Cam and Follower mechanisms

Hi everyone.

I am having a problem in Creo 2 creating a cam and follower for a simple wooden toy.

I have not done this for a while and I must have forgotten something and I think it is to do with the model parts creation as the cam assembly will not accept the surfaces of the parts to reference.

Looking on PLMS I see there is a blue line in the around the middle of the cam and a grid on the followers mating surface. I do not have these on my model. Can anyone tell me where I have gone wrong?

Is there a simple guide to creating these parts to refresh my memory as all the video tutorials I can find are for the actual assembly of the mechanism and not creating the parts.

Thanks in advance.

Andy