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  1. #291
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 4-5 years. Has a total post count of 968. Received thanks 164 times, giving thanks to others 5 times.
    On the whole it's the current being switched that matters rather than the voltage itself. A friend who worked on older systems that used extensive mechanical switching reckoned that increasing switch current to something around 10mA improved contact reliability. Sticking in pull-up/down (depending on how you arrange the switching) resistors of around 2K2 for a 24V system would be about right.

    However, consider the failure modes. For limit switches, we are forcing contacts apart. It is very unlikely that contacts will get welded together to the point that they will not separate although it's possible that contact corrosion will stop them "making". This is at least a safe failure mode. I have no idea what the likely failure modes of proximity switches are, but I suspect that they give more repeatable homing positions. This is all pointing at mechanical limit switches and proximity homing switches - which has already been suggested.

    On my own machine I have gone proximity switch all round, but I'm only using Nema 23 3Nm steppers which will probably stall before doing major damage.

  2. #292
    Yes it needs a little current on a normal switch, i think gold flashed ones will be listed as suitable for logic levels or PLC inputs, sometimes have a very low max current as well, unlike the usual power switches.

    With servos, we have index homing so accuracy in the switch is not needed - it works really well and insanely repeatable. On steppers as you said, damage is unlikely but the torque from a servo is frightening. :)

  3. #293
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 4-5 years. Has a total post count of 963. Received thanks 67 times, giving thanks to others 42 times.
    Argh, broke my long 10mm endmill and did some damage to the Z Axis, not too bad, just cosmetic but cant finish a slight hole enlargement I need to do. Pics to follow.

  4. #294
    Microswictches can be very very accurate

    http://www.baumer.com/us-en/products...ical-switches/

    Accuracy is 70 times thinner than a human hair ;) For me though that level of precision is not needed lol but maybe one day.

    Neale have you ever had a problem with stray chips triggering the sensors? I assume your using inductive not capacitive sensors.

  5. #295
    Quote Originally Posted by Davek0974 View Post
    Yes it needs a little current on a normal switch, i think gold flashed ones will be listed as suitable for logic levels or PLC inputs, sometimes have a very low max current as well, unlike the usual power switches.

    With servos, we have index homing so accuracy in the switch is not needed - it works really well and insanely repeatable. On steppers as you said, damage is unlikely but the torque from a servo is frightening. :)
    I'm wondering if the honeywell microswitches might be what I want (They're gold contacts, 3 each), or rob an old lady for servos lol.

    I'm pretty certain I've sent working servo stepper motors to the scrap yard because I didn't understand what I had at the time lol.

  6. #296
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 4-5 years. Has a total post count of 968. Received thanks 164 times, giving thanks to others 5 times.
    Quote Originally Posted by Desertboy View Post

    Neale have you ever had a problem with stray chips triggering the sensors? I assume your using inductive not capacitive sensors.
    Quick answer is no, but full answer is that virtually all my work to date has been with wood and only a tiny bit of aluminium However, the switches are mounted in fairly well-protected locations. I don't have any compressed air to blow chips around either. Yes, my switches are inductive. My only reservation about them is that the cheap Chinese switches I am using seem to have virtually no on/off hysteresis which makes them slightly less suited to home switch use. It's not a parameter that is ever quoted, though. Still, the IP/M allows me to work around this very easily. I do get very good home position repeatability.
    Last edited by Neale; 10-06-2017 at 08:37 AM.

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  8. #297
    Well designed switch elements in micro-switches (or thumping big panel switches for that matter) are designed to 'wipe' so that as the contacts open they also slide a tiny bit in what is effectively a cleaning action.

    A higher whetting voltage on contacts will overcome small amounts of oxidation but 'normally open' contacts that have been in previous heavy use, but are then left un-operated, will build up a troublesome oxide layer.

    My Traub TNC350G CNC 5 axis lathe had sat unused for several years before it fell into my arms (not literally - it weighs 4.5 tonnes!) and I had no end of trouble with oxidised contacts - got there in the end and it's now back in industry making widgets, but those contact problems took up quite a lot of time eliminating.

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  10. #298
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 4-5 years. Has a total post count of 963. Received thanks 67 times, giving thanks to others 42 times.
    Many thanks to AndrewMawson for the chiller. Yet to to and make it work.

    In terms of man cave, I've seen nothing like it on a 'hobby' level, very inspirational. Many thanks for the tour.

  11. #299
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 4-5 years. Has a total post count of 963. Received thanks 67 times, giving thanks to others 42 times.
    Can anyone help with some Fusion 360 and post processing.

    I use the standard Mach 3 post processor and override G28 in the options.

    However in the code I keep getting this. This command tells my machine to home the Z axis but always hits the top limit. So I manually delete it each time (which is a pain to do).

    Why do I get this and what does it mean / what is the purpose?

    I refer to the G43 line at the bottom. It seems to use the machine coord not the Z that I zero manually.

    7007)
    (T2 D=10. CR=0. - ZMIN=-29.99 - FLAT END MILL)
    G90 G94 G91.1 G40 G49 G17
    G21

    (ADAPTIVE3)
    M5
    M9
    T2 M6
    S4000 M3
    G54
    M8
    G0 X41.253 Y-56.367
    G43 Z15. H2

  12. #300
    But the G43 is a tool length compensation, so perhaps something is set wrong in your Fusion Tool Table ?

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