2 Quick questions

[idtkid]

If you have a CNC'd machine and you wish to manually control the axis does turning the screws create a current that is sent back to the drivers/boards?

Also, if your manually using a CNC'd machine that is run by servos, can you use the encoders to give DRO output?

Thanks for your help!

[escott76]

Originally Posted by idtkid If you have a CNC'd machine and you wish to manually control the axis does turning the screws create a current that is sent back to the drivers/boards? Also, if your manually using a CNC'd machine that is run by servos, can you use the encoders to give DRO output? Thanks for your help!

You have to shut the drives off the motors in order to use the machine manually.
To the second question the short answer is no. The encoders go to the drive not the computer, which will be off if you are using it manually.
Once again, as many have posted before me. There is no need to "go manual". Once you get comfortable you work pretty fast with no "manual mode" using things like MDI and jog. You also gain the benefit of power feed like this. There really is no reason to take great pains to "go manual" as it gives almost no gain. You may be more comfortable now with a manual machine, but it will quickly wear off.

[hoss2006]

Originally Posted by idtkid If you have a CNC'd machine and you wish to manually control the axis does turning the screws create a current that is sent back to the drivers/boards? Thanks for your help!

A small amount for as fast as you would crank by hand.

http://www.youtube.com/watch?v=B9emjJxXZ0c

http://www.youtube.com/watch?v=B9emjJxXZ0c

[Crevice Reamer]

That was very well answered. I will only add:

If your CNC machine has ball screws, then only locked up motor holds the axis. Without the motors powered, there is no friction to hold the axes against cutting force. Unless you locked all axes but the one you were moving, accurate manual milling would be impossible.

CR.

[idtkid]

Fair enough If you can clarify though, by shutting off do you simply mean turn off the power supply to the motors or would you need an inline switch between the motors and the drives to to stop the current from flowing back?

[Crevice Reamer]

Originally Posted by idtkid Fair enough If you can clarify though, by shutting off do you simply mean turn off the power supply to the motors or would you need an inline switch between the motors and the drives to to stop the current from flowing back?

Adding a switch between motors and drives is a sure way to see the magic smoke come out of the drive. You can never get the smoke back INTO the drive and it will not work thereafter.

CR.

[idtkid]

And if I could reply to Crevice Reamer specifically, our Bridgeport EZ-track at school was a ballscrew machine (still is) and is both manual and now CNC, wouldnt just the pitch of the screw determine if it could be easilly moved with out turning by hand or not?

[Crevice Reamer]

I have never CNCd a Bridgeport, but I'm sure that huge table has a lot more inertia than most benchtop machines. Perhaps all that weight makes manual control more plausable. Is that what you are converting? A Bridgeport?

CR.

[Crevice Reamer]

Or, come to think of it, are there BRAKES on the bridgeport axes?

CR.

[idtkid]

Not converting a bridgeport, was just using that as an example. It has stops you can apply by hand (locking of a nut on the table) but thats it.

Back to the previous question about current sent back to the electronics, id assume cutting power to the power supply first, then using a switch to break to circuit from the motor back to electronics would be fine? If the motors create such a small current would a simple diode protect the components?