Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.


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Thread: Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.

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    Default Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.

    we managed to get a few of these compact 5 pc from a local school. As most of you I started searching the internet for info on the lathe. I found this artical

    http://www.maxton.com/ebay/emco/EMCO...to%20Mach3.pdf

    from the digital machinist mag that explained how to remove the octal latch from the interface board, switching the board to step/dir and setting up mach. I did a search for the 74ls374 chip discussed in the artical. It looked like I could use linuxcnc to send the clock signal to the board. So after some figuring and searching I found figured out the printer port pins..

    x step pin 2
    x dir pin 3
    z step pin 4
    z dir pin 5
    index pin 12
    estop pin 11
    100 ppr sensor pin 10
    74ls374 enable pin 14
    74ls374 clock pin 1

    So I hacked together a hal file that used the 'reset' function of the printer port driver to send a clock every base period to latch the 74ls374 chip. After not remembering to set switch 1 to on on the emco interface board (sets the interface to step/dir) and scratching my I got linuxcnc communicating. The performance was not stellar. The article above talks about setting your max velocity to 19ipm. This is what I was seeing. Just pretty poor performance. Sounded crappy. Now it could be that I didn't have the timing perfect but read on.. (according to the article above - the original software did around 30ipm)

    When I forgot to set switch 1 on the emco interface board - I had decided (by twiddling bits on the printer port with linuxcnc) that the default setup must have been phase drive. The original software controlled the 4 phases of the stepper drives/motors. I didn't have much to lose so I modified the linuxcnc hal file to do 4 phase drive for each axis and set switch on on the emco board back to 'off'.

    HAL Component Descriptions

    So pins 2-5 ran one stepper and pins 6-9 ran the other.

    the stepgen in linuxcnc will do a bunch of wave forms - I was interested in - 5 through 10. (4 phase patterns)

    I started with pattern 9. This is Unipolar Half Step
    -This acted the same as the step/dir I started with. 19ipm max and sounded crappy.

    Next I tried pattern 10. This was a long shot as it is Bipolar Half Step
    -I don't think it worked at all - or at least it was way worse..

    Then I tried pattern 5. Unipolar Full Step (one winding on)
    -I had to half the steps per inch obviously - but it acted the same as the above. around 19ipm and sounded bad.

    finally I tried patten 6. Unipolar Full Step (two windings on)
    -Wow. This sounded nice. We started pushing it and it started sounding rough at around 40ipm. (didn't seem to be losing steps but I think I might be just fine with 35ipm max)
    We still have to up the acceleration as that could be pushed a bit also. this is around .0005 per step - very usable.

    Very happy.

    Now we need to get the index and 100ppl setup in linuxcnc and I will take some videos (threading and such). with this performance initially - I don't know if I will change the drives/steppers until they fail...

    one last thing I would like to try is putting the interface back into step/dir mode and from what I have read - you can put it into full step mode.

    So - Again - this is without modifying the emco electronics in any way. Setting up linuxcnc to output the 'clock' to latch the chip.

    when I get the encoder setup within linuxcnc - I will post the hal/ini files here.

    sam

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    index and 100 pulse per rev hooked up in linuxcnc hal. It threads air! video soon.

    sam



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    45ipm seems repeatable... (back and forth to an indicator..)



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    quick threading video.. (yes - not the correct cutter - and the exit move is a bit shallow.. but shows the spindle sync is right on...)



    sam



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    5/8 11 thread in plastic..



    sam



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    So - as far as I can tell - the original control did 1/2 stepping up to about 19ipm - then full stepping from there to 30ipm. Now the lathe runs fine on full stepping from 0 to 40 (maybe 45)ipm. Half stepping only works well up to 20ipm-ish. (stalls above that)

    But why stop there..

    I started thinking about if linuxcnc could do that.... (without coding anything)

    A couple advantages of halfstepping..
    1 higher resolution 0.000273403/step vs 0.000546806 per step
    2 reduced resonance.. (I have not run into this with full stepping on the lathe)

    Then at normal cutting speeds - < 16ipm you get a higher resolution.

    So why not have 2 stepgens running. One that half steps (type 9) with input scale of 3657.6073152 and the other full stepping (type 6) with a scale of 1828.8036576 (lathe calculation - metric screws)
    Then switch between the two stepgens at a specific feed (I picked 16ipm with a hysteresis of 1ipm)
    All I can say is - HAL IS AWESOME
    I setup a Lut5 with Jeff E's help (thanks jeff!) that switches the printer port between the 2 stepgens.
    A offset componant was used between the 2 stepgens to better align the phasing. (not tweeked 100% yet) but we jogged it around - could not tell that it was switching between the 2 stepgens and it always came back to 0.
    there is a bit more than that.. (ddt for calculating the axis velocity, abs of that, comp w/hystorisis, and stuff I have forgotten already.)


    And here is a halscope capture. Left side is halfstepping - right side is full stepping. The trigger is the velocity threshold.
    Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.-screenshot-jpg

    I think the offset could be tweaked more scientifically to maybe get rid of the blip. But as it is running the 4 phases directly - it didn't seem to effect the motion.

    here is the initial configs.

    Index of /images/emco/linuxcnc_configs/full-half_step_test

    again - jmk and everyone that has worked on hal - Very very awesome work!

    sam



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    After some slight tweaking... (it hasn't lost steps - but I wanted to get the
    alignment as close to perfect as I could.) it ended up being 1/2 step
    (0.000273403). Obvious I guess with the way the patterns line up...

    accelerating (halfstep left side - full step right - xswitch is the velocity
    trigger point)

    Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.-betterstep-jpg

    de-accelerating (full step left - half step right xswitch is the velocity
    trigger point)

    Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.-betterstep_de-accelerating-jpg

    sam



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    linuxcnc doing variable pitch variable diameter threading on the stock emco lathe.. (fusee for a rat trap powered car... - just playing around..)

    Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.-fusee3-jpg

    reference here
    Magic Smoke



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    Hi SAMCO,
    That do you do to "So I hacked together a hal file that used the 'reset' function of the printer port driver to send a clock every base period to latch the 74ls374 chip", i 've got a problem, i do'nt know how to generate a pulse for the clock of the 74.
    Can you explained.
    Sincerly



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    Default Re: Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.

    This is the waveform generated by linuxcnc

    http://electronicsam.com/images/emco/Waveform.svg

    Is this what you were wondering about?



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Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.

Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.

Emco compact 5 pc lathe - linuxcnc setup without circuit board hack.