Someone at my job recently felt the need to reinstall Mach3, trying to fix a very minor problem, and now I wish I'd have put up a much greater resistance to doing so. In any case, what's done is done, and it's my job to fix it.

There are a few terms that I use here, that I'm not sure I'm using correctly, and can't seem to find defined elsewhere. I'm going to define them so hopefully using terms incorrectly wont be a problem, as well as making correction clearer.
--machine home - where all 3 axes are 0 if you turn on machine coordinates
--DRO - coordinate numbers (can be either machine coords or work offset coords?)

I know that in Config>homing/limits, I can modify the distances between machine home and the point it moves to after referencing, but I don't know how to modify what machine home should be in relation to the home switches. This is essentially all I *think* I need to know, but in case it's important, I'll detail the rest of the situation better below.



Normally, when we hit REF ALL HOME, the machine finds its home switches, and proceeds to move .125 in the positive direction on the X and Y axes, and doesn't move the Z axis at all.

Now, however, not only does it move the X and Y more than an inch, it drops the Z by about 6 inches, I think it was!!! It started out at just 2 inches, but has somehow decided it needs to drop it further, and ended up at 6 by the time we gave up trying to fix it last night. Another half an inch, and even without the focusing tube on, it will ram the head into the table! I think my heart still skips a beat every time! I'm very glad we had the sense to remove the focusing tube early on, or it would have either snapped or rammed down HARD into the table.

Not entirely sure on all the specs of our machine, nor of much of the terminology, but I do know we have servos, not steppers. Also, fairly sure the X and Y are on rack and pinions, while the Z is on a screw.

Also, our home switches double as our limit switches. I'm sure this is not a particularly good idea, but it hasn't been much of a problem before, and I don't think it has anything to do with the problem I'm posting about. Figured better safe than sorry though, so I included it.

Normal operation still seems fine, after referencing.

The way Mach homes is it moves an axis to a switch and then when it sees the signal that the switch has been hit it reverses direction until the signal goes away and then stops. The axis does not move any further than that, the Home Off value in Homing and Limits is simply a place for you to tell Mch how far away from true machine zero the switch is. For example if you have a home switch that is at the fully positive end of your axis you can tell Mach that it is a distance away from machine zero so that when you home, instead of DRO reading Zero it will read the value you have set for Home Off.

Now your problem, sounds like either your switches are sticking on or you have a very large  value set for Debounce  Interval on General Config page.
Hood

So by the sounds of it, machine zero is the point that you can easily change on the fly by clicking Zero X (or Y, Z), is that right? I thought those were called work offsets, and machine coordinates were the ones that displayed actual distance from the switches...or maybe I'm thinking of the wrong fields in Config>homing/limits, as that's the main reason I think it seems like that

If the switches were sticking on, wouldn't it never stop trying to move away from them?

I've noticed that as it reaches the limit switches on each axis, it moves a slight distance away from them, that much hasn't changed. Normally though, it only moves from that point by the distances I put in Config>homing/limits...ever since we reinstalled Mach, it's gone by much more than that! the values I have in there now, are .125 for the X and Y, and 2 for the Z, but after it finds all the limit switches, it moves roughly 1 1/8 and 1 3/8 on the X and Y, and about 6 inches on the Z

Machne coords can only be set by Referencing the machine, They can be set to zero or can be set to the value you have in Home Off.

Switches could be sticking and only closing again after the axis has moved a bit away from them. Have a look at the diagnostics page when homing and see if the home switch LED stays on for a while.

The axis will only move until Mach sees the switch close again, the value in the Home Off entry is just so you can tell Mach where the home position is in relation to the machines true zero, as said above you would use that if your home switches were not fully negative on an axis.
It is NOT a way of programming a distance to move off the switch.

Hood

Been meaning to say, thank you for replying so quickly! Took me by surprise the first few times, I'm used to waiting a week or two on other forums, if I even get a reply O_o

It may be the day after tomorrow when I'm able to look at that, but I did look at the debounce interval you mentioned, and the value that's in there now is 1000 (x4 us)

sorry wanted to steal some info in this thread without making a new one.

I want to change my X axis homing direction. I goto homing/soft limits click reverse direction on X axis. That settles my direction problem... but now when it goes to home on X axis it hit limit switch and stays there... it doesn't come off limit switch like it did in other direction. 

How do I fix this so it comes off limit switch after I reversed direction?

You should not chose Reverse if all you are wanting to do is change the homing direction as that will change the axis direction as well under normal use. The option you should change is the Home Negative option as that only changes the homing direction.

When you hit the limit switch does it throw an error?
Does the LED for  X axis turn green when you home to the switch?
Do the machine coords go to zero when you home the X?

Hood

It may be the day after tomorrow when I'm able to look at that, but I did look at the debounce interval you mentioned, and the value that's in there now is 1000 (x4 us)

That should not be the problem, to me it sounds more like switches are sticky and slow to close.
Hood

well, I went to the Diagnostics screen and watched the lights as it referenced, as you said! they flashed on briefly as it found each switch, but went right back off...that's what they should do, right?

Also, it changed how far it goes again.
Saturday, the point it moved to on the X and Y remained the same, and not far from the switches, while the Z occasionally decided to drop further.
Today though, the X and Y both moved a lot more, but the Z decided to be kind to me, and only drop a few inches.

I marked the location it went to, and had it reference again, and it went right back to the same exact spot.

Hood, you referred to true machine home a few times...when I click on the Coordinates button in the upper right, that makes it display the DROs as machine coordinates, right? that is, it uses true machine home as the coordinate origin?

Yes machine coordsd are what you will see when you press that button.
When you reference (home), assuming you have auto zero chosen and have no home off (short for offset) value set, the DROs will read zero.

Can you attach your xml and I will have a look throuh it to see if I can find an issue.
Hood