Spur gear design

The manufacturing will be complicated, but most likely it can be broached. The cost will shoot up. Think about some other way of transmission.

Why not have two gears longitudenally with the portions of the threads washed off so that they do not engage?

sb, the spur gear would be 30cm in dia and fixed, with the connecting gear, the winch, being rotated around the fixed gear which would drive the winch, this has to wind rope on and off itself, the rope is attached to each end of a long weight, the action of the apparatus rotating moves the weight approximately 1m backwards and forwards, is it possible your suggestion would achieve this and if so how.

If your just intending to move a cable back and forth a simple cam or crankshaft system will be far more cost effective and simpler to make and far more reliable.

I think moving the cable back and forth is easy but becomes alot harder if the apparatus is rotating thru 360deg. The apparatus is 2m long x 150mm Dia and rotates continously at 15rpm the cable is attached to the tube and moves the weight backwards and forward inside the tube without any input of energy creating rotation of its own accord using gravity.Could a simple cam or crankshaft attached to the tube achieve the outcome desired, if so how?.

Yes. I think a spline or shaft coupling would suffice for the ID and a spur gear can be fit to it.

Can you build a flat washer with the OD smaller than the ID?

An AB-1.2 compression type...