I have gotten this question via e-mail:
Quote:
We're planning on adopting this design using 4 CIMS and 4 Dewalts to drive our machine this year. But I don't quite understand how pressing the Top Hat Carrier assembly to the shaft of the CIM shaft keeps it from spinning free without the use of a keyway.
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Here is my reply:
Quote:
Talking to an engineer friend of mine (Artur O. from team #469), he told me that I have voilated all the rules with the Chiaphua-Dewalt design:
- A press fit with so thin a metal ring left below the root of the tooth,
- In fact, I voilated the rule of thumb that you should have at least 1 tooth thickness below the root even without the added stress of a press fit,
- a first order stess calculation shows the part should break, and so on
- etc.
BUT... ...the things work. That is all I have to say in my defense. They work and they work great.
In engineering, many of our rules of thumb are conservative. Our team has had A LOT of hard driving on our transmissions. We have had no failures. I feel comfortable recommending it to others.
Now to your specific question: the part is a press fit. There is no room for a keyway in the root diameter of the gear that presses on the shaft -- though, now that I think of it, it suppose it is possible that you could put a keyway in the plastic tophat part.
But, in actual fact, we have had good experience with just using the press fit.
You need to be very careful to make the hole in the gear "to print" As I recall, .312+0-.0005 and the shaft itself is .313 so this gives a significant interferance fit.
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I make no guarrantees, but I believe that you will have a good result with this solution.
I thought I would share this exchange with folks in the interest of full disclosure.
Joe J.