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.

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.

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?

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.

wrote in message
oups.com...
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?


Sounds like the rockers aren't parallel with each other.

wrote in message
oups.com...
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?


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?

--

-Mike-

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?

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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"TeamCasa" wrote in message
...

The rocker rails are not parallel or the arc is not consistent. Round
over
the bottoms until the contact area is minimized.


Damn - how'd you do that? Cut right to the chase. Took me two paragraphs
to say that.

--

-Mike-

Damn - how'd you do that? Cut right to the chase. Took me two paragraphs
to say that.

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

It was somewhere outside Barstow when wrote:

The crazy thing walks toward one end --

You should have made the runners as a cylinder, but they're actually
foming a cone. One has a smaller radius than the other.
--
Smert' spamionam

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


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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On 1 Mar 2005 06:11:29 -0800, the inscrutable
spake:

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?

The rockers may not be precisely parallel to each other in all
directions. Try 10" of traction tape on the bottom of each rocker.

--
Remember: Every silver lining has a cloud.
----
http://diversify.com Comprehensive Website Development

It was somewhere outside Barstow when Larry Jaques
wrote:

The rockers may not be precisely parallel to each other in all
directions.

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