[adam_m]

I'm struggling a bit with homing and limits.

I've got my table measurements in the Min Max and Slow zone but when I look at the Machine co-ordinates they don't match what I think they should be.

For instance with all the axes at Home, when I look at the Machine coordinates they aren't zero? (see attached)

Now when I jog the axes they all plow through the Limit switches as if they weren't there and manually they don't trip either??

Thoughts?

Adam,

[ger21]

Whatever you put in the "Home Offset" column is the location of your Home switches in Machine Coordinates, which is what you're seeing.

Can you post your .xml file, or at least post a pic of Ports and Pins, Input pins?

[adam_m]

OK, so that makes some sense I didn't think to change the home offset..

Ports and Pins attached..

Thanks.

Adam,

[ger21]

So, you're saying that you can home the machine to the switch, but when it's away from the switch and you activate the switch, it doesn't give you a limit switch error?

If you go to the diagnostic page and activate the switch, do the limit LEDs light up?

[adam_m]

OK I think I know why things seem odd its because I have X, Y and A home/limit switches wired in a series so only one axis is going to home.

With that said I guess X will be the only axis that homes, makes sense now. Am I thinking about that correctly?

So, when setting the Machine coordinates, I should essentially travel to the point of where I want the Machine coordinate to be then click the "Machine Coords" button and zero X, correct? Once those are set its basically forgotten about to some extent, uncheck the box and use "Soft Limits"?

Adam,

[ger21]

OK I think I know why things seem odd its because I have X, Y and A home/limit switches wired in a series so only one axis is going to home.

With that said I guess X will be the only axis that homes, makes sense now. Am I thinking about that correctly?

No. The default homing in Mach3 is one axis at a time, so even if they all share the same pin, they all should home.

So, when setting the Machine coordinates, I should essentially travel to the point of where I want the Machine coordinate to be then click the "Machine Coords" button and zero X, correct?

Nope.
You can't zero Machine Coordinates. The only way to reset them is to home the machine (Ref All).

Whether or not you use Softlimits is up to you. But until you home the machine, you can't reliably use softlimits, as they are referenced from Machine Coordinates.

[ger21]

You might want to watch the Homing, Limits and Offsets" video tutorial at Newfangled Solutions » CNC Software Home of Mach3

[adam_m]

Then I misunderstood the wiring of limits and homes in series.. I was under the impression that would cause me to not be able to home the other 2 axis?

I'll definitely be watching the video's again.. I'll post back if I'm still struggling after that.

Thanks,

[rwskinner]

If all your switches are Normally closed, then you can put them all in series and when any switch opens, the entire circuit opens and triggers the Homing for the active axis. If your switches are all Normally Open, then they must be wired in parallel for it to work, so any closed switch will activate the circuit.

Can you verify tripping a single switch causes your Limit LED on the DIAGs page to come on? If it takes all switches to be active at once for the LED to come on then you have the wrong wiring scheme.

Richard

[adam_m]

Yes, so all my switches are normally closed.

X is wired alone on Pin1 of the G540.
Y, A and Z are wired in series to Pin2 of the G540.

So, as I read that then I should be able to home 2 axes since they are on separate pins on the G540?

[Spk64]

Assuming A is the slave axis. Most recommend putting that on a separate input.
Then put X,Y and Z in series for a second input.

All the axis home one at a time so actually all 4 axis can be homed.

It will work as you stated. More semantics than anything.





Steve

[rwskinner]

This is pretty much the way I understand it as well. All three axis can be tied together X, Y , Z and then your slave A must be itself. I'm about to do mine this weekend but everything I researched showed that exact layout.

[adam_m]

I'm sorry, yes A is the slave axis and is used for squaring the gantry.

So, on my machine X and A are on separate inputs...

Adam,

[adam_m]

So after watching the Video again if I manually move the 3 axes to where I want them Homed and hit the "REF ALL HOME" button this will set the Machine Coordinates and as long as I don't "REF ALL HOME" again and my machine doesn't loose steps that will hold true, is that correct?

Since I only am using 2 of the 4 inputs in the G540 for X and A what happens to Y and Z after the "REF ALL HOME", will they use what I set them for even though they don't individually home?

Adam,

[Spk64]

If you do not have an axis setup for homing it will just be reset to zero as you found out on the other axis.

I do this on my z axis. I move it to where I want home to be and the do ref all which then homes Y, then homes the gantry using X and A switches


Steve

[ger21]

If you have a home switch enabled, then Ref All Home will move that axis to the switch until the switch is activated, then reverse until it's deactivated. This point will be set to Machine Zero, or the value in the Home Offset column.
If there is no Home switch enabled, then Machine Zero (or Home Offset) is set at the current position of that axis.

The real purpose of Homing the machine is to have a repeatable position, which is required to use Softlimits. It's also extremely useful if you want to use a fixture over multiple sessions, or machine a part that may take multiple operations over several days.

If you're only using the homing to square the gantry, you might want to consider modifying the Homing script to just home the gantry axis only, and ignore the others.

[adam_m]

I just checked the ports and pins and I see that I currently don't have Y and Z selected to Home, I think that explains why they are not homing?

If I understand, if I were to setup the ports and pins to Home all axes will it home each axes individually or try to home them all at once? If it tries to home them all at once it would be a problem since they share an input on the G540...

The image on the left is the current machine setup..

[Spk64]

They only home one at a time normally.


Steve

[adam_m]

Making the changes in the ports and pins seems to have done the trick.. thanks for all the help guy's.

Adam,