Stripped the drive belt on my Chinese Mini lathe

Hello all

Great forum I've been viewing for a while, this is my first post, looking for help I guess.

So I am somewhat of a beginner, but I've been using my Chinese mini lathe (Sieg SC2 from ArcEurotrade) for a number of months now, with reasonable success.

Today however the motor was stalling. I stripped back the motor end to find a stripped drive belt, on the motor to headstock drive.

I have no doubt this is down to my lack of skill on the lathe, but my questions are

1/how might I prevent this from happening again?

2/ is the immediate fix just a case of slipping on a new belt?

Many thanks

JD

If the motor is actually stalling, I would expect a problem, downstream of the belt, that needs finding and fixing.

Either a mechanical issue or overload (by the operator) issue, I would think.

Replacing the belt is an obvious requirement, but I doubt that alone will solve the problem of stalling the motor.

If it is not actually stalling the motor, the problem might have been only an improperly tensioned drive belt.

As NDIY said, and the immediate fix is to fit a new belt. As that's done by slackening the motor fixing bolts you can take the opportunity to tension it correctly; not loose, just slightly tight.

How hard to drive a lathe is a learned skill. Two beginner mistakes are being either too gentle or too brutal. I run my lathe by ear; l like the motor to sound as if it's having a bit of trouble doing the work, but not labouring or being significantly slowed down. Not a good idea to flog the machine and it shouldn't be necessary.

Another possibility is the suitability of the metal you're turning. I started practising on odd bits of scrap which turned out to be a bad mistake because a lot of scrap metal doesn't machine well. Apart from Brass, DIY store metal is horrible too. Better to get a machinable Aluminium Alloy, Brass or Leaded Mild-steel of known specification. These cut nicely with sharp HSS or carbide inserts.

I wouldn't recommend strengthening the lathe. Trouble with doing that is something more expensive is likely to break next time. A stripped belt is much easier to fix than a broken Hi/Lo gear, damaged motor, or fried control board. Don't ask how I know...

Dave

Jim,

When you remove the stripped belt, could you please share some detail photos of the damage. ... These might help identify the cause of failure.

Thanks

MichaelG.

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Edit: Some useful notes here ...

 https://www.acorn-ind.co.uk/insight/top-6-causes-of-timing-belt-failure/insight/top-6-causes-of-timing-belt-failure/

and this is the page I was looking-for ...

https://fear.al/wp-content/uploads/2017/01/Probleme_Diagnostikimi_Zgjidhja_Rripa_Faze.pdf

Edited By Michael Gilligan on 02/09/2019 10:19:30

VERY true. I bought some offcuts from my local steel stockholders... bad move. If you want some bits to play with, I suggest eBay... selection of EN1a / Brass / Aluminium of varying sizes... perhaps 10, 15, 20, and 25mm round. If you get it all from one supplier, you may find the postage is OK. You don't have to get it all at once either, and the bits you don't use can go in a box of bar stock. That's how I've done it anyway. I think I paid £7.50 for the last piece of 25mm En1 - 300mm long. Maybe to avoid too much expense, start with 15mm brass, and a piece of 15mm En1a. That should give you a good start maybe.

Enjoy

Ex factory, the supplied belts are not always of the highest quality. I have a C1 on which the first belt simply disintegrated as if attacked by some sort of contamination. Replaced with UK sourced T5 belt, not had a problem since.

Was the lack of drive due to motor stalling or the belt slipping?

I suspect that you need to look at alignment and tension in the first instance. Prolonged high speed running on tight belts can cause accelerated wear. Have some mechanical sympathy, avoid loading up the lathe by checking/reducing the RPM drop under cutting load. Oh, and avoid hard mechanical 'stops' (jus sayin!)

Easy to replace, unscrew the plastic plate on the end of the motor pulley, slip the old belt off and the new belt on, then check alignment of the motor with the lathe bed , that the motor pulley is in line with the countershaft pulley and a reasonable tension on the belt - say 1/2 an inch play

ex factory the motor on my CJ18 the back of the motor was an inch higher than the front ( how do they do it?). Detected by the slight whine as the pulley wheel tried to pull the over tensioned belt off the countershaft pulley. Had it been left in this condition, the belt would have failed quite quickly.

Ah the mini lathe - dontcha luve em!

Edited By Martin of Wick on 02/09/2019 11:24:20

I suspect a lot of us have been there, they seem to be designed to make the belt difficult to tension properly. I removed the headstock on my son's Warco mini-lathe before realising the sound was a slipping belt and not the back-gear. The belt was so loose I didn't need to loosen the motor bolts to remove it, but as it was undamaged I didn't think it could be the problem.

I couldn't find any information on how tight the belt was supposed to be, so used the same method as for Volkswagen timing belts, setting it so that I could nearly twist the belt 90 degrees in the middle of the run, since which the same belt has been trouble-free

Brian

Assuming the belt is a toothed type and some of the teeth broke off, they may have been responsible for the stalling. These belts have a number on the outside, and are very easy to get. They don't have to be very tight as the teeth do the driving, but as already mentioned, check whether the pulleys are in line and parallel.

Thanks all. I don't think the motor actually stalled. I'm having trouble trying to upload a photo of the belt, bit suffice to say that almost all of the teeth are stripped clean off!

I shredded my belt after three years of use. As I couldn't get a replacement I bought a 5M set of belt and pulleys. Fortunately I had a mill so was able to bore out both pulleys. Still working six months later. I prefer the 5M setup as the teeth are a more positive drive form, a little more noise but not obtrusive. Also the belt is readily available.

Hard to imagine why so many of the teeth have been removed. I am not conversant with that lathe but its only the driving (motor) sprocket that can do the actual stripping, the driven sprocket has no power (other than inertia) to impart any shearing force on the belt teeth. My expectation would be that once a continuous group of teeth have been removed the motor sprocket would not be able to impart any significant force in section as it would just slip.

I can imagine that if the motor was running and the chuck was stationary (because of some stripped teeth) and the chuck was turned by hand bringing the first good tooth into play, it would most likely get sheared (snatched) off.

Timing belt drive is very robust and reliable technology. My money would be on either a poor quality belt or possibly the wrong pitch belt was fitted in error, some metric and imperial pitches look almost identical, also there are belts and sprockets that have different tooth forms (for low backlash, power transmission etc).

Ian P

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Start here, Jim: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

... it's easier than it looks.

MichaelG.

With thanks to Michael, here's the belt;

Jim, was yesterday the first time you experienced the the problem i.e. had the lathe been fine until then. Also what sort of work has the lathe been doing to date, any heavy work..?

Hmm...

always slightly worried when I read that replacement belts are hard to get... on both my Chinese specimens I have used a 5T replacement belt, readily obtainable from the usual belt and bearing factors. Maybe I have used the wrong belts...If the originals were not 5T then they must be very close as never had a problem with the 5T replacements.

HTD 5M is better for power transmission, (and belts are about half the price of synchroflex) but as pointed out, you have to change the pulleys.

The dodgy plastic motor pinion is a potential source of problems. From new, the supplied belt and replacement belts did not fit that well on my mini lathe (well the teeth fitted into the gaps, but not what I would call a precision fit). I have ignored the issue in the absence of any problems to date. May replace it one day with a metal pulley as I think could help reduce heat build up in the belt.

Ron, it wasn't running very well of late. However, I was attempting to part off and had the workpiece dislodge from the chuck, so perhaps that's the root cause.

While I am ordering the replacement belt, is there anything else I should order to improve the setup and machine performance in general, or are the best mods the diy ones?

..........I was attempting to part off and had the workpiece dislodge from the chuck

Aha! after remorse comes the confession... Don't worry we've all been there!

Thing is, given the nature of the belt, at the kind of RPM and torque load needed for parting, the 5T belt is right on the limit of its design parameter and close to tooth stripping territory and a lock up is the last straw.

Drilling larger holes is another activity that puts a large load on the belt and motor.

As above, switching to 5M system may help a bit, but the difference to T5 at low RPM is not huge.

Although it is a PITA, (particularly setting motor alignment and position) it is well worth ensuring all alignments and belt tension is appropriate to give the belt the best chance of survival. Loads of other DIY mods available on the net to suit any particular requirement.

Often you can hear the protest from the speed controller or see the RPM drop when the motor is struggling. Minimising strain on the machine comes with practice and experience and breaking a few tools is just part of the learning process.

Just crack on, and soon you will be lathing away like a pro!

Thanks Martin. Appreciate the words of encouragement. There are so many mods, I don't know where to start. My work is mostly turning down round bar, drilling cross holes, tapping all the way through cylinders of approx 4 inches long. And some knurling. So anything that might improve performance in these operations.

Thanks Neil. By the way, I've enjoyed your book on lathes.

Jim have you spoken to Ketan at Arc Euro? He is very helpful.