How to specify and check roller chain tension

[feb14]

I have a roller chain that drives a mechanism. It actually rotates back and forth about 120°. I have a turnbuckle in the middle to allow for tensioning since it's not a continuous running chain and both sprockets are fixed. My question is how to specify the required tension to the assemblers and how to verify that the tension has been attained. I am currently contemplating some kind of load cell and C-clamp arrangement. Can someone help?
Thanks in advance.

 

[MintJulep]

You need to do a Google search for "chordal action".

 

[BrianPetersen]

On motorcycle drive chains, there is a specification for the amount that the chain can be deflected mid-span using the amount of force that can be applied by hand. Is that good enough for this application? If not, why not?

 

[feb14]

Thanks for your responses. Brian I have a problem with the motor bike procedure because it is very subjective. Different people will apply different forces and will consequently get different deflections. I want to specify the force so it doesn't vary from one technician to the other. This chain is going into a sealed enclosure and once its sealed there is no way to get to it.

 

[MikeHalloran]

Then you embed a spring in the turnbuckle, adjust it to coil-bind, and back off some defined number of half-turns. That should give you a consistent tension, especially if the spring has a relatively low rate.



Mike Halloran
Pembroke Pines, FL, USA

 

[dvd]

I agree with Mr. Halloran's spring tensioner.

I also advocate for reviewing this application with the chain and sprocket manufacturer(s). Another aspect of determining proper chain tension is the load on the shafts and bearings.

Depending on loads and chain size, you may want to consider a Snapidle-type of tensioner.

 

[MintJulep]

Since you apparently have not done my suggested Google search, I will elaborate at bit.

The pitch circle of a sprocket is - well - a circle.

A chain, by its nature of being made up of side plates and rollers, cannot have every bit of its length follow a circle.

That means that as chain is driven around the sprocket, then length from the tangent points is constantly changing.

You need to have a spring in the system somewhere.

 

[MintJulep]

or slack.

 

[MikeHalloran]

Of course I meant to say it should be a compression spring, selected so that the force at coil bind is a little greater than the tension you want to maintain in the chain.

The adjustment procedure should also include putting the mechanism in a position where the chordal action is at its worst, and setting the turnbuckle so that the spring is just compressed to coilbind at that position, then backing it off to set the tension exactly where you want it.





Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Here is a reference from Tsubaki

http://chain-guide.com/basics/7-1-2-1-chain-slack.html

Recommended chain slack from this and other sources seems to be 4% to 6% of sprocket distance for horizontal drive arrangements. No force is noted when slack is measured. Chain is not like belts which stretch when a deflection force is applied. So no force is specified when roller chain is deflected to measure slack. Slack would also mean no chain pre-tension. I'd set up minimum slack to allow for chain wear.

Ted

 

[feb14]

Thanks to all of you your contributions. I should have also added that the chain drive is on a 45° slope and that I also have only 3" of space for the chain to fit. Please find attached the arrangement I currently have.
Thanks again

 

[Pud]

Use a continuous chain and one of these?

http://tinyurl.com/63lkmx

Cheers


Harry

 

[diskullman]

I'd trash the turnbuckle and put in a floating tensioner, like a snapidle

http://www.snapidle.com/

Russell Giuliano

 

[MintJulep]

Do the sprockets have to be fixed?

It is quite common to have one sprocket on a slide with a spring.

 

[pauljohn]

Why not use the motorbike procedure but specify a spring gauge be used to give the required deflection and specify a load in newtons or lbs.?