Unimat 3 lathe motor

[Robert HoltonParticipant @robertholton69149]

Hello everyone,

I have a problem with the motor on my Unimat 3. The motor suddenly started to make a rattling sort of noise a few days ago, which to some ears would suggest worn bearings.

I stripped it down to find everything looking like new, even the commutator was looks clean. there are no burn marks on the coils , the brushes are hardly worn., and the bearings (phospher bronze) are perfectly good.

I know the motor is not continuously rated, and I've been careful to stick to the 8 minute on 2 mins off rule.

I fitted this motor only a few months ago and it ran really well until the noise started. I feel this must be an electrical fault somewhere.

Does anyone here have any knowledge of these lathes and motors who might be able to throw some light on it. this is the second of these motors I have had with the same problem. The first one looks as if it's had a hundred years of use. there must be some way of determining the cause.

I need this lathe to make some tiny bits for my other lathe.

Cheers Rob

[Robert HoltonParticipant @robertholton69149]

[Ian PParticipant @ianp]

Its not clear from your posting whether the rattling noise is still present now you have stripped (and presumably reassembled) the motor.

Rattling sound would indicate a mechanical problem rather than electrical, maybe like a loose pulley. I am not conversant with your particular motor but it sounds like a common universal brushed motor and if the Unimat 3 does not have electronic variable speed control then fault finding is pretty straightforward.

What part (or which) country are you located? (someone nearby may be able to help)

Ian P

[Robert HoltonParticipant @robertholton69149]

Hi Ian,

Yes the noise is still there after stripping checking and re assembly.

It is as you guessed a universal AC/DC motor. it has 2 speeds switched, that appears to work ok.

As I said this motor appears to have had very little use. It is very clean inside. It doesn't appear ever to have been taken apart before I stripped it.

I live in Shropshire close to Ironbridge.

Thank you for your answer.

Rob

[Robert HoltonParticipant @robertholton69149]

Ian,

I forgot to say. there is no slackness of anything, bearings pulley etc. It appears to be in really good nick. As I said originally the other motor of the same type I have was really gungy inside but otherwise very sound bearings new brushes etc, but suffers with the same problem.

Rob

[Michael Cox 1Participant @michaelcox1]

Does the motor rattle if run on the bench and not driving the lathe?

[SillyOldDufferModerator @sillyoldduffer]

Sounds like a mechanical problem, and as it's unlikely two different motors have the same fault, I suspect the pulley system or lathe bearings. With the belt off check for a loose pulley, eccentric spinning, something catching on a rotating part, and noisy bearings. Misalignment of the belt in another possibility, usually caused by the motor mounts not being adjusted quite right. Over-tight belts can damage bearings.

Off-hand the only electrical cause of a rattling motor I can think of is a loose power wire, or one that has parted inside due to vibration and the ends are rubbing. If it's safe, try bending and shaking the wiring with the motor turning to see if you can effect it. If moving a wire stops the motor or cures the noise, replace it.

Dave

[Graham MeekParticipant @grahammeek88282]

I had a similar problem when I first owned a Unimat. I traced it in the end to the armature oscillating in the bearings. An extra shim washer was fitted and that cured the problem.

An easy way to check if this is the cause is to remove the motor pulley and apply end pressure to the armature while the motor is running. If the noise disappears then I would say you have found the problem. It should not require excessive force for this test and a scrap piece of plastic is useful to apply the pressure, as this will not damage the end of the shaft.

Regards

Gray,

[Robert HoltonParticipant @robertholton69149]

Thank for all your answers, but it seems that nobody has an answer as to what the problem might be .

The motor has been stripped it looks almost new inside, there is NO end play, there is NO slackness in the bearings.

the motor makes the same noise with it sitting on the bench or holding it in my hand.

It is hard to describe the sound exactly.

it is nothing what so ever to do with the lathe pulleys bearings or whatever

I have taken the motor pulley off the shaft, so it's nothing to do with that.

the motor is free of anything that can rattle, and I can spin the shaft perfectly easily. I turns very smoothly.

So that is it we are left with one moving part the armature. Once again it turns smoothly, and there is NO undue slacknesss in the bearings…

the brushes are not worn. The inside of the motor Looks as if it has had hardly any use.

I wish I could do a video of it running to prove this to you all.

Rob

[Jouke van der VeenParticipant @joukevanderveen72935]

Does the motor rotate at its “normal” speed(s)?

There are some small capacitors in it. Are they still OK?

[Martin ConnellyParticipant @martinconnelly55370]

Have you carrier out a resistance check over the armature windings? An open circuit in one winding will give a mechanically sound motor a very rough running sound.

Martin C

[Kiwi BlokeParticipant @kiwibloke62605]

Intermittent power supply? Have you tried by-passing all possible wiring, switches, etc., and hard-wired the motor (via a plug) to the mains? Are the brushes free to slide in their holders?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Kiwi Bloke on 01/12/2021 02:04:54:

Intermittent power supply?

+1

Given Rob has eliminated all the likely mechanical faults, there's not else much left.

Can't suggest much because I'm not familiar with the motor type or power supply arrangements on Rob's lathe, but a break inside a wire, loose connection, or malfunctioning power supply/speed controller are all possibilities,

Don't trust anything! Loose mains plug, dodgy socket, fuse loose inside plug, damaged mains cable: check it all, looking for dodgy connections, physical damage and previous repairs. Wire breaks inside the insulation are hard to detect, but gently flexing and pulling the cables with the motor running often helps. It may be easier to replace with new than diagnose.

I hate intermittent faults! Give me smoke or completely dead every time.

Dave

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