Mini guide - Setting up a Metrol poitioning switch



  • For info and as requested, I've done a bit of a write up on how to set up a Metrol positioning switch with the Duet. It's on my blog - link here - https://somei3deas.wordpress.com/2017/03/21/setting-up-a-metrol-positioning-switch/
    HTH
    Ian


  • administrators

    Thanks for the write up Ian. Have you had a chance to measure your repeatability for the sliding hotend design + this switch, now it's bedded in? Interesting to compare to the work done by the piezo probing guys.



  • @T3P3Tony:

    Thanks for the write up Ian. Have you had a chance to measure your repeatability for the sliding hotend design + this switch, now it's bedded in? Interesting to compare to the work done by the piezo probing guys.

    Hi Tony,

    I've got through about two 1 kg rolls of filaments so a quite a few 10s of hours of printing - maybe a couple of hundred hours?. I don't really know how I would go about measuring the repeatability in any sort quantifiable way though. The way it's set up, the switch triggers and at that point to get to Z=0, the nozzle needs to move 0.8 mm (or at least that's what the Duet "thinks" it needs) which is what I have set up in G31 as my trigger distance. All I can say is that the first layer keeps coming out spot on and when I've done the "thin paper" thing, it hasn't changed.

    I think the switch is spot on but I have concerns about the longer term repeatability due to the plastic wearing. Also, the Diamond is a heavy beast and although I've saved a lot of weight and gained a lot of axis travel, the engineer in me doesn't like the fact that the hot end is cantilevered off the side of a single rail. Using the nozzle as probe in this fashion, it isn't pushing straight up under the dovetail joint but at a point about 40mm off to one side. This has a tendency to flex the entire carriage rather than simply sliding the mount upwards. Thus far, it seems to be repeatable but I suspect this will be a cause for concern in the longer term.

    Having said all that, it is more repeatable than the mini IR probe in conjunction with 3Dlac. That's not the fault of the mini IR probe - just my practice of using 3Dlac which screws up the reflectivity of the glass.

    On the whole, I wouldn't say that these positioning switches are any better of any worse than using Piezo discs. It perhaps needs a bit more travel than a Piezo but I could fix it so that it only needed 0.3 mm or less. I guess wiring it up is a lot easier - no need for any sort of conditioning boards and if you can get hold of the non-LED version, it's just like wiring a micro switch.

    I'm considering other mounting options at the moment. I'd like to go back to using two horizontal rails with the hot end slung between, despite the fact that this will cost me in terms of axis travel and weight. Then maybe using some very short linear rails or smooth rods and linear bearings or some such instead of the sliding plastic dovetail. But, I still want to be able to change the hot end assembly quickly and preferably in a tool free manner so there is a lot to think about.

    It's also starting to get a bit manic with my "day job" - Mondays to Fridays building decks, Saturdays doing site visits, Sundays doing quotes and evenings ordering materials but with the occasional "admin day" such as today. Roll on retirement…........

    Ian



  • Ian if you went back to twin rails could you maybe let one side of the carriage float a little and use the flex to trigger the switch you could mount it on a hinge and spring load to print position and just allow it to rise slightly for the trigger may take a bit of messing to find the right Offset but it could work especially as you say there is a lot of weight in the Diamond head

    Doug



  • Hi Doug,

    Yes that's an option. Thinking about it, the nozzle assembly only needs to move a fraction of a mm in Z so linear guides or rods would be overkill. As long as the hot end is constrained from any side to side (X or Y) movement, that's all that really matters.

    I've also been thinking about somehow using magnets instead of springs. That way, when I want top swap hot ends I could just remove the switch, pop one assembly out and pop the other in, without having to remove any retaining springs…... Lots of ideas but not much time to evaluate possibilities at the moment.

    Cheers

    Ian


  • administrators

    Ian thanks for the explanation, certainly sounds effective. I guess I mean in measuring repeatability you would probe a point, move away, move back, probe it again and look at the difference. Doing that a representative number of time (how may is that?) gives a value for repeatability.



  • @T3P3Tony:

    Ian thanks for the explanation, certainly sounds effective. I guess I mean in measuring repeatability you would probe a point, move away, move back, probe it again and look at the difference. Doing that a representative number of time (how may is that?) gives a value for repeatability.

    Ahh OK. I'm assuming that if I did something like home normally (G30 using values from G31) and then repeatedly move away and back and do G30 with S-1 and note the Z height that would do it?


  • administrators

    yep should do it!



  • Might be a couple of weeks before I can get that done - could be a challenge trying to do it using Pronteface 🙂


  • administrators

    yes ofc!


  • administrators

    You could use G29 to probe the bed over a very small area using a very small grid spacing, then look at the height map. I think you can have a grid spacing as low as 0.1mm.



  • Good tip. Thanks David.


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