Image "ghosting" on Replicator 2X

[Chris - TheNewHobbyist]

Hi All,

I'm noticed an unusual thing happing to some of my prints. As you can see in the photo below the oil can logo seems to be "ghosting" to the top of the part printed below. The oil can itself printed fine and doesn't appear to be drifting at all. I haven't experienced this on my ToM. Any idea what's causing it? 

Chris / TheNewHobbyist

[Joseph Chiu]

Chris, the your print is "ringing" - either the extruder or the bed (or both) are vibrating from the sudden shift in direction.  Acceleration should minimize that, but I've noticed that for some small segments, you can still have a jerky motion that dumps a lot of mechanical energy into the system in a short period of time -- and it takes a while for that to settle down.

I'd suggest checking your X and Y belt tension - just feel hwo slack or tense it is.  The other thing I would check is to see if your Z platform has any play.  If you watch the platform while you print, does it jiggle when it hits that spot?  (I don't have a 2X, so I'm not sure how to take out any play that might be there.)  

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[Eighty]

It's called ringing, and it is due to accelerated printing.  You'll need to slow down your perimeter a bit more.  Are you using MBI firmware, or Sailfish?  Sailfish does a better job with this, IMO. 

[Dan Newman]

Corner ringing -- vibration induced by a sharp direction change. You need
to reduce your max acceleration and/or max speed changes for that axis.

Dan

[Chris - TheNewHobbyist]

Thanks for the quick response.

What what it's worth I'm using MBI firmware and Makerware. Still haven't found time to make the leap to Sailfish. 

I'll look into adjusting the acceleration. 

Thanks,

Chris

[Jetguy]

Actually, on a 2X, it's part of the mechanical design. You swing
around 2 extruders and motors + the X axis motor. The poor Y motor
must move and accelerate that heavy mass.

What is not intuitive about this is how it shows up.
The ringing will be most noticable in the X direction AKA parallel
with the from edge of the build platform or left and right. The reason
is simple.
Say you are printing a rectangle and its long axis left and right. The
extruder traces each layer and the mass of the entire extruder
assembly wants to follow Newton's Laws of physics. From a corner, we
basically start at a dead stop in one direction, say X, and start
accelerating in Y. At the end, we must stop in Y at the corner and
begin moving in X. The extruder wants to keep moving and the belts,
bars, and even the frame flex when the motor tries to stop the heavy
carriage. During that flexing, we began moving in X again but Y is
supposed to be dead still. The flexing is tiny motion where Y bounces
back and forth just slightly around the position where it is supposed
to be staying still. This shows up as a series of "waves" in the wall
of the print. As I said before, it ALWAYS will be more pronounced as
error in the Y axis, since the poor Y motor is moving 3 other motors
mass+ the rods and bearings for X. X motor only has to fight the
carriage and the 2 extruders. But, the error looks like it appears in
X long walls.

What I'm saying is, keep this in mind when placing models in the build
window of either makerware or rep-g. It's better to rotate around Z so
the longest part or straight wall is in line with Y since X doesn't
ring.

Really, the best thing is to place it 45 degrees to the normal X-Y and
that forces both axis to move all the time which greatly masks the
error.

You can test those theories with simple test object http://www.thingiverse.com/thing:8870
Print as normal first and note the errors and what direction they
happen in worse.
Then print again, but rotate 45 so no long axis is in line with X or Y
Report back and link pictures