Over 3 days last week I attended a workshop at which 14 of us converted a Little Machine Shop lathe to operate under CNC control. While everyone attained axis motions under control of Mach4, there remains a bit of fettling and adjustment to get it working to its utmost.
The design of the mechanical parts was done jointly by Ron Ginger and Joe Katona, while the electronics were designed and produced by CNC4PC. I believe that drawings and BOM for the mechanical components will be made public at some point, and CNC4PC will sell the electronics, so it should be possible for home builders to obtain the same machine. Cost for the lathe and everything needed to build it was $2770, which included a Mach4 Hobby license.
We started with a LMS 5100 Hi Torque 7x16 mini lathe:
After uncrating, the first task is to remove everything that wouldn't be needed. This included the saddle, both leadscrews, and all the change gears and associated mechanism, and the backsplash. We also removed the compound temporarily to expose and remove the cross slide.
The first operation was then to ream out the hole for the new X-axis ballscrew to 13 mm, and then to drill and tap two holes in the rear of the cross slide to mount a bracket for the ballscrew nut. Here's a photo of the bracket with the nut attached. A drill jig was used to ensure accurate placement of the holes.
Next the Z ballscrew is attached to a mounting plate, which in turn is secured using the same mounting screw as was used for the saddle. The right end of the ballscrew is supported by a pillow block containing a pair of flanged bearings. This pillow block uses the same holes in the frame as the original lead screw. The left end uses the original pillow block.
The right end of the Z ballscrew is secured with a nyloc nut and a coupling to the shaft of the Z stepper. The motor itself is attached to a bracket that itself is screwed to the frame. The bracket itself was used as a drill jig for drilling and tapping the holes.
The X-axis motor mount consists of the Z ballscrew plate, a second parallel plate which also uses a saddle mount screw, plus a pillow block that spans these two plates that carries the near end of the ballscrew. The motor itself is mounted to a plate that bridge the two support plates.
The ends of the motor shaft and ballscrew have toothed pulleys joined by a belt as seen above. Tension on the belt is set by the motor mount having three screws, with two in slots, allowing the plate to be rotated slightly.
On the left side of the spindle housing is located an encoder, driven by a belt and two pulleys. The encoder is mounted to a bracket, which in turn is held to the spindle housed by a screw. The bracket itself is used as a drill jig for this hole. A slot in the bracket allows adjusting tension on the belt. The spindle pulley is placed between the two locknuts.
The control box has estop and power switches on the front, and all connectors on the rear.
With the lathe power cord plugged into the control, starting and stopping the spindle is under control of Mach4. When I left the workshop, I was missing a cable that will be inserted into the lathe's PC board and thence to the control's VFD socket. This will allow speed control of the spindle by M4; until I receive the cable the spindle RPM will need to be set using the stock rotary switch. The speed control option, when present, will allow M4 to command constant surface speed when desired. With spindle operation delegated to the control, the oem start/stop switches were removed, and the hole covered with a plate.
Note that in the photos above one can see two homing switched, one for each axis. These are the orange proximity switches. For most users these are unlikely to be needed. However, using repeatable tool mounts such as a gang tool plate they may eventually have some use.
Here's the lathe as it sits:
The major adjustment that it needs now is making the Z ballscrew parallel to the ways. Presently the left pillow block is not attached to the frame, and securing it with screws as is causes some binding of the ballscrew and limits rapids. With the pillow block floating free movement of the end is obvious with carriage movement. Measurement and shimming is needed.