brushless DC motor for mini lathe

I need a new motor for my Boley Leinen 8mm lathe and my web searches have led me to thinking brushless DC motors have very good characteristics for mini lathes. Is anyone here using one on their lathes and if so, what brand?

Thanks,
henryr

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.

Many mini-lathes come with them as original fitting. Not sure what brand motors, but the lathes are mostly made by SIEG and Real Bull.

I would just get a suitable size motor and controller from a reputable supplier who can support you if you have any problems.

Neil

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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 !

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

It would not have been an ordinary domestic sewing machine, either.

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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.

That looks to be good value. It doesn't have a servo though, it's an ac induction motor with an inverter. Nothing wrong with that but I do wish suppliers would describe products accurately.

Russell

Edited By Russell Eberhardt on 22/03/2021 10:12:34

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

I've been investigating the use of Brushless DC motors for small machine operation and purchased an "Industrial Sewing machine motor conversion kit" to check them out given their described performance. They also appear to be excellent value for money compared to a 3 phase induction motor and VFD combination which doesn't come "plug and play". The other benefit of the BLDC motor is its small size and weight given the power and high torque it can provide. The high torque ( 3 N-m) aspect would allow a small lathe such as a Pultra to be directly driven without needing a countershaft/pulley system as BLDC motors can develop their full torque even at low speeds. The controllers of the sewing machine motors are described as providing servo speed control, which is needed for a sewing machines cyclic load variation and is a benefit for a lathe also. The down side is that a sewing machine is usually operated either off, slow speed for positioning and then full speed and the full speed is preset on the controller for what the machine or operator can cope with. The speed control unit has an operating lever connected by a rod to a foot operated treadle. Internally it has a linear Hall effect device so when the control lever is moved a magnet moves in a small arc above the Hall device. The Hall device is powered by 5V from the Motor control unit and produces an output from zero to about 4V when the operating lever is moved over its full range. From zero to 2.5V the motor is OFF, from 2.5V to 3V the motor operates at a fixed slow speed of around 200RPM and from 3V to 4V the motor speed varies linearly from slow to full speed. On my unit the full speed can be set from 500 RPM to 4500 RPM. If 500 RPM full speed is selected the 1V linear range of the Hall is used to proportionally control the speed from 200 RPM (jog) to 500 RPM. To check out what resolution the 3 - 4V proportional range was I replaced the Hall device with a 10 turn potentiometer and found that even for a high full speed setting, (200 - 4500 RPM range) the speed was essentially linear with no noticeable steps although I may test this further.

A word of warning !!! there is no isolation of the controller electronics including the speed control Hall device from the mains supply so adequate precaution should be taken to prevent contact with potentially live circuitry. The consequence of any error in this matter can be serious!!

I purchased a second similar unit from a different supplier and the motor used is a Permanent Magnet Synchronous Motor and works in a slightly different way to a BLDC motor.

Both motors are driven by sinusoidal waveforms so produce low torque ripple another plus for use with a lathe.

Being servo controllers when the manual speed control is moved to off from say full speed the motor is physically braked by the control and it stops almost instantly. I haven't explored this area of operation when the motor is loaded with significant rotational inertia. The controller also has the capability to position the output shaft which in a sewing machine relates to the needle position using another sensor which may be useful for a lathe ?

My investigations continue but so far they have the potential of being good for powering even larger lathes such as a Myford if this isn't heresy.

Clive

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

@Micheal G........We basically bought a motor that 'looked' ok and apparently offered a solution.....since it was quite cheap (seem to remember £62...might be wrong!) we ordered, removed supplied pulley, adapted baseboard, replaced pulley, fitted drive belt, and switched it on!.....20 mins later it had completed the first made part.....I did not expect a great deal, frankly, but it works extremely well.

I will say, that the clubs main watch lathes (IME mainly with a couple of Pultras) used on the watch side of the club all use convention al sewing machine motors which have always seemed underpowered to me, as well as awkward with the foot controller. The lathe mentioned here/above has lots of power and does not loose torque when deeper cuts are made using the compound (my prefered option)

Also, about 5 or 6 years back we had a member who famously used a model aeroplane motor called an 'outrunner'....basically a light-weight brushless motor to power his watch lathe, apparently very successfully. I did NOT see the resulting machine but I DID see the tiny motor which was rated at 900 watts (?!!)..it was about the size of a 35mm film cylinder for 36 exposures (if anyone remembers what that's like!)

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.

Interesting.....I'm not aware that a lathe motor (in this context) could be too powerful...certainly 'bigger is not always better', but you can easily turn down the power, which is usually what i do with these very small lathes...and it's useful to have more power available should you need it..also motor is not 'flat out' etc

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

MichaelG.

This may be of interest: **LINK**

https://youtu.be/4htyv7Bg3rY

Installation of a 550W sewing machine motor on an [Australian made] Advance Lathe.

MichaelG.

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Edit: __  and getting back to the opening question ... a BLDC motor on a mini-lathe:

https://youtu.be/BadXx8bJlnk

Edited By Michael Gilligan on 22/03/2021 17:04:39

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

Interesting dissertation, Dave ... But I think we should just note that the 'Industrial Sewing Machine Motors' [whatever their actual design and specification, both of which remain under-documented] are widely used in the garment-making sweatshops of the World: So perhaps we can reasonably assume that at least some of them are rated for continuous use.

MichaelG.

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