I have an old TS-15 w/a fanuc 6t-b controller. This machine makes excellent precision parts, including threading at 80 tpi in stainless, and holding diameter to within 0.0003" (with some effort).

The lathe runs i'd say about 20% of the stuff that goes through my shop though and I don't give it a lot of attention beyond getting it to do what I want when I want it. I have a problem that has existed since day 1 (i bought it used, 1 prev. owner) - that is, the lathe will just stop. right in the middle of a program, or maybe in the middle of moving the axis with the spindle on in manual mode. I only notice when the spindle is running, I don't know if that means that it only happens when the spindle is running or not.

When the lathe stops, the axis' hold position, the program stops, and the spindle brakes to a stop (not an uncontrolled spin, but a nice braking stop). It's almost as though the E-Stop was hit. Maybe it's an intermittent e-stop? As I'm writing this I'm thinking I may hook up a datalogger to the e-stop circuit and see if it spikes or cuts out or whatever...

In any case, the really bad thing about this is that the lathe loses it's G54 position. The machine coord. system still works (reported in mm in the bottom left side of the screen). This causes me a lot of grief when running parts - for example if the part has threads, then it's scrap or I have to write a new program to resume carefully. Worse, is that it's a big safety issue for the machine. I once 100% rapided the turret right into my collet chuck because the machine lost it's coordinate system and I didn't realize it. When I started the next program, it's G54 was somewhere random and it went like hell right into the chuck. I hit the e-stop just in time enough that the only consequence was the tool holder got pressed out of the turret. Had I not been watching, it would have really crashed hard.

I have the maintenance manuals, and have tried to use the diagnostics page to learn anything. Everything looks normal. Also, no alarm codes ever show. The machine just comes to a stop, sort of 'resets' in a sense, and loses it's G54 offset.

There doesn't appear to be a machine memory problem as my programs never get lost, and the machine parameters are all there without trouble. The fanuc 6 has bubble memory - no batteries needed so it's not that.

I wonder about voltage stability. I run my shop on an RPC and cannot run my mill and lathe at the same time because of the fanuc's tendancy to stop more often when other devices are running.

Any experienced fanuc guys out there seen something like this before? Help would be much appreciated. I'm thinking of swapping the motherboard, but I don't have solid evidence that I need to.

Thanks!