Cradle walks. Why?

I just started using the cradle I built for our second child. I rocked it a little bit and it started rubbing the wall. I pulled it out and rocked some more. Soon it was rubbing again.
The crazy thing walks toward one end -- quickly. It covers about 1/8 inch with every rock.
What did I do wrong to cause this? Or should a rough carpenter just not even try to play furniture maker?
thanks.
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Without more detail, all I can go on is physics (and I'm not the best at that)
I'd guess you are off-balance on your weighting with respect to the fulcrum. Is this a pendulum-type or a rocker type cradle? If you rotate it 180 degrees, does it walk the other way? Is your floor level? Are you inadvertently pushing it when you rock it (applying horizontal motion rather than swinging motion)?
Depending on your design, the checking of weight may or may not be as easy as letting the cradle come to a comlete rest and checking the top with a level. The weight can be thrown off by the rocker rails hypothetical ceter point not being centered over (under) the center of gravity.
Stuff to think about.
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Thanks for the prompt reply.
This is a rocker cradle, not pendulum.
I"ll do some of the tests you suggest when the baby gets up. Is weighting really the answer though, considering it walks end-to-end, not side-to side?
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Toward one end? Didn't notice that in the original post. That's rather perplexing. Weighting could still be the problem, though it would have to be pretty drastic to have an effect. Double check the floor for level. Check if the legs are plumb with respect to the ground on all axes (Unless the are angled out for stability, in which case walking would be really wierd).
The most likely culprit is human interaction. Rock it from all angles and see if it continues its walk. You may be pushing or pulling it slightly with each push. If that's the case, it may not be rocking smoothly enough, so you have to compensate with a firmer push. If it isn't rocking smoothly enough, that could be because of the floor (Are you on a carpet?) or because the rockers aren't smoothly curved. Did you cut them both at the same time or use a pattern bit in the router to ensure that they are the same shaped. Even if you did, you may have reversed them so they aren't rocking evenly.
If you figure it out, even if it isn't wood related, please let us know.
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Sounds like the rockers aren't parallel with each other.
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Are the (what-do-ya-callum), rockers dead parallel to each other and dead perpendicular to the cradle itself? A very slight variation is going to act like the front end of your car when it's out of line - it wants to go in other directions than you want it to go in.
Do the rockers have flat bottoms? If so maybe you can remedy the situation by radiusing them so that the rocker is actually riding on the crown of the radius and not on the flat of the rocker. That would certainly help overcome alignment problems - if they are the culprit.
Can you post a pic of the cradle over on the binaries group?
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The rocker rails are not parallel or the arc is not consistent. Round over the bottoms until the contact area is minimized.
Dave
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over
Damn - how'd you do that? Cut right to the chase. Took me two paragraphs to say that.
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Sorry Mike, I started the reply, took three phone calls and then finished it. Great minds think alike!
Dave
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The rockers are flat-bottomed.
Will just rounding them to get minimum contact help? Or do I have to skew the way I round them so that the contact areas come out parallel -- compensating for the fact that the rockers are probably off parallel?
Will using the thing on carpet mess up this strategy -- since sinking into carpet will give back some of that contact area?
Thanks for your help! dwilson
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Rounding the bottom of the rockers will help a great deal. In Addition, if you can easily determine how far out of parallel the rockers are, and the trouble it would take to fix, adjusting them would be preferable. You can remedy both the flat bottom and out of parallel by adding a metal track on the bottom of the rocker. Try a T-molding cut into the bottom of the rockers, or a thin piece of wood affixed to the bottom that is already rounded or V shaped.
Carpeting should not affect it to much unless the rockers are out of parallel.
Dave
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It was somewhere outside Barstow when firepower snipped-for-privacy@yahoo.com wrote:

You should have made the runners as a cylinder, but they're actually foming a cone. One has a smaller radius than the other.
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On 1 Mar 2005 06:11:29 -0800, the inscrutable firepower snipped-for-privacy@yahoo.com spake:

The rockers may not be precisely parallel to each other in all directions. Try 10" of traction tape on the bottom of each rocker.
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It was somewhere outside Barstow when Larry Jaques

That makes them walk sideways, usually swivelling as they go.
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