Mini-lathe motor speed reducer

Work in progress

This lathe has a good 400W DC motor with 4800 rpm max speed and a US made KB Electronics KBLC-240D DC motor controller. Motor and controller work together pretty well but sometimes at low speeds there is still a lack of power. Moreover, running the lathe at low speeds will tend to overheat the motor as the motor integrated fan will also run slow, thus coming ineffective.

Making a motor speed reducer has both the advantage of additional torque on the lathe spindle and, as the motor (and integrated fan) will run at higher speeds, the motor will stay cool even with hard lathe jobs. Of course some decrease on silent is also expected when the motor runs faster.

Prior to make this mod, used to have the motor without the sheet metal cover to check motor temp by hand. Many times had to stop working as the motor easily got to a high temperature. Later, when making this mod, it was running on a temporary assembly to test the mod and since then every time I check the motor it is always cool.

Mini-lathe motor speed reduction jack shaft

On this project the motor was relocated not only backwards but also towards the end of the change gears cover. Making it this way I was able to remove completely the motor from the rear of bedways and that's why the previous motor location under the headstock was partially covered when preparing the lathe bed. This will allow the saddle to move closer to the spindle and also swarf and coolant will fall straight onto the chip tray.

Mini-lathe motor speed reduction jack shaft

The motor support was made with a angle plate to ensure access to the motor mounting screws. This lathe is getting heavier with each mod I make, and having the motor mounting screws under the motor could made things harder if for some reason the motor has to be disassembled.

Mini-lathe motor speed reduction jack shaft

For the motor support only the small parts with the same radius as the motor were made on the lathe with a faceplate. All the others made only on the bandsaw and drill press. No accuracy needed here. The goal is that the setup must hold the motor aligned with the mini lathe bed. The larger base plate was drilled up to 8mm for the M6 screws bolting it to the bed foot in order to allow motor alignment. The angle plate was actually made from two plates bolted together.

Not bolting down the lathe

For long time I was planning to mount the lathe on a large cast iron base, but ended tossing out the idea. Many care is needed when bolting down a lathe to any rigid surface in order not to twist the bed. But even if it is well done and the lathe bed stay perfectly straight, when turning, repeated forces are applied onto the cutting tool, thus on the front side of the ways toward the bed vee, may wear or distort bedways.

If the lathe bed is left unbolted, and mostly on roughing cuts, part of these forces will make the bed to flex a little. This would be far better than bolting down the lathe to a rigid surface, as all cutting forces applied on a bolted lathe bed may cause deformation on the bed vee. Usually this would happen closer to the chuck, where most turning work is made.

Thinking even more about it, decided not only to keep rubber feet but also not to enlarge footprint. With the lathe footprint over rubber feet, any irregularity on a bench would not cause the bed to twist, due to the small height of this lathe. With a larger footprint things may not be so simple anymore.

Have thought about enlarging the footprint only under headstock, but it is really not necessary. Vibration is now greatly reduced since I started centering chucks from the chuck body, and relocating the motor backwards also help getting the lathe weight balanced from front to back. Differences are far greater than ever thought they could be.

Will continue, but not too soon.

Mini-lathe motor mod drawings

Mini-lathe motor speed reducer

Base plates for mini-lathe feet, made from 12mm thick steel plate. On left, the two M6 threads to mount the angle plate. The two 8mm holes are to make clearance to align the motor.

Mini-lathe motor speed reducer

The angle plate, made from two 10mm thick steel plates bolted together.

Mini-lathe motor speed reducer

Plates to fit the motor, made from 11mm thick steel plate. On right drilling position for left and right plate.

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