brushless DC motors for mini lathes

[J Tiers]

Yep, probably looks a bit like this, which is also a Boley. Bed might even be as long as 10".

[Paul Alciatore]

Oh! I guess I missed that in the "fog of posting". But then, perhaps some others have also.

Paul, Henry's little watchmaker's lathe is quite a bit smaller than your little Unimat. I think you and a few others are caught in the 7x mistake by the "mini lathe" in the title.

[BCRider]

Paul, Henry's little watchmaker's lathe is quite a bit smaller than your little Unimat. I think you and a few others are caught in the 7x mistake by the "mini lathe" in the title.

[darryl]

I built a brushless motor at one point. I used TR optical sensors to trigger the mosfets for the coils, and stick-on reflector tape to set the timing. The three sensors can be moved together over a small range to give a means of adjusting the timing. I set it for least current consumption at no-load.

The armature I used was a pancake style, wide but not long. With the circle of neodymium magnets surrounding it, the torque is amazing. I didn't get the ratio of magnet count to slot count right, and one of the consequences is that it has lots of cogging at slower speeds. As I try to slow it to feel the torque, the ammeter jumps way up and I can hardly slow it at all. If I had done the magnet count right, it would still have had lots of torque, but would have run smoother and been more efficient.

So- on to the next model. This was apparently a pancake style blower motor for a vehicle. Similar to some of the rad fan motors, only smaller- 80 watt rating for this one. I took it apart and replaced the seven ferrite magnets with neodymium. I also upgraded the brushes and mounted them on heat spreaders so they could handle higher currents. This is another motor that you really have to hang onto when powering it up- otherwise the torque will rip it right out of your hand. It has a printed pancake armature with no iron in it, so it's a smooth runner with very low idle current.

Could be designed to fit a lathe spindle and not interfere with the through hole.

[dian]

i have a small lathe, around 30 pounds maybe, and once its operational am going to run it with 1.5 kw/24'000 rpm spindle. just because i have it, but i see no problems with that, its not so big either, about half the lenght of the lathe.

[JRouche]

Brushless mottos to me mean lil tiny fans in 74, 1974.

Then the use of brushed commutator motors seemed much more profitable.

Loop around and brush-less is affordable now. Sweet/

JR

P.S> Brushless was very expensive before..

[Paul Alciatore]

That is described as a motor from an INDUSTRIAL sewing machine. If we are talking about sewing machine motors for heavy duty, industrial machines, shouldn't that be stated in the description and not just say "sewing machine motor". I have seen home style sewing machines stall out with just extra thicknesses of cloth. I didn't look at the name plate on their motors at the time, but I highly doubt that they had 1 HP motors. Probably not even 1/2 HP or even 1/4 HP.

I have a Unimat DB200 which has a 1/10 HP, brush style motor. It can be described as a 3 X 6. The mini-lathes commonly sold today are commonly described as 7 x 12s or 7 x 14s which I would dare to say is between 2 and 4 times larger than my Unimat. I have stalled my 1/10 HP motor with work that was well below the maximum work envelop of the Unimat and I dare say that a 1/10 HP on one of them would be fairly useless. I see numbers like 1/3 HP for the OEM motors on them.

So, if we are talking about a standard sewing machine motor for a 7 x 12, mini-lathe then I still say it does not sound like it will work. Your INDUSTRIAL sewing machine motor; probably yes. But just a basic sewing machine motor, NO WAY!

https://www.amazon.com/Genuine-CSM10...6350993&sr=8-5

More than enough power for a mini lathe. I'm using one for an overhead drive on a rose engine.

[darryl]

Just been looking at spindle motors. Sure not finding anything other than the 500 watt unit that everybody sells. And there's nothing to say what kind of motor it is- from the two wires only it would be a brush type motor. Nobody claiming anything special about the motor.

No doubt one of these would work. And it would be smooth. The power supply doesn't need much beyond encasing it in a safe box and running some wiring, so that sure would ease that side of things. Maybe that's important. Sure would be nice if there was a settable current limit or foldback capability so an overload wouldn't damage things.

[J Tiers]

somehow i lost track of whats needed. either torque is too low or hp is too high. whats the problem of running e.g. a 1kw spindle motor slow? you get the whole range of speeds. so are we trying to save $50 or save space or what?

It's a tiny lathe.... for watchmakers. A 1KW motor could, if it did not slip a belt, pretty much make it into a pretzel.

We are talking NOT about an actual "minilathe" such as a 7 x 12 machine, but a very little lathe with a swing that may be 65mm or less. They really do not need more than 1/10 HP or so, and the belt system generally cannot transmit much more than that.

[dian]

somehow i lost track of whats needed. either torque is too low or hp is too high. whats the problem of running e.g. a 1kw spindle motor slow? you get the whole range of speeds. so are we trying to save $50 or save space or what?

[elf]

The thing about sewing machine motors that bothers me is that a sewing machine motor does two things:

1. It pushes a needle into the cloth and pulls it back out.

2. It operates the mechanisms that move the cloth the distance of one stitch and that passes the thimble below the deck through a loop of thread when the needle is at it's lowest point.

OK, some sewing machines do have mechanisms to produce patterns, like button holes. But that is not much more than the items I mentioned in #2 above.

That's all that a sewing machine motor has to do. So just how much torque or power do they need, even at slow speeds? Not much. My grandmother made a living sewing draperies. The motors on standard sewing machines were so weak that she could not use them on many of the fabrics she encountered. She had to have an industrial quality sewing machine which had, among other things, a larger motor. But even then, just how much larger did it need to be just to handle heavier fabrics?

And keep in mind that a sewing machine is heavily geared DOWN. Things at the working end of the machine are using an RPM that is a lot slower than the motor's RPM. Most of the motors will be running at a higher shaft speed.

Are sewing machine motors that much better today? And if some of them are, how do you find that fraction of them while avoiding the vast majority that are designed to a price point to sell low end sewing machines?

See post #5. The Consew motors work very well. I also drive the spindle as well as X and Z axes on my rose engine with steppers. Full project is documented here. One nice thing about having the spindle driven with a stepper is indexing is free.

[J Tiers]

Low end sewing machines are not any better today but when you actually pay more for the motor&controls than entire low-end sewing machine you'll probably get something else.
Industrial sewing machines are typically quite beefy and built for high-speed sewing 24hours per day.

Old "home use" sewing machine motor might be something like 50 to 70 watts, industrial machines 500 to 750W

Home use Singer and industrial 3-phase Juki are same as 7x14 chinese lathe vs Monarch 10EE.

There is an intermediate type. The type of machine that quilt makers use is better than typical home machine, but still short of industrial. My wife's Aunt makes art quilts (sounds odd, but she is a good artist) and has a quite reasonable type of machine (made I believe in Finland). I have no idea at all what the motor is, but it does not make the typical sewing machine noise. It is something bigger. Quilt makers tend to need a more robust machine as they do rather a lot of sewing.

[MattiJ]

Almost related: This sewing machine appears to have air blast for needle cooling:

https://www.youtube.com/watch?v=0q7731IDXPE&ab_channel=HighTexHeavysewingtechnology

[MattiJ]

T

Are sewing machine motors that much better today? And if some of them are, how do you find that fraction of them while avoiding the vast majority that are designed to a price point to sell low end sewing machines?

Low end sewing machines are not any better today but when you actually pay more for the motor&controls than entire low-end sewing machine you'll probably get something else.
Industrial sewing machines are typically quite beefy and built for high-speed sewing 24hours per day.

Old "home use" sewing machine motor might be something like 50 to 70 watts, industrial machines 500 to 750W

Home use Singer and industrial 3-phase Juki are same as 7x14 chinese lathe vs Monarch 10EE.

[MaxHeadRoom]

Nobody has mentioned this yet, so let me put my neck on the chopping block and do so- there's another method of speed control that can be used- a mechanical governor. It used to be that the motor current went through a set of contacts that would open when something akin to a flyball governor opened the contacts.
Ok- chop away-

The modern version would be a speed pot input to 8 pin micro and using a slot opto-interrupter on the motor for RPM feedback, and PWM control of a DC/BLDC motor.
Someone on the CNCforum designed one for using router motors in a CNC application, due to the nature of the Universal motor & Triac control, the bottom end speed is 5krpm.
It uses a retro-reflector sensor for RPM feedback.
It can be found marketed now under SuperPID controller.