[RCaffin]

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

[pippin88]

I'm a little to tired to work out exactly what you are suggesting, but I'm fairly sure what you are talking about has been done with waterjets at least.

There are videos of waterjets on YouTube that use a rotary axes interpolated to cut straight lines. They are cutting cake.

Edit: found the video www.mttec.com-Special cake cutting with waterjet - YouTube
It's a bit different to what you are talking about, but it is interesting what different ways there are to control motion

[alan_3301]

sounds like you are describing C axis milling on a lathe.
here is a video
it is supposed to start at 1:05, just jump there to see.

[RICHARD ZASTROW]

Bostomatic vertical mills did just what you asked. We had two 1980 1440 models. They were employed to produce rotary cuttind dies and still are. Bostomatic was bought by Micron. Now they are multi-axis, true 4 & 5 axis.

Dick Z

[RCaffin]

OK, OK, it's not original. Fair enough.

But cutting cake with a CNC?????
Disgraceful!!!!
Or something.
Mind you, that video did look cute.

Thanks all, much appreciated.
Cheers

[Tom-AMS]

>> But cutting cake with a CNC????? <<

How about making a cake with CNC VMC? <grin>

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