Shoptask 1720 LinuxCNC

Finally automating my 1998 Lathe/Mill/Drill which was built for CNC

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The plan here is to set up CNC capability on this machine. As purchased it came with mounting points for stepper motors and the belts and pulleys but none of the rest of the CNC hardware. Due to budget and other priorities this never got done. Now is the time.

The general plan is to use the following main components to complete the job:

* LinuxCNC software
* 3 X 4.8N/m (680oz/in) stepper motors (stepperonline)
* 3 X 60V power supplies (stepperonline)
* 3 X DM860I drivers (stepperonline)
* Mesa 7i76E + Mesa 7i85 controller boards
* Raspberry Pi 400
* Position feedback from the existing DRO glass scales - I am hoping to avoid the need for ball screws.
* maintain configuration in github source control, using different branches when switching between mill and lathe mode.

The current state of the project is:

  • Main components built into the PC case and wired up. Case installed beside toolbench on some redwood decking offcuts.
  • Software and motor function verified
  • Pulleys bored out to 16mm, motors installed
  • 13" 1080P monitor acquired and installed with RPi on swivel arm.
  • HAL configuration done and PID values nudged to where I'm happy with them
  • HAL configured for encoder feedback. This seems to work really well.

Next steps:

  • Play with it and make things
  • spindle encoders for RPM feedback

Future stuff:

  • limit switches. I'm actually not sure I need them on the lathe. I'll crash into the chuck, the tailstock or the work before I hit the machine limits, and home is dependent on where the toolpost gets bolted down.
  • scale feedback
  • manual mode (DRO emulation) - I think I need to program "1/2" buttons. That's the only DRO feature I use that's not there. Ok, I used bolt circles once on the steam engine, but we can do that in G-Code/Fusion
  • semi-manual modes (electronic leadscrew, electronic compound) 

  • Pawn Army and Tool Setting

    Alastair Young08/26/2021 at 04:04 0 comments

    This is the pawn from the Fusion360 CAM samples, scaled 55% to fit in the 1" stock that I have. All cut with the 2mm cutoff tool.

    From left to right:

    0: The first attempt I had the cutoff tool programmed as 4mm width. Start again.

    1: Delrin. 2mm stepover and 1200RPM. Looks pretty good.

    1.9: Not shown. Aluminum same settings. Horrible screaming chatter. Then I typed G0X0 instead of G53G0X and crashed the tool into the work....

    2.0 Aluminum. 540RPM. 1mm stepover. Looks pretty good. But fat. Clearly the tool moved when I crashed it. Duh. Thers a clear step in the sphere - I think because the cutoff tool end was angled not square.

    3 Aluminum. Reset the tool library. Also ground the end of the tool square - it previously had a slight angle on the end for clean manual cutoffs. The end ball actually looks spherical. Happy.

    I also worked out my process for tool setting.

    1. Mount the Fowler electronic edge finder in the chuck - gently so as not to squish it.
    2. Offer up the tool to the edge finder radius and jog till the light it at on/off flicker threshold.
    3. Jog Z+ off the end
    4. Jog X-0.1
    5. Jog Z- till we find the flicker.
    6. Touch off 0:0

    I should be able to use this whenever I switch from mill to lathe mode too after clamping down the toolpost. (except for the 4-jaw chuck)

  • Display and Pi mount

    Alastair Young08/26/2021 at 03:44 0 comments

    I liberated part of an arm from a dual monitor mount I had lying around. As I had dismounted the DRO I had to manually machine the mount the old fashioned way.

    Power supply mounting for the Pi and screen is still up in the air (dangling wall-warts) as it turns out that USB-C power connections are complicated and powering from the chunky 5V supply in the control box is not going to fly.

    The backboard is a piece of 16" melamine shelving which give the whole thing enough weight for the support arm adjustment to come into range and the Pi tray is the last part of an old datacenter keyboard tray I've been gradually scavenging from. The monitor is mounted with industrial strength Velcro. 3/4" x 1/8" steel strap and #8/32 screws holds it together.

  • First metal cut on lathe

    Alastair Young08/23/2021 at 16:56 0 comments

    This is just a ball-end modelled in Fusion 360. It took a lot of fiddling and figuring to get the workflow working.

  • First Cut

    Alastair Young08/19/2021 at 15:56 0 comments

    It took a while to work out the encoder feedback and pid settings, but I think I am close. This is a G2 circle in pine with a blunt 3/8" end mill.

    Code not checked in yet.

    Now working on mount for display and RPI

  • Control Box Layout

    Alastair Young08/12/2021 at 00:13 0 comments

    I'm using a large PC case that was the last of it's kind display model purchased at Fry's Electronics just before they shut down. $80?

    It has:

    • a glass side
    • a decent amount of space for wiring below the "floor"
    • a large cutout in the "floor" for a water cooling system
    • a tunnel at the top that is PC PSU cross-section

    After a bit of Tetris and thought, I installed an 3mm aluminum sheet "mezzanine" on 50mm standoffs over the "floor". This gives

    • Enough space between the mezzanine and the glass cover to install the tallest components - the drivers.
    • Enough space between the floor and the mezzanine to install one of the three 6A/60V PSUs in the (slightly adjusted) water-cooling cutout.

    The other two PSUs fit end-end in the PSU tunnel, screwed to the top of the case.

    Around the three drivers there is two strips of DIN rail with the other component (see image).

    Seems to work...

    The 5V supply is 10A as I want to use it to power the Raspberry PI and monitor too.

    Fun fact: the 3mm aluminum sheet has been knocking around since the late 80s, originally a blanking plate for a Sun 3/180 server rack, which I used to make redneck motorcycle panniers out of. (Sun shipped way, way too much hardware for those racks)

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Alastair Young wrote 09/15/2021 at 16:46 point

I'll have to go back and look at what I did. I'll write the details up in a project log. Rough outline: I set it up dual-boot so I could always boot if I screwed up the LinuxCNC image, then built it up from a base minimal RPI image and followed the steps at the linuxcnc site. Oddities I remember off the top of my head: memory - it doesn't like all the RAM so some of that needs to be disabled. Also no driver for the on-board WiFi - I have an external CanaKit dongle. 

  Are you sure? yes | no

Charles Cordiez wrote 09/07/2021 at 14:15 point

I am currently setting up a PI 400 with a 7i96 but linuxcnc is giving me a lot of trouble. What image did you use ? 

  Are you sure? yes | no

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