Some Basic Questions on Home/Limit Switches

[vacextar]

I'm working away at my 4x8 plasma table using Precision Plasma gantry kit and CandCnc Bladerunner controls with Mach. Do I need Home/overtravel limit switches at each end of both my Y and X axis? Does Mach need these to home the machine? Can I run without home/limit switches in place?

On a related note, since I have a Master/slave motor set-up running both ends of my X axis, how do you keep the gantry square? It seems to me that as long as the machine is powered up, and you have it adjusted for square, it should remain there, but as soon as you cut power and the master/slave motors are free to move, if it goes out of square, and then you turn the power back on, do you have to go thru and re-adjust your square every time? I've got to be missing something basic here in my thinking. Is there a way to set up home limit switches on each side of the gantry so it will automatically "home" and square itself?

[plain ol Bill]

You don't really need "limit" switches with steppers. Weld or bolt a mechanical stop to the ends of your table so the gantry cannot take a flying leap off the table if you manage to mess up. Using steppers that way and stalling will not hurt the motors.
Home switches are a means so the table can find known locations and use them as 0,0. Unless your gantry is in a bind when it is squared (and it should not be in a bind) it will not move out of square when powered up or down. Really the only time I even use my home switches is if I manage to run over something I have left in the way of the gantry. Like ground leads, tools, gloves etc. Then I "home" the gantry and it squares itself up and you are off and running again.

Hope this helps.

[vacextar]

Yes, that does help! I guess my issue with squareness is that without the stepper motors installed, I have the gantry/rollers adjusted so it is square, and that's the way it wants to be....but with the motors installed and powered off, there is enough resistance-to-move in the motor that if you bump one side of the gantry, the side you bump will move, but the other side does not want to......and the motor on the side you bumped will hold itself to it's new position.....out-of-square.

So I'm wondering if the following is a good "solution". Adjust my hard-stops at the 0,0 home position so that if the gantry is held up tight to the hard stops, and it is square in that position, I can power the motors up with it held there to assure each time I power it up that I'm square?

Thanks for the help! I'm ready to get this thing running!

[ger21]

You can just jog it into the hard stops to square it up, then just jog back off of them.

[Dustin407]

I dont have any limit or home switches on my table. Except for the z axis for the floating head, it is hooked up to my table i/o card on the z home. I have never had any problems, just very careful in the setup process and double check twice. Sometimes I do a dryrun over the material before I crank up the plasma machine... This makes me feel comfortable and safe. Once I do that i pretty much leave the machine by itself and work on something in the shop... I will eventually add limit switches but probably no home switches, I just feel its alot of work for nothing really. As for squareness, I squared up the gantry and got it perfectly by hand. When the motors were off I manually turned the gear reduction pulleys until the gantry was perfect. I never touched the machine for at least a year. Checked it one day for square and it was still perfect, I have two steppers for the y axis. The only time my machine was out of square is when I accidently hit/nipped it with my forklift and slide the machine about a foot..

[vacextar]

Thanks guys! That helps me a ton!