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

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

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

+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