Weird Z Axis Problems and Skipping

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silviustro
Posts: 5
Joined: Thu Nov 30, 2017 10:27 pm

Weird Z Axis Problems and Skipping

Post by silviustro » Thu Nov 30, 2017 10:44 pm

Hello everyone.

For the past year I've been having some weird problems with my Printrbot Simple Metal. They failed to offer any help, as their support page is abysmal. So i thought i'd try my luck at finding help here.

First of all, the printer is modified, I've installed a heated bed platform with a glass surface in order to get better prints. The bed is not connected directtly to the PrintrBoard, it is controlled by a relay that is connected to the MOSFET on the board, as the MOSFET itself can't handle the current.

I have also tried changing the z axis acme screw to a T8 leadscrew in order to eliminate the Z wobble inherit to all Printrbot 3D printers.

Here's the problem. After a while printing, the Z axis stepper starts skipping steps uncontrollably, the print ends up "squished" and unusable. In order to troubleshoot this, i Tried switching back to the acme rod system, as the acme rod needed 2020 steps to move one millimeter, while the leadscrew needed 400 to move one millimeter. The Y axis being supported by the Z rod on the Printrbot is really heavy, so i thought the extra torque it needed to push the entire axis up was making the Z axis skip.

Suffice it to say, it didn't work. So i decided to up the current on the driver a little, the PrintrBoard only allows for a little adjustment, so i went full throttle, but it still wouldn't work, it still kept skipping steps. I gave up and i changed the stepper to a new one, but it didn't work either.

Something I've noticed is that the skipping doesn't occur that much when the heated bed is off. It happens more rarely, but it still happens. I've also noticed it always seems to happen at the same mark, at about 1 hour 30 minutes of printing. This also means that whenever i printed a 3D benchy to test out the printer, it never failed, because it takes less that to print. When i'm using the acme nut instead of the leadscrew the z axis still skips, but it makes no audible sound, it just vibrates in a weird way.

this problems are completely random, and I've tried everything on the checklist to try and fix them. I have been printing this past year by just starting a print and crossing my fingers. I'd like to fix them in order to have a reliable 3D printer at home.

any help would be greatly appreciated. Thanks!

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Weird Z Axis Problems and Skipping

Post by Stefan » Fri Dec 01, 2017 5:12 am

How's that driver doing? Could it be overheating? Try dropping its current or even replacing it if possible.

-Stefan

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: Weird Z Axis Problems and Skipping

Post by chumm » Fri Dec 01, 2017 10:53 am

Is the heated bed connected to the same power supply that runs the rest of the printer? If it shipped without a heated bed it might have a power supply that is too small to maintain current on all the motors and the bed simultaneously. You could test this by doing a long PLA print without heating the bed, or connecting the bed to another 12v source, like an old computer PSU.

If you're sure power's not a problem, then yea I'd look into the drivers, you could try swapping X and Z drivers and see if you start getting X problems instead, etc.

silviustro
Posts: 5
Joined: Thu Nov 30, 2017 10:27 pm

Re: Weird Z Axis Problems and Skipping

Post by silviustro » Fri Dec 01, 2017 5:04 pm

Thanks for your replies.

I also suspected the power supply might be the problem. So i recently replaced it with a MeanWell RSP-320-12

It is a 320 watt supply, and i measured the bed only using about 80W to 110W depending on temperature. I did try using separate power supplies, the problem still appeared, tho, more rarely.

Unfortunately, the PrintrBoard has its drivers soldered on, and cannot be changed. i tried changing the current settings with no success. Maybe it is time to retire the PrintrBoard and try another marlin based board?

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: Weird Z Axis Problems and Skipping

Post by slippyr4 » Fri Dec 01, 2017 7:23 pm

Could it be a break in the stepper wires that’s intermittent and more likely to occur at certain positions?
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

silviustro
Posts: 5
Joined: Thu Nov 30, 2017 10:27 pm

Re: Weird Z Axis Problems and Skipping

Post by silviustro » Fri Dec 01, 2017 11:11 pm

The first thing i did was to replace the stepper motor, wiring and all, so that can't be it.

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: Weird Z Axis Problems and Skipping

Post by chumm » Sat Dec 02, 2017 12:12 am

Sounds like it's narrowed down to driver or electronics, so yeah it might be time to try out a new board. The upshot will be more customization and upgrade options opened up as a result, downside is it looks like that printrboard is really compact and convenient for the size of the case, you might have a hard time finding something that fits.

silviustro
Posts: 5
Joined: Thu Nov 30, 2017 10:27 pm

Re: Weird Z Axis Problems and Skipping

Post by silviustro » Sat Dec 02, 2017 12:31 am

Indeed, the PrintrBoard is quite convenient.

I guess I could always run the wires outside the printer and have a box containing the electronics and the power supply. Unfortunately I wasn't able to find some enclosure I could buy.

I will try increasing the limits of the maximum federates, play a bit with the current control and test the temperature of the drivers outside the printer frame. If i'm taking the entire thing apart I might as well do it.

I will do some more testing and report back.

chumm
Posts: 176
Joined: Thu Jun 15, 2017 11:24 am

Re: Weird Z Axis Problems and Skipping

Post by chumm » Sat Dec 02, 2017 5:54 am

Taking another look at the printrboard, it seems the onboard drivers don't have heatsinks? This could be an overheating issue. You can get tiny heatsinks pretty easily, they're usually listed as VGA RAM heatsinks. Just stick them straight onto the top of the A4982 chips after cleaning with a little alcohol. A fan could also help but going from no heatsink to heatsink should make a very significant difference in the operating temperature.

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: Weird Z Axis Problems and Skipping

Post by slippyr4 » Sat Dec 02, 2017 11:22 am

Usually when stepper drivers overheat, they shut down rather than skip steps.

Is the motor very hot before it starts playing up? Can you check the Vref are all sensible?
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

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