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### Author Topic: home plus and minus = limit switches  (Read 4494 times)

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#### nobby

• 107
##### home plus and minus = limit switches
« on: February 21, 2014, 01:28:51 PM »
can you have seperate pins for an input of x y and z - or do all three go to one pin?
for the limit thing?

i think i have limit switches on both ends of each axis?
but only 2 wires coming down.

how do I using the motors - simply move the head manually on screen?

or how does the homing thing work, does it look for the switches front and left?

if for example I am only ever loading 2 foot square sheets in, can i set the machine to home at the front and to the left with the limit switches, so it knows it can only travel 2 foot back and 2 foot to the right?

in laymans terms?

i think i understand assigning a pin on the bob to mach 3 home in the pin set up, but do not understand the purpose? - is it to simply shut the machine off from squaling the couplers on the shafts - yes i did just do that

« Last Edit: February 21, 2014, 01:32:59 PM by nobby »

#### Fastest1

• 920
• Houston, TX
##### Re: home plus and minus = limit switches
« Reply #1 on: February 21, 2014, 02:30:18 PM »
There is a bit to learn here. It will help to read as much as you can. Especially the manual. I know it is a hard read especially if most is new. Some things you wont understand for years or ever possibly. I guess it would depend on how involved you will get. Not trying to offend, more like warn. Now on to some of your questions.

can you have seperate pins for an input of x y and z - or do all three go to one pin?
for the limit thing?

i think i have limit switches on both ends of each axis?
but only 2 wires coming down.

This is quite possible. Mach can use a variety of signals for homing or limits.

To check, take a continuity tester. Put it on both leads, it should be beeping continuously, trigger a limit switch. Did it stop beeping? Try triggering both limits. If pressing either limit switch causes an interruption of the beeping, then you have both switches wired in series with both switches being NC or normally closed.
This is the preferred method of using a switch. It will trigger if a wire breaks or a switch fails bringing all to a safe if not inconvenient halt.
Always error to the side of safety. Dont take little machines lightly. They dont understand how soft you are or when to stop ;-)

how do I using the motors - simply move the head manually on screen?

I am not really sure of what you mean here. Do you mean to make the head of the machine move? If that is what you are referring to, then a variety of ways are possible.
MDI (manual data input) a place where a simple GCode is typed and run line by line usually.
Hotkeys, these are keyboard keys assigned to specific functions. The functions can be almost anything from making an axis move a particular direction to triggering a limit switch, EStop or Reset. This can not be done before pins and ports are assigned in Mach (more on that later)
GCode, a language that generates specific movements or motion in machines.

or how does the homing thing work, does it look for the switches front and left?
In the section called homing/limits within Mach's configuration page there are many settings. An example of those settings will be, in which direction is the home switch?(this will be asked as a positive or negative direction), how far is the travel of this axis, how far would like this axis to go before it slows down and stops (again you want to give the machine a time to decelerate)

if for example I am only ever loading 2 foot square sheets in, can i set the machine to home at the front and to the left with the limit switches, so it knows it can only travel 2 foot back and 2 foot to the right?
Yes, home can be wherever you want to set it, limits on the other hand are just that. As far as the machine can travel

in laymans terms?
That was a brief description of what little I understand. Forget laymans terms. Read up, learn the terms of this trade or skill and it will get easier. The words used are specific and are meaningful, it just takes time to understand their use. Same with the math involved to calculate all kinds of things once machining. BTW in no way am I preaching as I know a lot. I was a true beginner only a few years ago, now I know a little more. Probably about as much as the guy sweeping the floor of the shop in his first year ;-)

i think i understand assigning a pin on the bob to mach 3 home in the pin set up, but do not understand the purpose? - is it to simply shut the machine off from squaling the couplers on the shafts - yes i did just do that

Dont know what squaling is. Maybe you meant stalling? If so steppers are forgiving, no big deal at all.
Ports and pin assignments are so the computer can tell the machine what to do. It is referring to each pin of a DB25 or parallel port. Pins communicate both ways (different pins for each direction, limit switch inputs, spindle speed output, relays and a host of other commands).

As I said there is plenty to read. Youtube also has some tutorials. Good Luck and enjoy

« Last Edit: February 21, 2014, 02:33:25 PM by Fastest1 »
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

#### nobby

• 107
##### Re: home plus and minus = limit switches
« Reply #2 on: February 21, 2014, 02:56:59 PM »

aha!!
so it does auto-home, thus you only need limit switches 'wired close constant' left and front - tell the machine 610 square in the doofer.
z axis is a minus number from the limit switch down = thats why I was going the wrong way with it earlier.

cool beans, so connecting it to the break out board, xy and z 3 pairs of wiresand 6 pins.

i meant to type 'squealing' motor couplers squealing on the shafts.

#### Fastest1

• 920
• Houston, TX
##### home plus and minus = limit switches
« Reply #3 on: February 21, 2014, 03:19:04 PM »
You can use 3 pins for your limits or 1. Mach's default is to home 1 axis at a time. It knows which axis is in motion and what direction. It is merely waiting for the trigger to indicate it has arrived at a predetermined location.

Constant, in electrical terms this is "closed".

What is 610 square in the doofer? Sounds like you are hitting someone with your fist.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

#### nobby

• 107
##### Re: home plus and minus = limit switches
« Reply #4 on: February 21, 2014, 03:33:44 PM »
I didn't even realise that you simply used the arrow keys to jog the blasted machine about
HA HA HA HA HA HA HA

been twisting the fecking knobs on the  motors

HA HA HA HA HA HA HA

so the steps per is a simply calculation?

simply times the setting you have on your driver by 400?
2 =800
4=1600
8=3200
16= 6400
32 = 12800
64 = 25600

so him setting it at 2000
his drives are set to 'metric 5

but it doesn't matter anyway? imperial or metric.......
or does it show it in the graph

what is the optimum trapesoidal shap in the tuning you want then?

I though that the motor turned 360 degrees using 200 steps?
have i got something set to half?

do i need to set the steps per to metric ? - i do don't I ?
« Last Edit: February 21, 2014, 03:48:56 PM by nobby »

#### nobby

• 107
##### Re: home plus and minus = limit switches
« Reply #5 on: February 21, 2014, 03:51:26 PM »
You can use 3 pins for your limits or 1. Mach's default is to home 1 axis at a time. It knows which axis is in motion and what direction. It is merely waiting for the trigger to indicate it has arrived at a predetermined location.

Constant, in electrical terms this is "closed".

What is 610 square in the doofer? Sounds like you are hitting someone with your fist.

great so allocate simply the two pins for the 3 axis - 3 wires for each pinwith the switches closed 'I don't know how they are on this machine - I hope they are closed'
2ft =610mm work area bed size.

#### Fastest1

• 920
• Houston, TX
##### home plus and minus = limit switches
« Reply #6 on: February 21, 2014, 05:16:23 PM »
Yes on the pins.
If you work in mm, then use that. Otherwise change your units of measure.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

#### Fastest1

• 920
• Houston, TX
##### Re: home plus and minus = limit switches
« Reply #7 on: February 24, 2014, 09:14:54 AM »
Just saw your micro stepping question among this. Most modern steppers are 200 steps per revolution or 1.8 degree. Lets just assume they are for simplicities sake. There is an issue called resonance that will make steppers stall at certain rpms. For example a Gecko G540 has no option but 10x micro stepping. That means it would take 2000 steps per revolution (not accounting for lead screws and gearing), theoretically it also means your individual step would now be .18 of a degree (again this is theoretical). One of my machines requires 101,000 steps per inch, another only 40,000.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

#### nobby

• 107
##### Re: home plus and minus = limit switches
« Reply #8 on: February 24, 2014, 02:14:29 PM »
is there a 'best all round' for this, or more simply why are there choices on the drives?

#### Fastest1

• 920
• Houston, TX
##### home plus and minus = limit switches
« Reply #9 on: February 24, 2014, 08:58:12 PM »
There probably is but it would involve a lot of mathematics most likely.

It is rpm oriented, optimizing your stepper electronically and mechanically to eliminate loss of steps.

Test it like you have it. If it starts cutting odd or missing steps, hearing stalling on quick directional changes or the like it will require a change. Or you might want better resolution? 1 unit \ 400 = .0025 per step. Those are big steps in the CNC world. If you were at 10x microstepping those steps would be .0005 per step. Quite a bit of difference in resolution.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)