How Much Steel is TOO MUCH?
 

Well I will give my answer based on the knowledge gained from one of our Advanced Development ME's that designed much of a proprietary GM robot called the PAAS/C-Flex (Now produced by Fanuc)

He takes the Diametrical Pitch of the Gear and subtracts about .300 for the area around the teeth, then we leave as much of the hub as required for it to be welded to the shaft (or other mounting method) We then take a common hole size (usually 1/2" to start) and array it radially around the face in a number that is easy to reproduce on a rotary table (16 for example) but always symmetrical using a polar array. For gear thickness he always chooses somewhere around .150-.200 for steel gears in applications like ours. As a final check he looks over the gear to see how the holes line up to leave spoked webs and sometimes we have to adjust the # of holes or the hole sizes. We have found this method easier to recreate with common milling machine tools versus having to use CNC for more elaborate 'spoke patterns'.

I guess as a final note never underestimate the strength of the steel parts, something like a 20 pitch 20 deg P.A. 1/2" face are overkill for most FIRST applications if left full weight.

I disagree

First, delrin is impractical for many applications. Say you have a 3 foot piece of 2" aluminum square tube that you need to lighten. Delrin or any other plastic would be hard to replace it with. Many times it's easier to drill holes than to design for other materials.

And as for drilling holes, the weight does add up. Especially if you're using 3/16" plate or larger. The weight adds up little by little, but it is worth it. Plasma Cutters can be used for larger holes and eccentrically shaped ones. Cutting unnessesarily long fastners off is also an easy way to get weight out.