Denford orac encoder

[terry1956]

Hi, I am part way through converting a Denford orac lathe. But I am unsure of the encoder fitted. It doesn’t look like a Denford fitting that I have seen before. Can anyone let me know the manufacture. Thanks. And is there away of testing this to see if it’s working or not.

[Muzzer]

Looks like an own design, presumably by Denford.

It looks as if the circular PCB has reflective pads that will be triggering the sensors by reflecting light from an LED. There are 2 sensors that will be at slightly different angles so that you get 2 outputs about 90 degrees apart.

If you supply the 12V to the signal PCB and turn the spindle, you should see the outputs change up and down. If you want more detail, you could look up the sensors if you can identify the part number.

And make sure the circular PCB is clean, as dust and dirt could cause rogue signals.

[Neale]

Interesting - not sure if that is what my Orac looked like when it was new! I bought mine from the estate of someone who had started to rebuild the control electronics although the evidence suggests that someone had already had a go at doing that. At least I had a pretty clean sheet to start with, and no hang-ups about "authenticity". Very much about ending up with a relatively modern system, not the clunky electronics from a previous era. Anyway, as far as I remember, mine just had a disc with a single slot on the end of the spindle which presumably generated an index pulse plus vague idea of spindle speed and position for screwcutting. Maybe there had been something similar to that PC disc once upon a time but no trace remained. Given that my chosen motion controller could do a lot better than that, I fitted a 100ppr encoder behind the spindle, mounted on a 3D-printed platform that picked up some existing tapped holes. This is driven by a toothed belt and pulleys 1-1 from spindle. Seems to work well, and potentially more reliable and accurate than the device shown which might well have represented the art of the possible when Denford did the conversion.

[Muzzer]

Both my CNC lathes use 1-1 toothed belt drives as Neale suggests. You can get Omron clone encoders from Aliexpress, Amazon etc for £20-30. That's the route I'd take if you are up to the mechanical design and construction.

Something like this:
https://www.amazon.co.uk/DC5-24V-Inc...zcF9tdGY&psc=1

If you go this route, it will also provide you with an index pulse which is required for screwcutting and rigid tapping from the tool turret.

[Neale]

I would watch out that you do not go for too high a ppr count - it would be easy to hit the limits of the motion controller with too high a pulse rate. I think that my controller suggested 100ppr which still gives a very good speed feedback for accurate threading. Muzzer also makes the important point that you really need the index pulse as well - look for an encoder that offer "ABZ" outputs where AB are the high-speed pulses and Z is the once-per-rev index pulse.

[Muzzer]

Good point about PPR and spindle speed. I have a 1000PPR encoder on my big mill that runs up to 7500rpm. That's OK with the Centroid Acorn on that machine but it's possible other controllers wouldn't be so happy with such a pulse rate.

Note that some controllers have a minimum PPR. For Centroid it's actually quite high (1000PPR min, 2000-4000 recommended). In contrast, IIRC, LinuxCNC can manage rigid tapping with just 1 pulse per rev but that's unusual. Worth checking either way.