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Router Accuracy Problem1/8
I've got a very persistent problem with our CNC router, I won't name the manufacturer because they have worked diligently to fix the issue. This is an entry-level machine that sells for approximately $25,000. It uses simple stepper motors (no encoders or servos) and a WinCNC controller.
The machine has certain areas of the X-axis that are up to .03" out of alignment, meaning that what should be X4.000" ends up positioning at X3.970", approximately. This error occurs most noticeably in a certain range in the travel, between about X0.000" and X5.000". The error is consistent, it will come back to the same position every time. Everywhere else along the travel is within an acceptable tolerance. I flipped the rack gear end-to-end and the problem did not move.
The manufacturer replaced the rack gear, with no results. The new and old racks mesh perfectly together, so it would appear there is not a defect in the gear pitch.
The manufacturer also has rebuilt the x-axis gearbox (stepper, belt drive and pinion gear). It is currently in transit, and we should have it by next week. If that doesn't fix the issue, everybody is out of solutions.
We need to get this machine back on line, there is a ton of work piled up behind it. Thanks for any ideas.
i dont know yours controler
My cnc Uses Mach3 PC controller. It has an option for screw mapping. Basically you can say at this part of the rack, accuracy if off by X amount, and it will compensate for it whenever it travels to that point on the rack.
So if you travel from one end of the table to the other, its accurate, but only in the middle its off? Sounds like there may be a slight bow in a rack or the table, making the pinion gear mesh just slightly differently in the middle of the table
There was a discussion on the Camaster forum with the same problem. Maybe check there to see if they had a solution.
Did you look @ the bearings on the x axis ?
stepper motors are likely your issue. they are perfect if only going to a position and holding but not for constant movement like you have on a router. For that kind of price there are likely also issues with the frame or gantry construction as well.
I have ran servo & stepper motors on all sizes of machines. No appreciable difference in accuracy or repetability for wood working (at least on the machines I have ran). 2 other things to check. 1- Proper grounding of the machine, dust collection & all electronic components. 2- Driver controller electronics. At about 10 yrs old my current machine would not hold accuracy in the x axis, I swapped the card with the y axis and problem moved. Replaced the card (~$1k). This was found after much troubleshooting with the Mfg'r. Electronic accuracies do change as components age, and while this does not 'always' happen, it is not tremendously unusual as a machine ages.
I think we have mostly ruled out mechanical issues.
1. The bearings run smooth, and if it was binding somewhere in the travel, it would be losing steps. This is not the case as the positioning is absolutely consistent and repeatable with no load on the drive.
2. Grounding/static issues are not at play here, as again the positioning is 100% repeatable.
I think the next place to look is the controllers. I will try swapping the X and Y cards to see if there is any effect.
The machine is just over a year old, but has had the problem since day one.
I had similar problem one time. Did all the above to no avail. Except I had ballscrews. Turned out the machine was out of level. Sounds crazy, but you never know. Good luck
You have mechanical and you have electrical. I can't imagine if it was electrical it would be in only one small area on the machine, especially when steppers really don't know where there at. Do you have home position switches? How do you know you are truly back in home position? My guess mechanical, machining for the rack is not right or the spur gear is binding. Throw a couple dial indicators at home position on each side of the gantry and be sure you are truly repeating.
On a side note,I had a problem with our stepper router years ago making weird moves and it turned out the serial cable to the controller across the room was to close to a fluorescent light fixture. Go figure.
The mechanical side of the machine is not sophisticated and I understand how it works pretty well. It's just gears and belts, and all of that has been professionally examined or replaced. Yes, the machine is level.
Which leaves us with electrical problems. My next step is to swap the x and y drives to see if the issue follows. Beyond that, there might be a software issue? Seems unlikely but what do I know.
Can you manually move the gantry to the area in question and gently rock it to see if there is an appreciable difference in the slop in the rack? Does it manifest the same way if you climb vs conventional mill? Ie if it is some sort of slop / backlash issue the way it leads up to a cut will load the rack in a different direction if you are cutting squares / rectangular type parts. We used to have lots of missed step issues with our old stepper machine (long since replaced with servo machines) but the discrepancy would not be consistent like that.