The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
awemawson:
Slowly cranking up the old engine Graham.
Yesterday I re-read the entire saga to try and refresh my memory of what I’d done and not done, I must say that it left my head spinning 👀
awemawson:
So having cleared away all the massively heavy bits from that pallet, today I had the oppurtunity to actually make a start.
First objective before changing anything is to check all the internal sensors on the turret are actually working, these are :
A/ Turret Clamped
B/ Turret Unclamped
C/ Index Position
D/ 4 channels of 'Tool Number' in binary
A & B are relatively easy, the massive 'tool disk' is moved forwards hydraulically to unlock and backwards to lock. In the forward direction the 'drive' curvic coupling is engaged and the front locking curvic coupling is disengaged. The two sensors ride on a tapered part of the shaft and measure really small movements of a few thou. The co-axial hydraulic cylinder is driven by a spool valve that has handy DIN43650 electrical connections - as one is driven automatically operated at power up driving to 'locked' it is only a case of swapping the connectors to drive the turret 'unlocked'. Glad to say both sensors test as good as these have given issues before.
The system is servoing onto one position of the drive system, and this 'should' be the Index sensor finding a notch on the drive system, however monitoring the Index sensor and forcibly moving either side of where it is homing (with a spanner on a convenient drive dog) the sensor doesn't change state. So this definitely needs investigation.
The Tool Disk happens to be set to 'tool #1' and reading the 4 tool number sensors indeed I am getting channel A=24v and channels B,C, & D all at 0v so that seems to be working.
So at least that's 3 of the 4 sensor systems given a god health check but the 4th one with need a bit of rigging up so that I can spin things by hand without fighting the servo but that's for tommorow.
However I did do a tentative MDI command to select tool#2 and amazingly not only did it work but I was able to re-select tool #1 and get back to square one.
Another issue I noticed is that the screen calls for a 'Turret Initialise' (code 6000) but after an initialise the demand remains. Almost certainly this is a program issue in the SMCC card but I don't yet want to risk trying the one I recently aquired as there are no more in the known universe correctly programmed for this lathe.
awemawson:
Up and at it early today as two sets cottage guests going and arriving.
Having cogitated the best way of isolating the Turret Servo #motor drive it came to me in a flash - the analogue +10-0-1-10 drive signal is on it's own plug with a few associated control signals, so it can just be unplugged - simples :(
This then allowed me to turn the servo motor by hand without fighting the drive, and I was able to detect the 'Index Notch' by monitoring it's proximity sensor, getting a decent signal of 19.1 volts when off the notch and 0v when on it.
As I was monitoring on a terminal strip up behind the turret (gymnastics involved!) I thought it bast to prove it all the way through to the SMCC card as quite a bit of chassis wiring is involved to get it there. The SMCC card is isolated by an adjacent PCB holding opto-isolators and relays - terminal 34 being the Turret Zero Ref signal. Sure enough it's working.
So that's all the internal sensors on the turret proved good so no perhaps I can risk the new (second hand) SMCC card. But that's for later as other duties call.
awemawson:
Loath to venture outside this morning as it's chilly -4 degC but I'd set the heating in the workshop yesterday to 15 so it shouldn't be too bad (?) It had managed to get up to 13C so tolerable.
Now I've long suspected that this problem basically is an erroneous slight offset on the analogue output of the SMCC servo computer card - very difficult to measure anything as it all happens a bit fast but the result (I think!) is a bias on the tool disk so when the front curvic coupling needs to mesh after a tool disk move it cannot lock into position as the fixed and moving teeth clash.
Certainly as a case in point this morning although I can hydraulically drive to tool disk forward to unlock, it would not return to locked until I disabled the servo drive (X111 plug out) and manually gave it a slight turn.
So heart in mouth I decided to install the replacement second hand SMCC card. It was complete with it's mounting bracket which is slightly rusty. If I fix this fault I'll swap the bracket.
The result is that I can move the tool disk to apparently any position and it will return to the locked position (so far!) every time. However the 6000 error message calling for a turret reset still won't clear so more investigations called for.
awemawson:
Well that didn't go to plan.
All sorts of issues emerged reporting :
6006 Spindle Drive Fault
6022 Axis Drive Fault
6030 Lack of Hydraulic Pressure (there isn't!)
6019 Chuck Pressure Switch Fault
Argh !!! I decided that I need to be able to talk to the PLC to monitor the internal ladder logic to see what's going on. But firstly I want to be able to connect the lathe through it's RS232 link to prove communication.
That went well and I was able to dump parameters to my desktop PC and they seem to make sense so the RS232 link is proven.
Next I need to steam up Step5 Siemens software to talk to the internal PLC but that's a job for tomorrow.
However I did then try again using the turret (this is after a 24 hour head scratching period) and darn me it's working. So tomorrow a bit more softly softly probing about to see what's going on.
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