Sprocket Wheel dimensions

[Epiphone]

Hey, I'm looking at sprocket wheels and have come upon something I don't understand.
I'm looking at the European Standard and if I want a wheel for a 5/8'' simplex (15,875mm) roller chain with 16 teeth I can only use a diameter of 12mm.
I can't connect the wheel to a shaft bigger than 12mm??
Could someone explain to me why this is so?
I apologize if the question is silly.

 

[diskullman]

This is probably the maximum diameter, allowing for a full keyway and setscrew. A larger bore may compromise the strength of the hub. If a larger hub is used, you may have to cut a groove in the hub close to the sprocket for chain clearence.

Russell Giuliano

 

[Epiphone]

My bore needs to be 50mm and I can't have a huge diameter for the sprocket wheel.
The biggest diameter I can choose from my table is 30mm and that gives me an wheel diameter of almost 600mm! I can't use that.

What I'm basically trying to do is turn a shaft about 180 degrees using chaindrive. The shaft is 50mm in diameter and I can't use a wheel larger than about 110mm..
Does this mean that this kind of chain drive is out of the question, or are there some clever solutions to the problem?

Thanks alot for your time!

 

[MadMango]

Not knowing the loads involved, or any other details, you may be able to modify a commercially available sprocket, or have a custom one built for you. Nothing is out of the question with enough time or money.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[Epiphone]

The resitance in the shaft I am trying to rotate is about 200Nm. I can maybe make the wheel 150 in diameter.That would give me 50mm to make the teeth and a keyway, sounds way too little to me.
What do you think?

Thanks again!

 

[dvd]

I think that the 12mm bore you are seeing is the minimum bore on a stock sprocket. I don't have European standards information, but for a 5/8"pitch, 16 tooth sprocket, Martin Sprocket lists a maximum recommended bore of 1.75 inches. I would have to imagine that you would have a similar range for your European standard sprockets also.

 

[Epiphone]

dvd: I found a Martin Sprock catalog and found what you are talking about.Thanks! Looks like I might be able to use one of those.
Kind of wierd that they didn't put max bore in the european one..

If I want my rotation to be somewhat accurate, are these kinds of chains a good choice? The rotation needs to happen within a second with an accuracy of about +/- 2 degrees. Are there perhaps other kinds of mechanisms I should consider?

Your help is greatly appretiated!

 

[dvd]

I happen to be a big fan of rotary indexers. Why spend a few hundred on a chain drive when you can spend several thousand on an indexer?

http://www.camcoindex.com/default.htm

 

[Epiphone]

Those are indeed nice and I like the way you think

The problem is that I only have 6 bar of air pressure to work with, so my actuator has to be pneumatic.

The other problem is that the shaft I want to rotate is horisontal, and my actuator "has" to be placed in a vertical fashion, so there most likely has to be some kind of transmission.

I won't bother you guys with my problems any more

Thanks alot for helping me out!

 

[dvd]

You don't say what you are rotating, but the inertial torque could be significant if you want to get 180 degrees of rotation including acceleration and deceleration in one second. How are you planning to stop this gizmo? Have you sized your cylinder to accelerate the load?

 

[BrianPetersen]

The sprocket that you are talking about is like the transmission output sprocket of a motorcycle ... very typical chain size and number of teeth, and the torque on those is much higher.

But, rotation accuracy is not a strong point of a chain drive. A 2 degree tolerance on a 16 tooth sprocket of that chain pitch works out to about 0.055" of movement. Depending how far apart the two shafts are, that might be marginal.

Industrial timing belt drives can be more accurate than chains if properly designed.

The accuracy of any belt or chain drive depends on how the tension is adjusted - you need the capability of adjusting the center distance between the shafts. Timing belts like having a certain amount of tension on them. Roller chains don't like it, they need a bit of slack (which implies inaccuracy). You can take up the slack with a spring loaded tensioner, they'll tolerate that, but not high tension at fixed center distances.

 

[Epiphone]

Thanks for the heads up concerning the slack, I'll look into that. I have read that one should not put to a sprocket wheel right over the other, but I don't see why?

dvd: currently I'm thinking about using a limit-switch that turns on a throttle. That's as far as I have come. How much throttling I will need and such, I have yet to discover.
By the way, I'm actually going to use some kind of pneumatic actuator as the "motor". A dobble rack and pinion actuator is currently the most attractive. Helical spline is also possible..

Thanks