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print head colliding

Posted by glyn 
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glyn
print head colliding
July 08, 2012 02:29PM
I have always experienced problems with the print head colliding with the current layer when it moves over part of the already printed area.
This is especially a problem when printing multiple copies of small items as the head will either knock some over or skip multiple steps and so ruin a print run.
What are the possible causes of this?
Thanks.
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sam0737
Re: print head colliding
July 08, 2012 02:35PM
Does your Z axis move correctly?
Will it ever hit the heated bed?
If you repeatably run it up and down manually, does it return to the same position? (Try both fast travelling, and walk it step by step)
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Nudel
Re: print head colliding
July 08, 2012 02:49PM
Make sure your retract settings are spot on.

Turn on lift/hop to lift the z axis while moving.

Add a fan to cool down the part faster so the plastic doesn't curl up.

Slow down acceleration and/or travel speed so if the z should catch on, it's at least with less force.

Print several small parts sequentially. (Advanced tab in Slic3r).

--
-Nudel
Blog with RepRap Comic
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jcabrer
Re: print head colliding
July 09, 2012 10:59AM
Have you calibrated your Axes, and the extruder?

If not, start there.

If you are printing with PLA (not ABS), and you don't have a fan, get one. PLA take a looong time to cool down on its own, and will cause dragging.
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glyn
Re: print head colliding
July 09, 2012 03:10PM
Quote
Does your Z axis move correctly?
Yes it is consistent
Quote
Have you calibrated your Axes, and the extruder?
and accurate.
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Turn on lift/hop to lift the z axis while moving.
I have tried to avoid this (extra time & blobs.)
Quote
Add a fan to cool down the part faster so the plastic doesn't curl up.
Quote
If you are printing with PLA (not ABS), and you don't have a fan, get one.
PLA yes, Using a fan causes my prints to detach from the bed.
Quote
Slow down acceleration and/or travel speed so if the z should catch on, it's at least with less force.
I suppose but prints take long enough as it is.
Quote
Print several small parts sequentially. (Advanced tab in Slic3r).
Speed again, individual small parts take a long time as you need to wait for each layer to cool.

Anyway my hot end is playing up so I'm going to have to strip it down sometime.

I may have another go with a fan and a big brim or resign myself to slow prints.

(I must admit my initial reprap enthusiasm is wearing off now.)
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Nudel
Re: print head colliding
July 09, 2012 04:02PM
glyn Wrote:
> (I must admit my initial reprap enthusiasm is
> wearing off now.)

Hang in there! We've all been at that stage, most of us many times. It will pay off in the end if you push forward. smiling smiley

--
-Nudel
Blog with RepRap Comic
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sam0737
Re: print head colliding
July 09, 2012 10:51PM
One more guess: is the hot end mounted securely...and that it wasn't pushed downward by the extruder?

(I hope I am helping by throwing in ideas..)
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Zimtower
Re: print head colliding
July 10, 2012 02:38AM
If you have a fan to cool down your part, your z-axis is calibrated and the hotend is secured to the carriage. The only problem I can think of is that your extruder is not calibrated enough and too much plastic is being extruded which your hotend is catching on.
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jonathanbyrn
Re: print head colliding
July 10, 2012 06:23AM
I have been having the exact same problem on my prints, it seemed to be colliding at exactly the same point though so I thought it was the gcode rather than something wrong with my z-axis. I turned on the lift setting and put it slightly above the height of my layer accuracy (when I set it to the same height it still collided) and it worked a charm, thanks nudel!
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djamwolfe
Re: print head colliding
July 10, 2012 07:40AM
sam0737 Wrote:
-------------------------------------------------------
> One more guess: is the hot end mounted
> securely...and that it wasn't pushed downward by
> the extruder?
>
> (I hope I am helping by throwing in ideas..)

I think you just explained whats going on with my printer. I have a printed J-head holder and it must be flexing down when I am extruding. Time to look at and fix!!!

End Thread Hijack
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sam0737
Re: print head colliding
July 10, 2012 07:49AM
djamwolfe Wrote:
-------------------------------------------------------
> I think you just explained whats going on with my
> printer. I have a printed J-head holder and it
> must be flexing down when I am extruding. Time to
> look at and fix!!!
>
> End Thread Hijack
Sorry for yet another hijack.

Printed holder - so the holder is made of ABS/PLA and you also extrude ABS/PLA? I guess you are asking for this to happen =P
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djamwolfe
Re: print head colliding
July 10, 2012 07:59AM
sam0737 Wrote:
-------------------------------------------------------
> Sorry for yet another hijack.
>
> Printed holder - so the holder is made of ABS/PLA
> and you also extrude ABS/PLA? I guess you are
> asking for this to happen =P

Yeah - its ABS and I'm printing with ABS... I dont know why this never occurred to me before. the groove mount came with my printed parts, so I figured it was ok. I have some MDF laying around, maybe ill make a holder from that.

Now im done with this Hijack, Sorry glyn!!!
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glyn
Re: print head colliding
July 19, 2012 03:47AM
Just an update to say that I fixed my hot end problem which turned out to be a worn hobbed bolt, I made another one using the dremel spiked method, (thing) although I did it by hand and amazingly despite the inaccuracies it is working ok.
I have now printed some nice parts using the lift option on slic3r and must say I am impressed with the results, a bit slower but not as blobby as I feared.
So all in all I am energised and have re-discovered the faith!
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