Member postings for Paul Mercer

Gents.

I have a working lathe!

I bit the bullet and purchased a replacement motor. I stayed with the same DC motor for ease! Thank you for all of your help and advice. It was really appreciated.

Paul

So I did some more investigation. I took the motor apart to see what if anything the new brushes had done to the newly cleaned up commutator

There were two distinct areas of burning on the commutator, with only 3 bars between them

First I did the “180 degree test”, I measured the resistance of the windings on commutator bars 180 degrees apart.
On most of the readings I got 7 ohms. On 4 pairs of bars I got 53K ohms.

Secondly I did the bar-to-bar test, which measures each individual loop.
On most of the readings I got 0.4-0.8 ohms. On 2 pairs I got 53K ohms.

The two individual loops around the burning, coincided with the 53K ohm readings.

With these more detailed measurements, I’m guessing that it’s a new motor needed.

Good afternoon all.

back home now for a couple of days, and found a set of brushes on the doorstep. I’ve just read through the previous comments and noticed a couple of typos - apologies, but I use my phone more than my laptop.

I checked every wire in the lathe and did find that an earth to the chassis was loose, so tightened that. Hopefully that explains the shock.

Starting up the lathe with new brushes and she blew the breaker again. Stripped it down and started it with the motor separate to the lathe, and it worked. Fitted the motor and it still worked. Added all the panels and it still worked. Put on the drive belt and it blew the breaker again.

There doesn’t appear to be any excessive physical resistance when turning the lathe by hand.
Running the lathe with no belt, but adding physical resistance to the motor with a length of wood on the pulley once it’s running causes the motor to start sparking.

Why isn’t anything easy! Does anyone have any further thoughts?

Thanks.

Edited By Paul Mercer on 15/02/2023 16:55:32

I’ve been away for a few days so don’t now work on the lathe. I stripped the motor down and had another look at the commutator. The gaps on the commutator had a lot of dark residue built up, presumably carbon, and the copper edges seemed slightly burred over closing the gaps down at the surface. I gave the commutator surface a cleanup with a bit of fine emery and removed the burrs abs dark residue.

I checked the resistance and there appeared to be no shorts between any prt of the commutator. I put the motor together and using the old brushes checked resistance. No shorts between wires and housing which was good. I’m wondering if when I checked resistance before, I checked continuity between the housing and the wires??

I’ve spoke to the lathe producer and ordered another set of bushes. I’ll fit them when I’m home midweek, and give you an update.

All electrical testing was done with the motor removed and disconnected. I’ll double check the resistance between the wires and the casing when I’m home from work tomorrow.

Jason, the spring on my brushes appears ok, but I’ll try and get some replacements. Current dimensions are 13.4mm X 5mm. The current length is 13.2mm. These appear to be quite large compared to replacement brushes I’ve seen online. Judging by the ration of others available, I’d guess these started off at 20-25mm

I’m based in Orpington, SE London/Kent borders.

Thanks

Here’s an update.

I double checked for swarf and loose wires, of which there were none.

I replaced the motor with a light bulb and the brightness changes with the speed controller which sounds good news! I tried it I’m reverse and again the lightbulb brightness changed.

I removed the brushes and gave it a good blasting with pressurised air. When turning the motor by hand, I noticed that there was a slight bit of darkening on one part of the commutator which reminded me of an arc burn. I cleaned up the brushes and reassembled. Upon starting the motor (outside of lathe) it ran, but sounded like it was sparking in the motor, looking up the rear end of it, confirmed that.
I took the motor apart and gave it a good blast of air, cleaning up the commutator and brushes. Upon reassembly, and starting the motor, it blew the circuit breaker again.

Electrical resistance on the motor was 0.9 ohms. Rotating the motor by hand the figure went up to 1.1 ohms momentarily every time it turned, the dropped back to 0.9 ohms.
Electrical resistance between each motor wire and the housing was 1 ohm.
Voltage on the motor wires increased when the motor was turned by hand.
Voltage between the motor wire and motor housing also increased when turned by hand.

I think I’ve (you’ve) narrowed the issue down to the motor. I couldn’t get and fast evaporating degreaser so that would be one last affront before I take the motor somewhere to be looked at.

Does that sound about right?

Thank you for the replies.

I didn’t notice any swarf or loose wires, but will check again.

The shock came from the frame of the lathe itself - although all circuit boards were loose at the time, all earth cables were in situ. I wasn’t touching any electrical items at the time.

I’m ok ’ish’ with electrics, but don’t know much about motors or controllers. This is clearly beyond my knowledge though!

I don’t have an airline but will get hold of one of those pressurised air cans and give that a go. I’ll also get hold of some fast evaporating degreaser and give that a go.

Thanks for the advice, I’ll keep you updated on progress.

Hello. After my lathe developed a fault earlier on today, I spent a few hours here reading some advice given to another member with a similar lathe issue.

I’ve had my lathe from new, about 15 years, and it gets light/medium use. Today, I was using it quite happily, and turned it off. When I restarted it, it tried to turn for a fraction of a second, then stopped and blew the circuit breaker. I reset the circuit breaker and upon trying to start it, the same thing happened. At that point to took to the internet, and this forum.

I thought it may be a Start Capacitor, so started to strip the lathe to find some specs for it. I was expecting to find a large capacitor near the motor, but found nothing, so presume it’s not that.

I found 2 circuit boards:
One is a DC motor speed controller ref: JYMC-220B-I. (I only know this because it says it on there.)

The second is an unknown circuit board. It has JD-013 REV B 070813 on it, and under that B43688. Research shows a similar lathe made by Grizzly who kindly have a similar part number and call this circuit board a Filter.

I don’t smell any burning on the circuit boards at all.

When I took the lathe apart, I closed the safety switches and tried to turn it on. The motor didn’t turn, but did make a buzzing noise, and the main chassis gave me a small shock. Figured that I’d mention that in case it made a different to anyone’s thoughts

Does anyone have any advice how I could start to find out how to repair this lathe?

Thanks in advance