The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

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awemawson:
As I thought, the Turret Servo brake was simply powered off the 24 volt DC bus, so I jury rigged a lab supply to pull the brake off, and was able to see the coupling. Getting a screwdriver onto the screws was another matter :clap:

The access hole is maybe 10 mm diameter, facing downwards at the tail stock end of the turret assembly. Trying to get a mirror and a torch and a screwdriver co-ordinated proved impossible. I got out my Wi-Fi endoscope for a good view of the coupling, but there wasn't room for the endoscope and the screwdriver at the same time. I then tried taping the endoscope to the screwdriver with the screwdriver leading the adventure, but the image got very confusing as I had to move the screwdriver. Eventually, with the endoscope porting the image to my iPhone, which was balanced inside the machine, and holding the camera bit close to the hole with one hand and poking with the screwdriver with the other EVENTUALLY I got it on each screw in turn and checked their tightness.

All very confusing, as the image has a significant delay, so you are seeing what you did, rather than what you are doing !

Anyway they were as tight as I could get them, so it was probably another red herring. Have a video of the coupling rotating

Having done all that I now cannot reproduce the fault :bang:

Could be that things have warmed up a bit, but really I'd like to try and set the servo card so it balances nicely. I'll have to get some numbers off the card and go googling

awemawson:
Possible reasons for the Hirth coupling not always being positioned where needed include the Siemens Simodrive Servo Card. However lacking any information on the card I was loath just to tweak away. Posting a plea for help on another forum has sourced the gen letting me experiment with a bit more confidence. The Beaver manual says very little about the turret, but what it does say is the the servo gain will need to be set quite high, but it's description of which pot was the gain is wrong hence not having played with it.

However at the moment I can't reproduce the fault :bang:

I've increased the servo gain slightly, and subjectively the motion seems a bit crisper, but maybe that's wishful thinking !

All this started when I was aligning the tool turret, and the tool disk face is now nicely set to match the X axis, but the tool turret rotation needs re-setting. My measuring dowel came in the post today, and it's out by 5 thou in about 5 inches, so not an enormous error. I now need to slacken the bolts securing the tool disk to the Hirth coupling, and gently tap it round however many degrees that error corresponds to, and hope that this time I don't expose more problems :clap:

awemawson:
Today is the day to set the Tool Disk angular orientation :clap:

The two part Hirth (or maybe curvic, documents refer to it by both names) coupling has one part fixed to the turret centre spindle, and the other bolted to the tool disk trapping a flange on the spindle. By loosening the ring of eight M12 socket cap screws it is possible to tap the tool disk round to adopt a changed angularity relative to the spindle. But what to use as reference :scratch:

With a 'normal' lathe tool holder clamped in the turret, what we are aiming for is the reference mounting surface for the lathe tool to be parallel to the X motion of the carriage. Fortunately I have a brand new, nicely ground holder that I mounted in position 6 (arbitrary - doesn't matter where!) with a balancing one in position 12, though this one wasn't brand new and it's surfaces weren't quite as pristine!

Then setting the electronic DTI in the chuck, placing the finger on the relevant tool holder surface, rotating the lathe spindle to give me a zero, then locking the lathe spindle, I could track it up and down the surface seeing a conssiderable discrepancy. (about 30 thou in the 100 mm length of the holder)

Now I had prior to this slackened off the ring of eight M12 cap screws and semi re-tightened them. It's worth noting that the internal hydraulic 'lock' cylinder is also holding the tool disk against its flange. Initially I thought that I was going to fall at the first hurdle, as the bolts were massively tight. Eventually bringing out a 4 foot tube as a 'torque amplifier' they all came loose, but I was grateful that my Allen Key was a decent quality Unbrako that stood up to the punishment.

Tapping the tool disk round with a brass drift, resetting and starting over, after several iterations I got the indicated error down to zero with an FSD of 1 thou on the gauge, which is quite pleasing. Rotating the turret round to the balancing tool holder and measuring that gave me an error of just under 2 thou over 100 mm which I put down to the fact it's a well used holder, but that discrepancy wouldn't be the end of the world.

I'd put all the removed tool holders in a 'Tote' to keep them safe, and when I went to move them out of the way realised how amazingly heavy they are - they ended up staying put! It made me have a greater respect for the servo system that rotates the turret.

Now I will have to go through the tool setting process once the tool holders are re-mounted, but that's fairly automatic now.

I did have one peculiarity during the process described above. I got to the stage where the adjustments had been completed, so the last action was to jog the tool holder past the DTI which was fine. I then left everything powered up while I boiled a kettle for a visitor. When I came back the machine looked ok, all lights correct, but it wouldn't jog. Even powering down and trying to go through the initialising process the issue persisted. Hunting for the error I removed the axis enable, axis brake and drive over travel relays relays one by one reinserting them as I went. After that everything was normal so what had happened I don't know. Obviously something to watch out for.

awemawson:
All done and dusted. Tool holders re-fitted and tool off set measurements updated.

I weighed the tote of tool holders that I'd removed, 39 kGs plus the two I used for measurement that were still on the turret at 3 kGs each so 45 kgs being rotated by that poor old servo unit. :bugeye:

No wonder it needs a reasonably high gain setting.

I was just about to re-run a previously run job to see how things measure up, then JUST stopped myself remembering that all the sheet metal covers are still off the turret and need re-fitting to keep the swarf, and probably more important the coolant, out of the works. Might get half an hour or so tonight to refit them as I believe I'm an orchestra widower this evening !

awemawson:
I got the turret covers back on this evening - by heck some of the screws are in awkward places !

All seems to work. I ran a simple job (a shaft with two diameters and radius-ed transitions). Have a very splashy video. As is usual with these things the coolant stops you seeing much !

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