I have a Craftsman Atlas 6″ lathe that has been a workhorse for years. Recently I have a couple of lathe projects that are difficult or impossible with a manually operated lathe. So I have been modifying the lathe to add CNC capability. Parts to convert the lathe include stepper motors, stepper driver, power supply, computer and modifications to the lathe to attach the motors.
I bought the pro driver board kit and a pair of steppers from Hobby CNC. It is fun to build up boards like this and it saves a bit from buying a complete board. It also needs a case for the board. I decided to keep the power supply and driver board assemblies separate so I can swap things around if needed so the power supply is in its own case.
It turned out that the transformer I bought for the power supply put out a little too much voltage. The maximum input voltage to the stepper driver is 42 VDC and the the transformer was putting out just about that when connected to a rectifier and filter capacitors. I think they rated the transformer output with 110 volts input rather than the 120 volts which it the line voltage around here. Actually it runs a bit higher than that most of the time. I really did not want to get another transformer so I decided to take a few turns off the secondary.
This is the transformer opened up with a few turns removed.
Here the modified transformer is hooked up to check the output voltage.
On a lathe there are two axis that need to be driven, the main lead screw and the cross slide screw. To attach the pulleys for the stepper motors I added and extension shaft on the ends of the lead screws. To do this I drilled a hole into then end of the screw and turned down the extension shaft for a close fit into the hole. This holds the extension straight while I silver brazed the extension to the screw.
Here is the cross slide screw and the extension shaft before brazing. Of course the machining work was done on the lathe.
Here is the cross slide screw just after the extension was brazed on. After I brazed on the extension I discovered it was slightly bigger than 1/4″ in diameter and the bearing and belt pulley would not fit. So I mounted it in the lathe and turned it down with a file and sandpaper.
An extension was added to the lead screw in the same was as the cross slide screw. The mount for the lead screw stepper motor is simple, just an angle bracket to bolt it to the table. The pulleys provide a 2 to 1 reduction from the stepper motor.
To mount the cross slide stepper motor two holes were drilled in the carriage. The back mounting plate has a ball bearing to support the lead screw extension.
So far I am pleased with the operation of the lathe. One of the difficult without CNC parts I have made is a brass rod with a long taper. That only took a few minutes to machine. Currently I am working on adding a spindle position encoder to the lathe. When that is complete I will be able to cut threads under CNC. Threading is difficult manually and the lathe does not have any gears to do metric threads. CNC will solve these problems.
Here is a YouTube video of the lathe in action. https://www.youtube.com/watch?v=vzmgTqwl5tA It only took a few lines of G code to do this operation.
Hobby CNC http://www.hobbycnc.com/
Linux CNC http://www.linuxcnc.org/