25 series chain skipping

[philso]

We are using some 25 series chain to drive our shooter wheel since we could only find sprockets in this series to fit the shaft on the CIM-u-Lator. We are using a 10-tooth sprocket on theCIM-U-Lator shaft and a 22-tooth sprocket on the shooter wheel shaft. There is a total of about 12 inches of chain. Both sprockets and the chain are from AM. We tension the chain by sliding the gearbox and tightening the mounting screws. The chain will deflect about 1/8 inch when "pushed firmly" half way between the two sprockets.

We have noticed that the chain skips every once in a while causing a lot of vibration. At speed, the chain can be seen "whipping around". Turning the mechanism very slowly by hand, one can see the chain climbing up the teeth such that over a span of about 3 links, the point of the sprocket tooth it directly under the center line of one of the pins holding the chain together. Turning the mechanism further, the chain then slips back into alignment with the sprocket. It is as if the spacing of the teeth on the 22-tooth sprocket is larger than the spacing of the chain links.

We notice a similar kind of thing happening on the 10-tooth sprocket but that seems to come from the teeth on the sprocket being a bit too long and the small tooth count forcing the chain to "bend" around too sharp of an angle.

We have some larger sprockets on order (16-tooth and 32-tooth, I think). We have also considered filing down the sprocket teeth on the smaller sprocket. We have verified that the chain is not hitting any of the set screws on any of the sprockets and that the two sprockets are in the same plane. The chain does not appear to be twisting.

Can anyone suggest a solution or point out what we may be doing wrong? I have only found posts here where people have used chains very successfully though they may be using sprockets larger than what we are using. We are in the process of building a second robot for practice so we will try out the larger sprockets and any suggested solutions once enough of it gets built.

Thanks for your help.

Phil

[JamesCH95]

It almost sounds like you've got a metric/english mix-up. I.e. ISO 6mm chain w/ ANSI 25 sprockets. The pitch is VERY close (0.25in vs 0.24in) which would probably cause the symptoms you're seeing.

[thefro526]

Originally Posted by JamesCH95

It almost sounds like you've got a metric/english mix-up. I.e. ISO 6mm chain w/ ANSI 25 sprockets. The pitch is VERY close (0.25in vs 0.24in) which would probably cause the symptoms you're seeing.

This could be true, but if the chain and sprockets were both bought from AM, how likely is it that there were a 6mm and #25 mix up?

It almost sounds like the cut on the sprocket teeth needs some finessing, we made our own sprockets for an off-season proto and had similar issues. A bit of careful file-ing of the tooth profile did the trick.

Another thing to look for is 'squeezed' link in one of your chains. I've found that it's very easy to squeeze #25 chain during the breaking process to the point that it's too narrow to properly sit on the sprocket teeth. You can open it back up with some steady hands and some pliers or just make a new chain.

[fox46]

I second the above-

You could try reducing the tension on the chain. I find many people try to tension chains the the nth degree and 9 times out of ten are overtightened.

Where did you source the sprockets? Is one of them waterjetted or custom made? It is possible they are out of tolerance.

[JamesCH95]

Originally Posted by thefro526

This could be true, but if the chain and sprockets were both bought from AM, how likely is it that there were a 6mm and #25 mix up?

It almost sounds like the cut on the sprocket teeth needs some finessing, we made our own sprockets for an off-season proto and had similar issues. A bit of careful file-ing of the tooth profile did the trick.

Another thing to look for is 'squeezed' link in one of your chains. I've found that it's very easy to squeeze #25 chain during the breaking process to the point that it's too narrow to properly sit on the sprocket teeth. You can open it back up with some steady hands and some pliers or just make a new chain.

Good point, I missed that tid-bit. Could very well be a bad chamfer on sprocket teeth, which I've read is critical to good sprocket performance. Especially in bikes where chain misalignment is expected.

[MrForbes]

Originally Posted by philso

We tension the chain by sliding the gearbox and tightening the mounting screws. The chain will deflect about 1/8 inch when "pushed firmly" half way between the two sprockets.

Did you try loosening it just a little bit? I think it should move about 1/8" when touched lightly, not firmly.

[Mr. Van]

I second the squeezed link opinion. If the chain is reluctant to bend freely at each roller, it will extend off of the sprocket. I think this would be even more pronounced at the high speeds you are dealing with.

- Mr. Van
Coach, Robodox

[philso]

Thanks for the quick replies.

The links did not look "squeezed", if I recall correctly. The parts of the chain that were climbing the sprocket teeth were not near the master link where the chain was broken.

We will try varying the chain tension on second robot.

Thanks.

Phil

[jspatz1]

AndyMark has apparently stopped tapering and deburing the teeth on their #25 sprockets. They used to include a gentle taper on both sides of the tooth, which should be standard for any chain sprocket, and were tumbled to removed burs and sharp edges. Now they seem to be shipped straight from the cutting operation with no taper, and have sharp edges. They are also now made with thinner .090 material despite being described as .125. We add the taper to both sides of the teeth by gently rotating on a sander, and soften all edges with a wire wheel. This makes a big difference in the sprockets running smoothly, and makes them more tolerant to misalignment.

[Madison]

Originally Posted by jspatz1

AndyMark has apparently stopped tapering and deburing the teeth on their #25 sprockets. They used to include a gentle taper on both sides of the tooth, which should be standard for any chain sprocket, and were tumbled to removed burs and sharp edges. Now they seem to be shipped straight from the cutting operation with no taper, and have sharp edges. They are also now made with thinner .090 material despite being described as .125. We add the taper to both sides of the teeth by gently rotating on a sander, and soften all edges with a wire wheel. This makes a big difference in the sprockets running smoothly, and makes them more tolerant to misalignment.

Additionally, we've run into some trouble with the tooth profile on some sprockets being a bit off such that you cannot wrap chain around the whole sprocket. Somewhere, the pitch is off just enough to make the chain unable to fit.

I think that may be the likely culprit here.

[sanddrag]

We have a virtually identical setup on our shooter and have not had a problem. I say improper chain tension or defective sprocket or chain. Have you checked the chain for any bound up links that do not pivot freely?