Stripped the drive belt on my Chinese Mini lathe

[Neil WyattModerator @neilwyatt]

Argh! I think I deleted my post by accident, managed to find it cached…

Older mini lathes had plastic motor pinions, not sure if all SC2s will have them.

Neil

[Ron LadenParticipant @ronladen17547]

Jim, as Jason suggests your Sieg SC2 should have aluminium motor and spindle pulleys, I think Martin is referring to his CJ18 which is what I have. As you obviously know your SC2 is a 500 watt brushless machine with direct drive to the spindle whereas the CJ18 is not brushless and is not direct drive (unless its the latest model) but has high and low gears housed in the head for the spindle.

Going back to your original post:

Is this an immediate fix..? Yes, providing the crash didnt do any other damage. Contact ARC for a replacement belt and probably best to ask Ketan or Ian about setting up the belt alignment/adjustment, they are both very helpful.

How do you prevent it from happening again..? Quite simply, dont crash the lathe because that is obviously when the belt got stripped and it was quite a crash to pull the work out of the chuck. Thats easy to say and I know from experience as I stalled my mini on 3 occasions when parting off and the third time broke the plastic gears in the head.

As for mods to the lathe I always found parting off a problem with the mini, I would never use a tool larger than 1.5mm in the tool holder and only parted small parts with it. I did modify my lathe and made and fitted a heavy duty cross slide with T slots to take a rear tool post, this transformed parting off but it is not a 5 minute job and I am not suggesting you do the same.

Once you have the belt sorted and hopefully things back to normal you shouldnt need any mods providing you use the lathe within its limitations and all mini lathes have their limitations. It depends on the type of work you are doing and how heavy handed your are, not that I am suggesting that you are heavy handed but the thing to always remember is they are not heavy duty machines. You will probably see or read bravado comments from some who say how they part 50mm stl stl with a 3mm tool with no issues at all or that they take 2mm or more cuts with steel, no problem…..well if they do good luck to them but having used one for over a year that is not my experience of the mini lathe. Smaller cuts means more time to complete a job but I just accepted that as the norm with a mini lathe.

I think that is generally accepted that max DOC for the mini is around 1.0mm in steel and 2.0mm in aluminium though with mine I brought that down to 0.75mm with steel and 1.5mm aluminium and most of the time I would go with 0.5mm and 1.0mm. 

Anyway that is my two penneth and good luck in replacing the belt and getting things back up and running.

Edited By Ron Laden on 03/09/2019 09:56:40

[JasonBModerator @jasonb]

Yes I can conform the pulleys are both Aluminiun. With the drive being direct between motor and spindle there are no plastic gears to strip so the weakest link is now the easily changed belt. Only uses plastic gears for the lead screw feed. I doubt much is the same as the generic 7x mini lathes as there is no lay shaft so the head arrangement is completely different.

I think the pitch of the SC2 belt is imperial 1.5×100 would be 0.1875" pitch with 100 teeth if the larger 2×65 belts are anything to go by as they are 1/4" pitch.

With regards to low speed cutting, on these machines it is often better to run at a higher speed and take lighter cuts 2 cuts at 1mm running at double the speed will take no longer than one 2mm cut at half the speed. For parting this will probably mean a narrower tool and for drilling working up to size in smaller steps rather than going straight in with a big drill. For example I'll turn a 9" flywheel at say 300rpm where as the Myford boys will be reaching for backgear and cutting at 50rpm but it keeps the motor in a more useful power band and the fan is running faster.

One last thing, buy two belts than you have a spare even if it is not needed for a few years you can bet it will go again on the friday evening before a bank holiday weekend.

Edited By JasonB on 03/09/2019 09:55:55

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 03/09/2019 09:49:10:

Yes I can conform the pulleys are both Aluminiun. With the drive being direct between motor and spindle there are no plastic gears to strip so the weakest link is now the easily changed belt.

[ … ]

.

Just a thought, from a non-user of 'the mini-lathe' …

A poly-vee drive would be [slightly] quieter and smoother, and would be less prone to self-destruction.

MichaelG.

[JasonBModerator @jasonb]

My similar belt on the X3 lasted 8 years before it gave up the ghost so hardly self destruction prone in the right hands and it had a lot of use. maybe that is why they carry the "Great Wall" brand name

[HOWARDTParticipant @howardt]

I would stick wth toothed belt rather than polyvee, as I would expect the belt tension to be higher on polyvee. The reason I say this is the life of the motor bearing with higher tension. My motor stops with an error if the cutting torque is too high for it and this has happened quite frequently over the three years or so I have had the machine with no electrical problems ( may be one day I will get a bigger machine!!).

[Jim Dalton 1Participant @jimdalton1]

Spoke to Arc they are indeed very very helpful. I was also advised that as I am using carbide inserts, that my speeds should be a lot quicker than that used with HSS tooling.

[Ron LadenParticipant @ronladen17547]

Posted by Michael Gilligan on 03/09/2019 13:16:40:

Posted by JasonB on 03/09/2019 09:49:10:

Yes I can conform the pulleys are both Aluminiun. With the drive being direct between motor and spindle there are no plastic gears to strip so the weakest link is now the easily changed belt.

[ … ]

.

Just a thought, from a non-user of 'the mini-lathe' …

A poly-vee drive would be [slightly] quieter and smoother, and would be less prone to self-destruction.

MichaelG.

 

Michael, a poly-vee belt and pulleys is what I fitted to my mini-lathe after changing the broken plastic head spindle gears to a metal set. It was Jason who came up with the idea suggesting that in the event of a stall or crash a poly vee belt adjusted with a degree of slack would slip and safeguard other more expensive parts. Despite the belt having been adjusted this way there was never a hint of slippage even on the heavier work when in normal use. So poly-vee gets a thumbs up from me though the only downside is you have to make your own pulleys as the correct size is not available off the shelf but they are not difficult to produce.

Ron

Edited By Ron Laden on 03/09/2019 18:15:26

[Michael GilliganParticipant @michaelgilligan61133]

Thanks Ron

Nice to have a happy user's confirmation.

Unless timing/synchronisation is paramount, Poly-Vee would be my first choice for most drives.

MichaelG.

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