FLEX COUPLINGS

Here's an anti-backlash helical flex coupling in two varieties. one is a simple setscrew type that uses a setscrew to screw onto the flat spot of the motor shaft.

The other variety is a clamp-on type that grabs the circumference of the shaft.

There are also oldham-type couplings which are three-parts: two shaft ends and a middle section that contains an acetal x-shaped coupling unit or a more flexible nylon (or other material) unit. (not shown)

In comparison, here's one of the smaller 1/4" shaft diameter flex couplings you see above with a 1/2" shaft diameter flex coupler. Notice the sizable difference!

One of the tricks when using the clamp style of coupling with a smaller shaft diameter journal is to use a home-made shaft adapter which is essentially a piece of metal stock (in this case we're going from a 1/2" diameter to 5/16" diameter) drilled to the journal diameter, then using a bandsaw, slotting saw or similar means, cut through one side along its length and into the inner portion half-way through the stock so that it's flexible:

Another version of an anti-backlash flex coupling is shown below. It consists of two plates with a metal spring washer sandwiched inbetween. This model is a 1/4" diameter shafted one but has a larger outer diameter than the ones shown above.