Manumatic lathe.

[dbsharp]

I am converting my 13x40 lathe to cnc. I would like to be able to do some basic manual turning still, and have designed for removeable handles to move the axis. I pretty sure I will use Mesa 5i25 an 7i77 with analog control of dmm servos. I know can disable the drives to allow for manual turning, but how will lunix cnc respond to seeing the axis move and not getting a response to its output signal? Thanks!

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[Jim Dawson]

With the drives shut down LinuxCNC won't see the drives moving because the encoders are powered down. I'm assuming that you would be using the drive encoder output connected to the Mesa. It is possible to leave the encoders and drive control circuits powered up by feeding L1 & L2 separate from the drive main power contactors, but it is necessary to power down the control circuit and start it with the main contactors to so the drive does an orderly startup and keeps the motor from running away on start up.

The alternate method would be to use linear scales and use LinuxCNC as a DRO in manual mode if it will work that way and I assume it will. You should only need to do a reset to cancel any moves made in manual mode.

One small problem that you may have already considered is, by installing a ball screw on the Z axis it will pretty much lock up the carriage, much like engaging the half nuts. The way around this would be to connect the carriage drive motor to the carriage drive shaft and control the backlash with an air spring. That way you would retain full manual capability.


Sounds like a fun project.

[dbsharp]

The DMM drives actually have an input for enabling the drive. If it is not enabled, the drive is still on and the servo can move with no resistance. I think the encoder data would still go to the drive and the controller.

My solution to driving the z axis (or is it called y?) is to use a fixed screw and rotating ball nut.
You can see the picture of this here: https://www.cnczone.com/forums/verti...6-cnc-cad.html

The machine already has glass DRO scales installed and I will keep them.

[Jim Dawson]

I had some problems with the DMM servos trying to re-zero on power up or enable on one project, but it may have been my lack of understanding all of the fine details of the system. I was up against a shipping deadline and didn't have time on that project to work out all of the details. I have not had that problem on my lathe, but I'm handling the enable differently.

The carriage on a lathe is the Z axis, -Z is tool moving towards the chuck.

The rotating nut is a good solution. Even though it is possible to back drive it, I think it might present too much resistance for manual use. Not saying it won't work. I'll be interested to see how that works for you.

I was going to do the same conversion on my GHB 13x40 Jet, but I bought a Hardinge CNC lathe and did a retrofit on it instead. I still may do the Jet some day but it's not a priority.

[dbsharp]

I think I may just ask them if this is permissible.