Hey all!

The mod:
The mod basically replaces the rack and pinion gear on the carriage with an ACME leadscrew for moving the carriage. The carriage handwheel now lives on the right hand side of the lathe, underneath the tailstock, much like it does on the Sherline lathes.



A pair of bearing blocks were made up for each end of the lathe to support the leadscrew, with the block at the headstock end sporting a pair of thrust bearings to support the cutting forces.

The mod replaces the powerfeed (see below for why) and allows very accurate control of feedrate and produces really nice surface finishes. It also allows you to stop bashing your hand into the cross-slide handwheel when moving the carriage and vice-versa.

Here's a picture of the surface finish my lathe is putting on 6061-T6 after my mod, much better than I was able to get before:


The backstory:
A few months ago I got the 7x12 lathe which I had been hankering after for a long time. The first thing I did when I got it was disassemble it and start thinking about how to CNC it...

Then I slowly realized that for normal users CNCing a lathe is far less important than CNCing a Mill, CNCing a mill adds so much capability, whereas for small hobby and custom jobs a manual lathe seems to be fine.

With this in mind I went to put my lathe back to factory setup and realized I had thrown out my change gears and leadscrew... what a silly idea that was.

While looking for a solution I realized that I didn't have much need for machine threading, but I definitely had a need to produce fine surface finishes, and the carriage handwheel arrangement was making that very hard, hence the leadscrew.

The next step: A semi-automatic lathe
The next step is to fit a spindle encoder and to built a stepper mount for the leadscrew. I know what you're thinking: "didn't you just say you didn't want a CNC lathe?"... While this is true, being able to have an easily controllable/adjustable powerfeed and the ability to single-point threads would be very nice. The basic idea is that I'm going to write up a microcontroller program that will read the pulses from the spindle encoder, and then drive the leadscrew according to a feedrate specified by the user on a small LCD interface. This will allow different threads to be cut without changing gears as well as easy and fast fine-tuning of feedrates for different materials. It will also allow the concept of an 'electronic carriage lock' by using the stepper holding torque to maintain carriage position rather than a mechanical device...

Basically this lathe is going to become a test-bed for a bunch of ideas I have about a lathe that I want to scratch-build.

Anyway, I realize this post has gotten a little long. All feedback welcomed, I plan to continue to update this thread with my progress.

-Aaron