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Thread: Orac / 2024

  1. #1
    addy's Avatar
    Lives in Dundee, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 0-1 years. Has a total post count of 4.

    I am trying to put together the parts for a ORAC conversion. The lathe is still functional with, all original electronics on it.

    So far, I do have a PlanetCNC control board, stepper motors, drives, power sources.

    I need of help regarding the spindle encoder and VFD required.

    Is anyone able to advise if the spindle encoder is a NPN or a PNP ?
    What VFD would you recommend for the conversion?


  2. #2
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 17 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,729. Received thanks 295 times, giving thanks to others 11 times.

    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

  3. #3
    addy's Avatar
    Lives in Dundee, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 0-1 years. Has a total post count of 4.
    Hi Brian,

    thanks for taking the time to reply to my post.

    I bought the late with the hope that I will easily find the information required for the conversion. It turned out that is not as obvious.
    Out there are different approaches and options that are not fully explained for a newbie. Plus not many replies on the forums that I joined.

    I ended up ordering the PlanetCNC board because they were the only ones prepared to offer support.

    Regarding the stepper motors, I went for nema 34. They are fitting the original brackets. I got the drives and power sources was a bundle. So no mess with the compatibility.

    So far, the board and the steppers should talk and there should be no problems wiring up.

    The lathe came with its original electronics. So, I do have the encoder. Apparently it can be used with the PlanetCNC board. They sent me in the parcel a connection board.

    The only part that is unknown yet is the VFD side. I was not aware that the old one can be used.
    Could you please help me with a bit more information about the use of the original one? Is just a matter of sending the control signal from the board to the unit keeping all the rest in place?

    Did you fit the new electronics in the box, under the lathe?

    So far, my controller board and the opto adapters are here. I am waiting on the steppers.

    thanks again for you reply,

  4. #4
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 17 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,729. Received thanks 295 times, giving thanks to others 11 times.
    Commenting more-or-less in order...

    Yes, the P-CNC board does the job. The only thing I have found that would be a nice-to-have is Constant Surface Speed (CSS). Instead of a spindle speed, you specify the surface cutting speed you want and the controller adjusts the spindle speed depending on the radius at which you are cutting. So, if you are facing a large disc, say, it starts with a slow spindle speed at the periphery and speeds up as you go towards the centre. Given that this is something that most manual lathes can't do anyway, it's not a show-stopper. Apart from that, the P-CNC software and hardware seems to be OK.

    NEMA34 might be a bit big for this lathe - one of the non-intuitive things about CNC machines is that sometimes bigger is not better! For example, my CNC router uses what seem to be silly little NEMA24 motors but they are happy shifting a heavy gantry. Bigger motors have much higher inertia and their inductance means that you cannot accelerate them as fast as the smaller motors. All the same, this lathe does not demand very high accelerations and machine travel isn't long enough for this to be a big deal. And if they fit... What I would ask is what voltage PSU you have - a number of "kits" have lower voltage PSUs than ideal and more volts typically means better perfornance. I'm running my original steppers off 50V AC - probably the equivalent of 65V DC or so. Again, though, it's going to work and the only downside is less than optimal performance - which probably won't matter than much. P-CNC to stepper driver connections should be straightforward.

    Are there any markings on the encoder? I can't help here as I have never seen the original. My new encoder is 5V but I have a feeling that I have seen mention of the Orac originally using 12V for the encoder. Shouldn't be difficult to interface, just not quite as straightforward. Useful if it has an index output as well as AB. I think that the P-CNC will do screwcutting with just AB (no index pulse) but I'm not sure. I think I have configured mine to use the index pulse.

    VFD - can you give us as much detail of this as possible? Make/model, connection diagram or photos of terminals, etc. That should help understand how to connect.

  5. #5

  6. #6
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 17 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,729. Received thanks 295 times, giving thanks to others 11 times.
    Specifically, if you still do have the original Denford-fitted VFD, then this is a pointer to the manual for it (pointer to PDF in second post).

    The Parajust VFD was a fairly early VFD, and from what I have read does not have the greatest reputation for reliability. However, when working, it does do the job. If you are going to use it, read the manual very carefully about connecting to it as some of the input terminals might carry dangerous voltages. Certainly you would be OK switching the forward/reverse inputs via a relay which would provide isolation, but I'm not clear about the 0-10V control voltage input. The manual describes how to use this, but as I say, I'm not sure about isolation from high voltages. In any case, you are going to need a PWM to analogue voltage converter, the same way that I did. The P-CNC board has a PWM output, not analogue, which seems a bit silly as almost everything wants analogue. However, you can pick one up for around a fiver off eBay. I used one of these but there are plenty like it. I didn't need to look for high-voltage isolation so didn't bother to check if these cheap little boards would do the job in your case.

    If there is any doubt about the Parajust VFD (if that is what is in there), then replacing it with a modern equivalent is very easy.

    Sorry for slow reply - the site seemed to be unavailable for a couple of days.

  7. #7
    addy's Avatar
    Lives in Dundee, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 0-1 years. Has a total post count of 4.
    Not sure what happened with settings here, I got a notification regarding the first reply, but nothing after.

    Thanks John, I will read through.

    Steppers: I went for nema 34 only because the original steppers have the 34 frame. Without much guidance, I was trying to limit the number of modifications to a minimum.
    But very soon, I ran into a "problem" : the belt profile is 100XL037, the original pulley has 12 teeth, and the new motor has a 14mm shaft. Can't find a pulley with such a spec.
    I ordered one 12T XL profile, but I have to open the bore and cut a key. I could have bought a nema 23 but only recently I found an adaptor frame 23 to 34.
    After your post, I ordered DM860H drivers and a 60VDC source to use the original motors. I will play with the 34 closed loop once more knowledgeable.
    Do you have an wiring diagram for the motors/wire color combination? I found a discussion about parallel and serial connection. I am planning to use the original wire combination.

    The encoder on my lathe is a 5V (four wires : SYN, +5V, SPD, GRN). I been advised by the P-CNC tech support to buy opto isolators for all inputs and outputs. There were some questions around the encoder being PNP or NPN that I could not answer. I will updated with the progress once my 5V source will arrive.

    VFD - If easier/ safer , I will buy a new one. No point of taking the risk of grilling the board. Any recommendations for a decent modern one? What should I look for? 1 phase to three? 750whats?


  8. #8
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 17 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,729. Received thanks 295 times, giving thanks to others 11 times.
    Sorry - I have just had a short stay in hospital and still banned from workshop!

    Have you managed to identify wire colours? As I say, I can't get outside to check, but there is a quick way to this with 4-wire motors. Best approach is to check resistance (cheap digital multimeter is invaluable!) between pairs of wires - any pairs. If there is maybe some few tens of ohms between two of them, label them as a+/a- (doesn't matter which). There should a similar resistance between the remaining pair - label b+/b-. Connect to corresponding terminals on driver. If the motor goes the wrong way, switch just one of the pairs, + for - and vice versa. Or do it via the appropriate software parameter.

    No meter? Take a pair of wires and connect together. If the motor is difficult to turn, that's a pair (as above). Check by disconnecting those and try using the other pair to confirm. Connect two wires that are not a pair and there is no extra resistance to rotation.

    Sorry - can't manage long sessions at the moment. Happy to continue discussion, though.

  9. #9
    addy's Avatar
    Lives in Dundee, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 0-1 years. Has a total post count of 4.
    Hello Brian,

    Sorry to hear about the hospital trip. I wish you a speedy recovery.

    After your first reply, I went for new motor drivers, a new power source and a chinese control board.
    When I got the lathe, I contacted a guy in my area that is selling few CNC converted machines to see if he would guide me. The offer was: conversion done for 1000.
    So, I have a bit of room to play and learn.

    At the moment, I do have on the table: two DM860H, a source 60VDC 1k, a 5VDC and a 12VDC, the original spindle encoder, P_CNC board and few opto-isolators.
    The lathe is still untouched. I need advice on buying the VFD before taking it apart. Is this along the 1ph 220v to 3ph 220v spec?


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