Another cnc conversion question

[Angus in Wyoming]

I hope this isn't a dumb question. If I get a mill and convert it to cnc, is it possible to still run the mill manually?

[jacampb2]

In most cases yes. If you are buying a kit, then you are limited by what they use in the retrofit. If it is something you are going to roll yourself, then it is up to you.

[vincemulhollon]

I hope this isn't a dumb question. If I get a mill and convert it to cnc, is it possible to still run the mill manually?

I find it quite pleasurable to run the mill "manually" using the keyboard and treating the CNC gear like an extremely fancy DRO. With EMC2 software some people spend a lot of time and energy adapting video game controllers and joysticks to run their machines. Flying a mill with a joystick would be a novel experience which I will try someday.

I was very confused when I discovered "dual-shaft" stepper motors. How would I route the X axis to one shaft and the Y axis to the other shaft? Do they mean "dual shaft" is dual torque? Is it like dual overhead cams? In reality a dual shaft stepper is one shaft, that extends out each side. So you bolt one end of the stepper to the machine, and the opposite end of the stepper has the handwheel stuck on that end of the shaft. Probably without any convenient pointer, etc.

Since a DC motor turned in reverse is a generator, spinning the steppers generates power, the faster you turn it. Opinions vary as to what that'll do to a stepper driver and are generally reported as "I know someone who heard of someone else who once saw..." I have not personally burned out my gecko drive stepper controllers by spinning my dials a bit. I'm sure with some unusual combination of stepper and driver it's possible to damage stuff. A truly giant stepper with a tenth the torque of a car engine plugged into the worlds cheapest controller might be a problem. I would think a servo motor makes an excellent generator and could burn out a servo controller. Someone will probably mention that some stepper controller out there shorts the stepper leads when powered down and that would make it a bit hard to turn, although I've never experienced this or even seen written proof.

Where "manual" CNC gets tricky is when you wire up the spindle to be under computer control... How to you "make it spin" without booting up the PC? Solution is to not hardwire the spindle to the solid state relay, but plug the spindle into a CNC SSR controlled outlet, or a plain wall outlet. Which brings up the interesting safety problem where you think the spindle is off because the CNC SSR is off, but the spindle is actually plugged into the wall and turned on... Be careful. Similar fun and games with coolant, assuming you're lucky enough to have a flood or mist coolant system.

Finally some folks greatly enjoy placing their CNC machine in the exact center of a giant clear lexan box. I'm not knocking that, it is a good idea for pure CNC use, but its going to be interesting learning way the heck over thru a small door to manually turn those wheels if the mill is in the center of a giant plastic box... And sometimes those folks wire a safety switch so the spindle can't get power if the door is open.

Or in very short summary, if you really want to, you can design it to work, but lots of people almost intentionally design it not to work.

[Paul Alciatore]

I am starting a small CNC conversion of a Unimat. My first step will be to add a stepper to the leadscrew and set up a manual control panel to operate it. Kind of like a power feed and slew system.

I plan to make it both up and down compatible. That is, I want the motors to be easily removable for complete manual operation with the original handwheels and I want the manual control panel to have a input that will accept commands from a computer so I can later upgrade to full CNC. I am planning the circuitry to allow both manual (with the control panel) and computer operation at the same time. This will be easy to accomplish as I am designing and building the system from the ground up.

I will add a second motor for the cross slide and it will operate likewise. I have a third motor for use on the quill feed.

[macona]

If you keep the leadscrews then yes you can still us it manually. If you convert to ball screws you dont want to use it manually. Ball screws are just too efficient. The will backdrive quite easily. This means that you have to lock the axis otherwise it will move under pressure.

Retrofitting a mill decreases its value. You would be better off buying a used machine with a dead control.

[DennisP]

I converted a benchtop mill to CNC a year ago. I did want the ability to use it in manual mode when needed so I made a shaft adapter and re-mounted the handwheel on the Y axis. I made a custom handwheel for the Z axis because the original didn't fit. On my mill, the X axis has the screw protruding from both ends so I just mounted the original handwheel on the opposite end from the one that has the stepper motor connected to it.

Dennis