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  1. #11
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  2. #12
    Having a think about a suitable test to confirm whether or not the BOB is being changed by Mach 3. If I took a red LED and a 150ohm resistor and connected them between the 5V supply on the BOB and pin 3, the x axis Dir, would it light when the axis was moving on one direction and not in the other? I was under the impression the BOB would give a High output for one direction on the motor and a Low output for the other?

    Many thanks

  3. #13
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 4 Hours Ago Has been a member for 2-3 years. Has a total post count of 541. Received thanks 72 times, giving thanks to others 14 times.
    Strictly speaking the BOB open-collector outputs are either a low impedance path to earth or a high impedance. This is why you need the pull-up resistors to get the required 0v or +5v output to your external transistors.

    The LED circuit should work. The LED must be connected the correct way round, test it first. You probably already know that but just in case there's somebody reading who doesn't know about diodes.

    Check that all three outputs, STEP, DIR and ENABLE are under MACH3 control. The step output will make the LED glow less bright than dir or enable when jogging since it will be pulsing when you tell an axis to move. This is a good sign!

    I don't use MACH3 and obviously know nothing about your individual mill so I'm at the limit of how much help I can offer.

    Engineering is the art of doing for ten shillings what any fool can do for a pound.

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  5. #14
    A quick update, after much head scratching I've worked out that the Mach 3 software will run on a 64bit windows OS, but it will not send any commands to the BOB as I am unable to install the drivers. I'm in the process of sourcing a 32bit copy of Windows then we should be in business.

    Thanks again to everyone for their input.


  6. #15
    Ive just skim read this so might have missed something but I had that exact same bob several years ago and couldn’t get any pulses out at all. Given that I have made quite a few machines I should know how to wire them up and how to configure Mach and what to expect. Only cost me 8 so not much lost other than time. I tried lots of things but that was my conclusion in the end. Did a straight swap for my current (even cheaper!) board and everything worked. These boards are made to Kit’s strap line.

    To answer one of your earlier questions a multimeter on the direction pin of the bob and on the ground pin of the bob (the terminal blocks that go to the driver) will read 5V or 0V depending on direction. If that is not happening no amount of downstream circuits with get it going.

    Another thought is to get the pin out diagram for the parallel port connector, unplug from Bob (but still in at PC end) and check direction pin vs ground in the cable end. Then toggle direction of that axis in Mach3 using the cursor keys (should see DRO move accordingly) and read 5V or 0V on the cable pin according to the direction. If this works then Mach3 is working and bob is under suspicion.

    Also the parallel cable needs to be the right type, one is crossed over and one is straight through. Can’t remember which you need but a quick search should find it.
    Last edited by routercnc; 07-09-2019 at 09:53 AM.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  7. #16

    After a few months of tinkering I'm slowly making progress. I manged to install a 32bit version of windows that is running Mach 3 and outputting the required pulses down the parallel port cable. Using the circuit suggested by Kit, and others, on the previous page I was able to get all axis running with reasonable success. I've also reconnected the micro switches that cut the power to the axis if they hit their maximum travel. Jobs left before I can start making chips; 1. Either revive the optical sensors on the mill or install more micro switches for homing. 2. Work out a means of powering the Spindle, this is where I could use some help.

    The motor that powers the Spindle is a SEM DC Servo motor, model number MT30U4-36. There are a few DC servomotor drivers on eBay but they seem to top out at around 80V and this one runs up to 140v, any suggestions would be much appreciated.

    Here's the info from the motor label
    Model MT30U4-36 No.00262-004
    Stall torque 4.5NM Amps 13.2
    Max 4000 rpm 140V 75A
    Tacho 9.5 V/KRPM IP44/65 IC 400
    Ferrite Brushed DC Servomotor

    I do have one other problem. The Y & Z axis move fine, but the X axis behaves in an odd way at full speed, bit hard to describe so I've uploaded a video with the link below. I have removed the motor from the machine and it runs fine with without any load, but connected to the machine it sort of cuts out at max speed. I can turn the lead screw without too much resistance so I'm not sure what's causing it? Any thoughts?

    https://photos.app.goo.gl/6StZyicUyWeMPB5XA In the video the problems start after I run it at full speed, the first few small jogs are intentional. You'll hear a high pitched unhappy motor sound when it cuts out.

    Thanks in advance for any help.


  8. #17
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 8 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,459. Received thanks 281 times, giving thanks to others 7 times.
    For the spindle motor, you need at least a basic SCR drive. Most common are KBIC drives, but you have to be aware the control circuitry is non-isolated, and floats near mains voltage. You can get isolated versions.
    IIRC Sprint also do fully isolated SCR drives. If you do a search on RS for "Sprint drive" they have various options.

    I've not watched the video, but I'd guess the X-axis motor is simply stalling. It's what happens if you try pushing a stepper motor too hard. Either drop max speed, or drop acceleration.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  9. #18

    I’m creeping towards the finish line on the milling machine conversion and have hit another snag, while trying to find the stall point of the x-axis I managed to cook the ‘single phase RFI filter’. I’m looking for a replacement, but can’t find an exact match. I don’t know much about these, would someone mind advising how to find a suitable replacement please?

    Here’s the info on the one I smoked.

    Single phase RFI Filter
    Type: RS 1010-IDF
    10A@40C, 250VAC, 50 - 60Hz
    HPF -25C to + 85C

    I’ve found this one on eBay, but it’s rated at 14A, will that be an issue?


    Many thanks. Dan

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  10. #19
    Sterob's Avatar
    Lives in Australind, Australia. Last Activity: 23 Hours Ago Has been a member for 0-1 years. Has a total post count of 68. Received thanks 4 times, giving thanks to others 4 times.
    A higher current rating won't be a problem.Its only when you go lower that you have to be careful.

  11. #20
    Thanks for the help Sterob. Just to confirm, because I really don’t want to buy the wrong thing and trash over a years work. The one on eBay is labelled ‘Mains input’ and ‘inverter’ where the one I have removed from my machine is labelled ‘load’ and ‘line’.

    Am I right to assume ‘line’ and ‘mains input’ are the same and ‘inverter’ and ‘line’ are the same? I’ve attached an image of the eBay item I’m referring to.

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