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Some hot air engines I've seen require cutting a staggered slot around the outside of a round rod for a cam follower. The following picture shows a method for doing this that doesn't require CNC.
A piece of bar stock that will include the cam piece is milled with the slot profile in the end of the bar stock. This can typically be done just with end mills and standard setups.
Next, chuck the bar stock in a spin jig mounted on the milling machine table. You'll need some kind of follower to ride on the end of the bar stock. The spin jig collars should be set up to allow axial movement of the bar stock as piece is rotated against the follower. The follower, riding against the end profile, will cause the piece to slide left and right as you turn the piece by hand.
Take shallow cuts and make multiple passes. You also want the rotation of the end mill to be pressing the workpiece against the follower as you turn it. Otherwise, well, you know what will happen...
Chuck
A piece of bar stock that will include the cam piece is milled with the slot profile in the end of the bar stock. This can typically be done just with end mills and standard setups.
Next, chuck the bar stock in a spin jig mounted on the milling machine table. You'll need some kind of follower to ride on the end of the bar stock. The spin jig collars should be set up to allow axial movement of the bar stock as piece is rotated against the follower. The follower, riding against the end profile, will cause the piece to slide left and right as you turn the piece by hand.
Take shallow cuts and make multiple passes. You also want the rotation of the end mill to be pressing the workpiece against the follower as you turn it. Otherwise, well, you know what will happen...
Chuck
