Losing position....

[mthboards]

Hi everyone, so I kind of finished my plasma cutter table, but I have just been using it with a router for wood until I get a plasma cutter.
My problem is I cut out a design in wood like my last name "HEWLETT'S" very simple, but when I go back to 0 it will be off over 1/4 of an inch so there is no way I can go back over it to clean it up.
Im using 1600 ounce longs stepper motors. The xyz are all rack and pinion on spring tension, there is no binding at all. I can put my body weight on all axis and it will move it with no problem.
I don't understand how I'm losing position, even in dry runs.
I was losing position really bad in the z axis until I turned up the speed in the homing and limits in mach 3 to 50% Seems to work but Im just eyeballing it. Maybe when it hits the limits thats where it loses steps for some strange reason if the homing limits speed is set to low IDK.
I'm running it with an old computer with windows xp 64
Any help would be great.

Another problem Im having is I tune the motors to what I need so they don't go to fast or jump to quick, but when I run the program it seems to override it and the machine jumps from cut to cut supper fast. When Im using the cam program in fusion 360 I know the cut feed rate but cant find anything to slow it down from one cut to the next.
Thanks

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[awerby]

You're probably losing steps on the rapids. With some controllers, the speed of rapid (G00) moves is set separately from that of ordinary (G01) moves. Acceleration also is a factor; if your motors seem jerky, it might be set too high. Those motors, while high in torque if they get enough voltage, can also be problematic if they don't.

If you're using these motors: http://www.longs-motor.com/productin...12_86_163.aspx you'll notice that they have 22 mH inductance. That means that to run at optimal speed without overheating, they want about 150v DC supplied to them. How much are they getting? For plasma cutting, which doesn't involve a lot of counter-force, you'd probably be better off with motors with less holding torque and less (a lot less) inductance.

[mthboards]

Thanks those are the motors, I got the kit from longs.
I just turned down the amps on the dip switches to 3.5 what it calls for and they run 80 percent smoother, I even tried lower amps and I think they run even smoother than that but its hard to tell.
The longs kit says 48 volts DC so I should use more volts or 150 volts combined with all three?
I have 4 power supplies 48 volts to each motor.

[mthboards]

I got the big motors because some day I want to build a nice mill that can cut steel and aluminum, I should get smaller motors for this but nothings is geared down and there is a ton of weight in steel to get the y axis moving. I think even gearing these big motors down to get them to spin faster will smooth it out a bunch and then I can just gear it back up to the speed I want uggg lot more work.

[awerby]

Thanks those are the motors, I got the kit from longs.
I just turned down the amps on the dip switches to 3.5 what it calls for and they run 80 percent smoother, I even tried lower amps and I think they run even smoother than that but its hard to tell.

[Well, that should help with the lost steps. A motor that's making odd noises is more likely to fault.]

The longs kit says 48 volts DC so I should use more volts or 150 volts combined with all three?
I have 4 power supplies 48 volts to each motor.

Each motor would require somewhere around 150v to run at full speed. But if your drivers won't support that much voltage, then it wouldn't be a good idea to give them that much, since the drivers will burn up. Saving these motors for your next mill (with high-voltage drivers) and getting different ones to run the plasma cutter would probably be more cost-effective than building a gear box to get more speed out of them, which would sacrifice torque. It would certainly be quicker. When buying the new motors, look for some with 2.5 mH induction or less.