brushless DC motor for mini lathe

Bob's comment about being able to turn down the power doesn't strictly apply to the sewing machine motor and their controller as it is configured to act as a servo motor. This means the motor will maintain the set point speed irrespective of the applied mechanical load and the controllers do not provide programmable torque limit that are found in VFD's. A delicate mechanism being driven by high torque servo motor can be damaged unless there is a torque limiting device which could be the drive belt slipping or a shear pin. Having said that most lathes, even small watchmakers types, are grossly over-engineered in order to limit spindle deflection when cutting so may not be classed as delicate mechanisms although the parts being made on them may be.

Clive

Been longing for an excuse to get one of these  motors and have a tinker as a potential for the CML.

£75, 3 days out of Germany no handling or VAT to pay - go figure!

Findings:

Quite a neat unit with assorted fittings that may be adaptable for mounting etc

As usual, modest documentation, but there was a parameter sheet covering basic set up BUT.... with this example some parameters could not be altered as per sheet (up to 5000 RPM), in particular speed which is set up restricted to a max  of 3500 RPM, motor torque adjustment, braking, ramp speed etc. adjustable.

Fairly easy to set up and run out of the box. Low speed limited to 200 RPM, appears to have some very serious grunt at low RMP, but sincerely doubt if duty power is anywhere near 750W - like most RoC products claim probably represents maximum power at the point of failure. I usually factor RoC Watts by 0.6 which in this case gives about 400W as a probable duty rating. Not withstanding the stump pulling torque of the motor, this feels about right, subjectively. Would be nice if anyone with access to a dynamometer could test one across the speed range.

You could lash one up and run a machine with the supplied control equipment - basically gives you forward, reverse, off, slow running, variable min to max (controlled by the hall sensor as explained earlier). There are basic interlocks, so if you leave the control position at high speed and power up, a warning condition is displayed and the motor will not start up until the control position has been zeroed.

It would be best to make up a basic control pendant in a small project box with a trimpot circuit say 2 x 5K Ohm with a decent wirewound 1 turn final pot (say 47K) tuned to control between 2.4v and 4.2v. Hopefully, about 10% of pot movement will output the non running signal, another 20% the slow running output and the remaining control movement will be sufficient for the variable speed range. You could always use a multiturn pot if you needed ultra fine control but I wouldn't have the patience for the amount of dial twirling required!

In addition, reversing can be taken from the S switch on the mini control panel to a momentary press release switch on the pendant (if you want reverse operation).

E stop will be accomplished by (press to break) interrupting the low voltage control signal input back to the motor driver. I haven't tested this exact mechanism, but if you unplug the Hall device from the motor driver, it shuts down the motor and sets a fault condition on the motor driver. The unit has to be powered down to clear the fault condition.

All in all, quite a good little drop in unit for the smaller lathes and mills to replace the usual existing 4000 RPM brushed motors. Problematic with yer trad Britisher lathe due to the high motor speed compared to ye olde worlde 4 pole 50Hz induction motor. May require an intermediate shaft for low speed lathes.

B for attainment

D+ for effort (lack of documentation and flexibility)

Edited By Martin of Wick on 27/03/2021 10:04:21

Edited By Martin of Wick on 27/03/2021 10:16:26

I've now reverse engineered the circuit of my Jack Sewing machine motor controller which uses a ATmega88 micro. Wanting to clip my scope to the circuit and mindful that it operates directly from the mains with no isolation I decided to see if it would operate off a bench power supply. So I connected my 60V/10A bench supply directly to the L & N pins of the mains plug and it started up OK. Surprisingly the controller didn't drop out till 20V and came back to life at 32V. At 60V and running at 200RPM no load the unit was drawing 200mA. The torque developed at this speed was wrist wrenchingly high but I didn't note the current being drawn but still a good contender for driving a lathe.

Clive

Hi, is there any further input on this thread please? I've just bought an old but beautifully made plain lathe 65mm centre height and am looking for a better motor and controller. The existing motor is a very small 3 phase with a capacitor across one phase and running on single phase. I could buy a vfd but they have recently got quite expensive so I am looking at one of these industrial sewing m/c motor setups which are still quite reasonable. Does anyone recognise the lathe? There is no name on it.

Looks like a watchmaking or instrument lathe. Needs a good headstock chuck and maybe collets.

John. If you want to use a VFD you would need to buy that and a matching 3 phase motor plus some sort of control box (pendant) which has the forward/off/reverse selector switch and speed setting pot.

A BLDC sewing machine motor kit comes with motor mounting components, motor controller unit similar to a VFD and a manual control box.

The downside is that the unit doesn't have an easy way to select reverse as the direction of rotation is a set up parameter. As mentioned before the controller has 3 operating regimes, Off, a fixed preset slow speed and a variable speed preset range. You will also need to make/acquire a motor pulley to match the belt size your lathe uses.

CS

Clive, please can you tell me if you solved the problem of getting the variable speed range? Did you add a potentiometer?

John.

I did for the Jack controller using a 3 turn potentiometer and an on/off switch to effectively short out the speed set signal. A 3 position switch can be used, plus a few resistors, to give OFF, Preset SLOW SPEED (jog) and then on to full variable speed. My Jack motor system is fitted to my Pultra lathe and works very well.

CS

Clive, thanks, I've just ordered one from Tysew in the UK for £99.99 including post. Please could you send me a picture of yours or a diagram, I'm not sure how it works from the description. I'd just thought of putting a knob on the metal lever and mounting it on the front of the bench. Lathe work is one handed anyway so you could use it as a sort of dead man's handle as is Electric Railway Locomotives.

+1 for interest in Clive's setup. I bought one of these moters (a "Jack" in 2021 after reading this thread (or another similar one.) The motor is small and smooth etc but I was puzzled by the control system and I put the motor on one side due to other distractions. So my Pultra is still unmotorised.

Rod

If you look at my photos you'll find 4 related to the fixing of the Jack motor and control box to my Pultra. My arrangement is fairly complex as I wanted the lathe and drive to be "portable" so I can pick it up as one lump and move it from bench to bench. Also the motor is mounted close to the lathe so it doesn't need a great depth of bench space. I'll add a picture of my pendant circuit but you can just take the return spring off the supplied controller, that's designed to provide foot control, extend the lever and some friction device to provide hand control.

CS

Good evening,

I fitted a 550w Husuper sewing machine servo motor to my Unimat SL lathe many months ago.

I use it practically every day and have nothing but praise for it.

It was effortless to fit and set up straight out of the box. It is very quiet and reversible at the touch of a button.

I use either of the pulleys that came with it, with different belts, to give two broad speed ranges. I have it mounted on one bolt so I can adjust belt tension easily, like an alternator on a car.

I set a maximum speed on the digital controller and control the actual lathe speed with the supplied Hall effect sensor lever, set up for left-hand control rather than foot control. I've put the hand control in such a position that I can flick it off in a hurry if any problems develop.

David

Thanks for the info. I've looked at your photos now Clive and like the very compact arrangement, I need to do something similar because I've very little room available where I am putting the lathe. Good to hear that you have had good results too David.

Hi Clive, I've got the motor now but I have a problem I can't see the way around. The braking effect is very noticeable and I am wondering what will happen with a chuck on the lathe. I can imagine is flying off spectacularly! I haven't found a way round this. Any input please?

Hi John

I ca't see how the chuck is fitted on your lathe. However for many lathes with screw on chucks an extra clamp is fitted to the spindle and links to the chuck. I had one on my Boxford lathe but can't remember exactly how it was done but I'm sure there may be other who can provide details. Having said that your lathe looks like an instrument makers lathe so probably would have mainly used collets. Another possible way is to fit a ratchet system to the drive pulley, similar to the freewheel fitted to bicycles, so when the motor stops the chuck can continue to "freewheel". Thee downside is you can't use reverse. Not ideal but if push comes to shove.

CS

Hi Clive, yes it's a screw on chuck. Funnily enough I had just thought of the freewheel as well, you can get them on ebay for about £8 made for electric bikes so they are quite robust and only have a 12T sprocket on them. There is room for a pulley so I would have to make up a little countershaft. I had thought of doing that anyway because I would like about a 200 rpm bottom speed. The pulley on the motor seems to incorporate the fan though I can't see how it would do much cooling. It has slots around the centre and radial blades cast in so it is quite a large pulley, about 55mm diameter. Does your motor run cool? The brushless dc motor on my mill always runs cool, even working hard.

John. Sewing machines can have very high operation duty cycles and run at high power and since the motor is located under the work bench it may not have the best ventilation so hence the fan. However for our type of use the headstock bearings will probably get hotter than the motor and I've not noticed mine getting hot. On my Jack motor, which is a JK-513A, the fan is the other end of the motor to the pulley.

CS

Good afternoon John,

With regards to your question about breaking efficiency and screw-on chucks.

I have a Unimat SL with this type of chuck and when testing the new motor I very casually stopped it from 4500 rpm and I got the chuck on my knee, at speed.

The breaking efficiency is, on my motor, a user defined parameter within the controller. It comes set at maximum as a default. Presumably to avoid sewing machine operators sewing more than two of their fingers together before it stops.

I reduced this setting to zero from 3 and the motor now coasts to a stop gently in a few revolutions.

I included a set of photographs of the parameter sheets for my motor in my album.

David

Hi David, thank you, unfortunately my motor isn't the same. The buttons are different and there is no adjustable parameter for the braking effect. I am drawing up a countershaft unit incorporating a freewheel. I don't need reverse since I won't be cutting any threads and there is no rear toolpost.

I'll have to check the Jack controller to see if it has any "hidden" parameters that aren't described in the rather brief user manual. In my investigation of Sewing machine motors I did get two different types. A Tysew (Jack 513A) and a Tansew (TH-550S-2) which looks similar the Husuper one that David has and has the same parameter list in the user manual. I was looking to modify the code to get rid of the low speed (jog) feature and the Jack controller uses a similar processor to that used on Arduino making the task easier!!!!!

CS