Help with CNC router

[Frenchie461]

Hi, I'm Brian French, I'm the person responsible for operating the CNC router for 461. Our router has been having an interesting problem where it loses it's zero settings, both the machine zero at the bottom left corner and the program defined zero at the corner of the piece. It only does this intermittently, so we can make parts, but it takes more tries than it should. The zero always shifts to the left, but the direction in the Y and Z are random; it's cut 3/4 inches into the machine bed, but it's also missed the part by nearly an inch above.

Just for reference, the toolpaths are generated by using the sheet metal function of Autodesk Inventor 2011. The files are then converted to a .dwf using the shop drawing feature. From there the .dwg is moved over to the CNC control computer, where V-Carve 6.0 generates the toolpaths that get executed on the CNC via Mach 3 CNC controller.

[Tytus Gerrish]

is it an open loop stepper motor system, or a closed loop encoder system?

[Frenchie461]

Originally Posted by Tytus Gerrish

is it an open loop stepper motor system, or a closed loop encoder system?

open loop, there are no encoders for it to take feedback from

[Tytus Gerrish]

well if its losing zero gradually while cutting it.
is probably the stepper motor losing count. that's caused by tolerance in the drive mechanism and backlash transmitted through the cutting tool. sharp well maintained tools designed for the material you are cutting are a must for such machines. my best suggestion to fix the inaccuracy it accumulates without too much work is to adjust and tighten all bearings, lead screws and nuts. put some clamping pressure on the machines tracks to take out some of the machine play and vibration. and make shure the whole system is well lubricated. also low quality terminations on the power wires and frays in the motor wires can cause intermittent loss of motor power and therefore loss of zero. i am cuttently in the process of converting my stepper motor 3-axis mill to ball screws because of these problems .also if you are having troubble losing count you can try adjusting the amperage to the motors. increasing it will make them hold position better, and you can also try changing between full step 1/4 1/8 and 1/2 steps if your board has that capability. single step has the most electromangets on at the same time for best holding and the fraction steps have higher resolution but less electromagnets activated simultaneously so less holding force

[DonRotolo]

...and if it is losing zero instantly some time during run, then it is likely a bad connection, electrical interference, or (depending on how zero is set) something accidentally resetting the zero. Soyy, I'm not familiar with V-Carve

Unplug and reconnect every connector and terminal, regardless of where.

has the machine been moved recently, or any new machines (or anything electrical/electronic) in the area? Like a welder?

When you run it, are any other machines in the shop in use?

[Frenchie461]

Originally Posted by DonRotolo

...and if it is losing zero instantly some time during run, then it is likely a bad connection, electrical interference, or (depending on how zero is set) something accidentally resetting the zero. Soyy, I'm not familiar with V-Carve

Unplug and reconnect every connector and terminal, regardless of where.

has the machine been moved recently, or any new machines (or anything electrical/electronic) in the area? Like a welder?

When you run it, are any other machines in the shop in use?

I opened the case up and everything was alright, so I doubt that that is the problem. However interference could be a possibility, so I'll check that.

[DonRotolo]

Honest. Unplug and reconnect everything. Unless you find the issue elsewhere, of course.

And if you do, tell us!

[paly]

Our CNC loses it's zero when our welder, which is stationed about 5 feet away from there, turns on. Interference by a welder or any other heavy tools is definitely possible.

[gren737]

Originally Posted by paly

Our CNC loses it's zero when our welder, which is stationed about 5 feet away from there, turns on. Interference by a welder or any other heavy tools is definitely possible.

Everyone here is on the right path, it is interference. Find out what circuit you are plugged into and make sure you don't run anything else on that circuit.
I used to design CNC machines and I had one that kept drifting during a test and randomly losing it's 0. Couldn't figure it out for the life of me. Took it apart several times, changed all the motors, changed out wires....

Some one else was making parts on a machine a few minutes away and kept using a shop vac to clean up the chips...culprit found.
The shop vac was plugged into the same circuit.

Good luck!

[Teched3]

Just a thought, but what kind of material are you cutting, and at what feed rate? A sharp cutter would also help with an open loop system.

[Frenchie461]

We found the problem, when it cuts to screensaver it rezeroed the path. We disabled the screensaver and we're good to go.