Attention trouble shooters...need some help

[patiencemetalfab]

I am new to this plasma CNC stuff, and have a second hand table that has been working pretty well with the exception of a glitch in the X axis sometimes. With my background in automotive diagnostics, I have narrowed down when it happens, and what it's doing but need help determining why.

Our plasma machine is an older home built machine using a Precision Plasma kit, C and CNC Gecko g540/steppers drive kit, the C and CNC licenced Mach3 on a dedicated windows XP PC. Cutter is a Hypertherm 45

I believe our issue is X losing steps and the slower the speed rate, the more pronounced it is. In fact, when the speeds get down to 15 ipm or so (1/2 plate cut), the X does not respond at all (a circle winds up a straight line in the Y axis). You can see in the DRO on Mach that it is commanding it to move, but it does nothing. Now, take that exact DXF and generate a tap file for 16 ga sheet, 350 IPM, and it cuts it perfectly-no issue with X what so ever.

While playing with it a little more today, I found another aspect of the problem while cutting 1/4 plate (54 ipm). When the tab pictured below is oriented long way parallel to the Y axis so that the left side vertical cut requires the Y axis to move, but not the X (clockwise direction), there is a delay before X starts moving as it begins the arc at the top. This causes the arc to be asymmetrical, and it also causes the hole to be off center because the lost steps in the delay for X to start moving results in the right side of the tab to be closer to the hole, as well as not line up with the lead in. (first picture)

If I turn the cut file in sheetcam to either 45 degrees where X and Y axis are both active to cut the same side of the tab, or turn it 90 degrees, where its X moving to the right, then Y moving to create the arc, it cuts perfect. (second picture)





Also, if I cut this same tab from 16 ga sheet at 350 ipm, none of these issues exist (or at are so minor they cannot be seen).

To compound the issue, it seems to be somewhat intermittent. If you see the picture below, this was cut from 3/8" plate (24 ipm). It started the cut file fine, then you can the the issues starting at the S and D, then it's good for a couple more letters, until it hits the C and X gives up completely resulting in a straight line cut parallel to the Y axis (its supposed to say "Let's Dance").



So what have we tried to far?
New parallel cable
Newest version of Mach3 updated in the computer
Swap driver pin assignments and motor cables to swap X and Y axis drivers

The problem still exists.

I have not had any luck in getting someone out here to help with this issue, so I have turned to the internet. Please, any thoughts would help greatly.

[tcaudle]

Have you posted on the CandCNC Support Forum? You nave to join but you will get answers on any equipment / designs still owned by CandCNC One thing I see from you cuts is that your lead-ins way to close to the cut line of the next piece . What you describe is opposite of the normal lost step problem: The slower you go the MORE torque you have and the less likely you will lose steps. Since its a G540 driver the power section and drivers are not CandCNC. It almost sounds like the current limit seeings on your G540 are wrong. Its an external resistor that has to be on the correct pins to match the amp rating of your motors.

[patiencemetalfab]

Have you posted on the CandCNC Support Forum? You nave to join but you will get answers on any equipment / designs still owned by CandCNC One thing I see from you cuts is that your lead-ins way to close to the cut line of the next piece . What you describe is opposite of the normal lost step problem: The slower you go the MORE torque you have and the less likely you will lose steps. Since its a G540 driver the power section and drivers are not CandCNC. It almost sounds like the current limit seeings on your G540 are wrong. Its an external resistor that has to be on the correct pins to match the amp rating of your motors.

Thanks for the advice. I will get on the C and CNC forum too.

Everything I have read agrees with you that it is opposite of the common issue. Fater=lost steps, not slower. In this case though, the slower the cut, the less responsive the X axis servo is up to the point of doing nothing around 15 ipm as I stated. C and CNC use the Gecko g540 driver with a lot of their kits. Unfortunately, having never put together a table myself, I am coming into this a step behind trying to learn how it all works. I under stand the external resistor and adjusting the current limit settings a little, but and still reading up on it.

As for the lead ins too close, this was a single piece cut file, we were just running it over and over to determine what was going on while watching the DRO on Mach.

[Bucket8577]

Have you tried using MIDI commands to make movements at different feedrates without the plasma cutter on?

I would start with simple G01 x10 y0 F100. Listen to the motor and measure the travel. Rinse and repeat at different feed rates. See if it moves the same in pos X and neg X.

I would also check all mechanicals such as gears/pulleys set screws, belts, rollers and bearings before delving too far into the electronics.

[tcaudle]

Mach uses constant velocity (CV) tha tgives preference of spped over accuracy. It will let the torch "cut " corners if it will help hold the velocity . The best performance is a combination of feedrate and acceleration . Where problems come up is if your table cannot physically do both high spped and high acceleration (at least 25 to 30 IPS/Sec accel) . Several tables are notorious for not being able to hit those numbers a couple could never hit more than 4 IPS/Sec . Your cuts look like its just not capable of making the instant transition from straight to the arc. It works on the slanted ones beacus e both axis are already moving so the amount of acceleration needed is less . Its easier to go from 80 ipm to 120 IPM than from zero to 120 IPM (example) . You need to determine what your table can do in both feedrate (IPM) and acceleration . Also not that motors can only do what they have the torque at RPM to do. The more torque you have at a given RPM (Stoppers roll off in torque the more RPM you push them to . As you approach more than about 60% of full RPM the torque drops off even more rapidly.
I don't think you have a mechanical or controller problem or you would not get a good cut with it tilted .

G540 has drivers that will do 3.5A at 48 volts and matched to the right motor can give really good results but the wrong linear mechanics and wrong motors can lower performance dramatically. Top cutting speed on most older Torchmate tables was in the 120 IPM max range .