extruder dragging problem

[Becky Stern]

Ok, so now that my bot is back up and running, I'm having the same
problem I was before with the extruder/z stage, which is that it
doesn't seem to raise the z stage up enough after each layer,
resulting in the nozzle being dragged across the previous layers,
which totally musses up the accuracy of the toolpath. It seems not to
be fixed by changing the layer settings, but maybe I just haven't
changed them to something optimal. On this last build, I got really
great results on one side of the object, and really bumpy results on
the other side, and I could see the nozzle being pushed around by the
already-printed object. It's done this same thing with the default
skeinforge settings, but just this last time I changed them (as per
http://wiki.makerbot.com/nozzlev2 even though I think I have nozzle1
in my batch 3 machine). Currently:

Carve
extruder width over thickness (ratio): 1.68
layer thickness: 0.25

Speed
extrusion diameter over thickness: 1.15
Feedrate: 45.0

I don't really have a good grasp on what exactly each of the different
skeinforge settings does, so any advice about different settings to
try would be appreciated. I took a few pics and a video of the nozzle
dragging:

http://www.flickr.com/photos/bekathwia/sets/72157622612701272/

Becky

[Andrew Plumb]

Check the bolts holding the electronics to the side of the main
cupcake body. Some folks have had problems with the z-platform
getting hung up on them because they protrude too far inside.

Flip them around so the hex head is on the inside and the nuts are
outside.

Andrew

Sent from my iPhone

[Becky Stern]

The z platform clears the nuts on that side of the body, but i noticed
in raising the z stage up and down with the control panel that my back
right threaded rod isn't perfectly straight, and sorta sways a bit
when the stage is moving big distances up and down. I suppose this
could throw off the alignment of the extrusion a bit, but it doesn't
seem to be inhibiting the movement of the platform.

Becky

[Rick Pollack]

Becky -

This is likely multiple issues:

What is your travel feedrate (in Speed)?

Few things to try:

- increase your layer thickness to 0.3 or 0.35 (or have you already tried these values?)
- try varying your feedrate between 20 and 45 (match your travel feedrate to your feedrate)
- try slowing down your extruder - maybe 245 (rather than 255)

Have you oiled the precision ground rods? Do you have a small level to determine if you build platform is flat? And, have you had better results in the past?

Rick

On Sun, Oct 18, 2009 at 4:40 PM, Andrew Plumb <and...@plumb.org> wrote:

[Andrew Plumb]

You could try adjusting the z-axis trim pot on the stepper driver
board. Might need to pump more current thru to get past the wobble.

Check the z-belt tension. It could be too tight.

Pop the z-belt off:
- Try finger-twisting each threaded rod back and forth a fraction of a
turn. They should rotate smoothly. If one doesn't then the top bearing
may be clamped down too hard by the top bracket.
- Check for too much vertical motion. You shouldn't be able to pull up
and down on a threaded rod and have it move.

Andrew

Sent from my iPhone

[bre pettis]

Another easy mistake to make that is a point of failure is having the belt too tight!

[Tox]

Try bumping carve layer thickess up to, say, .375 then slowly bring it
down until you're getting nice solid builds, or cut the feedrate, or
up the travel rate.

Fwiw, I found a combo at .368 that mostly works. Finishing up tuning
on it before trying for a finer set.

Good luck!

Tox

--
Scott Small

[zignig]

Hey O' sterniferous one,

I have come across this before and I assume ( perhaps wrongly ) that
it is the same thing.

When you took out the extruder for repairs ( and or removed the Z
belt ) the z platform got out of whack.

The position of the bolts on the four pillars may not be correct.

When this happened to me , I saw the same symptoms , smooth on one
size , blobby on the other.

The Solution:

I took off the Z belt and hand wound each pillar so the Z-platform
lined up with the laser marks ( I just chose one)
on the front and back window of the makerbot.

To check this callibration I wound the z-platform down so it was about
1mm above the build surface. Then moved the platform to it's limits
and eyeballed that it was about a mm up all over.

Try this out , may work :)

The other thing that I found when you do a rebuild of the extruder ,
you have to recalibrate the speed and PWM for some reason.

zignig

aka Simon Kirkby

[Bo Lorentzen]

That's the easy way - I just lift the corner of the platform and spin
the nut as required - :-)


Bo

Sent from my iPhone

[Becky Stern]

Thanks everybody! I've been working on combinations of all your
suggestions and will get back to you...

Becky