I need to add some limit/home switch's to my machine, what are the best switch's and mounting arrangement to go for so that I get decent accuracy when homing / referencing the machine and also whats the best way to wire them for mach3?
I have read the mach3 instructions and it says that wiring them all in series will work but not so sure as I have not tried it, surely wiring each one indepently to an input would be better but I presume that would need another LPT connector.
If you've got 3 axes, and limit and home switches for each of them, it'll add up to 9 switches in total - so you would need an extra parallel port.
But since you shouldn't ever really hit your limits, you should be able to get away with all the limit switches to one input, and you could put the home to three other inputs.
I can't comment on the Mach3 side of it though, but you can wire them in either series or parallel - series is the traditional way of doing it, as there's less wiring to go wrong (and it also means there's a fail-safe, so if your wiring breaks, it'll end up thinking the limit's been hit).
To me, microswitches are the obvious choice, but I'm toying with the idea of a magnetic switch of some sort, so there's no physical contact (I'm vaguely looking for an optical solution for home switches though). Get ones with rollers on, and make sure there's a gradual slope for them to switch (otherwise if there's a bit of momentum, you could bend the lever).
The advantage with microswitches is that they generally have normally-open and normally-closed connections, which means you can choose between series and parallel connections (normally-closed connections are used for series, normally-open for parallel).
The short answer is no........
Last edited by John S; 12-08-2009 at 09:42 PM.John S -
It's a good news, bad news answer.
First off you only need 3 inputs if you want to keep them separate which is a good idea.
If you are using Roy's Uniport board stuff the e-stop into pin 10 input 1.
don't link them as Roy shows in his manual.
Linking will work but they will only work as limits.
Bad news is Mach sees both switches on one axis as just a limit, it can't differentiate between the two.
this is a problem with Mach that I have been trying to get altered for ages but Brian just don't seem interested. The new mach4 is supposed to be able to see both switches so it may filter down into Mach3 ?
If you hit a limit switch it knows but not which one so it's possible to jog further onto the switch. Knowing which one would allow you to only jog off and not further on.
Good news is it can use one switch as a home [ that's the annoying bit in Mach, it know which switch is the home but not limit plus or minus ????? ]
This is why you need 3 inputs, two switches daisy chained for X,Y and Z input into pins 11,12 and 13, inputs 2,3 and 4 on Roys board.
Then go into config > ports and pins> input signals and tick them all down to Z home.
Set the port number to 1 and all the pin numbers on X to 11, Y to 12 and Z to 13.
that sets limits up.
Then go to Config > homing> and use home neg to set which switch you want to home at. Ticked is one switch, cross is the other.
PS Done with my bits yet ?John S -
Just watched video on mach3 website about limits and homing (http://machsupport.com/videos/), god that blokes got a boring voice, fell to sleep after 5 mins and only just woke up!
But in the dream I had whilst sub-limily listening to him, he did seem to make out that it was possible to have switch's working both as home and limits. But did not go into the wiring in too much detail.
What about using 2 inputs, 1 for the X+ Y+ Z+ and one for X- Y- Z-, would this get round the jogging off problem?
Found some limit switch's, bit big but they will do.
If you keep Z+ and Z- to one input at least you can see what the problem is on the diagnostics page if you have problems.
Link Z-, Y- and Z- to one input will work but if it stops it shows the input has triggered but which one ?
.John S -
The way I have wired my home switches and limits is that if it hits a limit at the home switch end the home switch is made at the same time, so could a bit of script be used that checks to see if a home switch is made then get Mach to drive that axis away from the home/limit then back onto the home? Then any axis thats not seeing a home switch drive it in the oppisite direction?
(hope that makes sense)
Only way for this to work is to use 6 inputs and then get a Brain command to check and do the necessary work.
Problem here is you need another PP
In the normal method of one input for Z+ and Z- one switch can be home as well. It will work as you say hits the switch backs off and touches back onto the switch, that's part of Mach
And that's the most infuriating part, it knows this and can do this but Brian can't be arsed to get it to do the same with limits, preferring instead to piss about with fancy gee gaws that other 'want' and never use whereas this is a basic CNC application and should have been in years ago.
'Rant over 'John S -
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