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Author Topic: Gantry tracking correction  (Read 1124 times)

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Offline c30232

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Gantry tracking correction
« on: July 23, 2017, 01:45:43 PM »
I have a 4x8 table upon which X is off perpendicular by perhaps 1/8 inch at the end of travel or 48 inches.  Does Mach 3 or any of the Mach's have a software compensation to accommodate this issue?   

Offline ger21

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Re: Gantry tracking correction
« Reply #1 on: July 23, 2017, 02:41:28 PM »
Is it only off at one end?
Gerry

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Offline c30232

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Re: Gantry tracking correction
« Reply #2 on: July 23, 2017, 03:10:58 PM »
Not sure I understand the question.  Is it off at zero and then the same at 96 inches?  I dunno.  Off means out of square.  Never made checks away from the center of travel.  

However, since the post we mounted a camera and introduced a variable by hand pushing the gantry to observe the end "twist" or "racking."  What seems to have happened is that the error was reduced substantially.  I suppose that it is under some mechanical tension as it always ends up off in the same direction.  

So the  aforementioned asks another question.  How does one set dual homing for a dual drive gantry running in slave mode?  Perhaps there is a combination of error.  That is, or could be, a manufacturing defect, setup defect, lost steps, and so on.  I am thinking that there is some mechanical tension that could be eliminated by loosing the various attachment points and re-torquing them.  That's a project, but combined with dual homing could take the boat anchor aspect out of this machine.

We made index marks with using the camera and the diagonal at 48x48 was, as best a tape will tell, off by about 1/32.              

Offline ger21

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Re: Gantry tracking correction
« Reply #3 on: July 23, 2017, 04:09:18 PM »
Lets assume that the gantry is out of square the same amount at each end of the machine.
In that case, you should set up the homing to square the gantry when homing.
You need a home switch on each side, one assigned to the master, and one to the slave axis.
In general Config, make sure that "Home Slave with Master" is NOT checked.
When you home hte gantry, each side will home to it's own switch. Adjust the switch location to make the gantry square.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline c30232

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Re: Gantry tracking correction
« Reply #4 on: July 23, 2017, 04:37:24 PM »
Thank you!

I think that will do the trick.  I assume that I will need to abandon the looped sensors that are currently used for homing and assign isolated switches to the Y and A axis.   

We did run the camera around and it appears consistent from 0 through 98 inches.

The next question will be running the VFD from Mach.  I'll start a new post.



       

Offline ger21

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Re: Gantry tracking correction
« Reply #5 on: July 23, 2017, 05:27:16 PM »
Yes, both the Y and A home switches need to use their own input pins. But one or the other can still be in series with the other switches.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline c30232

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Re: Gantry tracking correction
« Reply #6 on: July 23, 2017, 06:00:38 PM »
If I understand correctly, we would then simply need to add a switch for "A" with a home-run to its own circuit and pin.  Yes?   Then Mach will home Y followed immediately by A.  Or A followed immediately by Y.   Any other order would makes a coffee grinder noise     

Offline ger21

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Re: Gantry tracking correction
« Reply #7 on: July 23, 2017, 06:24:21 PM »
Both at the same time, until each hits it's switch.

However.

If you have a chinese USB or Ethernet controller, this may or may not work . The controller handles the homing, rather than Mach3, and many chinese boards do not support all of Mach3's functions.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline c30232

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Re: Gantry tracking correction
« Reply #8 on: July 23, 2017, 06:30:58 PM »
See the link.  We have the combo board in this machine.  So we are Mach to BOB to Chinese drives.

http://www.campbelldesigns.com/Combo-board.php