Unimat SL lathe motor conversion.

[Steamchick]

Hi all,
I just thought I'd post something I have started, in case others "need to know" some of these details for their own conversions.
I have an ancient (1960s?) Unimat SL - with attachments for up-ending the whole headstock to make a drilling/milling machine! (Never actually tried it with that).
It is a bit worn, but I wanted it for tiny stuff, as the main lathe (when I acquired this 20 years ago) wasn't particularly accurate at very small stuff.
Suffice to say it worked fine but was very noisy. So I changed the bearings for new parts. GOOD> But I was just running it (enjoying the results of my labours) when my wife called me away, but I hadn't stopped the lathe. When next I returned, the motor was burned-out (Armature Open circuit all windings).
So I made adapters for an old "similar" Universal (series wired armature and field coils) motor of around 200W (?) - from a spin drier, or lawn mower or something, that was for continuous running. BUT It ran at 12000rpm, instead of the 4000rpm of the Unimat 90W original motor.
I bought a cheap (£4) voltage controller off E&@y. Worked fine, but the noise from this motor did my head in after just a few minutes! - Probably worn out bearings, but sounded very like it could be winding noise or armature noise, as well. It is also an open design, with cooling fan, which adds more noise. On 1970s electrical appliances, if it worked and was cheap it was used. Nowadays we expect a lower noise level.
So I studied what is available., then concluded a 500W 220V DC PM motor would work, except it runs around 12000 rpm. Seeing that I already had a controller to drop voltage from the mains, all I needed was to add a diode pack to rectify to DC, then I could drop the 500W to maybe 167W by dropping it to 4000rpm.... (Or is it a square law?) but that should be better than the original motor anyway. I rarely used the lowest speeds with the original motor, and as this DC PM motor will produce bags of torque from the magnets at lower voltages/speeds, I expect it to be adequate. I shall always use the motor at a reasonably high speed if possible for the job, using the belt gearing to drop the speed (and improve torque), because I can.
Here are a couple of pictures showing the various motors I have:
Parts of the original motor with the replacement Universal motor:

Parts of the original motor with the new 500W DC PM motor in half of the original casing, as a mounting on the lathe.

And mounted (loosely):

So far so good: What I had to machine:

• A spacer to fit the 15mm new motor boss into the 3/4" bearing location of the SL motor casing.
• 4 x mounting holes for the new motor to be held in the SL casing.
• Some ventilation slots: The SL casing is totally closed, but the new 500W motor has ventilation slots in the end plates, so I need similar in the SL casing.
• A new pulley: The SL uses a 6mm shaft diameter, with 2mm pin to carry the drive, but the new 500W motor is 5mm diameter, and a different fixing (flat on one side of the shaft for a locking screw). It is also too short, so the new pulley will extend the shaft the the pulley centre I need. (More later).
• Screws needed to be shortened, and 2 small bosses inside the SL casing had to be machined back to permit a good flat mounting for the new motor in that casing. I used the lathe, but a Dremel would have worked.

That's all for now,
Enjoy!
K2

 

[Steamchick]

This was the previous Universal (series) motor: Inside a plastic tube for aiding the forced cooling-air flow).

And the comparison to the new 500W DC PM Motor.

I think these pictures should have started the thread... but I only just found them!
Cheers!
K2

 

[Steamchick]

Incidentally: The original motor (4000rpm & 90W) was giving spindle speeds of 365 ~6000rpm with the various belt ratios. On the "highest" reduction ratio, with the 12000rpm series field motor, I was using the controller for speeds from 1100rpm down to ~400rpm. So I expect to use the controller on the 500W DC PM motor to do the same.
I am concerned about "motor torque" at full speed, being multiplied by the belt ratios and being capable of a higher torque of cut than the machine can withstand without significant distortion under load. I may therefore have to limit the motor speed (input voltage) and use the belt gearing to get the appropriate spindle speed from the reduced speed from the motor, or simple have to be careful when applying the cut!
I understand the power is the square function of the voltage (or current) and power is a function of torque x rpm. So, max torque derived from a "90W" output motor (design limit of the lathe chassis) from the 500W motor would mean dropping the speed (I think?) to Motor Limiting torque and speed, so the torque at the spindle cannot exceed what the designed motor could do...
My Operational plan is to have a speed of motor that will be set on the supply voltage controller, then use the belt ratios to get the cutting spindle speed for the job. (But I haver twisted my head around with this today and can't think clearly!)
I have considered limiting torque proportional to power/rpm:
90W motor : Torque = k x 90/4000. (k is a constant for sake of calculation). = 0.0225 (bananas). I think my "bananas" may be Nm? and k includes Pi in the constant? But as I am comparing different motors for the same torque I can avoid "absolute" values I think?
500W motor: torque = k x 500/12000. = 0.04167 (bananas).
So I need to reduce the speed of the 500W motor by 0.0225/0.041667 => 54% of the 500W: = 270W...(Is this reasoning correct?): hence a speed of 12000 x 0.54 = 6480rpm ...(Is this reasoning correct? - I am doubting this already!).
Any expert advice?

Cheers!
K2

 

[Steamchick]

Here's my table of belt settings for spindle speeds using the new motor: 12000rpm is FULL power and torque, but 6500rpm is where I think I need to set a motor limit to avoid too much torque on the lathe when machining. (Distortion under load = loss of accuracy!).
Hope this is of interest?
K2

 

[Steamchick]

I thought I'd add the "Electronics" I am using to tame the 500W DC PM motor:
Originally, the 240V 50Hz mains went directly to the SL 90W 4000rpm universal Motor.
When I fitted the 12000rpm 200W universal motor I fitted a speed controller (from E&@y): AC 220V 2000W SCR Voltage Regulator Dimming Dimmer Motor Speed Controller Module:

But the 500W 12000rpm DC PM Motor Needs DC... so I'll add a diode pack on the output from the voltage controller, to make DC for the motor. This one is cheap enough and looks well capable: Bridge Rectifier KBPC3510 35A 1000V from E&@y.

I thought the DC output may need to be smoothed before feeding the motor, but I am reliably informed that a large smoothing capacitor is unnecessary, as the motor will naturally smooth the power by its inductance (Reluctance?). Also a large capacitor is very likely to frighten the voltage controller and diode by the inrush current when switching ON. I would not want to fry these super cheap electronics!
For someone doing this from scratch, I suggest a "proper" controller may be something like this one? AC 220V To DC 180V Knob Motor Speed Variable Control Controller For 0-400W Motor

Or maybe this will do?
220V AC Single-phase Motor Speed Controller Governor 4KW DC Speed Control | eBay

There are a number of similar devices, some of which need a proper enclosure making to protect all the lively electrical terminals, etc. from probing fingers! - I use proprietary "project boxes".
And if you don't understand electricals, GET AN EXPERT to do all the wiring and ADD EARTHS AND FUSES, to make it all safe.

Today I'll be wiring-up my new motor and will let you know the result (if I don't fry myself in the process!).

I can only recount a tale I experienced with a "professional" electrician. It was at work, and I had engaged the "approved contractor" to install a motor speed controller onto a large 440V AC 3-phase fan motor. The boss did the job himself, as all his electricians were busy on other (much bigger) electrical installation jobs, and he liked to "keep his hand-in"! And "hey! It's only 3 wires in and 3 out of the controller, so not a major job". All wiring fitted in steel conduit, between the existing switch box (just ON/OFF isolation) and the plastic housed speed controller... After wiring it all up, we went back to be main isolation board (50 feet away, and switched ON to make the fan circuit live. But first he checked there were no earth faults. Then we went to the fan control, switched ON, and using the controller knob checked the speed varied as planned. But I asked if all the earthing etc. was safe - a "standard question" in the checklist. He said "of course" and touched the piece of conduit between the old switch box and the new speed controller. When I checked he was safely alive, he picked himself up off the floor, shook his head and said the conduit was LIVE... so I switched OFF the circuit at the main board and locked it down safely. - Too much confidence, a missed earth and a hair wire touching some metal had made the conduit live from a single phase. If he had checked earth continuity properly it would not have tried to kill him. We can all make mistakes, so get your wiring professionally checked to the latest regulations for earthing, etc. And an RCD device is better protection than just a fuse. (And use the correct fuse rating). Be especially aware that the 220V DC output is not like AC... With AC, the shock makes you jerk violently. The heart can fibrillate, and be restored by a de-fibrillator after the electricity is removed. With DC, you just lock - fixed by all the muscles tensing and not relaxing - and the heart just seizes-up. So do TAKE CARE.
K2

Website controller: Please check this message is "safe and sensible" before publishing?

 

[Steamchick]

I have temporarily wired-up the circuit (well, the 5 wires that needed fitting!). checked and all OK so I ran the motor and it turns with variable speed, and the belt runs smoothly. What more is there to do?
Modify the old SL Motor Brush-end cap, with vent slots, fit wiring properly, new shorter studs to hold the 2 old end caps together.
Then I can use it again!
K2.

 

[jmille7916]

Hi all,
I just thought I'd post something I have started, in case others "need to know" some of these details for their own conversions.
I have an ancient (1960s?) Unimat SL - with attachments for up-ending the whole headstock to make a drilling/milling machine! (Never actually tried it with that).
It is a bit worn, but I wanted it for tiny stuff, as the main lathe (when I acquired this 20 years ago) wasn't particularly accurate at very small stuff.
Suffice to say it worked fine but was very noisy. So I changed the bearings for new parts. GOOD> But I was just running it (enjoying the results of my labours) when my wife called me away, but I hadn't stopped the lathe. When next I returned, the motor was burned-out (Armature Open circuit all windings).
So I made adapters for an old "similar" Universal (series wired armature and field coils) motor of around 200W (?) - from a spin drier, or lawn mower or something, that was for continuous running. BUT It ran at 12000rpm, instead of the 4000rpm of the Unimat 90W original motor.
I bought a cheap (£4) voltage controller off E&@y. Worked fine, but the noise from this motor did my head in after just a few minutes! - Probably worn out bearings, but sounded very like it could be winding noise or armature noise, as well. It is also an open design, with cooling fan, which adds more noise. On 1970s electrical appliances, if it worked and was cheap it was used. Nowadays we expect a lower noise level.
So I studied what is available., then concluded a 500W 220V DC PM motor would work, except it runs around 12000 rpm. Seeing that I already had a controller to drop voltage from the mains, all I needed was to add a diode pack to rectify to DC, then I could drop the 500W to maybe 167W by dropping it to 4000rpm.... (Or is it a square law?) but that should be better than the original motor anyway. I rarely used the lowest speeds with the original motor, and as this DC PM motor will produce bags of torque from the magnets at lower voltages/speeds, I expect it to be adequate. I shall always use the motor at a reasonably high speed if possible for the job, using the belt gearing to drop the speed (and improve torque), because I can.
Here are a couple of pictures showing the various motors I have:
Parts of the original motor with the replacement Universal motor:
View attachment 136231
View attachment 136232

Parts of the original motor with the new 500W DC PM motor in half of the original casing, as a mounting on the lathe.
View attachment 136233
And mounted (loosely):
View attachment 136230
So far so good: What I had to machine:

• A spacer to fit the 15mm new motor boss into the 3/4" bearing location of the SL motor casing.
• 4 x mounting holes for the new motor to be held in the SL casing.
• Some ventilation slots: The SL casing is totally closed, but the new 500W motor has ventilation slots in the end plates, so I need similar in the SL casing.
• A new pulley: The SL uses a 6mm shaft diameter, with 2mm pin to carry the drive, but the new 500W motor is 5mm diameter, and a different fixing (flat on one side of the shaft for a locking screw). It is also too short, so the new pulley will extend the shaft the the pulley centre I need. (More later).
• Screws needed to be shortened, and 2 small bosses inside the SL casing had to be machined back to permit a good flat mounting for the new motor in that casing. I used the lathe, but a Dremel would have worked.

That's all for now,
Enjoy!
K2

That SL motor does indeed look ancient. You should know that the “original” design was a sewing machine type motor. 90 watts, intermittent duty, etc. Don’t know if the old type sewing machine motors are still around, but, if so they should be much simpler to adapt. Just my 2 cents worth. BTW, your work looks great.

 

[Steamchick]

Hi jmille. I looked at sewing machine motors, but even modern ones about the same power were "intermittent operation", as is the nature of most domestic sewing machine work.

 

[jmille7916]

Hi jmille. I looked at sewing machine motors, but even modern ones about the same power were "intermittent operation", as is the nature of most domestic sewing machine work.

I totally agree with you, but you should know that the SL was designed for intermittent work. It is a small machine, and the designers originally assumed that the usage was for home use and that the sewing machine motor fit perfectly in that equation. I am not against your modifications, just adding a bit of historical perspective.

 

[Steamchick]

Thanks jmille, I didn't mean to offend, just explain why I wasn't using a sewing machine motor. Having burned out the SL motor, I decided I needed something more "Ken-proof"! As my "continuous running" Universal motor (about double the SL Motor power) was really noisy, I have spent a couple of years biting the bullet and doing Aa "proper job" of getting a more modern motor. - The 500W DC PM motor. So far, it seems like a step forward..., time will tell if I melt the armature on this one!
I'll be running at half-speed, so to stay within the original limits for main-shaft torque. (Any fool can add more power and torque and permanently damage a machine by over-loading, causing a permanent twist somewhere! - I am sometimes "any fool"...).
But discussing things on this thread may teach me the lesson I didn't know, or have forgotten.
Thanks for your input,
K2

 

[ddmckee54]

One of the problems with the DB/SL Unimat is the flex of the bars used for the ways. It was noticeable with the 90W-100W stock motors, with a 500W motor I imagine that it will be more pronounced.

A lot of the guys that do a DC motor conversion on the Unimat will use the 120W-130W 24VDC scooter motor. It'll be interesting to see what this 500W monster does. (It's only a monster when compared to the Unimat's original motor.)

Does your motor have a cooling fan? If not you should probably limit it to intermittent duty, or it won't be "Ken-proof" either. However having a cooling fan on the motor does not cure-all the problems though. At reduced motor RPM's the cooling fan doesn't work as well as it should and the motor could overheat. At one half speed the cooling fan should still be fairly effective. It's usually not recommended to go below 20% of full speed, this is to maintain motor cooling.

Good luck with your conversion.

 

[Steamchick]

Hi ddmckee.... my reason for running at max 6000 rpm with this motor, is to restrict the torque at the Mainshaft to the same as seen with the SL 90 W motor at 4000rpm. If my calculations are correct.
Finished installation today and I am very happy!
10 mins machining some steel screws, no problems. Just warm on the SL motor casing. But it has no fan. I have added a small fan to my bigger lathe motor, and I may do the same to this one. Just not sure how!
Computer fans are cheap. But where is the 5v or 12V. supply? That is the glitch. I'll need another box... and more wires...l
K2

 

[ddmckee54]

You got an old PC power supply laying around? Then you can take your pick of 12V or 5V.

 

[Steamchick]

I was thinking of an old phone charger - wall wart! First I'll decide which fan, and how to blow air through the motor. Some old vacuum cleaner flexible tube? Held with gaffer tape? I have more power supplies than other rubbish!
Just a matter of selecting n buying a fan, then the power supply.
Thanks for the suggestions!
K2

 

[animal12]

These are the sewing machine motors you want to use . They are made to run all day in a commercial environment . They come with a speed control , which usually is a foot pedal , just get a potentiometer of the same value & your good to go . There's folks that have been running these on their full size lathes & smaller mills for years with no hick-ups . They come in different wattages . Here' some links to folks that have installed these motors .
https://www.google.com/search?q=consew+motor+on+a+lathe&sourceid=chrome&ie=UTF-8

here's the link to the motor
https://www.amazon.com/Genuine-CSM1...ords=consew+servo+motor&qid=1652844844&sr=8-5
animal

 

[Steamchick]

Thanks animal. Having finished my conversion I am happy with the result, so posted this as an alternative option.
I did 5 years research before going for the motor I have selected. But we are all free to choose other options, as have many before me.
Thanks for the info, for others to make their decisions..
Mine works, for me!
K2

 

[Steamchick]

Total cost is something like £20, if money is a point for decision making.
K2

 

[Steamchick]

Hi Animal, the first link to videos worked, but the Amazon link threw up security errors!
"Don't go there" warnings!
I'll try some searching later.
K2

 

[animal12]

go to Amazon & then do do search for a Consew Sewing machine motor . These motors are servo motors . They may seem a bit pricy but for the results it's worth it . When I get to the repower stage it will either be a 3 phase motor with ah VFD or one of these servo's .
animal

 

[skyline1]

Hi Ken

A very cost effective solution using cheap and readily available parts.

It will be a little noisy but any motor running at high speed is going to be quite loud. Modern permag motors are much better in this respect than the old universal motor you were using, these are notoriously loud. They are falling out of favour these days and their terrific noise is among the many reasons why.

In a permag motor where the excitation is fixed If you halve the voltage you also halve the current so the power input (and output) is around 1/4 It is a square law as you thought. Motor efficiency varies with speed for many technical reasons but output power being a square law with voltage is a reasonable rule of thumb for modest speed changes (down to about 50% depending on motor design.

I have checked the spec on this motor as best I can and the manufacturers state that it is rated down to that speed but it is at the bottom end of the range so you should keep an eye on the temperature and possibly not run it for very long periods.

Best Regards Mark