Stepper controller to manually input a specific degree

[HankMcSpank]

I am thinking about building a 4 axis for my manual mill using an old lathe headstock shaft and a stepper. What I am looking for is a controller for the stepper that I can set manually ie something that I can input say a specific degree of rotation via a keypad or suchlike.
Think of gear cutting but setting the degree of rotation manually for each tooth.
Anyone seen such a beast?

Ian

If you don't get a custom solution, this should be do-able from within your standard CNC app using something like a g-code command e.g. G0 Axxx command (where 'A' is the label given to your 4th axis & xxx is your required rotation in degrees 0->360).

Assuming a 1.8 degree per step stepper

You need to arrange it so that your CNC application thinks that one full revolution of your 4th axis stepper is 360mm

So, assuming you work in millimetres as the unit of measure within your CNC app....

A standard 1.8 degree per step stepper would mean 200 steps = 360mm

therefore 1mm (or 1 degree of rotation) = 360/200 = 0.55555 steps per millimetre ....which obviously isn't ideal, so for the 4th axis stepper, crank your driver micropstepping up as far as it will go, let's say you can get 64 microstepping, then it would be

200 x 64 steps = 360mm

12800 steps = 360mm

1mm = 12800/360 = 36.5 steps per unit

So set your steps per unit for your 4th axis to 36.5.

Now in your CNC app

G0 A1 = 1 degree
G0 A10 = 10 Degrees

etc...

I think I have the maths right, but no doubt someone will correct me where I'm wrong!