Streaking on the surface finish of PETG print

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jfstanley
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Streaking on the surface finish of PETG print

Post by jfstanley » Wed Sep 26, 2018 1:24 pm

Hi All,

I'm having these diagonal streaking issues along the top finish of a flat service tray I'm printing - I started having them when I changed filament from Hatchbox to Priline. Can anyone suggest what this may be due to? I'm using manufacturer's suggested temps.

Image

Thanks for any help out there

Jim

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ednisley
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Re: Streaking on the surface finish of PETG print

Post by ednisley » Wed Sep 26, 2018 2:57 pm

jfstanley wrote:
Wed Sep 26, 2018 1:24 pm
diagonal streaking issues
That's the nozzle just kissing the top surface as it travels from one spot to another.

If you haven't recalculated the Extrusion Multiplier to match the new filament, the layers may be ever so slightly overstuffed. Rather than blindly reduce the EM, make the measurements, set it correctly, and see what happens.

You can then reduce the EM very slightly (from the correct setting!) to starve the threads, at the cost of reduced mechanical strength and suchlike. The tradeoff depends on what's important in your application.

However, the nature of building an object from threads of molten goo doesn't produce a nice (or predictable) surface finish. The slicer determines the top surface fill pattern based on the geometry, so, should you like the way it looks now, changing anything will make it completely different.

If surface finish is important, you must apply post-processing to cover the fused threads.

jfstanley
Posts: 7
Joined: Fri Apr 27, 2018 10:11 pm

Re: Streaking on the surface finish of PETG print

Post by jfstanley » Wed Sep 26, 2018 3:07 pm

Thank you! I will go with your suggestion about recalculating EM due to the nozzle dragging the surface. Finishing with a food-safe resin I have works very well on vertical surfaces, but tends to give inconsistent results when applying to a flat surface like these trays. There is some pooling and uneven filling of the grooves in the surface. The unfinished surface is actually pretty nice with the Hatchbox filament I used - sort of a brushed metal look. But these streaks don't look good, so I will try your suggestion and hopefully it works!

Cheers,
Jim

airscapes
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Re: Streaking on the surface finish of PETG print

Post by airscapes » Wed Sep 26, 2018 6:09 pm

If the EM does not fix the problem there is an option in most slicer (I think) to raise the nozzle during retraction (know as Z hop) I have not really tried it but that may be helpful if the EM is spot on. I would guess that doing this will have it own set of pros and cons one of which is adding to the print time. But this is the nature of the art of 3D printing!
Good luck and please return and let us know what works as I have the same streaks and as of yet not bothered to do anything about it as it is not important for my parts to be perfect in appearance. Also I know my EM is spot on thanks to Ed's training on the subject! :D

jfstanley
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Joined: Fri Apr 27, 2018 10:11 pm

Re: Streaking on the surface finish of PETG print

Post by jfstanley » Wed Sep 26, 2018 6:34 pm

Yes, I do have a Retraction Vertical Lift setting of .3mm in S3D applied with a Retraction Distance of 1mm, but I think I want to be careful raising that value to prevent stringing. I'm finding that some stringing is going to occur with PETG, and increasing it might make it worse. I will definitely report back with results after I adjust EM though..

airscapes
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Re: Streaking on the surface finish of PETG print

Post by airscapes » Wed Sep 26, 2018 6:46 pm

on the stringing.. you can greatly reduce it by lowing the x/y speed in S3D under the speed tab. Default is 300mm/s and of course this will increase print time. I lowered mine on one print that was stringing (not sure which material was using) to 200 and the stings were gone.. took a lot longer to print as all the moves are slower but stopped the strings.

jfstanley
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Joined: Fri Apr 27, 2018 10:11 pm

Re: Streaking on the surface finish of PETG print

Post by jfstanley » Wed Sep 26, 2018 7:11 pm

Ah - thanks. That's a setting I haven't touched and it's set at the default of 300mm/sec. I will reduce to 200 then.
I've always just adjusted the default print speed (set at 50mm/sec at the moment).
Glad I came here with this - learning more and more with experts' advice.

airscapes
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Re: Streaking on the surface finish of PETG print

Post by airscapes » Wed Sep 26, 2018 7:16 pm

HA! I am not expert, just like you learning all the time.. check your print time after you change that.. will go up considerably depending on how much traveling the print head does when not printing..

jfstanley
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Joined: Fri Apr 27, 2018 10:11 pm

Re: Streaking on the surface finish of PETG print

Post by jfstanley » Wed Sep 26, 2018 7:24 pm

Everything's relative..compared to me you are.. lol. But with this particular job, the print head just goes back and forth without any "idle" time, since the dessert tray I'm doing almost fills up the entire bed. SO hopefully any a additional print time is negligible, or I could probably bump up the default speed a bit. I'm eager to see the results..

airscapes
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Re: Streaking on the surface finish of PETG print

Post by airscapes » Wed Sep 26, 2018 8:28 pm

where are the strings occurring? Normally that is when the head leaves one part of the print and travels to another portion of the print or another model that is being printed at the same time, without printing in between..

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