Denford Orac cnc lathe

[George]

Hi there,
I have purchased an orac lathe which would have run on the bbc software and wish to upgrade to work from my PC.As I am new to this can anyone give me any advice/help on where to start.
I have successfully upgraded a Conect Minor cnc Milling machine so am not completely green on the subject, nor am I an expert.
My machine runs on manual, all axis working and the spindle controllable.
If anyone has upgraded one of these I would be grateful for any advice on the least cost option.
Thank yoy,
G Walker.

[Mr Magoo]

Hi George
Thought I'd drop you a few ideas...
The Orac will operate as a stand alone lathe and doesn't need a PC or the BBC to work. BUT it is very limited in it's capablilties compared to modern machines.

Option 1) Download the ORAC software for IBM from this forum (have a search - it's somwhere here). I think it only works with Orac '85 models. Oracs built before 1985 had slightly different serial protocol and may not link. This should let you prepare and simulate programs offline and download / upload these to the Orac. You can find the cable diagram to link a PC to the Orac here too.

Option 2) Do a retrofit to upgrade the machines electrics to something like Mach.This will greatly improve the machines capabilites but a good knowledge of electrics is required. Again, have a search on the forum for others that have done the same.

Cheers
MrMagoo

[david l]

Hi George

I acquired an Orac lathe last year. All of its control system/ power supplies were missing. I have since converted it to run off Mach3 (fantastic) software with all new electrics. I used the existing stepper motors and installed two MSD542 microstepping drivers and a PS407 power supply bought from Motion Control Products Ltd. The cost was about £110. On top of this I bought an VFD off ebay to control the spindle motor and a C6 variable speed control board from cnc4pc in the States to allow constant surface speed capability. The results of the conversion so far have been outstanding and I personally have found it all very educational. I know a lot of people seem to go for the Gecko drives but I have found no problem whatsoever with the MSD542 drives I have installed.
My recommendation would be to take a similar route rather than trying to salvage any of the existing electronics.

Dave

[Denford Admin]

installed two MSD542 microstepping drivers

Sorry if its a bit off topic, but I'm curious to know if you've had any issues with position loss with these ? I've found that the MSD556 behaves much better than the 542's. And thats using the same current setting, step count and motors

[david l]

I have not experienced any problems with lost steps using the MSD542 drives. I did check for this when setting up the drives by running a program repeatedly and with a dial test indicator verified the position at the end of each cycle was exactly the same.
I have the current set at 3A which is below their maximum rating of 4.2A. I don’t know if being nearer the top limit could cause problems.

[Denford Admin]

A very belated follow up to the MSD542 losing position - we ended up not using the drives so the problem went away...for a while

Recently, we ended up using some larger current drives that appear to be based on the MSD542 logic... these gave us the same problems of occasional lost steps.
To cut a long story short, we fixed it by setting the StepperDelay on the Baldor control card to 4 microSeconds.
This parameter in effect, stops the step pulse from changing just before, or after the direction output has changed state.

Stepper-Delay-Pulse-Width.gif (1.05 KiB) Viewed 8424 times

We think that the Motion Control Products drives were losing position because they were outputting the occasional step at the previous direction (ie, it hadn't been fast enough to notice that the direction had changed, before outputting a step pulse)

HTH - it's the kind of issue you'd probably only notice with a very fast move-buffering system and a program that changes direction often.