Addy,

I have just finished updating (almost) all the electronics in an Orac myself. I bought the machine from someone who had been going to replace the electronics but had only got part-way through. I stripped out what he had done (he had a rather nasty USB-based breakout board and was planning to use Mach3), leaving the original steppers, spindle motor, and a 24V power supply that was intended to drive some low-power stepper drivers. There was also a VFD suitable for the spindle motor - a Teco device from Drives Direct (according to the labels). I did get it partly working with the electronics it came with but quickly decided that the stepper drivers were significantly under-powered, and Mach3 and that break-out board were a step backwards in technology. There was no spindle encoder, but someone had fitted a hall-effect device that was supposed to be triggered by a small magnet on the spindle. It was not wired in anyway.

I replaced the stepper drivers with CWD872 from CNC4YOU. More capable than needed but with the advantage that they accept an AC supply so I did not need to buy the bits to build a DC supply. I used a 2x50V toroidal transformer to supply the drivers. Overall, a bit cheaper than smaller drivers plus DC supply. The existing limit switches work fine. I'm not interested in super accuracy from them as I don't use them for home switching in practice so spot-on repeatability isn't an issue.

I also use a PlanetCNC control board and the associated software. I would like to have used a UC300ETH with the UCCNC control software (as I use that with my CNC router and CNC mill) but at the time I bought the PlanetCNC board, the lathe support for UCCNC had not been released. It came out about two weeks after my PlanetCNC board arrived... However, it all seems to work OK, just a different user interface to get used to. And another set of parameters to configure. One thing I did find was that the P-CNC board input and output interfaces are not very well documented. They assume that you are going to use their adaptor/interface cards, which I did not do. The UC300ETH and associated breakout board manuals actually include circuit diagrams so that you can see exactly what you are connecting to. I bought a number of ribbon cable to screw terminal adaptors to make connections easier, although there was still a little trial and error involved.

As there was no encoder fitted, I bought an Omron-compatible 100 line encoder from eBay for around £25 and mounted it on a bracket inside the spindle drive enclosure. I added a couple of toothed belt pulleys and appropriate belt to drive 1-1 from the spindle. The spindle pulley size was dictated by the need to provide a clearance hole to match the spindle bore (so as not to limit work that passes right through). The pulley is bolted to the disk that had a slot (presumably originally to drive an optical spindle position sensor) already fitted to the spindle. I ended up with 42T pulleys, T5 pitch, and 10mm belt. A bit OTT but the pulley size needed put limits on what I could use. I had a bit of a problem configuring PlanetCNC to read the encoder output reliably and in the end, via trial and error, managed to get it to work after I selected the "invert signal" option in the software. It does work, though, and gives steady and plausible speed readings. The PlanetCNC board supplies a 5V output that works with the encoder I use.

The VFD is fine - you don't need anything special. It's only a half-horse motor, I think, and that's all my VFD is rated for. I'm a bit of a belt-and-braces guy and if starting from scratch would have uprated the VFD a bit, but it's OK. Remember that to get full spindle speed, you need to drive the motor at up to 100Hz, even if it is nominally a 50Hz motor. That seems to be what Denford did! The main problem with the VFD is that it needs 0-10V analogue input and the PlanetCNC board can only deliver PWM. I bought a cheap PWM to analogue convertor (about a fiver off eBay) which, after calibration, works well enough. The linearity between demanded speed and actual speed seems more than adequate. I have forward and reverse motor running, driven from the PlanetCNC board. This needed a couple of small 5V relays - again, a cheap eBay or Amazon buy.

The guy before me had installed a couple of rotary switches and a MPG on the front panel. No idea what he was going to do with them, but I use one switch for X-Z axis selection, the other for jog speed (actually, two speeds and one fine step for accurate tool-setting) and the MPG for actually jogging. I plan to replace the front panel and tidy up the switchgear but that is more cosmetic than functional. I would also like to add start/stop/pause switches but that looks pretty easy to do.

And that's about it. I am using Fusion 360 to generate gcode, using the PlanetCNC lathe post-processor. Again, it seems to work. I have only recently got my machine working. Then I discovered the little problem that the leadscrew seemed to be a bit bent which affected cutting accuracy but I was able to straighten it. I am still exploring what I can do with the machine, particularly things like screwcutting, but I'm getting there.

I'm sure that there are a lot of things that are missing from this brief description and happy to answer any more questions. But I can't answer your original question as my machine was missing the original encoder!

- Brian