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mpymike

Homer's unsightly stubble

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Hi,

I made my first print yesterday... and I am very excited and pleased with the amazing quality ...

For print number 5 I downloaded Homer Simpson, and he came out mostly perfect, except for

some unsightly stubble. (see piccie below)

I've seen similar issues on this forum. I'm assuming the hanging strands are that due to

overhangs?

What's the best way of dealing with this? should I try:

1) Rotate him so he's leaning back so his chin doesn't overhang so much

2) In Cura enable one of the support structures settings

3) Change some of the print settings speed/temp/layer thickness etc.

For the print I used a brand new UM, PLA, default print setttings, (220C, 0.2thickness, 50mm/sec)

running Cura 12.12A, windows XP

cheers , and thanks for any help and a great community

-mike

11173545_10153825203162589_1833064523_n.thumb.jpg.b301b4119c1c63d78ddd12af51064871.jpg

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Rotating would be the best option, you could also use "exterior only" support, but that will be less pretty. I would also rotate the model so the back points at the front left corner, this is where the "scar" usually ends up, that you see crossing his eye.

I would also lower the temperature to 210C

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Thanks for the tips... I was going to mention the 'scar'

What is the cause of the 'scar'?

Is it backlash? (due to loose belts which I should tighten)

or is it overshoot? (possibly needs to be printed at a slower speed, or

change the deceleration in the software/firmware)

cheers

-mike

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The scar is called more specifically the z-scar. It's the little bit of material that gets pushed out at the machine alters it's z-height. There are several ways to try to combat this, namely utilizing the "Joris the outer edge" (where it creates an ever changing height for the outer edge), but in my opinion, it's more of just a hazard of the print. Rotating the model to where it's going to be in a location you are okay with is the easiest solution.

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I did another print with Homer leaning back 30deg so that there was less of an overhang under his chin.

The quality of his chin was still not very good. I probably need to make him lean back further.

I also enabled 'exterior support'. Although the support worked, the quality of the surface

was very poor after removing the support. I guess this feature is not perfected yet.

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Here's a photo of them side by side to show what I mean.

 

WP_20150430_010.thumb.jpg.c38952cf2316e7ebea48042e7409efd8.jpg

Homer on the left is my original printed standing upright, with no support (50mm tall, 220c 50mm/s)

Homer on the right was the one tilted back 30deg with support (40mm tall 220c 50mm/s).

The support material was mainly around the base of the model, and there

were two pillars of material supporting the back of his head

Notice also his chin area is still not that good only marginally better than

the original.

Is this the best that can be done with this model? or are there any other

tricks that can be tried? How does the other software compare when dealing with

supports and overhangs?

I'm just trying to find out the limits of my printer.

(

http://www.thingiverse.com/thing:17441

)

I just remembered that Daid suggested 210c, How would that effect the build?

cheers

-mike

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A slightly lower temp means that the machine is keeping the material closer to its solid state. So when you have a larger overhang and a fan blowing on it, it can turn to solid midair more easily. If it were me, I'd try flipping him all the way down on his back. Kinda like you did in the photos, only rotated 90* so his nose is straight up and see how that prints. The other option you could incorporate would be the "pause at height" plugin and print him vertical again. Preview your g-code to see where it starts making the big overhangs and use one or two of those. Rather than swapping filament out, you would be placing your own, easily removable, support (a platform of tape) in there for the first layer of it. Then it's kinda like the printer is starting over again. I would maybe try that at the bottom of his chin and the bottom of his upper lip. But I also wouldn't mess with it if laying him down can give you the surface quality you are after.

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Thanks for the tips!

I'll give the lower temp a try and I'll try lying him down,

But I'm not sure I understand your two stage print idea.

What we need is zero gravity! Anybody on the ISS with an UM willing to give Homer a try? :D

If not has anybody tried printing with the whole UM tilted at an angle?

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The pause at height command inserts code at the appropriate location in the gcode file to move the printhead away from the part and wait for user input. That gives you the ability to put some taped support in there for his chin/lip. It's what I would try as a next step.

It has been proven that you can print with the UM upside down. Not a lot of difference in quality.

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