Hi all,

We are getting our milling machine up and running, and all is going pretty well. I have proximity switches for x,y,z home/limit. When we home the machine, it seems to work fine, however, coordinates are always -0.0147, -0.0147, -0.0147. Is there someway to make these 0,0,0? Is it a function of the machine slightly backing away from the prox's after triggering them? Any help would be appreciated.

-Mark

When the motion control device completes the homing process, Mach4 then assigns a Home Offset value to that location. Note, this does not imply that the machine moves again, rather it just adjusts Mach4's internal understanding of what that location is know as. It is possible that your Mach4 initialization string could contain actual movement commands, but that is not the usual practice.

You will can set the Home Offset value in the chart found at:  Configure >> Control... >>

Look for it in the Homing/SoftLimits tab on that page. The relevant values are in the third column labeled "Home Offset".

Initialization code strings are set on the page for Defaults under Configure >> Control.

Thanks for the reply. So, you're saying I should enter my non-zero values when homed into the Home Offset area to zero it when homed? That makes sense, as I believe these values are 0 at this point. I'll have a look at this on Monday and report back.

-Mark

If you want the DROs to show 0,0,0 after homing you should have zeros in the Home Offset column, and your Initialization Code string box should not have any G0 or G1 commands in it.

If both of these are true and you still have non-zero values, then something that I do not understand is happening.

Normally the function of backing off of the home sensor/switch is done in the motion controller and has no effect on Mach4's readouts.

Oh, there is another possibility. You could have saved Work Offset that is being applied after homing. Read up on G54 usage in Mach4.
 

Backing off the home/limit sensors work fine. Would this have anything to do with soft limits? Do they need to be set up? I'm not using them currently, since I have 6 limit switches, protecting each axis +/-. I'm also using the Hicon Integra 7866, if that helps anything.

As for the Work Offset, we do have a G54 offset, but it is 5-6 inches away from machine home, so I don't think the initialization string is moving it towards that.

Hi

Is it a function of the machine slightly backing away from the prox's after triggering them? Any help would be appreciated.

No, at least that is my understanding.

The homing process is done by the motion controller not Mach. Mach supervises and supplies the settings data, aka the Home/Soft Limits data page.

Each axis is in turn, determined by the Homing Order setting is driven in the Home Dir at the Home Speed% setting. When a limit switch event
on that axis is detected the controller stops the axis at the max deceleration permitted, and then backs up until the home switch de-activates.
At that moment the controller sets the machine coordinate of that axis to 0, or whatever value you have in the Home Offset setting. Those coordinates
are reported to Mach4 and they form the machine coordinate positions displayed by Mach.

That is what Mach expects and to my knowledge all Mach4 ready controllers comply.

Why the Hicon should be reporting 'residual' machine positions is I suspect an issue with the Hicon rather than Mach.

I personally dislike the use of proximity switches for home switches, they work well for limit switches but are less than ideal for home switches.
Good quality snap action micro switches have a definite and repeatable hysteresis that proximity switches lack.

I use these as home switches and achieve 0.02mm repeatability without any special indexing operations.
https://nz.element14.com/honeywell/bzc-2rq18-a2/switch-basic-top-roller-plunger/dp/1525198

Would this have anything to do with soft limits? Do they need to be set up? I'm not using them currently, since I have 6 limit switches, protecting each axis +/-.

No, Soft Limits have nothing to do with Homing. Once the machine is homed (also called referenced) then and only then do Soft Limits become useful.
Note that it is still advisable to use soft limits, set up to 'go off' a few mm 'inside' the physical limit switches. The advantage of that is that the machine
can decelerate on detection of a Soft Limit violation without loss of machine reference. A physical limit switch violation causes an EStop which is a crash
stop which loses machine reference.

Physical limit switches are the absolute last line of defense against machine damage. All previous steps including checking Gcode and Soft Limits should
have detected a violation prior to physical limit switch violation, and you would have to explain to your boss, possibly in writing, why it was that those
techniques failed to safegaurd the machine and you stacked an axis into a limit switch Estop. A second event like that will see you taken off a machine
and put on floor sweeping duty, if you have a job at all.

Craig

Thanks for the reply. We are still finishing up the machine, so we will certainly have soft limits programmed in before we run an actual program. Just working through initial kinks. I'll have to check with Vital systems regarding the Hicon and see if there is something weird going on there.