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

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vtsteam:
ah, a test loop  :med:

mc:
I'm trying to understand what bits of the turret actually slide/turn. Looking at your second encoder wheel picture in reply/post 240, I'm confused.

I'm assuming it's the hirth coupling showing, but what I can't figure out is what's attached to what, and what moves.
It looks like the encoder wheel is attached to the nearest side of the hirth coupling, but assuming that's the tail end of the main turret/tool disc shaft, that means it's going the wrong way to lock...

awemawson:
MC there are two Hirth couplings. One with half on the body of the turret, and half fixed to the rear of the tool disk. The second has half connected to the central shaft and half connected to the belt drive system. They are arranged so the when one is engaged the other is disengaged. So the hydraulic cylinder pushes the tool disk and shaft to the left freeing the disk to rotate and coupling it to the servo motor drive. A combination of the SMCC card, the 820T controller and the Simodrive servo cards rotate the turret to the demanded tool and the hydraulic cylinder then locks the front Hirth and disengages the rear one, leaving the servo motor free to drive the powered tooling.

What differs from the patent application is that the encoder has been removed from the rear of the main shaft and put on the rear of the servo motor, and the addition of the four proximity switches that count the tool position in binary. In the first version the encoder could both count the disk and provide servo feedback as it was fixed effectively to the main shaft and hence tool disk. Once it was moved to the rear of the servo motor it could no longer keep track of tool positions, as at times it would be disconnected and not keep a fixed relationship.

mc:
It makes sense now.

I've just had a read through of the patent, and hadn't realised the first diagram was for a basic turret without live tooling.

One final question, is the turret is also held locked by hydraulic pressure?
The patent mentions springs, but it would need a fair bit of force to keep things locked under load..

awemawson:
Yes Moray, item #17 is a co-axial hydraulic cylinder that is double acting, operated by a two way spool valve.

I've come to the conclusion that there must be some setting up proceedure to get the front half of the rear Curvic Coupling synchronized - it carries the notch that the Index proximity switch detects. So that the rear Curvic mates smoothly when the front one disengages their angular relationship must be controlled, or when they come together either in the worst case it could be 'tip to tip' or if not so much out of place then a tendency to rotate a bit to engage.

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