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Small layers too hot...

Posted by billmi 
Small layers too hot...
September 18, 2012 06:08PM
This winter I'd just built my Prusa Mendel and done some initial printing (with much fine-tuning left to go) when the launch of a new business took time away from the project. I've gotten back to RepRapping, and just installed a heated bed - I can't believe how much more convenient printing on glass is than blue painter's tape.

I'm printing Ultimaker 3mm PLA through a .35mm nozzle with .1mm print height, and slowly but surely dialing in my settings in Slic3r 0.9.2 for progressively better prints. I've got the hot end at 195C (200 for the first layer) and bed at 60 (65 for the first layer) and getting a good base layer. I found a 5mm step calibration object on Thingiverse and it does a great job of showcasing a problem I'm having. Printing gets worse as layer size decreases. My first layer, has nice smooth walls. The next step, where layer size is reduced, I start seeing little blobs of plastic. It gets progressively worse up to the top step (in essence a 5x5mm cube) which doesn't really form, it ends up a blob of molten plastic wiggled around by the nozzle as makes its x/w moves for each layer.

My initial though is to try a lower temperature from here - but at 190c I'm not getting smooth extrusion. Cooling? I have a small fan on the x-carriage, but it just directs air at the cooling fins of the tube holding the J-Head. I've got a larger fan continuously blowing across the build area, but I don't know how much impact it's having.

I expect just pulling the head away and giving things a few seconds to cool between layers when they get small would help a bit here, but didn't see an intuitive way configure Slic4r to do that.

Any thoughts?

Edited 1 time(s). Last edit at 09/18/2012 06:10PM by billmi.
open | download - 5mm_step_calibration_object.jpg (49.8 KB)
Re: Small layers too hot...
September 18, 2012 08:25PM
You need to give the plastic time to cool.
Printing cooler will help.
Printing slower will help, the minimum layer time in slicers cooling tab can do this only on the smaller layers.
Printing multiple copies of the object can help, since it takes longer to print a single layer.
Having a fan blowing on the plastic can help.
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