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Nozzle hits print

Posted by Stephanel 
Nozzle hits print
April 19, 2015 01:12PM

I have a problem with my delta printer that hits the printed material. This only happens when I have printed a number of layers. Apparently, the nozzle hits solidified material, and then misses some steps. From there on, the print is screwed...

I calibrated the printer already numerous times, and as far as I can see, it should be correctly calibrated. It seems however that the print head does not move up as fast as it's building the printed product. After a while, the print nozzle will touch the product, and eventually will hit a block and the nozzle will be disturbed. The product itself sticks well to the heated bed and does not move at all.

Is there any setting that I should check and optimize to ensure that the print nozzle does not eventually, once the print product will move up, hit the printed product?

Re: Nozzle hits print
April 20, 2015 02:03AM
Assuming your tower stepper motors steps per mm is correct I.e you command a Z move of 10mm and it moves the nozzle up or down by exactly 10mm then the only thing I can think of is that your extruder is pushing too much plastic. Mark your filament, where it enters your extruder say 100mm away from the extruder. Heat your nozzle to print temp and command a 50mm extrusion. Measure from the extruder to your mark. Is it 50mm? If not adjust your extruder steps per mm accordingly
Re: Nozzle hits print
April 20, 2015 04:03PM
Thanks Andy!

Sadly, I indeed checked that my belts were OK and that the carriage moved correctly. The extruder also extrudes at the correct pace... The problem seems that the accuracy of the calibration of my machine is not sufficient to print more than a few lines... Or maybe I'm just looking in the wrong direction...
Re: Nozzle hits print
April 20, 2015 05:57PM
What is your layer height? I was thinking (could be wrong) that not all layer heights are possible given a printers configuration due to rounding errors. So perhaps a layer height of 0.32 is actually coming out as 0.3 and after a couple of layers, the nozzle is at 1.2 instead of 1.28, thus hitting the previously printed layer.
Re: Nozzle hits print
April 20, 2015 06:06PM
I have a layer height of 0.35 and a nozzle of 0.4mm. I can set it to 0.4mm, if that would help :-)

I did some more tests with other prints, and apparently it seems that the print that did not work was a bit special. It had a lot of support, and that support actually came loose. Printing a full product (with limited support) seems to work better. I also tweaked a bit the Delta Radius parameter, so the build is a bit let convex. However, it still seems that when I move up in the product, the nozzle buries more and more into the product, which should not be...

Next, I will try with the 0.4mm layer height as you suggest. That's a pity, as the print quality will suffer... But better that than no print!

Also, I still am having trouble with my Bowden Extruder hicking (moving back once in a while because the pressure builds up too much in the nozzle). This while I am now even underextruding to try and fix this pressure buildup confused smiley Strange, because before (previous printer), I never had issues with that...
Re: Nozzle hits print
April 20, 2015 07:31PM
I would go with a 0.3mm layer height with your 0.4mm nozzle.....
Re: Nozzle hits print
April 21, 2015 02:47AM
I would go with a 0.3mm layer height with your 0.4mm nozzle.....

I would second that!

Re: Nozzle hits print
April 25, 2015 07:41AM
Sorry for the late answer, I was abroad, and not able to work on the printer...

Thanks for the suggestions! I however tried 0.3, 0.35 and 0.4mm as layer thickness. All seem to have similar issues that the print is being pushed down by the nozzle. If I watch closely at the second layer, I indeed see that the heated bed is being pushed down (1/2mm or so) by the nozzle. That doesn't seem right to me, or is this normal/acceptable behaviour?
Re: Nozzle hits print
April 27, 2015 05:43AM
Hi Stephanel,

i have also a 0.4 nozzle and i have the best results with 0.24mm layer thickness.
Did you already checked the thickness of your Filament?
Maybe you can Play a Little bit with this number in your slicingtool???
Re: Nozzle hits print
May 01, 2015 01:17PM
Cool your drivers. We had similar problem. Suddenly after about an hour ( when printing short range infill) the head drops down a bit. 1.2V on stepsticks were too high and they are getting too hot. Now 0.9V and the problem is gone.
Re: Nozzle hits print
May 05, 2015 02:01PM
Do you use retraction? With my Delta, I also had issues with the nozzle hitting previous layers and then shifting the print.
Changing retraction settings reduced this behaviour.

I use Cura for slicing and have setup retraction as follows:

Minimum travel (mm): 2 or 3 (depending on the small details in the print)
Enable combing: off
Minimal extrusion before retracting (mm): 0
Z hop when retracting (mm): 0.1

A little experimenting with these settings helped me a lot!
Travel speed (Non printing moves) I have set to 150mm/s. I do have nice clean prints and almost no layer shifts with these settings.
Re: Nozzle hits print
September 13, 2015 12:48PM
Are you endstop wires routed with your steppers for your extruder?

Try separating them into two cable bundles - the endstops may be picking up noise from the extruder on retraction.
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