Another chinese lathe rises through the smoke

Working in the workshop today, on myCL300 lathe, turning down a 200mm length of 30mm bar and not working the machine particularly hard, when I heard the dreaded "Phut" of a fuse blowing and the lathe stopped. Checked the fuse and it was black. Tried another fuse without much hope, but the speed LED's lit up showing there was power. gently started tuning the speed control and the chuck started turning and the stopped as the new fuse blew.

I have since opened the control box and having disconnected the motor, tried the lamp test, which worked fine, brightening and dimming as I rotated the speed control. Tried the motor on a 12volt battery and it does turn, but doesn't sound right to me, so I am inclined to think it is what's at fault. I will remove it tomorrow and give it a proper check.

A new motor from Arc Euro is £125.88 but I am considering getting an early Christmas present by buying a motor, inverter and control box from Newton Tesla. That will set me back about £340 but hopefully, no more drive problems.

Any helpful comments or advice will be appreciated. Thank you in advance .

Anthony

Anthony

You don't say what size motor but £340 seems expensive for a that size lathe, what size motor have you priced for ?

Emgee

For those with the cash, the NT solution will be simple, robust, safe and least faff.

If 'twere me, I would find a new 3 phase 350W or 500W motor circa £80 to £100 and a generic 750W VFD circa £50 to £70. A s/h motor would be OK, but you may have to search about to find the right one and they never seem that much cheaper than new.

If you do not feel completely confident/competent to wire up such power devices and make a simple control box to suit your purpose, I advise you to take the NT route.

Depending on motor speed selected, (ie. 2 or 4 pole) you may need to adjust the drive pully arrangements to suit your requirement.

PS -  avoid open frame motors if possible, sure they run cooler but they have a propensity to ingest swarf unless well protected

Edited By Martin of Wick on 14/11/2021 20:06:57

The existing motor is rated at 250 watts. I have priced the new motor, inverter and control unit combo for 1/3rd of a horsepower, which is just over 300 watts.

I would go for half a horse min. I have a 350W induction motor on an equivalent lathe and it certainly doesn't feel over-powered. However it does feel substantially more powerful than the DC motor it replaced (that bogusly claimed 550W!).

If I didn't also have the 1HP Myford, I would probably up the drive unit to 500W.

Edited By Martin of Wick on 14/11/2021 20:37:41

Correction to previous post. The price I quoted IS for a 1/2 HP package, not 1/3rd HP (which would only be 247 watts)

"Another" chinese lathe bites the dust?

Might be interesting to compare Mean time between failure for these lathes compared to equivalents of the same age from other manufacturing areas.

I bought the lathe when I retired in 2008. Shortly afterwards, I destroyed the control board when I ran the tool post into the chuck. A new PCB sorted that out and it's been OK until now. MTBF in this case is 13 years.

Recently bought a 1HP package from NT * , and its a nice bit of kit. OK bit more pricey than a home-brew setup, but quality units and good backup if needed.

My old chinese lathe was manual (no electric speed controls etc) just wanted a bit more versatility and a little more power than the original 3/4 HP single phase motor.

* I have no association with this company.

Anthony

Have you ever inspected the brush gear on the motor for wear or carbon dust build up? It could be that the brushes need replacing or it just needs a good clean out. After 13 years use, depending how hard/frequently its been used, it would benefit from a service.

Edit. Moving a comma

Edited By Martin W on 15/11/2021 10:31:21

As an electronic ignoramus I do wonder why the design does not include protection against the consequences of this sort of mishap (which for some just results in belt slip).

Whilst I think the OP has not been unfair to his lathe, I must say that I feel that the title of this thread could be thought so. 'Another Chinese lathe.....'

The lathe has not bitten the dust but its motor might have done, as indeed a motor on any other lathe might have done after 13 years.

According to the MEW 145 (Dec 2008) this lathe retailed new at £399.99 from at least one supplier whilst a secondhand Myford without gearbox in the same issue was up for sale at £2450 (both prices plus VAT).

I consider that both machines have many different advantages and disadvantages in differing circumstances but this price differential ought to be considered too.

To put it in perspective I am not using the same camera, car, cooker, fridge, freezer, central heating boiler, bed, most of my clothes, dishwasher, bathroom, kitchen or glasses as I was in 2008 so, while not looking at cheap imported machinery through rose tinted glasses, please give them a break!

Finally please don't come back with the 'British iron' v. Chinese arguments - in my opinion they are quite different things and most comparisons are irrelevant but everything has a reasonable life and price.

Nick

Edited By Nick Clarke 3 on 15/11/2021 12:12:45

Is the Chinese lathe design of using a variable speed DC? motor and a box of electronics just a cost cutting exercise? I feel that it is much cheaper than the traditional belt, multiple pulley and fixed speed single phase motor system.

Obviously it is not. The dealers tell me, through their adverts, it is what buyers want.

JA

Edited By JA on 15/11/2021 12:17:57

250 watts is not a powerful motor, even by mini lathe standards (Now in the 500W brushless league )

The operator manual for a mini lathe with a 400 W brushed motor quotes 0.010" for roughing.

This seems very conservative, but I would not regard it as a slip of the decimal point and try taking 0.10" cuts!.

Not that I suggesting that is what was being done when the fuses blew

the fact that the fuse blew almost immediately says that there something has gone short circuit..

Based on the evidence, so far, it sounds as if the Circuit Board is functioning, but the motor "Not sounding right" suggests that perhaps at least one coil on the armature might have failed and is shorted.

It would be worth removing and stripping and checking each pair of commutator bars. You might find one pair with quite a different (VERY low ) resistance from all the others.

Just a thought

Howard

Progress report.

I have removed the motor from the lathe and done some resistance measurements on the armature, firstly via the brushes and then with them and the end cap removed. Metered the commutator segments 180 degrees apart and found as I went round, the resistance varied from about 15 ohms down to just over 2. Looks like the windings are kaput, still, it lasted 13 years and has done some good work. I do have a spare control pcb, which is the original one I destroyed and have since repaired. No good having a spare control pcb when it's the motor that's broken. Law of Sod strikes again. New motor ordered. Watch this space!

Don't forget single-phase motors are also cost-cutting. Their performance, vibration and reliability is considerably inferior to DC and three-phase motors.

But single-phase isn't completely daft. When the ML7 and friends hit the streets after WW2, almost no hobbyist could afford a big AC/DC converter or a three-phase supply. Instead they made do with a single-phase motor, even though the type isn't ideal on a machine tool. Single phase motors have low start torque, buzzy power output, complicated reverse, no speed control, and unreliable capacitors and centrifugal switches. The advantage was the lathe could be powered from ordinary mains, which saved a lot of money. However, if you really care about quality, get rid of single-phase: it's only 'good-enough' rather than the best available.

Today, affordable electronics make it easy for hobbyists to exploit DC, 3-phase and brushless motors. Better torque and good speed control, perhaps pushed too far by getting rid of back-gear. No electric motor is perfect and low duty cycle hobby machines are often worked harder than is wise!

Keeping it in perspective, aren't more single-phase motor problems raised on this forum than any other?

Dave

That may be so but many of those single-phase motors are 80 or more years old and have served 2 or three generations of ,model engineers, and are easily replaced by 3 phase motors and VFDs when they finally need repair or expire.

Rod

May be, but there are an awful lot of Chinese electronics/motors failures reported on the forum.

One of the few persons I know who has bought Chinese had the motor and electronics fail on his milling machine after a few years. He now powers the machine by a mains electric drill. I do not know of anyone who has had problems with a single phase motor on any machine. Perhaps I live in a narrow closetted world.

JA

It might be a little unfair to describe an electrical fault not yet investigated as 'lathe failure'. And was it indeed a Chinese part which failed, I wonder?

Tim

.

Perhaps it's just me, Nick; but until Jon Lawes and yourself emphasised 'Another' ... the thread title didn't trouble me at all: I just took it to be a witty play on "Another one bites the dust"

MichaelG.