How do you tension a chain drive ?

Pretty standard ...

A tensioner , fixed hard rubber block or spring loaded...whatever....on the NON driving side of the chain... eg the side with the slop in it when the engine is driving the load.
If you don't know what I mean...open up an old Lambretta engine.

Del

Ok Del

but where do you fasten it to since you can`t fasten it to the surrounding structure?

I didn't read that bit...

But I don't care as it is nonsense... of course you can fix it to the surrounding structure, or build some structure to support it.

Hypothetical questions deserve hypothetical answers... so just bolt it to a hypothetical support or sky hook.

Or just buy a KrisDel^TM Tensiomatic virtual chain tensioner this will tension all virtual or hypothetical chains without recourse to lubrictaion or adjustment

Del

Hello Del the cat,

I know this is off topic but thought you might be interested...................

I got a couple of sky-hooks in a sale the other day. The seller said they were flying off the shelf..................Sorry, that was real bad

jfmfit

Keep the chain a bit slack and suspend a weight from the lower portion using a pulley!If the chain is slack enough, the weight will move to the middle. When it's in motion, the weight will always be trying to go up hill but never make it! (unless of course, the pulley is rusty and won't turn freely!)

I could start writing a long winded, full blown idea for a twin pulley, free floating, tensioning device that has a fixed space between the pulleys smaller than the diameter of the sprockets so the same 'pulley trying to go uphill' theory holds I'd imagine but, I prefer PJ and the oily rag technique better, it's a more hands on approach!

Ok Mr T but why pulleys and yes it is hypothetical Del but interesting.

Less friction to overcome! The pulleys can slide a bit if they need too! Pulleys are cheaper! Pulleys don't get bent teeth if they get dropped! I like pulleys!

and yes it is hypothetical Del but interesting.

Not really, because there is always an attachment point even if you have to machine a collar to float on one of the shafts! There I've done it now... A collar or each shaft with a bar between them...that's your supporting structure.

It's like saying here is a problem ...but you are not allowed to solve it.

Del

It is an "L" shaped piece of tin with a pad of nylon attached that lifts the chain. The other leg attaches to the case ...

Hello Pj3ns3n

Please advise linear speed of the chain, in either feet or metres per second.

Kind Regards....

A chain drive always comes with a tensioning sprocket or an adjustable mount. Turn the adjustment screw to push the tensioning sprocket in or to push the adjustable mount away from the fixed mount sprocket. If the chain is sufficiently elongated, shorten it. If the chain drive you are describing doesn't have any of these features, there must be something wrong with the guy who designed it.

The question was posed as a puzzle not an actual situation although I do have a solution in mind myself. The chain speed hasn`t been considered but a fast chain could whip so you would have to control the slack to stop this. If the sprockets were very wide apart then any fixed tensioner would only act close to the sprocket. a longer tensioner would have to be quite sturdy and would break the spirit of the question. There must be situations envisaged where moving the sprocket axis to tension the chain would be prohibited. A single gravity tensioner might work at low speeds. Any other ideas for chains not pulleys though.

I'm a bit narked off at not being able to use pulleys! Can I call them tensioning wheels instead?

Ok here is my idea for you to shoot at. Its not far from Mr T`s in that a free floating pair of sprockets linked between two side plates, slotted at the bottom sprocket, mounted with a spring pulling them together. When I was an apprentice 38 years ago I suggested this and was quickly told it wouldn`t work. So being a cocky 16 year old I made it and it floated happily between the sprockets taking up the play. you would think it would jamb up but each sprocket is trying to go in opposite directions above the top chain and below the bottom one so they cancel each other out. Just need somewhere to use it now?

Sprocket, pulley....Pulley, sprocket.....!

'I made it .'

Yup, those are the 3 magic words... Have a tin of my finest Tuna

Del

Build tensioners into the sprockets, of course.

http://www.freepatentsonline.com/EP1255063.html

A chain drive will lose proper tension from wear of the chain rollers or of the sprocket teeth. Worn sprockets damage the chain, and worn rollers don't engage correctly, so they wear the sprocket teeth. Maintaining proper tension in a chain drive encourages rollers and teeth to engage smoothly, which reduces wear. Temperature changes will also affect chain tension.

Chain tension is usually adjusted by changing the distance between sprockets, or with an idler sprocket or shoe. If the idler maintains tension with a spring (like a dérailleur) it will compensate for temperature changes as well.

Building a tensioner into the sprocket may work, at least for a while, but it further complicates an already complex system. It is probably best avoided unless there is no other way .

Hello Pj3ns3n,

not sue if it will work or why you asked the question but.....................

you could try fixing a say 300 mm cog/sprocket to both the fixed and opening jaw of a clamp. Enter the cogs one above the chain and one below. Tighten the clamp until most all the slack has been taken up, and add a Lock-nut to the clamp screw.

You could use smaller cogs/sprockets but they will wear quicker.

In theory, (at least in my mind) the clamp will probably stay where the chain pulls in to its narrower point. But it is only a guess. But still worth a try as I say.

Its worth a try if this is not a leg pull!

jfmfit

I was thinking of a pair of sprockets each on an axle supported by yoke. The two yokes positioned one above the top chain run, and the other below the lower run. Join them with a turnbuckle. If I had my choice I would use the identical sprockets as the drive and driven sprockets. Less inventory needed. Other than the yokes all parts should be off the shelf parts.

Hello Pj3ns3n,

do I get any points (Or a free can of tuner) for being quite close? Sorry I didn't use pulleys.............

jfmfit

Some years ago I came across an interesting commercial solution offered by a chain manufacturer - unfortunately I have no recall of the company. It was a thermoplastic ring with a toothform around its outside. The ring sat in between the two sprockets applying tension to the chain runs and was held in place purely by the tension of the chain and the engagement of its teeth to the chain. Imagine the two sprockets with a larger ring sprocket in between and the chain wrapped around them all (like a diamond shape with rounded corners). The ring is flexible and becomes elliptical in shape due to the chain tension. Its flexibility allows it to maintain tension in the chain.

I suspect that this device would not be suitable for accurate, synchronised drives with a non-uniform load as the length of the driving side chain would vary due to the ring exerting a force on both the driving and non-driving sides of the chain (i.e. the 'diamond' would be asymmetric and its asymmetry would vary according to the drive load).

I would have thought something along these lines should work fine. The tensioners are to be fully floating and not connected to anything else, just floating on the belts or chains. They could of course be made adjustable and will float up and down as power is applied to one of the main sprockets.

Hello Andy Germany,

you have illustrated my answer! Thanks.

jfmfit

Maybe, but I could not get there (visualize it) from what you said, I read it all through.

But 2 minutes with a sketch program and you get a simple picture....the idea I had came before I read anything else from anyone.....its something I made for a friend about 40 years ago who had a really tall one wheel bike that he had made and the chain kept falling off!! Throwing him off too!!!!

We had no money in those days.......everything had to cost less than nothing!!

Remember "a picture is worth a 100 words!"

Hello Andy Germany,

I to answered before I read any other posts, if there was any...........

Another way to imagine it is with the two tensioning cogs on your first finger and thumb. Move them together and the tension increases. Just exactly like your drawing. As you may realise, explanation may not be my forte!

How can you get drawing on as examples? I only have a computer no scanner or printer

Jfmfit.

I used Paint which is on any windows computer, its simple and does the job well and its free!!

There are other free CAD programs around, or "Light" versions for free, you just need to search on the web.

Hello Andy Germany,

sorry to be a pain............I have paint. But, how do you get the round shapes and-straight lines?

I am afraid I have not used it because I cannot get strait lines and angles.

jfmfit

That's the same idea I had in answer #6! I'm sure it would work but it would look more like this when in operation!

True.

Andy,

What are your views on the 'Ring' in post #30?

It is not retained in any way that I can see and if the load on the chain is very high, then it could fly out or suddenly compress/collapse as it looks flimsy....

A bit late ,but, how about this:-

Good one!!

Thanks for the answers , the ring idea was very strange but some of the best ideas are like that. Its like the internal combustion engine its about 100 yrs old and still relys on pistons going up and down ( ok Wankel had a good go at it). Isn`t it about time someone invented a better solution.

Keep thinking!!!!!

That's not a bad design for small lengths of chain, but for one that is hung between 300mm dia sprockets 10m apart, I don't think it would work as well as the 'pinched' chain method! I'm thinking, big ring of about a meter in dia with teeth!, (v. expensive!?) held in between the top and bottom of the chain! With 5m of chain zipping either side! It may fly out! The example you posted, had a guide board behind limiting sideways movement! I would not like to be in the same room as the ring when the button is pressed! Apart from that, I like it!

Use a pair of #29. Add a bar between them so they'll stay away from each other. We can add spring to help maintain a constant load on the chain.

A little bit of lateral thinking.

All the "floating" devices look good, but I'm sure we all share that uneasy feeling that they will come adrift with spectacular consequences.

We do have two fixed references available to us. (The axles of the sprockets)

If we consider the sprocket that is driving the chain.

On the axle, mount a fluid/torque coupling (similar to those used for radiator fans in cars with electric cooling fans) on the axle and mounted to that is an idler sprocket/wheel/skid that holds the slack side of the chain.

As the axle rotates, the idler is then held against the slack side of the chain progressively taking up the slack as the chain stretches. The force against the chain is determined by the coupling selected.

Same could be achieved with a counterweighted device on a bearing on the same axle.

There should be no fear of the floating chain tensioner moving anywhere. In the case of ring, If it is sized correctly it is captured in the four relatively straight chain sections. In the "sprocket" style chain tensioner, if the tensioner is doing it's job the chain is again left with four straight sections, and the tensioner could not move anywhere because any other location other than in the center would require the two tensioning sprockets to move further apart. That could not happen except on a chain tensioner that uses spring or counterweight to remove slack. And that would only happen if the chain speed were fast enough to experience centrifugal forces acting on the chain.

A spreader bar with idler sprockets?

OK, THAT is slick! I Like!