Need some help to tweak the prints

dislegal

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.

dislegal

I've tried to calculate the X and Y steps per mm - 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 confirm the print bed size is correct in EEPROM and Repetier Host settings as 200x200mm.

http://i.imgur.com/CxmigyC.jpg

dislegal

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

http://i.imgur.com/NtLvE6p.jpg

http://i.imgur.com/zTxLStO.jpg

dislegal

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

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)...?

dislegal

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.

Repetier

Does the skew always go away from endstop? In that case your endstop triggers while printing. You could then try disabling endstop test during print (ALWAYS_CHECK_ENDSTOPS in repetier firmware).

It also might be acceleration, which is the critical part of a move. 1000 should be no problem and give smooth moves.

dislegal

Thanks for the info @Repetier. FWIW, it was skewing towards the X endstop and away from the Y endstop.
However I gave up on the K8200 earlier this week and sold it, and yesterday I bought a Mendel90 - which I'm happy to report is printing exceptionally well!

LouGeezer

@dislegal, Happy to see something is finally working for you!  FWIW, I had crosstalk between endstops (thanks to @Repetier for diagnosing this), which I corrected by rerouting cables, adding shielded cable to endstops, and doing away (for now) with Max endstops altogether.