Re-motoring Unimat SL

[Bert Coules]

Izzy, that's really helpful, thanks.  And a very neat bit of construction.  I want to incorporate an on/off control as close to the lathe as possible for operational convenience and safety, which means putting a switch into the 24V cable: the PSU will be fed from a conventional switched mains wall socket but obviously I don't want to use that to control the lathe.  I presume that your lathe has a switch built-in but the Unimat is rather more basic. 

 

I'll also be including an electronic speed control, which presumably is best placed after the DC switch.

 

 

 

Edited August 1, 2020 by Bert Coules
Improvement.

[Izzy]

Have a look here. https://www.rmweb.co.uk/community/index.php?/topic/17222-lathes-mc-tools/page/34/

 

This is the post I made concerning the conversion I did. This confirms I put the on/off switch before the PWM control board, but also adding a LED indicator. The switch is of course a emergency type one fitted originally to the lathe, press down to cut power, but needs turning to energise, so no starts when not intended. Another welcome safety first aspect to help avoid injury.

 

Izzy

[Bert Coules]

Izzy, thanks for that.  As I said, my natural instinct was to put the speed controller between the switch and the lathe: it's good to have that confirmed as the best practice.  I also like the idea of an LED indicator to show when the switch is on in case the lathe is powered up but not rotating - I believe I've seen switches with built-in illumination which would be a neat way of achieving this.

 

I didn't know that it's considered desirable not to switch the PSU on and off too frequently, so I'm grateful to have learned that.

Edited August 3, 2020 by Bert Coules
Correction of a foolish slip.

[Bert Coules]

I bought the power supply I linked to earlier: ordered on eBay on Saturday, delivered today (Monday): excellent service from the seller.  It is fan-cooled, with the fan set to kick in when the unit reaches 45 degrees C.

 

Izzy, I'm undecided about an overall housing but whether I go down that route or not I'll certainly follow your example and arrange something to tether the input and output wiring: I don't  want to trust solely to those screw terminals.

 

I await the motor and the speed controller...

 

[Izzy]

I cased mine on the double insulated principle as the case is metal. Would be okay if it was just tucked away somewhere I didn’t handle it, but as a unit I touch whenever I use the lathe - I put the lathe on the workbench and pack it away between use - I wanted to ensure I never got any kind of electrical shock. 
 

Izzy

[Bert Coules]

That makes  excellent sense.

 

[Bert Coules]

I now have the motor, the speed controller, and the PSU.  A question about the type of switch I need for the 24V DC feed to the lathe: is it sufficient to insert a switch across just the positive output from the PSU and take the negative output direct to the speed controller? 

 

Many thanks.

 

Edited August 5, 2020 by Bert Coules

[Bert Coules]

As a follow-up to my switch query, I've been advised by an electrican to route the power as follows:

 

mains  >

 

switch (located near the lathe and used for switching it on and off operationally)  >

 

PSU  >

 

speed controller  >

 

motor

 

This seems to run counter to the advice I've seen elsewhere to avoid switching the PSU on and off too frequently.

 

I'd be grateful for any thoughts.

 

 

 

 

Edited August 5, 2020 by Bert Coules

[Bert Coules]

I now have the new motor up and attached and running,  The lathe isn't working, since I've yet to get the motor drive pulley, but that's not going to stop me being pleased with progress so far.

I don't know if anyone else found this, but for me the hardest part by far was reassembling the motor after adapting the spindle end plate for bolting to the Unimat.  Keeping the brushes in place while re-inserting the bare motor into the housing really needed three hands - and the fact that when the magnets catch hold the motor shoots into the case like a nuclear-powered guided missile didn't help (and my word, that gave me a [non-electrical] shock the first time it happened).  And then you have to be sure that both of the end plates are properly aligned, and fiddle about getting the long bolts into their threaded homes while they're constantly pulled off course by the magnets in the case.

 

But it's done now.  Many thanks to everyone here for all the help and advice.

 

Bert

 

 

 

Edited August 8, 2020 by Bert Coules

[Izzy]

I put the on/off switch between the controller & motor because that is how the original setup was done. I can think of many electrical products that are the same. In this case however I think another reason to leave the PSU ‘on’ when connected to the mains and supplying power on an intermittent basis is because as the power draw rises and heat is produced so the fan kicks in to keep the electronics down to a safe heat level. This will continue to cool even when the motor isn’t running. But..if you keep turning the PSU on/off there is the danger the heat level might rise above a safe one with the fan not running all the time it’s above what’s needed.

 

Izzy

[Bert Coules]

Izzy, that's a good point about the heat dispersion, thanks.  So far, lacking the pulley, I've only run the motor for short bursts in order to test everything, but in actual use I expect things to be rather different. 

 

The speed control works beautifully and over a wide range.

 

Incidentally, my speed controller has an on/off switch at the start of the rotary control.  For my tests I've been using that to stop and start the motor rather than adding a separate switch, but I don't know about its long-term reliability.

 

One thing which did strike me was that I had to reverse the

connections to the motor to get it to rotate in the necessary direction: clearly its usual setup in a scooter requires it to revolve anti-clockwise.

 

 

Edited August 9, 2020 by Bert Coules

[heavymetalwagons]

hi all

after buying my unimat (must by 15+ years ago) decided to have a play with it. well the belt was on its last legs but it nearly did the "test" job 

then the motor started running slow and getting VERY hot and smoke!= its dead, plus the previous owner had "repaired" it with a new cable.

As I don't use it much and even then only on small brass/plastic etc i went for the cheap+easy fix.

so after a bit of research I got a cheap sewing machine motor from ebay 

it was counter clockwise but took 5 mins to change round and didn't even have to get the soldering iron out 

the shaft the same dia as the old one so pulley will fit ok.

just need to make a bracket or adapt the unimat one to fit the motor more securely (its not lose at moment though plus the new belt holds it tight)

the new motor will fit nicely inside the old motor case with a few shims so "may" try that when my brain works it out !!!. the old case will need drilling for more ventilation

I already own a sewing machine foot pedal I converted for my home made RSU (just cut the sewing machine plug off and fitted a 3 pin socket) so that acts as a on/off switch.

Don't know how long the new motor will last looks a bit basic but ok ish .but it has a metal case and is really easy to dismantle(and put back together lol) at least so we'll see.

plus I'm going to try and leave the lathe out to encourage me to make use of it more and if I do then I may consider doing a better upgrade with the scooter motor+psu