Sick Unimat

andrew jukes
Posts: 211
Joined: Thu Mar 05, 2009 4:15 pm

Re: Sick Unimat

Postby andrew jukes » Sat Mar 15, 2014 9:47 pm

I have followed this list:

unimat3@yahoogroups.com

for some time and the subject of failing Unimat 3 motors has come up often. The most strongly recommended solution has been to replace the motor with a 24V DC motor and appropriate power supply. Here is an example from 2011:

"My poor little Unimat 3 motor is starting to expire so I will go down the DC brushless motor path with a 24v DC motor of around 120/135 watts, I have found a suitable (7 Amp) power supply and will choose a Motor and speed controller from that well known auction site very shortly.

My plan is to used M3 toothed belts and http://www.motionco.co.uk/ seem to stock everything I need and even have a handy calculator for belt lengths. Which leads me to my question.

Given that with a bit of imagination I can gear it to a no load speed of around 4000RPM and will have infinite speed control do I need any more than a direct drive from the motor to the lathe? Also how do people attach the drive gear to the lathe input shaft?

I have to say I am not an engineer and my turning is usually very basic things in aluminium and this is the only lathe I have so I am quite limited in what I can do."

Andrew Jukes

Terry Bendall
Posts: 1597
Joined: Sun Jul 27, 2008 7:46 am

Re: Sick Unimat

Postby Terry Bendall » Sun Mar 16, 2014 8:47 am

Andrew

If you go down this route you would have to arrange a way of mounting the motor shaft in line with the mandrel. Not particularly difficult but the two shafts would need to be in line as far as possible. To actually connect the two the best soultion would be a flexible coupling which consists of a metal flange on each shaft and a hard rubbler or similar material between the two. The flanges have projecting pins which fit into holes in the rubber. The use of a flexible coupling will allow for small discrepancies in the alignment of the motor shaft and mandrel.

One flange of the coupling would have to be bored out to fit the mandrel where the final drive pulley goes and I believe these are threaded so this will be tricky. It might be possible to bolt a suitable flange to the face of the pulley.

I think a better way would be to mount the new motor in place of the existing one and use the existing pulley drive system, or at least the last part of it. This will be a neater arrangement and will save having the motor projecting from the left hand end of the lathe. The hole in the pulley may need to be changed to fit the new motor shaft. If it needs to be made larger then it can be bored out which is easy. If the hole is too large you will need to make a bush. This is in effect a tubular spacer and I described how this could be made in Scalefour News 157 page 6.

One problem with all this is that you need a lathe to do the work and if you are taking bits off the only one you have this makes things difficult. :)

One thing to check is if the speed controller will deliver full power at low revs. I expect that modern electronic ones will but it would be worth checking. Some modern lathes and ones which are larger than the Unimat do have electronic speed controllers fitted and they seem to work well.

Terry Bendall

andrew jukes
Posts: 211
Joined: Thu Mar 05, 2009 4:15 pm

Re: Sick Unimat

Postby andrew jukes » Sun Mar 16, 2014 9:38 am

Terry, not sure why you thought the suggestion was anything other than to mount the 24V DC motor in place of the existing one.

As I recall (I haven't had to do this myself), most of the discussion was about how to mount the pulley on the new motor shaft and obviously how to bolt the motor to the existing end plate.

After posting my comment yesterday, I googled for 24V DC motors and was amazed how you can get a 130W scooter motor for £15 or so, so that's the way I would go, if I ever have to.

Andrew

Terry Bendall
Posts: 1597
Joined: Sun Jul 27, 2008 7:46 am

Re: Sick Unimat

Postby Terry Bendall » Mon Mar 17, 2014 6:58 am

andrew jukes wrote:Terry, not sure why you thought the suggestion was anything other than to mount the 24V DC motor in place of the existing one.


Apologies Andrew, I misunderstood
andrew jukes wrote:do I need any more than a direct drive from the motor to the lathe?
:( A direct belt drive from the motor to the mandrel using suitable pulleys would do the job. There is of course still the problem of fixing the new pulley to the mandrel. If you used the existing threaded end then the hole in the pulley would have to be bored out and threaded to suit.


Terry Bendall


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