Software

Another of the reasons I decided to use the Centroid Acorn control board, is that Centroid also supply their own software.

It has a really nice touch screen interface.

There is a basic version of the software, and this has a restriction of max file size of 50Kb and 20 blocks of conversational code.

The "Pro" version also supports a spindle encoder, which is required for threading.

I wont need the Pro version until all the hardware is finished and tested.

Stripping

First task was to remove all the parts that are not required on a CNC lathe.

Items removed:

  • Feed gears
  • Feed gearbox
  • Apron gearbox
  • Compound slide
  • Leadscrews and rack

I listed all this stuff on Ebay and recouped $200 towards the project. 

Installation

I hired a ute and collected the lathe from Machinery Warehouse.

Getting off the ute with a forklift was easy, but unfortunately I did not have room to move it around using the fork.

So, I moved it into place with a pallet trolley and lifted it onto the stand with an engine hoist.

Z Axis

I am going with a 20mm ballscrew on the Z axis.

The closed loop stepper will mount where the feed gearbox was previously located.

Ballscrew mounts and stepper motor mount were attached with socket screws. Was easy drilling cast iron, hardest part was keeping the drill perpendicular. Tapping was also quite easy using Tap Magic as a lubricant.

Timing belt pulleys will drive the ballscrew. A 20 tooth pulley on the motor will drive a 30 tooth pulley an the screw. This will give a little extra torque.

Lathe - Stripping

Naturally, there is quite a bit of stripping involved to remove parts not required for the CNC conversion.

This includes feed gearbox, apron gearbox, leadscrews, compound slide and the main gear train.

Here are some pics before and after.

It took about 2 hours to get to this stage.

External Electronics

This is to cover the electronics which live outside the main controller case.

An Omron 2000 line encoder will be used for spindle index. This will be driven by a timing belt from the spindle itself with 1:1 gearing. This will supply accurate spindle position for threading. It connects to the DB9 connector on the Acorn board.

Motors

I used hybrid closed loop steppers with encoders on both Z and X axis.

These were ordered from steppersonline via Ebay. They look to be rebranded Leadshine products.

Z axis is 8.25Nm (1200 oz in), and X is 4.25Nm (600 oz in). I am certain that these are overkill, but would rather have too much power than too little.

These require 48V DC, so I will add an extra 20A power supply to power these.

They will be geared via timing belts. This should give better accuracy and increased power.