Just had a thought about a novel design for a very compact 3D CNC mill. What I want to know is whether anyone has ever seen one?
Start with a VMC lathe. You have a turret which moves sideways (call that X) and a head which moves vertically (call that Z). At the end of the head you have a standard rotating mill fitting (BT30 upwards) rather than a lathe tool fitting. It points downwards, very conventionally.
Now, what about the Y axis?
Assume you have this huge backplate for the chuck - it's sitting horizontal, and the axis of rotation matches the CL of the mill head. Call that the A axis. To get conventional X & Y axis movement, combine the VMC 'X axis' movement AND the 'A axis' rotation, and you can get an effective conventional X & Y movement on the face plate. You may need to check this with a disk of cardboard to see. Yes, you would need very little backlash on the A axis, and very high resolution on the encoder. Assume that for the moment.
Now, there is absolutely no way you would ever build such a beast for manual operation. But with a computer running the motors, the transforms for the X & Y axes can be automatic. Yeah, I'm serious: it can be done. You can add B & C axes to the milling head to get a full 5-axis CNC - and there are NO limitations as to what tool paths you can get with this. It's just that visualising it and programming it is ... not easy. That is, UNLESS you have an automatic coordinate translation system doing it for you - which is possible.
The advantage of the design is that it occupies somewhat less floor space than a conventional 3-axis machine, and you don't have to worry about getting X and Y at absolutely right angles. With a rather large diameter crossed roller bearing for the A axis, you would have none of the common alignment problems for the Y axis linear ways either.
OK: does it exist? Has anyone ever seen one?
Cheers
Roger