Author Topic: Gears and spokes  (Read 2722 times)

Offline mamell

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Gears and spokes
« on: January 01, 2016, 11:46:41 AM »
Just wondering if there is anything critical about various spokes or are they more about aesthetics?  I know that if the spokes are to thin, etc., it would be a strength issue, but short of that is there any other issues critical about spokes?

Offline steve323

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Re: Gears and spokes
« Reply #1 on: January 04, 2016, 05:20:45 PM »
Hi Mamell,

I have wondered the same thing also.  I think the answer depends on what material the gears are made from.

Brass has a uniform rate of thermal expansion, so it should simply be a matter of strength.  Plywood should be similar except the expansion is caused more by humidity than temperature.  Criss crossed layers attempt to prevent the humidity based expansion.  Small spokes might delaminate and loose all strength or accelerate the warping.

Solid wood gears using wedge shaped segments have the issue of humidity based warping.  If the grain runs from center to edge, then the outer diameter will change with humidity but the radius will be held constant by the long grain spokes.  This seems like a recipe for warping or cracking.  A spiral shaped spoke might allow the radius to change with the diameter changes.

Another option for solid wood gears is to use long grain spokes with long grain segments around the outer edge.  This requires a lot of glue joints and accurate miter cuts to get a perfect fit.  The result should resist warping with humidity changes.  One downfall is the teeth are slightly weaker.

In the end, I think spoke diameter is a balance.  The spokes should be as small as possible to reduce weight and as large as needed to hold everything together.