Boxford TCL , Spindle motor problem

[John11668]

Am having problem with the spindle revs on this machine .

I fitted a Sprint 340 i DC drive unit quite a while ago in place of the lenze controlller which had gone pop .

All was fine for a couple of months and I had no detectable problems . It then began to fluctuate in speed but this could be "tuned out " using a range of adjustments in particular the IR compensation pot. It soldiered on for a while until the fluctuations returned accompanied by some apparent light knocking which seemed to be coming from the back end of the motor, ( or possibly from the Choke which is a 40 mH unit fitted as standard) . There also appeared to be significant arcing at the motor commutator in time with the knocking

I should add that this can be intermittent but often shows itself when the machine has been on for 20 mins or so.

I took advice from the suppliers of the DC drive unit (https://inverterdrive.com/group/DC-Thyristor-Drive/Sprint-340i-3A-Drive-DC-1PH-LV60-Isolated-1Q/)
(they assured me that these drives either work or go bang, they do not behave in this way)

On their advice I carried out extensive checking to ensure that the mains supply was not being interrupted . Checked all mains connections, replace any crimps which seemed dubious , isolated the drive from the bob relay and used a simple link to put it into the "On" position, and fitted a pot in place of the 0-10v analogue input . I then ran it essentially bare except for the control signal from the pot .

It was not long before the problem returned. At a speed of about 600 revs I was seeing a steady control input of about 2.6v but the output was fluctuating wildly around 45v , on occasions dropping to zero . The spindle speed on the computer display was also fluctuating
I concluded that the erratic output was causing the knocking which I felt I was hearing from the choke , along with the arcing at the commutator . The supplier assures me though that the problem is external to the drive unit.

The same motor connected to a 42 v regulated PSU runs sweetly at steady 42.3v and steady 650 revs showing on my computer screen.

Is it possible the choke is faulty? Can I test it ? Can I leave it out of the circuit to see if it runs better without? Indeed , Is it needed anyway? Can I replace it with something different ?
Is there anyone out there with a spare one lying about ?(I dont see any on Ebay)

If I try to run a program it will run relatively sweetly ( slight fluctuation )on straight cuts , but on thread cutting it will just drag the spindle down to a stall.
Likewise on parting.

Clearly the machine is useless until I can get this sorted .. Any thoughts folks ?


No doubt there will be suggestions to go to 3 ph motor and inverter but there is no room. This motor sits in a space 125mm wide /deep
The nearest 1/2 hp motor I can find is 145 Diameter , 3/4 hp which I understand would be correct for the machine is 165 so neither will fit.

[Doddy]

The choke is simply a wire wound around magnetic core - usually either ferrite or iron. If it's mounted on the motor, if there's access, you could migrate it to the controller (so it's still in circuit, but mechanically separate and not subject to vibration) That's the only way I'd suggest testing live. The choke is a "good thing" - it'll help to suppress high-frequency, high energy noise coming off the commutator - wouldn't recommend running without. You can replace the choke - obviously it needs to be suitably rated, value isn't quite so critical (+100%/-25%) - if it came down to it you could wind your own - plenty of resources to explain how online.

But, the behaviour you describe - "it was not long before...." - suggests the problem isn't immediate - but after a period ("not long") of operation - my money is on a temperature-related fault in the controller. Now here's a question - does it similarly fail under no-load? (on a lathe I'd suggest removing the chuck, or the drive-belt, or whatever to remove the mechanical load on the spindle and therefore the current drawn. If it works off-load, but fails under load, that's really a strong indication of the controller failing. If it fails off-load as well, then depending upon buggerance of strip-down, I'd be inclined to get everything together on a bench, video it, and send the video to the supplier and ask them to explain.

If it helps for bench-test - I could post you a (100mm dia, 180VDC spindle motor - only 1/4Hp, unfortunately, just to bench test? (an excuse to post back your old controller at the same time!).

[Doddy]

Actually.... thinking about it - might be worth throwing a test-lamp in place of the spindle motor - just an incandescent (if you can still find them!) - if you can pursuade that to flicker then that takes all the motor/choke out of the equation, and very visual for a blame-vid. Just another option.

[John11668]

The guy did suggest that. (Even in parallel with the motor) Havent got round to it yet .
Would it be a bad Idea to take choke out of circuit for trial purposes

[Doddy]

Removing the choke would remove some protection from the drive and increase the electrical noise in the system - at least with the motor attached. I'd be cautious with the motor in circuit - but very more relaxed with just a lamp.

[John11668]

Just a follow -up

Used the lamp in parallel with the load and it was flckering up an down,
Took motor belt off and not much better .
Tried with only lamp connected and it was steady (able to turn lamp up and down) so sounds like drive is OK.
Bypassed the choke and tried briefly with just the drive and motor and we are back to flickering so pointing to motor.
It seems the Drive regulates motor using armature voltage feedback so may well be that a surging motor sends all kinds of rubbish back to the drive .

Took motor off and found a worn brush, andd one which had a loose connection.
Switch brushes , tweaked brush springs , and ensured brush connections were tight and all seems much improved .
Proof of the pudding tomorrow when I try some screw cutting and parting off.

Thanks for the pointers Doddy
Will PM shortly

[John11668]

Not there yet .
More Consistent spindle speed , and pulsing and knocking all but gone , but not a lot of torque and a very slow ramp up despite adjustments to ramp time .
Am thinking the dead brush has left a bit of carbon shorting at the commutator . New brushes on way so a thorough clean of the comm, and a new pair of brushes and we will see what then transpires

[John11668]

All cleaned up , New brushes carefully bedded and thoroughly run in.
Motor runs sweet, lamp steady, holds speed consistently, until you load it with a cut , then it just droops away to a stall.
I am thinking the Armature voltage feedback function has fallen over . I guess this would tie in with slow ramp up!
(Checked brushes again and they have run in to a nice polish over the faces)
But still gutless.

Anyone had such experience or able to throw any light?

[Doddy]

No. The offer remains of a 180V 0.5 HP spindle motor to test. If problem remains its the controller, if not it's the motor.

[John11668]

Kind offer but did you not say it was 1/4 Hp.
Would take you up at a stroke but not sure if it would help . My problem only shows when I start cutting,. On the bench mine runs like a sewing machine :thumsup:

Will see what suppliers say tomorrow. Failing that it is maybe a 3 phase option .
Or someone told me you might be able to point me to an economic servo set up. Any I have seen seem well beyond my DIY budget

[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.

[John11668]

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.

I have done all of this johnny ( Just had motor apart a second time to re-bed brushes again this time with 320 grade paper and now running in again)
Makers tech rep suggested that I run the motor with a current limit of half capacity (set about 2 amps ) and use the belts to gear down. I tried this now normal running is at about 0.8 amps, 100 volts max at 9.7v dc input, but it still stalled on screwcutting. No signs of any motor problems , no arcing at the com , . Motor runs sweet just no torque boost when needed.
And as I have said before it was fine initially and handled all the loads I was going to put on it . Frustrating! :chargrined:

[JohnnyK]

That is frustrating. The motor should be able to draw up to 7 amps if its the original DC motor. The original lenze 534 controller was set at 8 amps max. Are you using the Lenze driver module.... if not whatever you replaced it with may have a problem with the ramping circuit something like a feedback resistor or amp has reduced gain due to damage from earlier brush problem. It responds but slow in outputting extra amps under load.

[John11668]

I ran the motor today on a separate 42v power supply and of course it would only run at about 500 revs but at that I could take a millimeter off diameter in a single cut without stalling. So the motor seems to have the guts for the job.. Speed drops a tad and current goes up but the torque is there despite low voltage.
I reckon the drive has fallen over . Now waiting to hear what suppliers will do about it .
Drive is supposed to be self protecting so should look after itself if a brush wears out (you would think anyway)

[John11668]

So Drive unit is heading back to the makers for testing.
Watch this space!
I expect they will find a problem with it . Just hope they accept it as warranty problem. I am confident I did nothing wrong

[John11668]

So they said no fault , but they did me a deal on a 12,2 amp upgrade . (???)
Still no improvement and motor would only draw about 1.5 amps max settling down to 1.2 . I have concluded that brushes may be limiting the current input . No arcing , but brushes did not seem to be giving a "witness" over their full face width.
The brush width spans 3 comm segments so maybe only 1 in 3 being fully supplied .
Motor stripped again, segments cleaned and brushes bedded in another lathe using a jig. Then re-assembled taking care to keep the same brush orientation.
Seems better already although back to running in again, so will keep you posted .

[JohnnyK]

Hey John. Are you still using the LENZE 534 driver module? I'm not sure if motor can handle 12.2 Amps as Boxford set max to 8 Amps ,,,but learning learning. My LENZE 534 has stopped working and I am trying to trace fault. I had to replace capacitor across the mains input but it still does not function. I am trying to work out how the Simplatron DCVT-2 interface board controls the input of the LENZE driver. I have traced fault to output of DCVT-2 board. I just need to know if the DCVT-2 generates the 10v reference from A (white wire) on DCVT-2 connected to Pin 9 labelled +VCC in Useless LENZE manual. Can you disconnect white wire and report if 3 to 10 volts dc is present between A and C terminals on DCVT-2 board or that 10 volts is generated on pins 7 and 9 on LENZE board---with white wire disconnected. That would help a lot thanks.

I have checked that 180 volts is present and the IXYS Half Controlled Single phase Rectifier Bridge is fine and waiting for dual Gate control to start motor.

[John11668]

Sorry Johnny but my Lenze unit died so I cant test anything for you.
My Sprint 340i was not even giving its full 3.4 amps unless I stalled the spindle, but Sprint felt that 680i might be under-rated hence recommending 1220i.
It is however governed down to an I max of about 50% or 6 amps .
Having said that, since I rebuilt the motor torque is much better but I have not seen the motor draw more than 1.5A.

But as I said on another thread there are a couple of GEC gemini dc controllers on Ebay at the moment .
Looks like Boxford used these as an alternative to Lenze

[JohnnyK]

Thanks John