Replacement motor choice for SEM servos on a Harrison M300 lathe

[PeteL]

Hello all, first post! I’ve got hold of a Harrison M300 CNC machine in excellent mechanical condition but with an old Anilam Crusader controller so the electronics are all out now and I’m planning the rebuild with up to date electronics. I’m looking at motor options and am a bit confused…

It was running SEM DC servos (with tachos), models 30E4-30 for the X axis and 30M4-48 for the Z. They are plated as follows:
X Z
Stall torque 1.1Nm 3Nm
Volts 120V 144V
Pulse amps 22A 37A
Max RPM 3000 3000

I have found an old spec sheet on the internet and plotted the torque /rpm curves; my decision is whether to use conventional steppers, closed loop steppers or try some of the BST Automation 220V servos (which work out at similar cost to the closed loop steppers).

For the servos option I think that the 600W ‘110ST-M02030’ will suit the X axis (2Nm continuous / 6Nm max). For the Z axis, either 1200W ’110ST-M04030’ or 1500W ‘110ST-M05030’ (4/12Nm or 5/15Nm ratings). Can anyone advise if these look about right for this application and has anyone tried the BST units in anger (I found the test video posted on here and they look pretty good!).

Second question – if I go down the closed loop stepper route I was thinking of ES-M23440 & M23480 units. Again I found a few curves and plotted them as below. The ‘70V / rated current’ curves that I found suggest torque above the continuous rating of the servos up to 1500rpm, but then another curve marked ‘68V 40% holding torque’ makes things look more marginal marginal….or should I in fact be looking at the intermittent capability on the old servos? This is where I am confused – will these units be OK for this application?
Last question - are the closed loop steppers worth the additional cost over conventional steppers? They look impressive but if I get things sized right and the mechanics are good I’m struggling to convince myself that there will be huge benefits.




I have estimated the moving masses of the carriage & cross slide to be 100Kg & 44Kg and the ball screws are 5mm pitch – I did a few quick calcs on that basis and it suggested that the steppers should be OK but comparing the curves has now led me to confusion!

Any guidance gratefully received before I start spending £s!