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  1. #11
    They look exactly like the ones I purchased about 10 years ago for my machine. I only had problems with one of three that I got and it was my fault for not designing a proper mount and interface to the moving parts. I sealed the electrical connections and use flood coolant with no problems.
    Art

    AKA Country Bubba
    (Older than Dirt)

  2. #12
    I got a heap of these recently:

    SN04-N DC 10-30V NPN NO 3-wire 4mm Inductive Proximity Sensor Switch Detector | eBay

    There's good reviews about them on CNCzone. I'll post when I've tested them, but that may be some time.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  3. #13
    Big chunky limit switches do not not necessarily give you good positioning, they are more concerned with reliability than a fine switching tolerance.

    The best positioning switch is probably an opto slot with a built in Schmitt trigger. But if the switching point chances to align with a completed step you can still go +- one step.

    Perfection is probably a side paddle arm on the screw that winds into an opto slot. That would allow you to adjust the switching point to mid step.
    I'm going to give it a go, but that's only because I am totally anal

  4. #14
    Quote Originally Posted by Robin Hewitt View Post
    Perfection is probably a side paddle arm on the screw that winds into an opto slot. That would allow you to adjust the switching point to mid step.
    Perfect perfection would be to put the opto slot on the stepper motor or ballscrew - the rear shaft on the motor would be pretty convinient. If you put the sensor/slot at say 30mm radius then one step is amplified to just under 1mm movement instead of 0.025mm (or whatever). Trivial to detect 1mm, but you would need two sensors. One standard switch on the axis as normal to get it close, then look for the signal from the 'rotary' sensor to get it spot on.
    That's what I'm doing on the next machine anyway - inductive to get it close, then optical on 30mm radius disc for perfection.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #15
    As I've no need to machine metals I'm thinking of Hall Effect devices. I'm concerned mechanical switches or slotted opto devices might be affected by dust. No firm decision made yet.
    Last edited by boldford; 30-08-2012 at 10:15 AM.

  6. Quote Originally Posted by boldford View Post
    As I've no need to machine metals I'm thinking of Hall Effect devices. I'm concerned mechanical switches or slotted opto devices might be affected by dust. No firm decision made yet.
    No need to use hall effect... simple magnetic reed switches work well although need debouncing just as a microswitch would. A hall effect device might just be too sensitive. With modern high-strength mini-magnets I found for one application I needed the hall effect device over 5cm away from the magnet before it stopped recognising it. Also the reed switches in burglar alarm sensors are ideal and not expensive 3.99 from maplin or 1.45 on ebay

  7. #17
    I think the inductive switches I linked to in post 12 sound a lot easier than using reed switches, unless there's some advantage to using reed switches over them? SN04-N are the same ones DMM-tech use with their servo systems.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #18
    With so many ideas to choose from it will probably come down to cost v repeatability.

    Hummm. . . . . So many design decisions. . . . . .

  9. #19
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Has been a member for 9-10 years. Has a total post count of 1,838. Received thanks 192 times, giving thanks to others 5 times.
    I'd vote for Robin's suggestion of opto slot sensors.
    I used Buy Photoelectric Sensors U-shaped thru-beam sensor,PMR44P Sunx PMR44P online from RS for next day delivery. for the X-axis on my lathe, and repeatability is good. They come in various mounting styles, so you can normally find one that will fit with minimal effort.


    From experience, inductive sensors generally have quite a wide tolerance, both in range and switching time. I've tried using a few different ones to control hydraulics in the past, and I could never get them consistently detecting motion. Good old fashioned mechanical heavy duty limit switches worked far better, even though the occasional one would get wiped out when things moved.

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