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I am designing a small metal lathe for home use, and I am having trouble sourcing a motor for it. Disclaimer: I am aware that such lathes are available for purchase, and anything home-built will be nowhere close to the quality and repeatability of commercially available ones. It is being made for fun and education purposes.

The requirements for the motor are:

I will be running the lathe in my apartment, so the motor must be as quiet as possible. Brushed motors are out of the question. Brushless (three phase) would be my first choice.

It must be compact in diameter. The motor will be housed inside the lathe, and I can fit a motor only as large as 60mm in diameter and 90mm in length.

It must be powerful enough. I am hoping to get something close to 1 HP (750W). 500W is probably bare minimum.

I will be designing reduction gearing, so RPM doesn't matter much, but I'd prefer somewhere around 1000 RPM to make things easier. Definitely no more than 4000 RPM.

It must be able to run for a prolonged time without overheating.

I am located in Lithuania, and the local parts supply is really scarce over here. I do most of my hardware/electronics purchasing from Aliexpress/Ebay.

There are plenty of BLDC motors on Ali that fit the size and power requirements, such as this one, or a much more powerful this one, but while they are incredibly powerful for their size, I seriously doubt they would hold for long before overheating in full enclosure, since they seem to be made for quadcopters. I could add a cooling fan, but that would cause way too much noise.

I have considered reusing a motor from a scooter (like Segway), since these motors are powerful and designed to run in full enclosure. Problem is, I can't find one that is small enough, and their stator is typically in the axis (and the wires run through the inside of that axis), which would make it very difficult to adapt for a lathe.

Perhaps I should be looking for a more traditional three-phase motor (perhaps with VFD controller), but I can find nothing of sufficient power that would fit into the frame of my design.

I have been searching for 3 days now, but the difficulty comes from the fact that sellers and manufacturers of these generic motors rarely provide info on the overheating characteristics of their motors. Which is why I'm posting here, hoping that maybe someone could suggest something from experience. Specific models of motors would be best if you happen to know what fits these requirements, but even general comments on the types and characteristics I should be looking for would be very helpful.

Thanks!

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    $\begingroup$ Recommendations for specific products are off-topic here, but product categories or classifications is not. By the way, a BLDC is a 3-phase synchronous motor which is almost identical to a PMAC motor. The difference is the BLDC has a trapezoidal BEMF while the PMAC has a sinusoidal EMF which makes them more suited for square wave drive vs sinusoidal drive. But some make no distinction in the terminology. Then there's the 3-phase induction motor and that's the "traditional" one but you are correct in that you won't find a small one. $\endgroup$
    – DKNguyen
    Commented Feb 7, 2022 at 22:18
  • $\begingroup$ You're also not going to get around cooling. I think your priorities are a bit off with wanting to be quiet since the the gear train is going to make noise anyways and you're worried about the noise from a fan? Unless you feel like just circulating water around the motor for water cooling but since no fan = no radiator it's just going to be a huge reservoir of water that hopefully heats up slower than the amount you use the machine. I am also curious how you managed to size the motor to fit inside the lathe already without knowing the gearing. $\endgroup$
    – DKNguyen
    Commented Feb 7, 2022 at 22:26
  • $\begingroup$ I will be using belts instead of gears, and I already worked that part out - belt drive is extremely quiet. Thank you for the explanation. So what kind of motor should I be looking for? That BLDC from the second link looks very promising to me (because it is so powerful and small, and likely quiet), but it will probably overheat. What kind of motors do similar small lathes (7x10, 7x12, etc.) use? Perhaps I'm re-inventing the wheel here... $\endgroup$
    – Justin8051
    Commented Feb 7, 2022 at 22:27
  • $\begingroup$ As far as small sizes you probably are stuck with a BLDC motor of one kind or another. I'm still not sure how loud you are envisioning the cooling fan to be. Something like an electric airplane propellers of the size you are talking about is lot quieter than something like a vacuum cleaner. $\endgroup$
    – DKNguyen
    Commented Feb 7, 2022 at 22:28
  • $\begingroup$ Well, I don't know, since I have no idea how much cooling a BLDC motor actually needs for a given voltage and current... But if I imagine a drone propeller - these can get pretty damned loud. That is the reason why I'm asking this question - I don't know how to estimate these things, and buying a motor just to try it out is very expensive... $\endgroup$
    – Justin8051
    Commented Feb 7, 2022 at 22:36

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Here in the states there was a popular fad of buying electric treadmills for indoor exercise a few years ago. These had permanent magnet DC motors in them which were nice units. Within a few years most of those treadmills wound up in junkshops or the trash when their motor drive boards blew up, and the hacker community here sprang into action and starting tearing the treadmills apart to have the motors out of them, and inventing more robust driver boards for them.

These motors are now very popular for driving full-size milling machines when coupled with variable speed control boards which can be bought or built using plans off the web. They are rated at about one horsepower and are not noisy as they are capable of driving the cutter spindle directly at low speeds. These salvaged motors are bigger than what you originally wanted, but there's a whole community of treadmill hackers out there ready to support you in your endeavors!

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  • $\begingroup$ I have tried searching for these motors that you mentioned. They seem to start at 2HP (that is no problem), but their size is WAY above what I mentioned in the requirements in my question. Perhaps you meant some compact variant of such motor? Can you please clarify? $\endgroup$
    – Justin8051
    Commented Feb 8, 2022 at 22:04
  • $\begingroup$ the most common ones from 5 years ago were 110VDC, 1 HP and yes, they were bigger than your constraints allow, but please consider the following: small motors generate high power by turning at very high RPM, at which they are SCREAMING and running HOT AS SNOT. Bigger motors of the same HP rating run at slower speeds and can be cooled with fans and are not SCREAMING loud. $\endgroup$
    – niels nielsen
    Commented Feb 9, 2022 at 5:13

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