Boxford TCL , Spindle motor problem

[Doddy]

John, you're absolutely right - it's 1/4 hp, not 1/2. Clearly limited use, and my previous post was intended for bench test, where presenting a load might be challenging, and knowing the cutting forces on threading on a lathe, likely too puny to fit to the lathe. Agreed - silly idea. Even for bench test it could be inappropriate if you end up stalling the motor before the oscillation kicks in. Yeah, bad idea.

3 phase - my only caution is battling the combination of the PID on the LinuxCNC spindle control and the PID on the 3-phase driver, I could never persuade LinuxCNC to quickly setting on an actual speed - from memory maybe 30 seconds to get within 2%, with speed hunting around the desired speed. Annoying, and I expect useless for threading (there is the argument, of course, of a spindle encoder negating this - but it's a less than idea starting point). You could battle/inhibit the PID on LinuxCNC - but I grew too many grey hairs going down that path.

Servo?, that's the route I took, in part to remove the whole 3 phase malarky and to provide the energy to remove the need for the belt speed selector (and bull-gear) by rather over-egging the original 1/3hp motor, but also to provide a much more accurate rotational speed drive - LinuxCNC, for me, providing step/dir control into the spindle. But that's largely supported by the mesa control board as well. I'm not suggesting that it's a solution suited to any/all, but for me it was also in part "because I could".

[m_c]

Sounds like a problem with the drive.
I'd personally just replace it with a servo.


A 110 frame servo is 110mm square, but generally have fixed connectors you'd need to allow for.
Smaller frame sizes often come with connectors on fly leads, so can be squeezed into tighter spaces.

Have a look at Lichuan servos - http://servo.xlichuan.com/ProductsSt_jlcfjl.html
They're available via their AliExpress store - https://www.aliexpress.com/store/1907567 and Jazz also stocks some Lichuan stuff.

Depending on what spindle control method you use (I'm assuming you're using 0-10V for the Sprint drive), you'll have to check what drives would work, as IIRC not all accept and analogue input. If you can use step/dir to drive the spindle, then I think any of the drives will work.

[John11668]

Thanks for the input folks .
But this drive cost me nearly £200 inc vat and carriage , and is still in warranty so I am still hoping they will look at it .
In tests today 9.3v analog input gave me about 50 v output and spindle speed of 2200revs , but still gutless .
Am thinking these numbers dont tie up!

Occasionally I feel it is improving but no more than a feeling. (brushes must be run in by now) .
Cant harass them until next week now though.

[m_c]

Is the voltage remaining constant under load?

The drive output voltage should remain reasonably constant even under load.
If the output voltage from the drive is dropping, then it's a problem with the drive.
If the output voltage is remaining reasonably constant, then the problem is else where.

[John11668]

So voltage is pretty steady.
With 9,5 v analogue input driver puts out 93v. (Forget readings above I was reading positive to ground. positive to negative is 93v) and this gives me 2000 rpm which is all I expect to use .
At about 5v input I get a spindle speed just over 1000 with output voltage of 55v or so and all very smooth. Clearly getting nowhere near the 170 v which the drive is rated for but I am guessing that would be giving me around 4000 revs. which I think the motor is good for.

At 1000 revs the current is steady about 1.4 increasing to 1.7 or 1.8 under cutting loads , but whereas I used to see a torque boost when i applied a heavier cut there is now a hesitation before it compensates , and if I turn my ramp pot down to where I would expect the spindle to come up to speed in 2 seconds or so, it still seems to take 4/5 seconds to get up to speed.
Still stalls on screwcutting and current goes beyond range of Drive to 3.6 or 3.7
I do believe the problem is in the drive , but I think I may have problems persuading the suppliers

[m_c]

What happens to the voltage under load?

[John11668]

Increases a little. but not a massive amount. Current shows a fair jump (Hard to see the actual amount on a digital MM )but then settles back to a steady current 0.1 -0,2 A increase on before .
It seems to me as if it is not responding quickly enough to the sudden application of cutting load so if the load is not massive it gets to coping after a second or so.
At screwcutting speeds the torque is already low so just droops away.
To me it would seem to tie in with the slow ramp up response (ie it is struggling at low speeds) I am guessing it needs quite a boost to get up to speed from zero quickly . Just doesn't seem to be getting that.
And I guess it needs a quick boost to hold speed on threading . Just isnt getting it .
.

[m_c]

If the drive output voltage is remaining constant (the slight increase is it compensating for motor load), then the fault isn't the drive.

With motors, Voltage = Speed, and Current = Torque.
So if the motor is getting the expected voltage, drawing maximum current, and still showing as under powered, then it sounds like the motor is the problem.

[John11668]

You may well be correct m_c but it is the slow response which is bugging me
Very slow to ramp up, (never used to be) , and when it does respond it seems to give required torque to hold a cutting load,
but if the load is large and dragging it down ,( as in threading) it seems to get dragged down before it can respond so loses in the catchup race .
The fact that I cant reduce the ramp up time suggests to me it is the response of the drive to AvF that is letting it down,
Motor is running like a dream otherwise .

[JohnnyK]

John you may find that the worn brush and loose connection has sent spikes back to the controller over a period of time and stressed some components on driver board. Knocking may have been the instantaneous changes in speed. It also may have damaged some segments of the commutator or has carbon shorting out in slots. You can clean segments out with a groundown back of hacksaw blade and run along slots to remove carbon. If commutator worn you can lathe down commutator and scrape out the insulation to below segments using sharp end of hacksaw blade as mentioned above---old trick used in automotive industry before throw away society became the norm. Can you check if commutator still arcing with new brushes by leaving the cover off to test. You may be able to reach in and clean slots without disassembling motor.