The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
vtsteam:
Chased that one down. :clap:
awemawson:
I think the combination of digital cameras (iPhone 7 in my case) and Google have made this sort of thing so much easier.
I was puzzled by the gear changing motor, as the bit of the label that I could see (upside down) implied that it was a single phase motor - but I've traced it's cable back to a standard interlocked pair of contactors wired for three phase reversing operation as I'd expect - but not with a single phase motor :scratch:
I managed to stick my iPhone into a place where I could get a decent picture - and all is revealed
It can work single phase with a 4 uF capacitor or 3 phase !
awemawson:
Today's foray into the electronics of this beast was to resolve some oddities regarding the pair of 24 volt 7.2 amp power supplies that are housed the the rear left hand cabinet with the turret drive electronics.
First Quandary: They seem to be wired in parallel - this isn't good practise as being regulated they will be bound to be trying to achieve slightly different voltages - although equipped with remote sensing inputs, these are directly wired to the PSU's output terminals hence not used. The effect will be one power supply taking a larger share of the load than the other.
Second Quandary: The -ve output cable is numbered '102' and the +ve output is labelled '100' - cable '100' doesn't feature anywhere else on the machine (*) and +24 volts on this machine is cable '103' - OK a simple wire labelling error - careful tracking proved it should be labelled '103'
Third Quandary : and this is the BIG one. With no load the pair of PSU's deliver 24.2 volts, but on load this rises to 33 volts :bugeye: It was this strangeness that got me hunting in this area in the first place. Now at the moment the 24 volt rail is only being used for relays etc which won't have too much of a problem with the over voltage, BUT also the Baldor SMCC microprocessor card that manages the turret movements for tool changing runs off this 24 volts and had lights flashing all over the place when the fault was on - I hope it hasn't damaged it.
I could reproduce the fault with a 10 ohm load resistor as I disconnected the PSU's one by one in situ - the left hand one was U/S, the right hand one seems OK
Removing one PSU for testing the Baldor card seems to have calmed down now it only has 24.2 volts attacking it from the remaining PSU, and it's green ready light is coming on - so fingers crossed.
Bench testing I loaded the faulty one with a 48 watt 24 volt lorry bulb (actually a spare from my Startrite Bandsaw!) so drawing about 2 amps, and sure enough the output rose to 33 volts!. Simple transformer, twin diode rectifier and big electrolytic capacitor produces about 35 volts. There is a series pass regulator comprising three 2N3055 power Transistors with load sharing resistors in the Emitter circuit, and this group of three is driven by a fourth 2N3055 making a 'super alpha pair' (well quad in this case!). The base of the fourth 2N3055 is driven by a UA723CN voltage regulator IC
I suspect the 723 chip, but equally it could be one of the 2N3055's breaking down - I was amazed to find I have neither in stock - used to have masses of these things !
Although I've ordered some components, and I will repair this PSU, I am going to replace the pair of Kayser 24 volt 7.2 amp supplies with a single switch mode supply rated at 20.8 amps - over rated so it will be under run - which eBay has provided.
(* not quite true as alarmingly the three phase 415 volt input cable to the KTK Mentor Spindle Drive are labelled 100, 101, & 102 - some draughtman made what could have proved a expensive error )
vtsteam:
This machine seems to have a lot of surprises under the hood. The manmade type! Good detective work, Andrew. :beer:
awemawson:
I suspect most machines of this age have a few issues lurking un-noticed, after all it IS 29 years old - almost older than ME :clap:
Being a bit OCD I'm going through everything with a fine toothed comb, firstly to try and understand what I've got and secondly to try and iron out as many of the issues as possible before the controller goes back in. When that starts taking control of hugely powerful X and Z axis servos, to say nothing of the 26.5 kW spindle motor I want peace and quiet to reign and minimise that nasty expensive bangs !
There are still areas on the machine I've not been able to access. There is a curious set of 'lazy susan' type linked bars behind the tail stock under covers that just let me a slight glimpse of them - I suspect that they support the swarf covers but I can't get in to see properly.
I'd like to be able to remove all the swarf covers but I don't think it's feasible. There is evidence of a bit of rust under the moving carriage but I can't get at it to clean it up, and it's not nice to move the carriage to do so. I have been manually triggering the automatic oiling system so areas like this are at least lubricated before thing moved.
Progress on the wiring diagrams - they are being scanned to .PDFs and expected in a day or two :thumbup:
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