In my clock club (EFHC) we have a Chinese watch lathe 8mm which was donated in 2019…..a copy of a Bergeron lathe. We equipped it with a Chinese industrial sewing-machine motor…..either from EBay or Banggood..can’t recall which but it is very small, about 1hp, came with switch unit fitted giving forward/reverse & variable speed. & was well under £100

Due to the virus it has not had much use but I did use it once and was impressed….it worked well and I preferred the speed knob much better than the foot controllers on our other watch lathes.

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Reading back through your post, Bob

I realise it’s variable speed, etc, … but

is there any justification for a 1hp motor on an 8mm lathe ?

… Not arguing : Just a little surprised by the choice.

MichaelG.

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P.S. __ @Henry

I had a look through your Album … The B&L looks very nice indeed !

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Here’s a link to one ‘U.K. Supplier’ of such items: **LINK**

https://vevor.co.uk/products/sewing-machine-motor-220v-750w-brushless-energy-saving-servo-motor-industrial

MichaelG.

Those are Chinese ponies, not the same kind of horses we rate motors with. I think maybe they talk about the power consumed while we talk about the output power. That's their excuse anyway for selling "2.5HP" air compressors that are nothing of the sort by the normal way of rating such things. And not at their price of $100. So the sewing machine motor might be half a horsepower output. Or something…

Edited By Hopper on 22/03/2021 10:26:24

Edited By Hopper on 22/03/2021 10:27:19

As a sewing machine motor fan I sincerely hope You will put up more writing and video concerning potentiometer substuting.

Personally I think the Hall Sensor is more fail safe,but hearing contra views is interesting.

A Myford with 500Watt BLDC(smallest size) is an overkill.It will maybe selfdestruct.

My latest motor is a 1500 Watt /12Nm/3500rpm and that will make a Myford look like an (Expensive) corkscrew.

Although I would like to present more details about the substitution of the pot for the Hall device it was just a way of exploring the controller functionality and not a recommended conversion. As an experienced electrical/electronics design engineer I understand the electrical safety issues but others may not have that understanding and in experimenting put themselves and others at risk.

Even commercial VFDs only have Basic insulation between high internal voltages and their control potentiometer input and any failure of this insulation could cause the Pot circuit to become live so supplementary insulation/isolation needs to be added externally in the way of putting the pot in say a plastic box and using a plastic knob.

In the case of the sewing machine motor controller the Hall circuit is directly connected to high voltage (160V DC) with regard to neutral or earth so supplementary insulation/isolation is imperative and needs to be done correctly.

The hall sensor can still be used but there may be mechanical limitations to the fineness of control achievable when zero to full scale output from the Hall device is brought about by a 3mm movement of the magnet. However fitting a shaped pole piece to the magnet may improve the situation and worthy of a try as the Hall device would be more reliable as there is no moving contact.

Clive

Thanks for the reply, Bob

… if it works for you, that's great

It's just that I would have never thought to put a more powerful motor on my 8mm watchmakers' lathe than I currently have on the Myford ML7R

MichaelG.

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I fully accept that, Bob … in fact I implied it in my first post on the subject.

MichaelG.

Perhaps a subject for another thread, but isn't there confusion about what 'power' means in connection with motors?

Power is a rating, not a fixed output. It's the rate at which a motor is sized to do work where both 'power' and 'work' have specific technical meanings different from ordinary English. Say you buy a 1000W motor:

• The 1000W could refer to input or output. Knowing the input wattage is useful for sizing fuses and wiring etc, whilst the output wattage is useful for gauging the amount of work the motor can do in a given time. Potentially misleading because the output wattage will be 10 to 40% less than the input though it also depends on run time and the load.
• An idling motor isn't doing any work so it's power output is zero, despite 1000W being claimed on the plate. The plate means the motor has potential to do work at the 1000W rate, not that the motor is fixed at 1000W. The actual output could be well above 1000W or down to zero.
• The same motor grossly overloaded is likely to deliver considerably more than 1000W out, but exceeding the rating causes the motor to overheat, up to and including magic smoke. Exactly how much power can be delivered beyond the 1000W rate depends on how quickly the motor burns out or stalls, not on the plate.
• Accepting that motors can be deliberately overloaded provided they stay below magic smoke temperature means different power ratings can be claimed for the same motor. The continuous power rating will be the lowest because the windings has to stay under about 200°C, and a 10% duty cycle will give a much higher power rating, because the motor can be grossly overloaded in bursts provided it's allowed to cool down between them: it only has to average under 200°C. As many motor applications are intermittent, more off than on, it makes good sense to use a smaller, cheaper motor rather than a motor of the same power rated for a higher duty cycle. This can cause tears before bedtime, as when a domestic pressure washer is put to work full-time. Although it can deliver the necessary power for 10 or 15 minutes in every half hour, it can't work full time like a pro-pressure washer. The two washers are identical performance, except the expensive one can do it all day everyday.
• The power rating of a motor can be exceeded if the motor is cooled by a fan. A motor rated at 1000W with an impeller fan will only achieve it's rating above a certain rpm – below the specified rpm the motor overheats.
• As power out varies with load, so do torque and speed. As the relationship can only be described graphically, motor plates are just a broad hint of motor capability, not to be taken seriously unless they also explains the terms and conditions – duty cycle, operating temperature, type of load, operating speed etc. Designers read motors specification, not the plate!

I suspect many assume power output is a problem when it's the duty cycle or motor type that matters. And also true that advertisers highlight the parts of the specification that appeal to the customer, perhaps claiming correctly the motor can deliver 2HP out, whilst not mentioning it will only do so for 5 minutes in every hour without burning out.

Motor power is likely to be deceptive, either optimistic sales-speak, or due to purchaser not undertanding the detail. It's not like buying a kilo of cheese where weight is defined exactly. Instead, output power is a rating, indicating roughly what to expect, and it can't be trusted unless the other factors are defined, and they are often only available in the full specification. Applies to heat engines too: the power output of a car engine varies considerably, being quite low when the car is cruising at 40mph on a flat road, and far, far higher towing a heavy caravan over the Simplon Pass. (One of my fond childhood memories is dad's Ford Anglia passing several boiling performance cars going up the Simplon, perhaps because their designers depended on speed to keep the engine cool…)

Dave

Edited By SillyOldDuffer on 22/03/2021 17:55:59

SOD, s points remind me why many bought Japanese audio gear ! They quoted Peak power, whereas We quoted RMS – Half the value !!! Noel

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

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.