Can I use a mill converted to CNC in manual mode?

[Doddy]

Pretty good summary there Neale. Another issue is that with replacing the trapezoidal screws with ball screws - and the associated increase in efficiency, unless you lock each axis (good practise, in any cases on a manual machine) you'll likely find that the axis will move under the cutting force under load.

The cogging effect of a stepper connected shouldn't be underestimated - I finally removed my cross-slide hand wheel on my lathe conversion (to replace with MPGs) as I realised that it did not afford the finesse that you normally associate with a manual control (plus, it was a stomach-ache [glad the stand is as tall as it is] if working close to the machine when it decides to do a rapid movement).

OP: Twin shaft is one way - another is a belt drive onto the screw - offsetting the motor away from the screw and allowing the original hand wheel to be retained.

But... think hard about why you want to CNC... and why you want to retain manual control. I stripped my mill (SX2.7 long-bed) of all manual controls - except the quill feed lever.

[Muzzer]

I did my Bridgeport conversion so that I could retain manual operation, thinking I was being clever. I retained the large cast iron handwheels on the X and Y, and had a clamp nut on the Z axis so that I could release the ballnut, rather like Elrod's concept.

Much of that was a waste of time. The large handwheels had massive moments of inertia which really buggered up the servo response (dead sluggish, so I removed them) and I've never used it in manual mode anyway, so the complication on the Z axis ballnut yoke was pointless.

You really need a wireless MPG. That way you still have your "manual handwheels" but they are not stuck on the end of the table, you can change the feedrate from the MPG and you can use the MPG where it is most convenient eg with your nose right next to a tool when touching off etc.

Besides, if you are in manual mode, surely you want to use a DRO readout to know where you are. There's not a lot of manual work you can do freehand where a DRO wouldn't be useful.

The torque on a stepper is a lot higher if the wires are shorted out or if the driver is unpowered, which has a similar effect. If you were to disconnect the steppers you would likely find the drag torque was pretty low. On my machine before I fitted ballscrews, I often had the slide locks lightly nipped up, particularly if climb milling. Afterwards, the servos and belt drives provided enough drag not to need any help when unpowered and when using them in manual mode (ie powered up), they hold position very solidly, so little chance of drift! If you simply fitted ballscrews and nothing else, you could nip up the locks as much or as little as you need, so it shouldn't be an issue.