Another Question for Maximal Roller Chain Speed

The speed limitation for chains is related to lubrication. Working inside an oil mist and driving an engine cam at hi speed is OK. But in open air, oil or grease will dry off quickly helped by by centrifuge and dust, (no o-ring or x-ring will hold it at hi speeds), and chain will overheat to destruction. And this at enough speed can be lethal. S.M.

Okay-so if make a housing for the chain, with oil on the lower part of it-how fast can it revolve?

In all chain catalogues you find graphs which indicate the limits of correct use. In stead of asking and not getting always the right answer why not try to use Google (or any other search engine) and try to have a look in such a document?

The chain function is based on 2 factors: the specif load between pin and bushing usually limited to 4.0 N/mm² and the speed of relative movement between two adjacent links at the loaded branch of the chain. The smaller the number of teeth the bigger the angle thus the bigger this relative rotation speed and correlated wear. The other limitation which for you not to be looked at is the centrifugal force (other will insist to say the centripetal force but for different reasons I stay with this OLD way of thinking which buy the way is more logical in machine design then in astronomy!). Since friction generate heat the higher the product between pressure and sliding speed the higher the grease temperature and the easier its expulsion. And without grease pin and bushing wear and the actual pith becomes bigger so that the chain cannot stay any more correctly on the gear and this can destroy the teeth.

So again the best is to look in a catalogue !

It could more than fast enough, if done right, I've seen it work, but at an estimated cost 10 times over what it should. Why not do it the rational way, use a belt for first stage and use the chain for the slower, final drive? By the way read your calculations for required reduction, and something is seriously off scale. Total reduction over 100:1 !!!!! About enough to (slowly) push a WWII tank. S.M.

For sprockets of less than about 12 teeth, be careful about chordal action, which tends to cause whipping of the chain.

Camshaft timing chain, also known as silent chain, is constructed differently from roller chain, and can handle higher speeds, partly because it is constantly lubed in an enclosed environment.

'...I read that a 9 tooth sprocket is limited to 100rpm!...'

Don't believe everything you read. There is good evidence to the contrary.

Shimano has been selling Capreo rear cassettes for quite a while with a 9 tooth sprocket as the top gear. Cyclists can easily maintain greater than 100RPM. Coupled with a common 52 tooth chain ring, the 9 tooth sprocket can be expected to commonly exceed 600 RPM.

Remember this is a chain that is open, exposed to the elements. Lubrication must be discreet, without excess that would trap sand and grit. All the while these chains hold up at greater than 600 rpm under the strain of competitive racing.

This also happens to be very close to your application.

It appears someone has been 'yanking your chain'.

If the bicycle's rear wheel (say 27" o.d.) is turning at 600 rpm, the bike is going at ~4241 ft/m ≈ 48 mph. That's possible in special circumstances, but rather unusual. Ideal cadence is around 68; I forget whether that is defined as 34, 68, or 136 rpm.

Some bike wheels are much smaller. 20" (~23" OD) wheels are the norm in many events.

But even sticking with the 27" OD example the '100 RPM Limit' on the 9 tooth rear cog is exceeded 3 fold at just 24 MPH....Anything over 8 mph would be over the limit. Even with our paltry hills here in Florida, you can crank downhill and have that rear wheel over 600 RPM. Someone was definitely 'yanking his chain'.

68 is pretty low as far as idea cadences go, but some people claim down to 60. Most ideas for ideal cadence range from 85 to 110. Cadence is counted off one leg, so it is the same as RPM.

Just try it. Information to date seems to indicate that it will be just fine.

Use a proprietary (non-flinging) chain lubricant or other grease with good adhesion properties.

If you can get o-ring (sealed internally lubricated) chains in bicycle sprocket size then you could run the chain dry.

In the last year I finally threw away my old "racer" bike with a gasoline engine. It used an approx. 3 in. direct-drive wheel pressing directly on the top of the back tire. I kept waiting for the rear tire to wear out, but it didn't. I think it was 25 cc, and would provide at least 20 mph.

I counted a nine tooth spocket on a Bike Friday which has twenty inch wheels. That would give you a speed of about 30 mph. I have a Moulton with a thirteen tooth on a three-speed internal geared hub. It acts like an overdrive to keep my rpms down at higher speeds.

AZ,

To see the low speed that a 9T sprocket is limited to, you probably were looking at industrial roller chain drive tables. These tables usually are set up to some rating, such as "x" hp transmission, at so many hours/year operation.

Since your operation will be very light duty, I would not place much faith in the industrial drive tables, as they are vey conservative.

If you look at motorcycle drive chains, that drive from the transmission output to the rear wheel, they are usually RC40 or RC50 pitch (but usually a narrower chain: RC420 or 428, for example. The smaller (transmission end of the drive) sprockets can be anywere from about 10T to 18T. I have found they wear quite quickly, (a year or so of hard riding) especially on dirt bikes where oil and dirt make a very decent grinding compound. But they do last. And comparing the HP of a dirt bike to the size of the chain the manufacturer installs on the bike is very surprising--comparing to the industrial drive tables it would NEVER work!! I scratched my head at this many years ago when I was looking at industrial roller chain drive tables as a Mechanical engineer in a sawmill and comparing to my motorbike chains! It didn't add up by a long shot!

If you are puzzling about the primary speed reduction from your engine to a jackshaft, and worried about the engine sprocket turning 10,000 rpm, yes, you have some concern. But even at those speeds, I can point to some older 2 stroke dirt bikes that used a double row roller chain for a primary drive from the crank shaft to the transmission (Maico) that, in an oil bath, worked OK. They used double and triple chains because they were transmitting upwards of 50 hp on some of their bigger bikes. And the old "step thru" Honda 90's, of which gazillions were made, and chinese clones of these engines are still made, had a camshaft drive with a little roller chain. Those engines would rev pretty high too. Oil bath, of course.

Since you are not going to run this a lot, I would simply try it! I would use a RC35 roller chain from the motor to the jackshaft and a bicycle chain (which is really very narrow RC40) from the jackshaft to the rear wheel. See if you can fashion a simple oil bath for the primary chain. If this is too hard to do, maybe just rig an oil drip cup and put a cover over it to avoid getting oil splash everywhere.

I suggest RC35 because both the chain and sprockets are cheap and universally available.

Good luck!

Jon.

Thank you ,this kind of answer, and specific, the comprehensive and detailed answer will help me very much.

Toda Raba [thank you very much on Hebrew]

There's a discussion on LinkedIn about bicycle chain servicing. I gave them this link because I though it would be of interest. Here is their link: http://www.linkedin.com/groupAnswers?viewQuestionAndAnswers=&discussionID=91480451&gid=150324&commentID=66410621&trk=view_disc&ut=15zZ5RmAj4Kl41

And check out this link: sheldonbrown.com/chains