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?