that generates a huge range of output gear ratios (especially since this ACRA can thread both standard and metric.

Luckily the crash was nothing fatal and, despite a manual that was mediocre at best, all that had to be ordered were a few new gears, bearings, and circlips. As with most transmission work, the hard part is keeping track of the gears, splines, retainers, selector forks and all the other fun stuff that’s wedged in there.

In the end we got everything back up and running without any trouble and had students making chips in no time!

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