zero machine co-ordinates?

[peteeng]

Hi All - Is there a trick to zeroing machine co-ords? Mine won't on the X and Y co-ords z does. Peter

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[joeavaerage]

Hi,
I can't speak for UCCNC but with Mach (3 or 4) you cannot set the machine coordinates at will, you can ONLY set them by Homing or Referencing the machine. Within those procedures there is the means (workarounds)
that allow you set set them to some arbitrary value....but only as a part of the procedure. If the software allows 'Home in Place' then there maybe a trick you can use.....I have used it but now that I have decent Home switches
there is never any need for that sort of skullduggery.

Craig

[peteeng]

Hi Craig - It may need the homing switches to "zero" but the manual says it can be zeroed using the buttons. So, someone in the UCCNC world may be able to clarify that. I don't particularly need to zero the machine co-ords at the moment but I'm looking into the homing switch procedure and associated issues at present. Peter

Hi Craig - My machine co-ords are way away from the machine (like 7m away) that is the principle reason to correct this at the moment. I did it by taking UCCNC offline then drive the machine back to a reasonable spot on the "machine" so machine co-ords are about 0.0,0 then going back on line and zeroing the work co-ords. Now at least the machine co-ords are more correct. Now I'll start looking at the homing issue... So I think I have answered my own question...Peter

But the new black screen version of UCCNC does not seem to have an off-line button/mode? I did this with the old screen... Opps found it - in plain sight!! All good. Peter

[joeavaerage]

Hi Peter,
I'm guessing that like Mach IF you have no Home switches and you then Home (or Reference depending on terminology) that the machine will 'Home in Place'.
That is to say it will zero the machine coords WITHOUT moving anywhere. If you do have Home switches then it will move to those switches and zero the machine
coords once there.

If UCCNC behaves similarly you can use that Home in Place feature to trick the machine into setting arbitrary machine coords, but really just get and install Home switches.

I always had a few crashes with my mini-mill (preceeds my current machine) until I got decent Home switches then I managed only three crashes in seven years, all operator error.
Adding Home switches was the single best addition I ever did to that little machine.

Craig

[peteeng]

Hi Craig - Homing switches are on the list for this build. Generally, if the part is going to be close to the envelope, I do a boundary move check before I start., I rarely have envelope "crashes" as I do small jobs on a big machine. I do clip clamps occasionally but then that would happen with homes anyway. Putting the brain in gear always helps... I have not come across a home in place feature in the UCCNC manual but it was easy to take it offline and bring the machine in from the yard to the shed....Peter

[mactec54]

Hi Craig - It may need the homing switches to "zero" but the manual says it can be zeroed using the buttons. So, someone in the UCCNC world may be able to clarify that. I don't particularly need to zero the machine co-ords at the moment but I'm looking into the homing switch procedure and associated issues at present. Peter

Hi Craig - My machine co-ords are way away from the machine (like 7m away) that is the principle reason to correct this at the moment. I did it by taking UCCNC offline then drive the machine back to a reasonable spot on the "machine" so machine co-ords are about 0.0,0 then going back on line and zeroing the work co-ords. Now at least the machine co-ords are more correct. Now I'll start looking at the homing issue... So I think I have answered my own question...Peter

But the new black screen version of UCCNC does not seem to have an off-line button/mode? I did this with the old screen... Opps found it - in plain sight!! All good. Peter

Check in the Work Offset Folder an see what G54 is set at for X and Y Axis this will need to be Zero for both if that is, the edge of your work, this would need to change to 0.0 as you have no Homing

If you move the machine to somewhere and call that home, then setup your Job X0 Y0 then the G54 will have a distance number set in G54 for X and for Y from the point you called Home

For Home proximity switches you only need (1) for each axis so can be less than $20 to add a Home switch this will give you soft limits as well, and will solve most of your work setup problems

[joeavaerage]

Hi,

For Home proximity switches you only need (1) for each axis so can be less than $20 to add a Home switch this will give you soft limits as well, and will solve most of your work setup problems

I prefer roller plunger snap action microswitches....but Matec is right, fit three Home switches so now you have SoftLimits and life just becomes so SO much easier.

Craig

[peteeng]

Hi Mactec - Understood about G54. I also prefer roller micros, used many on bespoke machinery over the years but will micros also give me soft limits? Peter

[joeavaerage]

Hi,
what I like about microswitches is that they have a reasonably well defined hysteresis.

With Mach at least, and presumably UCCNC, when an axis is homing it travels towards its home switch, until the switch activates, then decelerates to a stop and then backs up until the switch de-activates.
At that point it zeros the machine coordinates. Thus it is not the position of switch activation but rather the position of switch activation LESS the hysteresis of the switch.

Proximity switches do not have a particularly well defined hysteresis and I found that I could get as much as a 0.1mm variation depending on that hysteresis. With Omron roller plunger microswitches
the hysteresis is quite well defined and even specified. Using such switches I can get 0.02mm repeatability....and that's without index homing, which of course could be an order of magnitude better again,
but at 0.02mm I find it unnecessary.

Craig

[peteeng]

Hi Craig - Yes I have used proxis in various applications and have had to deal with hysteresis and statistical positioning. Good brands publish all of the sensitivity curves and stats info. But I like mechanical in this application. Peter

[mactec54]

Hi Mactec - Understood about G54. I also prefer roller micros, used many on bespoke machinery over the years but will micros also give me soft limits? Peter

Like I said only (1) switch is required for each axis and this will give you soft limits that you setup as your work / machine envelope, the cheap Micro switches are too noisy they cause electrical noise that will give you problems Proximity switches are the best cheap, and they give you a clean accurate signal

[mactec54]

Hi,
what I like about microswitches is that they have a reasonably well defined hysteresis.

With Mach at least, and presumably UCCNC, when an axis is homing it travels towards its home switch, until the switch activates, then decelerates to a stop and then backs up until the switch de-activates.
At that point it zeros the machine coordinates. Thus it is not the position of switch activation but rather the position of switch activation LESS the hysteresis of the switch.

Proximity switches do not have a particularly well defined hysteresis and I found that I could get as much as a 0.1mm variation depending on that hysteresis. With Omron roller plunger microswitches
the hysteresis is quite well defined and even specified. Using such switches I can get 0.02mm repeatability....and that's without index homing, which of course could be an order of magnitude better again,
but at 0.02mm I find it unnecessary.

Craig

If you are not using your servo motor index or Z pulse you are not serious about any kind of repeatability, so anything is good enough as it would make zero difference as to what repeatability you have