Mini lathe chain drive conversion dead idea?

[amillertobe]

I have a Sieg type mini lathe and a mill (SC3 and SX2P brushless DC), and I realized that I will be very likely facing a belt change soon. To be honest, I'm surprised I haven't had issues with them yet, because I have never machined anything else but steel with them. Thinking of changing the bearings at the same run and having some interest in improving the machinery, I thought about different belts - and chains. Since for example bike parts and chains are readily available everywhere, turning a mounts for them for the spindle and motor could actually be rather doable. Apart from availability, the gear ratio could be readily changed, the chain length can be adjusted freely to any size by re-linking it, and it is mechanically likely stronger than any other part of these toy machines. (Which is of course a little issue, as something else will give up if they are crashed, but mine just trip if they are overloaded)

So, is this a completely dead-born idea, or has someone actually done this?

[David Powell]

I cannot say anything about your proposed conversion because I do not have Sieg type lathe or mill.
However, long ago , I rebuilt a Southbend 9 inch lathe for a friend, and, for various reasons, tried a chain drive to the mandrel.
It worked well BUT was noisy and seemed rough running. We soon acquired belt pulleys and removed the chain
and sprockets.
On the other hand I ran a Pedersen horizontal mill for some 20 years, It had a chain drive, running in an oil bath in the main casting and it ran smoothly and silently.
Perhaps modern toothed belts might be a good answer for you.
Regards David Powell.

[Jonesy]

A recent high speed project build at home used a chain drive to begin with but as mentioned above it was noisy and rough. A horrible noise to have when your working. I ditched this project but not because of the chain drive... had too many other issues.

Another project, which is in almost daily use does use bike chains and sprockets and works well, but is very slow in comparison to a mini lathe. I wouldn't recommend it.

[RB211]

Belts are smooth, you want smooth, low vibration. Simply switching to a high quality belt may solve any concerns you have. It’s a mini-lathe after all.

[mattthemuppet]

chain drives are great when you want lots of torque and no slip (or change in the relationship between 2 pulleys), so connecting rollers, wheels, cam shafts stuff like that. They're also pretty robust and low maintenance. They're also noisy, somewhat inefficient due to all the moving parts and rough feeling. For your application belt drive (V, polyV or cogged) is the best option.

[David Powell]

As far as I understand things chain drives are very efficient drives when properly aligned, running at reasonable speeds without overload ,in good order. and enclosed with appropriate lubricating arrangements. They will tolerate poor maintenance and misalignment, but at the expense of increased wear. Those as final drives in full size vehicles have, in some cases, worked for over 100 years, open for all to see.Regards David Powell.

[chipmaker4130]

Sounds like you've had good service from the original belts, especially if you're changing bearings because you've worn them out! "If it ain't broke, don't fix it".

[Mcgyver]

what problem would it solve? Is this a V belt, round belt, or?

I can't recall another chain drive example other than Davids (and being a horizontal perhaps speed where mostly lower). While I've hardly seen it all, I'm thinking is fair to say they are not common and that most manufacturers, including the high end ones I've looked under the hook on, chose belt drives. If they slip there is a problem, and of everything I've had to redo and replace on a lot machines over the years, belts are usually ok and don't need replacement, i.e. they seem to really last. Good ones (a consistent cross section) are also smooth and quiet; running in the opposite condition could produce noise in the finish

[reggie_obe]

Van Normal knee mills used a silent chain drive for the table feed on some models. Quiet and efficient, but not cheap.

[chipmaker4130]

Van Normal knee mills used a silent chain drive for the table feed on some models. Quiet and efficient, but not cheap.

Yes, but that's a slow-speed application compared to a spindle.

[BCRider]

Bicycle setups are very smooth running with new sprockets and chains. They have to be since the "motors" are often pretty darn poor. Due to the size of the bigger sprockets and the short chain pitch there's also very little cogging that occurs that can be felt. Perhaps it'll still be too much for a lathe application? But consider that many lathes use gears for their headstock drives. And gears are no more or less "toothy" than a well made chain and sprocket.

Frankly I think it's worth a try. Even if you start out with a fairly crude mockup to start out as a proof of concept.

If you find that it works well enough to consider I'd also suggest that you alter the stock setup. I've seen enough videos on these lathes to appreciate that the low speed operation modes is rather poor with the motor having very low torque at the low speeds. Moving the motor off the lathe to become part of a rear drive jackshaft arrangement as seen on many other bench lathes would give you an option of extending the gearing so the lathe can run at the desired slow speed ranges with the motor running at mid or even higher speeds where it's more efficient. This would cure the low torque issue. In fact it would act similarly to a back gear situation and multiply the torque.

Also moving the motor off the rear of the lathe's bed and onto a separate jack shaft rear drive setup would make correctly tensioning the pair of chains from motor to shaft and shaft to lathe a simple issue. One lever that operates an eccentric would slack off both chains to permit moving the loops of chain between sprockets. And with suitable covers to keep swarf off the sticky sort of open gear and chain grease you would want to use there's no reason that the chain and sprockets won't last for many years.

And no, you would not be able to use derailleurs. Derailleurs do not tolerate negative loads at all. Heck, some of them tend to choke if the chain is a bit dirty and sticky and we back pedal.

A couple of design and convenience factors. First, in case you've not played much with chain setups. The proper "tension" for a chain is actually NO tension. You don't want the chain going snug at any point as the sprockets weeble and wobble around. So it's normal to run them with a bit of slack. Not much though. Just where you can hold the chain at the mid point between sprockets and feel a little obvious free play before it goes snug as you push in and pull out along the plane of the sprockets. If in doubt look up "testing chain tension on motorcycle" on YT. Sorry if you're already a bike person, chainsaw owner or other chain friendly sort and this is already known.

Second is that think I've got an idea for a little chain tool to use for lifting and slipping the chain from sprocket to sprocket. Imagine the cross section of a measuring spoon but with the "spoon" being just a flat bend in some flat stock. With something like that it should be possible to lift a slack chain off and slip the tool around to shift to the next sprocket in the stack without goobering up your fingers.

Of course with the variable motor speed to handle most of the speed changes you shouldn't need too many gear ranges. But then again the rear wheel cogsets come in at least 5 speed versions.

Another interesting option as I consider the gearing also occurs to me.... Can you say Rohloff internally geared hub? The only downside that would make that a tough prospect is the internal freewheel feature. That would need to go.

At any rate between rear cogsets that could be broken apart and front chainrings there's no doubt that setting things up for a very nice gearing would be highly doable.

I hope you do give it a try.

A final thought.... For the last highly geared down option where you might be loading the cutter on a larger diameter there's also an option where you could double up on the sprockets that directly drive the lathe spindle if needed. It would not be that hard on this "back gear" option to have the stack of sprockets that fits the lathe and other end of the jackshaft to have the slowest speed setting paired and just have a second loop of chain that goes on when doing more demanding jobs. I'm thinking something like turning the outer faces and edges of a 6.9" cast iron or steel blank flywheel for a steam engine on your 7" swing lathe as a possible example.

At the very least I hope you do have a go at doing this even if it initially starts as just replacing the cogbelt to start. Although given that you can't go TOO small on either sprocket without running into the cogging issue mentioned I think you'll be looking at a fairly major modification even as basic replacement. After all the sprocket for the cog belt on the motor is VERY small. You can't go that small on a bicycle chain. Even on rear setups with 11 teeth as the final I've noticed that I can feel a slight amount of the cogging they are talking about above. You really don't want to go smaller than 13 and I suspect more like 15 would be better for smoother operation. And of course that means the driven sprocket grows to maintain the desired gear ratio. And that means that you'll run out of room under the stock end cover setup right off the bat. So it starts to look like it's an all or nothing project.

[amillertobe]

EDIT: Ah, you just hit a post as I press send. Well, let's evaluate the things. First, I'm gonna replace the belt to make sure it doesn't break and I'm left with fully useless lathe. Then, I do some measurements and see what kind of bicycle gear I got readily available. I've built a couple of e-bikes from bafang kits, so I'm not an absolute imbecile with cycling gear, but in no way experienced either. I qickly noticed that it would be impossible to fit the sprockets where the original belts would come, so perhaps the best way would be to turn and machine an extension part for the spindle, which is threaded directly on the locking nut threads and locked in place, and machine a mount for a sprocket to this stock and pull it to a motor, either original 500W DC, or other, and making a new mount for it. Indeed, no extra tension is needed, the chains are pretty sloppy in bicycles, as long as they align. And no, derailleurs would make the thing a huge mess. Likely, a well-thought gear ratio would serve the whole range, I rarely use the higher RPM so I could likely easily cut 30-50% off the max RPM and get the extra torque out

+

My current belt is pretty worn, but kept quite the shape considering what I've fed to the lathe. It needs replacement in near vicinity. I've turned mostly A36, but also variety of stainless, 4140 up to 40mm, and also some tool steels like silver steel, S7 and HSS with carbide inserts with it, and generally it has worked pretty nicely when I keep the DOC low, at max 0.5mm, I never push it more than it cuts nicely and just take my time to skin the bars layer by layer. I have casted a 500kg slab of reinforced concrete table where I have mounted the lathe and the mill with cast-in threaded rods, and tightened all the slides and carriages as tight as they are useable by hand still and shimmed the rest, resulting in a quite sturdy thing compared to it's size. Doing partings to steel is still pretty much a no-go, but it appears to be limited by the rigidity of the bed and lack of sheer power, and it has usually just resulted in cracking my parting blades, so I don't just do it but with a hacksaw, or angle grinder if I'm mad. The lathe or the mill alone are very lightweight and prone to chatter, when I got them first, they would literally tremble off the table when I did some cutting with them, breaking a pile of cutters too.

I ordered spare parts for now so I can assure my lathe does not suffer downtime when it really gives up, belt 425-5M-9 and timing pulley gear, 16T, 10mm wide, 14mm bore and just change them in. These are cogged timing belts, of pretty pity sized. PolyV belts seem to be a great option, and someone had done a change to these and said he never had any slipping issues. Pity the pulleys must be custom machined to this kind of machines, and the size must be carefully fitted.

The bearings are original, and after reading about how they chatter, I have began suspecting that the resonance of the lathe bed is just on par with the vibrations caused by turning, because I rarely get any vibrations and chatter, the concrete block seems to just absorb it. However, getting the rest, I'm planning on changing tapered roller bearings the same time I change the belt, because I need to take the machine apart anyway and everyone has been happy with new bearings, so I wanna get the max out of it.

But like it was said, if it works, don't fix it. To be honest, I hate fixing these toys, and while they have served me mostly well, I'd have the funding to get bigger machines, but not the space, so I gotta deal with what I do. Also, my works are usually between 0-500mm in size, 80% in the first 200mm, so larger machine would only serve the rigidity in most cases. The belts cost few $ apiece, so It seems that just buying a big box of them and firing away would be the cheapest way.

But I'm not gonna abandon the chain drive, if I just can find a doable way to fit them to the lathe. If not else, for curiosity how it works. The motor sprocket mount is easy to machine, but the spindle may get a bit tricky, unless I find a tube with fitting internal threads which I can just cut, turn and machine to shape to adapt a sprocket.

Sorry for the long rant.

[David Powell]

My main exposure to chain drives was with large ones on full size steam lorries.
They had to be run slack to allow for the rear axle springing to work. If correctly tensioned and well oiled they made a sizzling noise at speed. If tensioned too tight they literally screamed.
The sprockets on the one I once owned were well worn, indeed you could see the wear in the teeth and the rear axle had been turned round to get a bit more life, the chain pulling on the less worn side of the teeth when going forward.
I have two chain driven model lorries, both are relatively new. When tensioned appropriately and well oiled they work smoothly and do not seem to take much power to do so.Mind you, even the fastest drive seldom sees 500 rpm.
Regards David Powell.

[reggie_obe]

Yes, but that's a slow-speed application compared to a spindle.

I'm not suggesting it for the lathe, even if it was workable. It would be lipstick on a pig.

[BCRider]

I'm not suggesting it for the lathe, even if it was workable. It would be lipstick on a pig.

It IS one of the mini lathes so as much as I hate to poke at a person's tooling it does make one want to stop and take stock and look to see if there's room, money and weight tolerance for a bigger machine.

But not everyone has room or floor load allowance for a bigger and heavier machine. So sometimes picking out a nice shade of lipstick IS the better option.