Now that I'm pretty sure about the way in which I want to hold tools on my PolyBot, I need a single piece effector (tool holder).

This derivative puts the axle mounts on the base plate directly. This makes for a single piece to print instead of the keyed version it derives from.

The axle holes are designed to take a sleeve bearing (OD - 3/8", ID - 1/4", length - 1/2"). It is a very tight fit, and you might need to use a vise to get the sleeve bearings into the axle mounts. Once you do though, you have a nice axle where you can attach a male clevis: http://www.thingiverse.com/thing:8130

If you use a 1 1/4" steel dowel pin as the axle, you will have a nice, minimal wiggle, axle/joint combination.

Although the axle mounts are angled outward, it is still a tight fit for a tool to be mounted. A future design might change this arrangement. In the meantime, you can simply print the tool larger to get more separation.

This is challenging to print as there's a lot of surface area, and it will tend to want to warp. So, print with a high raft to absorb some of that warpage.

1) Print one of these
2) Press fit sleeve bearings into the axle mounts
3) Put 1/4" steel dowel pins into the sleeves as axles
4) Attach male clevis, or other rod ends to axles
5) Rejoice!