Servo Alignment and THC issues

[cccweld]

We are needing to have our servos aligned since the table is not cutting straight. Do we need an IT for this or what would you recommend?

Also, we use MACH 3 and the THC does not work correctly. We never know when we need to use or not! We adjust it on each project but we always have issues! Any ideas?

We start out with Inkscape or ViaCad then use SheetCam. We have an Apache Industries water table using the MACH 3 program.

We appreciate any assistance we can get!

Thank you!

[weldguy]

Not familiar with your setup but it must have limit switches. Is there a button for each axis that sends the gantry to the limits switches?

[cccweld]

I'm not sure.

[acourtjester]

First off how many servos do you have (3 or 4), you can use Mach 3 to check the calibrations for the axis movement. As to the square you can use the 3-4-5 routine to check the square of the gantry/axis movements. If you know how to get into Mach 3 software you will not need IT. Have you been using the table or did you just get it (used).

[weldguy]

I'm not sure.

Are sure they are servo motors and not stepper motors?

[cccweld]

Yes they are servos

[adbuch]

First off how many servos do you have (3 or 4), you can use Mach 3 to check the calibrations for the axis movement. As to the square you can use the 3-4-5 routine to check the square of the gantry/axis movements. If you know how to get into Mach 3 software you will not need IT. Have you been using the table or did you just get it (used).

Tom offers some good advise here. Once we know more about your system, we may be able to give you some better ideas. When you home your gantry - does it hit the stops at each end of the gantry at the same time? Or is the gantry out of square with the table?

David

[cccweld]

The gantry is out of square with the table. Each time we use the table we need to home the gantry to hit the stop then we can use it for a time and then it gets out of whack just enough to cause cutting issues. So yes I would say the gantry is out of square with the table and doesn't seem to stay like it should. We have had this table since 2015 and have had various issues occur. Between the gantry/servos not square and the THC it has been a challenging adventure indeed.

[adbuch]

If your gantry is driven by two stepper motors with one at each end of the gantry, then you will need to set the turns ratio so that it is equal for each motor. I'm not in front of my shop computer right now - but one of my AvidCNC tables runs from Mach 3 and there is a spot in Mach 3 to do this calibration. If your turns ratios are set to the same value, then I would take a look at your mechanical drive components - gears, pulleys, belts, springs, etc. to make sure they are in good condition and that the pulleys are tight on the motor shafts. A slipping pulley could cause your problem.

David

[adbuch]

https://www.youtube.com/watch?v=xLUViu65qXg

[adbuch]

https://www.youtube.com/watch?v=2HbeyggcwU4

[cccweld]

Great! Thank you. I am not currently at the shop but will check this out when I get a chance. At least I may be headed in the right direction!??

[acourtjester]

There are some things you will need to check and correct. First is the drive assembly, there can be no slipping of drive components. Many problems like this have ended up being a loose setscrew (grub screw) on a gear or pulley. This cause the actual distance the axis travels. With power on (locking of the servos) try pushing each side of the gantry in both directions, it should not move. If it does find the reason and correct it. Sometimes if this has been happening for a while there will be a groove in the the motor or shaft that will need to be fixed. Next the steps per for each motor will need to be checked to be sure they are the same in the software, axis servo and slaved servo. There also could be a difference in the limit switch position so that the rail is not exactly square. Then measure each side of the gantry travel to see if both sides move the same distance. Now for the calibration of the servo steps per, mark the rail at a start point and tell it to move maybe 10 inches (MM if you use that).
and them measure how far it actually moved. Here is a formula I have used with many different software packages. find the step per value and multiply that by the amount you told is to move (10 ) then divide that by how far it actually moved (say 9.5). This is the new value you copy to the steps per value in the software location. This is where the steps per value is located in Mach 3 for each axis. Remember to save it after you change the value. I do this about 3 time each time moving a longer distance, that makes the error smaller each time.

steps per.JPG

[cccweld]

Thank you for the helpful tips! Will put this info to good use and hopefully tackle this beast.