Bad layer shifting problem on Y axis (starting a new thread from previous discussion)

Hi folks -
Machine has been running great for about 6 months and then it started stepping on the Y axis badly.
Not sure what that heck has happened. Thought it might be a fried stepper driver board
so replaced it and unfortunately problem still present.
The motor seems to run nice and cool or slightly warm.
I have a fan cooling the Ramps board and stepper drivers to make sure things run cool and no overheating.
I have fried the Arduino - Mega 2650 - voltage regulator a couple times by accident before, but replaced them easily.

I'm wondering about some possibilities here but could use some fellow knowlegable repapper's thoughts:
1 - Could it be a failing Ramps board? and if so, what part of the board is the culprit here?
2 - (Similar) Could the Arduino be a failing?
3 - Or - could it be Cura? Up till recently, it has performed wonderfully.
4 - Motor seems smooth and quiet, shaft seems to turn normally by hand, no binding.

Any thoughts gents or ladies?

Thanks - JD


Software is Cura (latest version) using expert settings.
Heartbox model seems to be ok - from Thingiverse.

overall print speed: 30mm/sec
temp: 190c
layer height: .2 mm

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Prusa I3 - Rework (home built)
w/ heated print bed. Borosilicate glass plate.
Ramps 1.4 board, Arduino 2650
Thermaltake 750watt power supply
Ulti-panel lcd controller
Marlin firmware
Cura - slicer/print software

To me it looks like a classic case of skipping steps. Open loop drive systems like we use send step commands, but do not measure to insure all the steps happen. That would take the next level of encoded steppers or servos.

I think your problem is below the software, program, or drivers and caused by the axis encountering a load that it cannot overcome.

If it was the nozzle dragging, I think it would be smaller, since it is a major shift, the axis stalled while the software continued to count steps and ratcheted the hardware, eventually, it overcame the stall and went on its way, until it happened again..

There are clues in the print ( I always say "machines speak to me") the overload started where the skip started to shift. I would look there with either the guides or the belt/sprocket combination. Since it seems same axis but different locations, the guides are less suspect. More like a belt or sprocket? If you study the drive, you may find that it happens at the same position of one of the drive components, for example, every time the sprocket is in a certain orientation, it starts to skip.

If it is purely random, it could be a sprocket slipping and catching on a drive shaft, or not. Even higher speed will cause the motor to skip steps.

The burned area on the heart in the near side of the second picture looks like it could have caused higher feed force, The level of the burned area seems like it about the same as the skipped steps. Once it finished that, it seems like it was done skipping?

Edited 1 time(s). Last edit at 12/21/2014 11:12AM by kengineer.

kengineer -

THANK YOU BUDDY! You sir - are awesome!
And funny coincidence, I'm also an engineer type, actually, do the same job but
have to call myself a mechanical designer (no official engineering degree).
Your deductive reasoning is fantastic and damn close.
First - I decided to look into your thought of the lower guide rails. In my case I used
low cost smooth drill rod and custom Delrin bearings. I have been lubing the rails up occasionally
with a drop of Tri-flow. Technically speaking, the Delrin has graphite embedded in it and is a great, low
friction bearing surface, without requiring any lubrication but can still have just a bit of 'stiction' or break away friction in some cases.

What I did not see was that the slightly oily surface of the rods were catching tiny filament hairs probably fell away from nozzle lifts during prints.
These I think were causing some intermittent binding at random times. Also - the waterjet cut aluminum print bed has slots that don't quite lock the bearings in place so they slightly shifted,
also causing binding that i did not see till now.

The burnt looking part of the photo is actually from seeping melted PLA that kept dripping down the side of the nozzle
in brown globs - now fixed by replacing the nozzle.

Thanks again and happy holidays!

cheers JD

Edited 1 time(s). Last edit at 12/22/2014 02:48AM by jdmech.

UPDATE: - The shift problem returned - So I decided to check out the connector.
IT WAS THE CONNECTOR - argh! I used a crappy pin socket (chopped down to 4 pins) as a motor plug, which wasn't able to handle the vibrations
of the machine. It was losing steps when it started to enter into rapid infills - which makes sense now why the connector was
so intermittent. Anyway - I switched the old one out for a 4-pin I2C connector from Fry's, which fits great and has much better contact and grip on the pin.
Lesson learned - thanks for your help kengineer!

when i generate G-codes from my Slic3r and have a serious problem of layer shifting / drifting from 2nd layer to onward and at the end i get a ruined object.

but when i upload a sample g code generated by some one else that i downloaded from internet search, that g code make perfect object means my slic3r settings and bad , i any body can solve this problem i have snaps of my Slic3r and repetier settings on google drive. if some like to study that case, please write me to provide the links of that snaps.

regards
suhail

After many attempts to correct my original shifting problem, I ended up changing out my Ramps board and that worked.
So, I would suggest trying that as a troubleshooting step. Swap out your Ramps board and if the problem repeats itself,
then you know it's definitely software. You can get a cheap new board on ebay.

JD

Is there an bug in the New Released Repetier Software from July 2015? I updated and since then the sliced gcode is printing 3 layers suddenly the y axis is drifting off in zigzag. I tried a different model but still the same. Can I measure the resistance from the trimpots with an ohm-meter on my 8845drivers whilst switched on or off to determie the setting of x and y are equal?

Thx for help

Edited 1 time(s). Last edit at 07/26/2015 01:15PM by Daniel Pfau.

I didn't see anyone mention tuning your stepper drivers here.. Still haven't had my printer for more than a few months, and still can't figure it out (shameless plugs: forums.reprap.org) but I know that if your drivers are under powered this can happen. Not sure if overpowered drivers can do anything but melt something, but it might cause skipping. See how hard it is to get your motors to skip a step. Just jog an axis via pronterface or LCD control so the motors engage, then see if you can't twist the pulley. If its really tough but not impossible your probably good.

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Master Tinkerer