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Printing making blobs on first layer

Posted by ruggb 
Printing making blobs on first layer
September 20, 2017 11:03AM
This is very obvious on the first layer most recent extrusion. The first few lines don't seem to do it.



Marlin, Slic3r, 0.3 nozzle, 0.3 first layer, 0.2 other layers, bed set with paper, PLA, temp 205, 60mm/sec
I am running it at 0.2 and 0.12 now but it is still dong it to a lesser extent.
Where to look, what to look for?????

thanks
Re: Printing making blobs on first layer
September 20, 2017 10:38PM
1st layer at 60mm/s is a bit fast IMHO. 0.3 layer height with a 0.3 nozzle is too much. Max. layer height should be 80% of nozzle diameter.
Also make sure the nozzle height is right. with a bit of squish. ( How much squish depends on the bed surface )
Re: Printing making blobs on first layer
September 21, 2017 08:42PM
1st layer speed 50% or 30 mm/sec
it looks good on the first few perimeters than goes nuts.
Why wouldn't it start doing it on first perimeter??
Just trying to understand what is happening.
I keep reading about 80% but no one says anything about why.

Edited 1 time(s). Last edit at 09/21/2017 08:43PM by ruggb.
Re: Printing making blobs on first layer
September 21, 2017 09:47PM
Layer height should always be less than nozzle diameter so that the extruder lays down a flattened line of plastic. A flattened line has more surface area in contact with the layer below, yielding a stronger print.

If you have a bed with a wavy surface, it can be helpful to print the first layer extra thick (but still less than nozzle diameter) in order to get the print to stick.

I believe your current problem is over extrusion or the nozzle is too close to the bed or both. It looks like the plastic starts piling up after a few lines are laid down and then the nozzle starts tearing up the previously deposited plastic. That's why the first couple lines look OK but get worse as more lines are put down next to them.

Calibrate the extruder using Triffid Hunter's Calibration Guide, paying attention to the fine e-steps calibration. Be sure you measure the filament diameter in 20-30 places, calculate an average value, and use that value when you slice for the calibration. Mark that average value on the spool for future use.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Printing making blobs on first layer
September 22, 2017 06:50PM
hey doc, THAT ranks in the top ten best answer I have ever received. Thank you.

I was thinking over extrusion but since I can't see it on subsequent layers, I couldn't rationalize it.
However, I thought I had that covered. But then I've changed nozzle size since I did that exercise so that may have something to do with it.
Since I went to 0.2 layer height, it is hardly noticeable. So that may be the prime cause. But at 0.2, that is 66% so the extrusion may be a factor now.
thanks
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