proximity switches

[reefy86]

how reliable are they for stopping the machine from clashing against something? whats the safety margin because i have a 17mm gap between the switch and the plate its attached to which is scary close lol.

Thanks

[Muzzer]

You may be better off using the switches "sideways" so that they are not destroyed if the machine doesn't stop or takes too long to slow down.

My machines use microswitches or proximity switches that are triggered by passing targets or ramps. If you can't rely on the system to stop safely when you drive the axis at the hard stop at full rapid speed, it's not much of a safety feature. Rather like standing in front of a car to flag it down, hoping it will do so!

I have had occasions where the limits weren't set up correctly and the axis went on until it jammed on the end stop. Not nice - but at least the limit switches weren't trashed and in my case the ballscrews / bearings etc survived.

[Muzzer]

double post. nobody knows why.

[reefy86]

Sounds like you was lucky there mate

[JAZZCNC]

how reliable are they for stopping the machine from clashing against something? whats the safety margin because i have a 17mm gap between the switch and the plate its attached to which is scary close lol.

Thanks

When they are working they stop the machine within millimeters, it's when they stop working you pucker up.!!. . . But that's the case with any switch or safety circuit, it's only safe while it's working so factor in for when the shit hits the fan and they stop working which in this case, the only safe solution is a strong bump stop and a fault signal which is hard-wired into the E-stop system for when the drives faults.!

[reefy86]

Thanks Dean definitely will look into this.

[cropwell]

How often do people do a check that homes and limits are working before continuing with the work for the day? It only takes a press with a finger or a waft of a screwdriver tip. I know I haven't done this for 18 months (but that is only because the machine is still in bits following a revamp of the cave).

[Neale]

As it happens - every time I use the machine! But only because I use the same switch for home and limit. Initial homing is done at some fraction of machine speed, and experience says that the physical machine limits can take the load if all else fails. Although that has only been tested rarely, I'm glad to say. On the router, max limit switches never get tested (apart from Z, obviously, as that's where it homes) but the mill does not have any. Have to rely on soft limits there.

[JAZZCNC]

As it happens - every time I use the machine! But only because I use the same switch for home and limit. Initial homing is done at some fraction of machine speed, and experience says that the physical machine limits can take the load if all else fails.

Every machine I build is done this way for this reason among others, why have extra limit switches which very rarely get used or tested then the extra wires and wiring which open up noise opportunities.
On the issue of reliability, I have had the same Chinese proximity switches on my machine for over 6yrs, they are still working and accurate as the day I fit them and we use the machine every day.
Likewise, on the machines, we build and sell I fit the same switches so have fit laterally 1000's and I've probably had less than 25 failures in the last 10yrs, most of which just haven't worked out of the packet with very few actually failing when in use.

[reefy86]

Which ones do you use if you don't mind me asking Dean?

[JAZZCNC]

Which ones do you use if you don't mind me asking Dean?

These https://www.jazzcnc.co.uk/product-page/proximity-limit-switch

[reefy86]

These https://www.jazzcnc.co.uk/product-page/proximity-limit-switch

Thank you

[cropwell]

As a matter of curiosity, I had to test out an assumption, that these LJ12A3-4-ZBX (NPN NO 4mm) proximity switches are pretty much bullet proof (unless you run end-on into them).

I connected 3 of them up to a 15v power supply and used an LED and a 4k7 resistor as an indicator. If you common the outputs and trigger one sensor all 3 indicator LEDs on the sensors light and the output goes to GND to indicate a Home run. No smoke, no drama.

Connecting the output to GND lights the indicator goes on, even though the sensor is not triggered, but the unit is not damaged.

Connecting the output to +15v and triggering the sensor - OUCH, I thought I had caused it to fail, but a few minutes later it was back in service.

So maybe these units are idiot proof by design, but it seems difficult to turn them into smoke generators.

Cheers,

Rob

[Neale]

There are cheaper options available than those shown by Jazzcnc. I bought a box of ten for about £12 when I built my router some 5 years ago.

One was clearly the wrong type - the fact that it had only two wires, not three, was a clue. One was faulty from day 1 - as I discovered after wiring it in. Since then, two have failed in service. I think that means that I have now finished the box, so if any more fail, I'll be looking to buy from a reliable source!

[cropwell]

I did the same, but all of mine were good (so far) (LJ12A3-4-ZBX (NPN NO 4mm) proximity switches. After jogging end on into a switch, I bought a replacement from a certain Company in Devon for £17.95 (It still stings!!). I changed the approach to sideways on. I suppose it depends on who makes them as to how reliable they are.

Dean would be obliged to replace any faulty switch he supplied, so his mark up is to cover that. Also he has his reputation to think of, so he will have found a reliable supplier of quality switches (:peaceful:) and I would expect the switches are tested before dispatch...

[reefy86]

Exactly why I would buy from him even if it did cost more if he sells it I know its good to use. Literally got a huge list ready to send him from his store lol.

[JAZZCNC]

Dean would be obliged to replace any faulty switch he supplied, so his mark up is to cover that. Also he has his reputation to think of, so he will have found a reliable supplier of quality switches (:peaceful:) and I would expect the switches are tested before dispatch...

Exactly, Yes you can always buy cheaper if you want to go direct to China and wait. That's all we do, as does just about every other UK supplier, but we have overheads to pay for like any business does so we need a certain amount of profit to survive, that's just business.!
Everything we sell on the website we fit on the machines we build and sell so obviously they have all been well truly tested and it obviously goes without question that if for any reason we had a faulty, anything, it would be replaced ASAP and FOC.

To be honest, that's how the website came about, we had the parts on the shelf that we fit on the machines we build so thought why not offer them for sale. This is why there isn't a massive choice or selection of components. For instance, you've probably noticed we don't offer ball screws or Profiled linear rails even though we have those on the shelf, this is because they are sized and machined to the machines we build and don't want to get into Custom lengths and machining, etc.
As time goes on this might change and if the site builds up then the selection may increase as people enquire about different components and demand warrants the investment.!