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Limit switch locations on Outback CNC (lead screw and linear bearings)

Discussion in 'CNC Mills/Routers' started by Heath Raftery, Aug 17, 2022.

  1. Heath Raftery

    Heath Raftery New
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    I'm putting together a 1.0x1.5m Outback CNC from MakerStore and the specific instructions on the mechanical build went well. But the general instructions for the limit switch installation are hard to adapt without know what works in practice.

    Given there's a dearth of info on the Outback, perhaps some advice on lead screw / linear bearing CNCs is applicable, since the reach/mounting challenges might be similar.

    Here's my first attempt.

    limit switch locations.jpg

    Ignore the fact that I went Front - Right - Bottom instead of the recommended Front - Left - Bottom. I'm hoping that makes my wiring easier but we'll see.

    The major issue is that on all three axes the gap from the V-slot to the gantry is too big for the switch to span. So the recommended locations won't work at all. The easiest workaround I found in each case was to hang the switch over the edge and angle it so it is contacted by the bearing block instead.

    This **seems** like it will work, but until I wire everything up I won't know. So I'm hoping from your experience you might be able to make some suggestions that will save me having to re-do this part too many times!
     
    #1 Heath Raftery, Aug 17, 2022
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Best to take that up with the Vendor
     
    #2 Peter Van Der Walt, Aug 18, 2022
  3. David the swarfer

    David the swarfer OpenBuilds Team
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    put the switches so that when the tool is 'back right up' the switches get activated.
    This is by far the easiest way to setup the controller since it is the default position for Machine Coordinate home.

    as for mounting them, cut some random bit of wood as a spacer and cable tie them in place, then once the machine is working use the machine to make 'nice' parts for the mountings.
    I would mount the switch out of the way then mount an adjustable bumper on the moving part.
     
    #3 David the swarfer, Aug 18, 2022
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  4. Heath Raftery

    Heath Raftery New
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    Thanks @Peter Van Der Walt . I've done that too so hopefully they can supple.ment their documentation. I thought this might have been a general issue with linear bearing machines or there might be general strategies for mounting these things. I don't have any experience to be able to apply judgement, so I appreciate knowing this is something I should expect from the vendor.

    Excuse the mid-word dot... eventually figured out that word was triggering the spam filter :-/

    That makes a lot of sense thanks @David the swarfer ! These are all great ideas I had in mind, but with no ability to weigh it up. Thanks for the guidance.
     
    #4 Heath Raftery, Aug 18, 2022
  5. Rob Taylor

    Rob Taylor Master
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    Depending on your controller, limit switch placement is kind of irrelevant, as long as actuation is consistent. Ideally on a gantry type machine it would be back-right-up, but that's not fixed in stone; it's why we have seek direction values, time out values, pull-off values, and everything else. You could, in theory, hit a switch at one side of the gantry, set the pull-off to be the entire length of the gantry, and then set the final location as G53 machine zero. These machines are just big dumb robots; there may be best practices and traditions, but there's not always a "correct" way of doing things. Do whatever works for you.

    Also I prefer to mount switches parallel with the axis and use a printed wedge cam that gradually depresses the switch rather than firing the axis directly into the switch.
     
    #5 Rob Taylor, Aug 19, 2022
  6. Heath Raftery

    Heath Raftery New
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    Oh that's great to hear @Rob Taylor . I had an inkling that was the case but didn't want to upset the CNC gods with my first pledge. Makes a lot of sense, thank you.
     
    #6 Heath Raftery, Aug 19, 2022
  7. David the swarfer

    David the swarfer OpenBuilds Team
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    But, not following established practises does pose a safety hazard and a high frustration level warning (-:
    If this is your first machine, PLEASE follow the standards.
     
    #7 David the swarfer, Aug 19, 2022
  8. Rob Taylor

    Rob Taylor Master
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    Depends how much self-directed learning you do ahead of time. I'm generally of the mindset that you should understand the machines *before* pressing the order button, which doesn't seem to be widely shared. But CNC is a marathon, not a sprint; "wasting" a few months on learning can be a huge advantage in avoiding lost time and frustration later.
     
    #8 Rob Taylor, Aug 19, 2022
    Giarc and David the swarfer like this.

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