Hi,
Well those sewing machine motors run up to 5k rpm I think and can generate 3/4 hp, much more suitable than a 130W servo motor IMHO for a lathe.
On the basis of power output I'd have to agree. There are some countervailing arguments which may prove otherwise.
I've been using servos (Delta B2 series) for a year or more now and they never cease to amaze me how much power they produce, it seems rather more than the
nameplate would suggest. I think the feature that we overlook is a servos overload capacity, commonly three or four times its rated output. It would certainly not
work to design a system that
required that overload capacity, but that capacity can and will be exploited and so make you believe that it has much more power
than you guess. On this basis I would suggest that this wee servo could well behave as if its a motor of 260W, so a little over 1/4 hp.
The second area that suggests a servo is better is because it can be position controlled. Things like rigid tapping become possible when you your spindle
has positional capability rather than just a closed velocity loop.
I have a second hand 1.8kW Allen Bradley servo that I use as a secondary spindle motor. It has so much more torque than my regular 24000 rpm asynchronous
spindle, I use it for steel and stainless. Mostly I use it in velocity mode, ie just a free running spindle with a closed velocity loop, but I can and sometimes do use it
in position mode as a C axis which allows me to do rigid tapping. For instance:
g1 c3600 z-10 f10000
c0 z0
Will result in the C axis, ie the spindle, rotating 10 revolutions at a speed of 10000 /360 = 27.8 rpm while the Z axis does a coordinated move of -10mm., ie a pitch
of 1mm per revolution. Then the C axis will stop, with deceleration, and coordinated with the Z axis, and then unwind ten revolutions with the Z axis coordinated
to back out of the thread at 1mm per revolution.
Note this does not require any specialised Gcode or any extra motion control support, it just relies on the coordinated movement of two axes which Mach does that and more all the time.
Craig