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

[hermetic]

Nice Job Andrew! It seems like these CNC machines (of which I have zero experience) suffer from the same disease as modern motor cars, the electronics pack up long before the mecanicals wear out, and this makes them an uneconomical repair, because few know enough (me included) to repair at board level, and boards are expensive!. Can't wait to see it spinning! Having said all that, I often find myself repeating an old mantra that was hammered into me when I was an apprentice, "Don't always assume that the fault is complex, and Dont always assume it is in the electronics"! My wife has a mild form of motor neurone malfunction, and the other day her stairlift quit. I tore into it with the AVO, and was baffled.........untill I ticked myself off for not lifting one end of the fuses when I was testing them, and sure enough, an aged fuse failure, quick repair with 5a fuse wire (6.5a fuse) proved that there was no excessive current, and it has worked faultlessly since.
Phil.

[awemawson]

Thanks Phil, glad the stair lift is working again 

Clean clothes called for this afternoon as guests arriving, so as an exercise I drew up a 3D model of a 'blanking plug' for the Tool Turret. In an ideal world I would have blanked of each open hole before using the wire brush, but had no blanking plugs. They seem astronomically priced at about £30 each - so my Cetus 3D printer is cranking one out as I type.

It's an interesting tool clamping system. The 40 mm diameter spigot has a rack of 4 mm pitch cut into it. The spigot enters the hole in the tool turret, and as you rotate the 8 mm hex locking key, an internal rack  advances and engages the spigot pulling it tightly against the reference flat on the tool turret. There is a dowel to ensure alignment, and a pick up for 'through coolant'. System seems to work quite well.

[awemawson]

I escaped this evening "to see how the 3D printing is going" and managed to clean up the Tool Disk of the Tool Turret - this is the big round thing with 40 mm holes in it that takes the VDI40 tooling.

It was mainly baked on coolant, but the odd spot of rust. Fine wire wool and neat IPA shifted most of it, followed by  1800 grit silicon carbide paper and WD40 - came up as perfectly serviceable 

. . . the 3D printer - oh yes - it still has 90 minutes to go but looking good

[nrml]

I am getting the impression that compared to the Traub, this lathe is poorly designed as far as the ergonomics of serviceability and choice of some components (like powers supplies) goes. Is this merely related  to the age of the machine or does it confirm the stereotypical ''superior German engineering'' myth?

[awemawson]

Well the Cetus finished making what it was told to make - pity I forgot to include the location hole in the 3D model 

Never mind, nothing a drill won't sort out ! Hole drilled and blanking plug fits nicely.

So this morning I re-worked the 3D model including the missing hole, and put a few chamfers here and there to tidy it up. Mk2 printing as I type 

[awemawson]

I am getting the impression that compared to the Traub, this lathe is poorly designed as far as the ergonomics of serviceability and choice of some components (like powers supplies) goes. Is this merely related  to the age of the machine or does it confirm the stereotypical ''superior German engineering'' myth?

Well NRML no I don't think that follows. As the Traub had been in much more recent use, I wasn't so concerned to access every nook and cranny - believe me, it had it's idiosyncrasies. I never dismantled it mechanically to the extent that I have with the Beaver, and mechanically the Beaver is far more stoutly built. After all it is a significantly smaller lathe yet weighs 50% MORE than the Traub.


Don't forget the controller in this one IS German , and the poor placement of the battery with lack of forethought caused all those problems. And the twin paralleled up power supplies  were made by a firm that was originally German .

Nowt wrong with British Engineering

[awemawson]

I went to check on printing progress of the Mark 2 VDI40 blank plug and was amused to find that the Cetus 3D printer had a passenger - a grasshopper had (presumably) hopped onto the build plate and was taking a ride - remember in this printer design the build plate traverses back and forth - little chap was lucky that I hadn't turned the plate heater on 

Came out OK, and fits which is the main point. I'll print one or two more but don't think that I need a full set twelve 

[awemawson]

So coming out to inspect the finished (third) plug I thought I might as well see if I could set it going overnight to print a pair side by side. They just about fit on the build plate, so I set it going and wanted to wait until it had at least begun the second ones first layer.

So while waiting I investigated that mystery box on the rear of the contactor panel. A bit of stretching out and applying a 3 mm allen key and the L shaped panel came off - actually quite a weight, it's going to be fun aligning those screws on the way back !

As was expected there's a three phase transformer in there of a blooming big size - I'd hate to have to lift that into position on my own. But surprisingly there were also 'continental' fuses mounted down the side of it integral with the DIN rail terminals. Not the easiest place to get at to change fuses - mind everything also seems to have MCB breakers. (But I suspect that the transformer with the terminals and fuses is an off the shelf unit)

So the print software is predicting 13 hours before it's finished so I'll leave it to play over night

[awemawson]

Well the overnight run printing two plugs at the same time came out a bit of a mess. The left hand one must have detached itself from the build plate shortly after I left it, resulting in a birds nest of PLA in pretty pink 

Actually not too bad, as the other one came out fine. The mistake I made was not to turn on the heated platen ito improve adhesion. Two more printing, this time on a hot plate !

Meanwhile the postman brought an armful of parcels:

a/The replacement 24 volt 20.8 amp switch mode PSU, which I've put on soak test

b/ A 5 volt 5 amp switched mode PSU to replace the 78T05CT 3 amp 5 volt regulator that apparently is a regular failure on these lathes - also reduces the load on the 24 volt PSU by up to 3 amps

c/ Some DIN rail clips to mount the 24 volt PSU - it'll need an adaptor plate to pick up existing tapped holes in the PSU

d/ An extremely expensive Renishaw TP02S optical probe system

The original optical probe was a TP02 that had it's cylindrical battery within it's integral mounting spigot. The 'S' version take a standard PP3 version that can be changed without disturbing the probe mounting. This one has the 90 degree adaptor fitted, which I won't use - they just unscrew.

Bought 'sight unseen' my greatest fear was that it may have been left with a discharged battery within, (been there before) but my fears were unfounded. Yet to prove that it works. Information on the 'S' version seems a little sketchy (unless your Google Foo is better than mine . . .  )

[John Swift]

Hi Andrew

I have been watching your latest epic CNC re build with great interest

how long are the leads to the 5V regulator ?
I have had problems in the past with spurious oscillations without a capacitor close to the regulators input terminals

how close to the maximum 35V limit is the regulator  being run
 (  how high does the 24V supply go when lightly loaded or has inductive spikes added to its nominal 24V output )

running any semiconductor at its limit shortens it life 
equipment with transformers designed for europe  instead of the UK   does not help

( In my part of the UK the single phase supply is 248V at times
and some european 220V devices don't last long )


  John

[RotarySMP]

You got lucky with only a birdsnest from your 3D printer. Whenever I leave mine alone, the filament ties itself into a cloves hitch on the spool, and then the Z Axis climbs itself up the filament untill the Z nuts are free. Causing birdsnest plus need for realignment and leveling.
Mark

[awemawson]

John, when the faulty 24v psu was in it went to nearly 35 volts. The regulator is fine at the moment, it's just that talking to a chap who used to be involved with these lathes, apparently it's a common point of failure. Anyway nicer to have a separate 5 volt supply off the mains rather than draw up to 3 amps off the DC.  (24-5 = 19 volts drop at maybe 3 amps is 57 watts just there alone and the 24 volt supplies are regulating down from 38 volt to 24 at 14 amps - there's another 196 watts !)

Remember this cabinet is the one that they found necessary to equip retrospectively with a Vent Axia fan in the roof so it obviously ran hot. Replacing the three linear power supplies with two switch mode ones will dramatically cut down on the heat.

Admittedly I'm only soak testing the replacement 24 volt supply with a 48 watt bulb, but it's been on for several hours and isn't even warm to the touch. Same load on the repaired 24 volt supply and it was too hot to touch.

So all this time the twin plugs have been printing away and I've been shifting tons of earth round the back of the tractor shed. (*)



(* https://madmodder.net/index.php/topic,11819.msg150824.html#msg150824 )

[awemawson]

Time to install the new power supplies, first I made up an adaptor plate to mount the DIN rail clips on the back of the 24 volt supply, then I removed the remaining old linear one to make way for the new.

DIN rail cut to size and drilled for 3 off M4 screws and the back plate drilled and tapped. Then, clip on the new supplies and wire them up - simples. The 24 volt and mains wires are all original, I just re-terminated them with boot lace ferrules, so if it were necessary to re-fit the old supplies the wire lengths are still correct. The 5 volt from the new supply replacing the little 3 amp regulator is all new though.

Took an amazing time  to do it all - about 3 1/2 hours !

[awemawson]

Well at last I've received the drawings for the wiring, so a bit of printing out and studying called for today 

I've also received three faulty 'driven' tooling holders from a seller in the US. Advertised as seized but seeming to be the correct Baruffaldi fitting with the segmented drive dog, I thought that rebuilding them was a better prospect than building from scratch as I had intended.

I expect that the in line co-axial ones will have needle rollers and thrust races, whereas the right angled one will have bevel gear as well. Back burner job to investigate them as too much on my plate at the moment.

These things are horrendously expensive to buy new - the simple one are of the order of £1000 and the right angled ones at least £1500. Needless to say these were a very small fraction of that price - £150 - I thought that I'd better grab them as they flitted by as they are not the most common of items.

[awemawson]

OK time to bite the bullet and put the controller back in - a bit fiddly, but far easier than taking it out - at least now all the connector retaining screws work, rather than having to be sheared off due to the corrosion !

Massive earths went back first - at least they will tether it if it has a desire to plunge off the shelf, then the mains input, then all the interface connectors. At the moment it's just pushed in unscrewed - I'll leave final screwing in until everything is working otherwise I reckon I'm pushing my luck.

While this was happening, Adrian the Parcel Force man delivered some DIN rail stop blocks. When I replaced those power supplies the day before yeaterday, I'd thought I had some but no, wrong again. Well I have now 

So stop blocks fitted to stop the PSU's sliding along the rail in case we get a sudden gravity surge. Actually, it's quite easy when working in a cabinet, to accidentally move something and stretch cables - been there - done that - now fit stop blocks 

[awemawson]

Time to grit my teeth, and power the machine up 

OK Press the Emergency Stop Button in, hold your breath, press controller start. No dramas but loads of error messages. The NC (Numeric Controller - part of the Sinumerik 820T) is reporting X-Axis and Z-Axis working area limits.

The PLC (Programmable Logic Controller - part of the Sinumerik 820T) is reporting all sorts of errors most of which can be accounted for by the fact that the NC won't go 'Ready'. When 'Ready' the NC outputs a digital output that enables several relays that supply power to the Hydraulic Pump, and Spindle and Axis Drives, and also a '24 volts OK' relay which drives an input to the controller. The 24 volts IS OK but the monitoring mechanism isn't powered up !

A bit of furtling about produced details of how to set the working area up, and that cleared the two Working Area Limit errors.

However the state of play at the moment is that the NC remains in 'Emergency Stop' (Yes the E-Stop button HAS been released!) and I need to find out what it's missing to go 'ready'

[vtsteam]

All door lock sensors functional, Andrew?
Limit switches?

[awemawson]

Amazingly there are no interlocks on the cabinet doors, and the sliding door giving access to the actual lathe not only has an interlock, I can read it as a logical 'bit' coming in and changing as I open and close the door.

Even odder, the output that signifies 'Control Ready' is most definitely not 'true' it's at 0 volts at the point it's supposed to drive a relay . BUT poking about in the PLC "Q" bits which are  outputs, it IS logical true. Without it coming to the outside world, the E-Stop button is ignored.

It's possible the output card has popped but I wasn't able to investigate any further today as I had to change the main hydraulic pump on the digger - it's in now but I probably have 5 hours work with it tomorrow shifting earth before the weather breaks. Also guests for super and two sets of cottage guests arriving, so not much play time on Friday.

[awemawson]

So Hydraulic Digger Pump replaced, earth shifted and now back able to play 

Trying to make sense of the circuit diagram that I have I firstly went round each relay and contactor on the panel matching it's wire numbers to the diagram and sticking a label on when I'd identified it's function - trouble is they don't differentiate between relays and contactors which is confusing as often you get a relay driving a contactor 

All this so I could bottom out what initially looked to be a trivial circuit monitoring the 24 volt rail. Two relay's 'CR10' and 'CR20' which ACCORDING TO THE CIRCUIT each had their coils across the 24 volt rail, and each had a normally open contact in series with each other and connecting a digital input to 24 volts. How simple is that ?

Well actually a bit complex as 'CR10' isn't connected to '0 volts' but to the overload trip circuit for several motor contactors, and 'CR20' derives its '24 volts' from the digital output 'NC Ready' and it is this very signal NC Ready that is in the wrong state and keeping E-Stop asserted 

So OK lets go round the 'NC Ready loop' a few times until dizzy. If I look at the logical bit for NC Ready in the PLC 'Q' word the relevant bit IS set but not physically set to the outside world.

If I trot along signals from the same input / output card that DO have bits at 'logic 1 (24 volts)' I can also see the relevant bit in the appropriate 'Q' word. Now the PLC documentation implies (but doesn't explicitly say) that a bit set in the Q word appears as an output. Now I am aware that some manufacturers have a further logical step between the register data (Q word equiv) and driving an output - the Mitsubishi in the Traub did this, but I've not found any mention of it with the Siemens Sinumerik controllers.

So what are we left with  Well it could be a further internal logical step, or it could be that that particular output on this I/O card is faulty. I think that the later is the most likely but time only will tell.

I could exchange the two I/O cards that I have and see if the fault moves, but it's an utter pain removing the I/O rack as it involves pulling the controller and the Operators panel out - and if the fault DOES move it'll all have to be done a second time once a replacement is found. OR I could source a replacement on spec, swap it in, and if that proves to have been the fault no more fiddling about. If it doesn't then at least I have a 'shelf spare'

This course of action probably sounds rather spendthrift - BUT there are loads of these cards 'tested good' on eBay in Germany for £15 each so I've ordered one.

According to the Siemens book of words on the PLC it is possible to write into the Q word bits to generate output, so I chose an unused output, wrote to the Q word and measured no output, but when I looked again at the Q word it was back to before I wrote to it. I suspect that the PLC program is cycling round writing it's wanted outputs so if I change anything it is promptly changed back 5 milliseconds later  I'm sure that there is a way of stopping the PLC program running, but then I'm not sure whether anything would be output 

[awemawson]

Well, progress through adversity 

I decided to 'bell out' the core in the cable that represents 'NC Ready' - this involved pulling the 34 way IDC plug from the rear (and most inaccessible) I/O card. Cable belled out OK, but when I tried to put the plug back - this is an entirely 'by feel' operation, I managed to bend a pin on the card 

Now after a few cusses I decided that I might as well dismantle the I/O Rack using keyhole surgery though the aperture that holds the control panel. Just possible but it hurts your wrists 

Well doing it I thought that I might as well swap the pair of I/O cards and see if the fault moves - IT DID 

So now we have 'NC Ready' coming true, and the E-Stop button does things - naturally there are other errors but at least this particular mystery is solved and my hunch about the card being faulty is proven correct - as I said earlier, I've ordered one (well actually two !) so PROGRESS !!

[vtsteam]

Finally!

Amazing how much reverse engineering you have to do, even with manuals for these things. You wonder, is it a faulty component, or is the manual accurate, or are both the problem? Then if you do something and get the green light it's like Christmas! Except, on to the next.... anyway: 

[awemawson]

After more 'going round the houses' with a meter and wire sniffer (*) I've eventually deduced that those two small relays are nothing to do with monitoring the 24 volt power supply 

The one on the left is monitoring the overload trip circuits for various motors, and the one on the right is NC-READY ! - relays suitably labelled. But the controller is still reporting a 24 volt psu problem and I have no idea how it is monitoring it  The relays shown on the diagram as CR10 and CR20 are nowhere to be found and I did eventually find the correct bit of the diagram showing the Overload and NC Ready relays.

Oh well maybe they will turn up somewhere else but I thought that I'd been everywhere by now in the mammoth structure of a lathe  !

(* Tempo 200EP Inductive wire tracer intended for telecomms use)

[awemawson]

  Well guess what I've found 

The only places left were the hydraulic cabinets for the tailstock and chuck - and on their control cards we have - CR10 and CR20 - hoo blooming ray 

The odd thing is that they both have tell tail green LEDs which are glowing away merrily when the power in on, but at least now I have a further avenue of investigation to follow 

. . have to stop now as entertaining for lunch and need to be presentable 

[awemawson]

Back from entertaining relatives at the Pub, and straight back to the workshop to chase that fault. Lucky I was the driver, so my head is quite clear on only Soda and Lime !

Chasing now I know where the relays are, it turns out that CR10's contact is working, but CR20 - either the relay or the wiring is duff. I have temporarily wired round it, and guess what - things started happening.

She's ALIVE

I could jog the Z axis up and down as I wished. Initially the X axis moved a fraction then something tripped - repeatable problem - I thought that perhaps it was on the limit switches, and wanted to remove the cover from the servo motor / ball screw drive to wind it by hand, but it was in an inaccessible place too close to the tail stock. But - hey - I can JOG Z where I want it. So the saddle was trundled down the ways giving access to the belt cover.

Cover off revealed the expected drive belt and pulleys and what I had forgotten - the X axis brake unit. As the X axis is tilted up at a step angle, without a brake, and with low friction ball screws, it will descend under it's own weight. I checked the current though the brake coil (0.6 amps) with my clamp on ammeter - no way can I turn the pulleys, and I dare not remove the brake or the X axis will plunge.

Well it looked a bit grotty with surface rust - perhaps the plates are rusted together. A few gentle taps with a plastic mallet, and guess what - X now moves as it should. As you jog it's slightly disconcerting hearing the loud 'click' as the brake comes off, and on again when motion ceases. (Brake is spring loaded ON with no power)

SO - I was able to move X & Z to their home / reference positions to make the controller happy, and was just starting initialising the Tool Turret when there was an almighty    BANG  and the workshop filled with acrid smoke - it still stinks as I type this .

I leapt to the main switch to kill the power - smoke was pouring out from below the KTK Mentor main spindle drive. Closer inspection (holding my breath) showed that in fact it was coming from the Field Coil Controller which is mounted below the Spindle Drive, and the culprit was one of those 0.1 uF  500 volt AC RFI suppressor capacitors, identical to the ones I replaced on the Mentor drive. Luckily I still have some left over.

Oh boy it made a loud bang and a huge volume of smoke - fortunately due to the hot weather I had my roller shutter door open and fans blowing. Knowing how hard it was to clean the mess off the Mentor board, I quickly set to with some IPA to try and clean the mess off the grey trunking - no way was it shifting, and I can see globules of molten solder have embedded themselves in various places.

However I am a happy bunny - this is a major milestone passed. OK I need to bottom the CR20 relay problem, I still need to replace that I/O card, and no doubt there will be a few more 'issues' along the way. I've not yet got the Main Spindle turning under power, nor the drive for Powered Tooling.

. . . but satisfying . . . 

[awemawson]

Well no point in putting it off - remove board - replace capacitors - return board to it's rightful  place and switch on keeping fingers crossed.

It all went ok - capacitors replaced and now I can jog X & Z, I can send the X & Z axis to their reference points, and I can jog the spindle. What I can't do at the moment is initialise the Tool Turret - it's asking me to do it but the format of the command is eluding me at the moment.