First Layer question

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TomR
Posts: 30
Joined: Wed Dec 03, 2014 3:12 pm

First Layer question

Post by TomR » Sun Apr 26, 2015 5:45 am

I have a question about the bottom layer quality and thickness. Using Esun PetG, I have calibrated the extrusion parameters: width 0.42, filament diameter 1.71 extrusion multiplier 0.85 and layer height at .2mm. One layer wall width is right at 0.42 so that seems right on the money. I calibrated the Z axis with a feeler gauge. The 0.206 gauge just fits when the z axis is homed. Printing with these settings and layer height and width at 100% gives a height of 9.81 for a 10mm high test cube with a very smooth bottom with a little lip at the edge. When I adjust the z height in the GCode by .12 the height now is 10.0 and the lip is gone but the bottom is not smooth as I can feel the threads with my fingernail. I have tried different GCode Z adjustments but it seems that the closer I get to 0 the more lip I get, smoother the finish, and lower Z measurements on the cube. I want no lip, smooth finish and correct height. Am I just asking for too much or what should try. Oh, the infill (20%) looks great. A cube with the .12mm z adjustment and no top or bottom layer were perfect.

Any advice is appreciated. I plan on using PetG as my primary filament and want to get my M2 as tuned as possible.

Thanks.

lem
Posts: 162
Joined: Thu Jan 15, 2015 6:44 pm

Re: First Layer question

Post by lem » Sun Apr 26, 2015 1:20 pm

Feeler gauge 0.206? Is that a typo?

TomR
Posts: 30
Joined: Wed Dec 03, 2014 3:12 pm

Re: First Layer question

Post by TomR » Sun Apr 26, 2015 1:46 pm

Just rechecked and is actually 0.203mm or 0.008in

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ednisley
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Re: First Layer question

Post by ednisley » Sun Apr 26, 2015 3:11 pm

TomR wrote:I want no lip, smooth finish and correct height.
Pick any two?

Remember that you're building something by mashing goo through a nozzle against a hotplate. The plastic emerges from the nozzle as a round-ish rod that's smeared sideways into a rectangular-ish bar by the relative motion of the platform.

The legendary nophead explored the problem in the context of flow and dimension adjustments:
http://hydraraptor.blogspot.com/2011/03 ... -rate.html
http://hydraraptor.blogspot.com/2014/06 ... wrong.html

It's worse on the first layer, where the nozzle must squeeze molten goo into a corner before it solidifies against the relatively cool platform. Running a hotter platform doesn't help much, because it's still under the plastic's glass transition temperature.

So the choices seem to be setting the nozzle:
  • too low = smooth bottom finish, short layer, lip on the side
  • at the right height = small gaps, good size accuracy overall
  • too high = the object won't stick to the platform
The total difference amounts to a few hundred wavelengths of deep red light.

If the surface finish of the bottom layer is really, really important, then jimc's finishing techniques will get you all the way to the goal. Of course, applying that much labor to a 3D printed object turns it onto a rare and precious item, but ...

TomR
Posts: 30
Joined: Wed Dec 03, 2014 3:12 pm

Re: First Layer question

Post by TomR » Sun Apr 26, 2015 3:32 pm

Ed,
Thanks so much for your reply. That is what I wanted to know. I can set the height to get the finish I want for a piece. Good to know I have those options.

Tom

lem
Posts: 162
Joined: Thu Jan 15, 2015 6:44 pm

Re: First Layer question

Post by lem » Sun Apr 26, 2015 3:53 pm

oops. mm vs inch

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