Need Help!- Limit and Home Configuration

[neomagik]

Hi all,

I am about to wire in my limit/home switches but I'm not sure if what I am proposing will work.

My BOB has 4 inputs so I was planning to use one as an E Stop, one for X Y & Z limits wired in series (NC) with the X & Y doubling up as home switches and one normally open input for my Z home switch but using my cutting tool/mill and a piece of aluminium of a known thickness on the table to close the circuit.

Can Mach 3 be configured to work in such a way?

[Fastest1]

I dont think you can use the same switch for a home and a limit. When the home switch was touched, Mach wouldnt know and would stop. Use the 3 inputs (1 for each axis) and 1 input for the E stop. Wire each pair of switches of an axis in series. When homing let it hit the switch and back off, then proceed to where ever your "home" would be (this will be a physical amount of distance or location from the switch set by you thru software). It works very well. If you use the the input pins as I have described you can have 3 axis simultaneous homing.

[neomagik]

Fastest1

What I meant was to have a home switch at the X-- and Y-- end that also acts as a limit switch if needed wired in series with limit switches at the X++, Y++ and Z++ end.

I wanted to keep an input free to home the Z axis as it needs to be configured as a normally open contact if I am to home it using the method I descibed earlier.

I thought Mach could be configured this way??

[M250cnc]

neomagik

All limits and homing can go to one input. When homing the switch is used as a home switch. When running it is used as a limit.

I also suggest you set soft limits to come into play before you hit an actual limit. This has the advantage of Mach not running the code if you are trying to go beyond the physical machine limits.

One input to be used for Auto Tool Zero

I suggest the E STOP be wired in such a way that if you had a computer malfunction that the E STOP would still work IE it turns everything off including the spindle DO NOT RELY ON SOFTWARE FOR THIS FUNCTION

I use the E STOP input as follows as i am using a VFD to control my motor there are times when the VFD will switch off due to excessive braking or acceleration it also has an inbuilt relay so the 5v goes through the relay so should the VFD switch off then i get an automatic E STOP in Mach

Phil

[Fastest1]

Originally Posted by M250cnc neomagik All limits and homing can go to one input. When homing the switch is used as a home switch. When running it is used as a limit. I also suggest you set soft limits to come into play before you hit an actual limit. This has the advantage of Mach not running the code if you are trying to go beyond the physical machine limits. One input to be used for Auto Tool Zero I suggest the E STOP be wired in such a way that if you had a computer malfunction that the E STOP would still work IE it turns everything off including the spindle DO NOT RELY ON SOFTWARE FOR THIS FUNCTION I use the E STOP input as follows as i am using a VFD to control my motor there are times when the VFD will switch off due to excessive braking or acceleration it also has an inbuilt relay so the 5v goes through the relay so should the VFD switch off then i get an automatic E STOP in Mach Phil

Though I agree that you can acheive a software home this way, I dont believe this is actually a home switch. From what I have come to understand, the machine can not pass a limit but can pass a home switch. they can not be configured to do both. All limits can be on 1 pin and all homes can be on another pin. but all cant go to the same pin. Also you can only home 1 axis at a time unless all axis' use their own pin.

[brtech]

Nope, that's not true with Mach. Read the documentation. Many routers have combined limit and home switches.

There is a consequence, which the manual mentions. You can't start a home operation with the router either at the limit/home (tripped) or on the "other side" of the limit/home. It's going to move the tool in the direction of home assuming the tool is presently somewhere in the middle, and it better be able to do that. It can be just off of the home switch, which is where the tool usually is placed when you home.

It is true that if you have more than one home switch on the same pin that it can only move one axis at a time, but at least in the default configuration, it always does that. Mine homes Z, then Y, then X. I have 4 inputs, combined home and limit, because I have a double drive on X. If you have dual drives, you slave them, but they home independently. This squares the gantry to the table if you align them correctly.

[hemsworthlad]

Personally I wouldn't use limit switch's.?
Unless your machine is very small or very fast you'll find that you never get any where near the limit's.! Save your self the hassle of installing and the potential noise issue's related with limit switch's, soft limit's work fine.
The combined home & limit on 1 input is ok but does have issue's if the home switch is far away from the limit and it's a pain remembering to drive it back the right side of the home switch.
Really if you must use limit's and it's done properly thru hardware/relay's etc then you also need a way to over ride the system so you can drive them off the switch's, a mometary button type override something that cant be permently left switched off bypassing the limit's.

DONT RELY ON SOFTWARE TO ESTOP. You want everything to cut dead and shut down in a controlled way when the O-**** button is pressed and the only way to do this properly is thru relay's etc. . . relying on software for e-stop is dangerous.

Cheers
Dean.

[neomagik]

Basically, I want to set the X-- and Y-- limits as 0, 0 (home) and the table top as 0 for Z--

I can then use offsets as needed.

Can I use a separate input for the Z axis homing?

[neomagik]

Surely the easiest way to do an E stop is to plug the router and power supply to the controller to a common switched supply. Then you just hit the switch and cut all power in an emergency.

[brtech]

Yes, you can, but usually you set home for Z at the top.

Among the reasons for that are that if you have a random tool in the spindle, and you drive it to the limit switch, you can ram the tool into the table.

Usually, you home to the top, and then you use a touch off tool to work surface top.
There are some folks who have a surface zero routine with conductive button in the table that zeros the tool to the table. I haven't spent the time to figure out why they do that.

[brtech]

Most controllers have E-Stop inputs. It's good to use them, rather than just cut power.

[M250cnc]

Originally Posted by hemsworthlad Personally I wouldn't use limit switch's.?

Dean i take it from this statement that you yourself do not use limits ?

Originally Posted by hemsworthlad Unless your machine is very small or very fast you'll find that you never get any where near the limit's.! Save your self the hassle of installing and the potential noise issue's related with limit switch's, soft limit's work fine. The combined home & limit on 1 input is ok but does have issue's if the home switch is far away from the limit and it's a pain remembering to drive it back the right side of the home switch.

Lots of mistakes with the above as the home switch and limit are the same, then you will not be far away from it if you hit it. The other thing is if you lose position then soft limits are useless and you will hit something hard. I already mentioned to use softlimits as well, potential noise issues can be overcome but i have never suffered from it.

Originally Posted by hemsworthlad Really if you must use limit's and it's done properly thru hardware/relay's etc then you also need a way to over ride the system so you can drive them off the switch's, a mometary button type override something that cant be permently left switched off bypassing the limit's.

Not true, there is a setting that enables you to drive off a limit switch after you press the reset button (ON SCREEN)

Originally Posted by hemsworthlad DONT RELY ON SOFTWARE TO ESTOP. You want everything to cut dead and shut down in a controlled way when the O-**** button is pressed and the only way to do this properly is thru relay's etc. . . relying on software for e-stop is dangerous.

Yeah i already mentioned that.

neomagik

There are lots of ways of doing things and everybody does it differently, but i agree with brtech in using the top of the material as Z zero when you take a cut this way you are going below the surface which is a Z minus number. Why this way, well say i have a vice on the table with some stock and i want to cut a 3mm deep slot, so i zero to the top surface set Z to -3 easy, now try it your way zeroing from the table surface, lots of potential for error.

Now it's true with combined home and limit switches that you can only home one axis at a time but it can be quite an accurate way to continue from where you left off or if you have to reset after a collision. This is a very fast way to get very close to where you were at and is not possible without homing switches.

I use separate home switches now (Optical) on my lathe and mill and they are accurate to 0.0001"

HTH Phil