Need some help to tweak the prints

Velleman K8200.
Mega/RAMPS, running Repetier-Firmware v0.92.3

Just got the printer's manual controls operating again after a catastrophe involving the previous firmware and the build quality thanks to the previous owner. I'm having the following issues based on a 20mm hollow test cube that I'm trying to print.

1. Print not centred. I place the object in the centre of the bed in Repetier Host v1.5.4, but the print actually occurs towards the front left of the bed. Definitely not in the centre.



2. Print dimensions incorrect. The 20mm cube is printing at ~25mm.


3. Print crooked as it builds up layers. Not every layer is off, but many are. I've checked and the print is stuck to the bed and is not moving.


Edited 1 time(s). Last edit at 07/31/2015 08:01PM by dislegal.

Seems you have 20 tooth pulleys instead of 16 tooth. That would explain the 25mm/20mm ratio.

Does the nozzle scratch across the layers?
If not, then the current for one of the steppers is to low, that´s were the shifted layers come from. ( or printing to fast )

If it scratches, reduce flowrate or calibrate e-steps.
-Olaf

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o_lampe
Seems you have 20 tooth pulleys instead of 16 tooth. That would explain the 25mm/20mm ratio.

Does the nozzle scratch across the layers?
If not, then the current for one of the steppers is to low, that´s were the shifted layers come from. ( or printing to fast )

If it scratches, reduce flowrate or calibrate e-steps.
-Olaf

Hmmm, I count 10 teeth per pulley. When I input 10 teeth into the Repetier Host belt calculator, it tells me to make it 160 steps per mm, however I did try this setting and it was way off (sped right to the end and smashed against the side until I cut the power) so I reverted it back to 80 steps per mm. I've also tried slowing the print speed by half but it still moved sideways during the print. I'm not sure what you mean about the nozzle scratching across the layers.

Thanks to a gentleman (to whom I now owe a beer) over on the Velleman forums, I now know the K8200 stock setup is:
1.8° per step
1/16th microstepping
5.08mm belt pitch
Tooth count 10
Which results in 62.9921 steps/mm on X and Y axes.

Once I set the firmware to 63 steps per mm for X and Y, it turned out to be the best test cube I've ever printed

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dislegal

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it turned out to be the best test cube I've ever printed

And here I was, getting all cocky! Still have the sideway skipping Occurred after about layer 15-20 on this one.

GVL2kl0.jpg

After setting max jerk to 15, I still had layers shift. I have checked the tension of the belts - they seem right. Any tighter and it becomes difficult to slide the print bed. I have checked the pulleys and they seem tight on the motor axles.

After setting max jerk to 10, I had a successful print of a test Marvin without any layers shifting. Although he is a little droopy on the right as you can see.

Before I go adjusting the stepper driver voltages, what would be symptoms of too high volts? I wonder if they were set to 5.5v before I bought the printer, but when I bought it I swapped out the faulty 12v PSU for a 15v PSU - could this have caused a higher voltage at the stepper drivers (or is it regulated before it reaches them)...?

Don't jump at my throat but are the pulleys all fastened? Are the belts all tight and fixed?
This layer shifting typically results from loose pulleys. Even though the cube printed nicely before.


EDIT
oops hit send too late.

Edited 1 time(s). Last edit at 08/04/2015 03:58AM by ianmcmill.

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Quote
ianmcmill
Don't jump at my throat but are the pulleys all fastened? Are the belts all tight and fixed?
This layer shifting typically results from loose pulleys. Even though the cube printed nicely before.


EDIT
oops hit send too late.

Haha that was obviously very close timing! I'm stumped...

Quote
dislegal
After setting max jerk to 15, I still had layers shift. I have checked the tension of the belts - they seem right. Any tighter and it becomes difficult to slide the print bed. I have checked the pulleys and they seem tight on the motor axles.

After setting max jerk to 10, I had a successful print of a test Marvin without any layers shifting. Although he is a little droopy on the right as you can see.

Before I go adjusting the stepper driver voltages, what would be symptoms of too high volts? I wonder if they were set to 5.5v before I bought the printer, but when I bought it I swapped out the faulty 12v PSU for a 15v PSU - could this have caused a higher voltage at the stepper drivers (or is it regulated before it reaches them)...?

evs4EM5.jpg

Too high voltage results in hot stepper motors. Basically I adjust my drivers so that the stepper motors never get hot. I have seen people putting heatsinks on them but that is generally unnecessary. I did this with my first printer too (QU-BD TwoUp).

I always do the adjustment like follows:
Go from low voltage to higher voltage. While one axis moves, try to hold it with your hands. As long as you can retain the movement with your hands and you hear the motor losing steps, there is to few voltage.

PSU: The drivers regulate the voltage of the steppers. No mather what PSU you have.

Edited 1 time(s). Last edit at 08/04/2015 04:06AM by ianmcmill.

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I adjusted the voltages of all stepper drivers to 0.55V. Then the very next print skipped sideways during the first layer. this seems even worse that previously, when it was only skipping sideways many layers into the print
It appears from looking at the manual, as if the stepper drivers on my RAMPS board are different than those that come standard with the K8200. Could this be part of my problem? Here's a photo of my stepper drivers if that helps identify them.

Thanks to everyone for all of the help, support, suggestions and advice however I've given up on the K8200. I just don't have the time and effort required to get it going. Fortunately I found a new home for it with someone who does.
Hopefully my experience with what I intend to be my next printer (a fully assembled, tested and working Mendel90) runs a little smoother than this one...

You getting that Mendel90 from a guy down the coast? If so I did that EXACT thing. Bought a k8200, hated it, bought a Mendel90, brilliant. K8200/3drag is such a terrible design.

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ntoff
You getting that Mendel90 from a guy down the coast? If so I did that EXACT thing. Bought a k8200, hated it, bought a Mendel90, brilliant. K8200/3drag is such a terrible design.

Yep, that's exactly what I did. Bought the Mendel90 from Mike yesterday. Brought it home, plugged it in, and it just worked without any issues. Very happy with it after the first few prints!