Print Issues - Retraction?

Discussion in 'Calibration, Help, and Troubleshooting' started by Jasons_BigBox, Oct 17, 2016.

  1. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Afternoon all,

    I've been printing some parts recently that have thin fins on them and I'm seeing some odd surface finish issues (they're scale engine cylinder heads btw). Rather than re-printing the full item I've cut it down to a slice and am getting the same problem. On the upper layers of the fins there's a thickening and rougher finish that is difficult to get rid of by sanding, filing etc. Photos below illustrate:

    DSCF1291.JPG
    DSCF1292.JPG DSCF1293.JPG

    The parts are printed hollow but when I watched the print this time, the rougher surface appears to coincide with the point at which the nozzle goes above the inner cylinder and it can print the full width of the fin across the part in one go. Before that, the finish is good. I thought it maybe cooling or speed related but the fan's on full for most of the print and the speed's reasonable @2400mm/min.

    My thoughts are that it could be a retraction issue, too much or too little?

    My S3D settings are to retract by 1.5mm @4500mm/min with no restart distance and no vertical lift.
    There's no 'Coast at end' or 'Wipe Nozzle' use.

    The material is Silver everyday PLA and it's printed at 210°C / 60°C with 0.1mm layers and a 0.25mm nozzle.

    Any suggestions? Even an easy way to post-process them would be good but I found that sanding just seems to fill in the gaps and a razor saw just seems to move the fin out of the way rather than removing the blobs.

    Thanks

    Jason
     
  2. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    OK, I think I now know where the problem is, I just don't know how to fix it!

    Looking at the code for the fins in the later layers I see this:

    G1 X156.901 Y107.586 E0.1317 F1200
    G1 X156.907 Y107.553 E0.0004
    G1 X167.454 Y107.553 E0.1316
    G1 X167.460 Y107.586 E0.0004
    G1 E-1.5000 F4500

    So, the nozzle is running along the fin and extruding but is then stopping and going back across the same line but with only a 0.0004 extrusion i.e. hardly any. I think this something to do with Simplify 3D always running two lines around a perimeter.

    I've spent a while this morning going through trying different settings to try to get it to stop but looking at the previews it always does it. I tried increasing the extrusion width but as soon as it goes beyond the current setting S3D stops the fin printing altogether.

    Any suggestions, would other slicers be any different?

    Thanks!


    Jason
     
  3. Alex9779

    Alex9779 Moderator
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    Yeah that's something on my list of things I don't like in S3D and I also had issues with it... But I have no solution.
    As you said, S3D always prints a closed loop perimeter even if the structure is very small maybe just only the extrusion width. If you make it smaller or increase the ex width it disappears because it is smaller than your resolution, at least the current algorithm in S3D thinks so...
    Only thing you can try is smaller nozzle size or manually edit the gcode file...
     
  4. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Thanks Alex,

    I tried all kinds of things on a small test piece. The thing I don't understand is why it prints fine when the fins are on either side of the cylinder, it does two passes there and still looks fine. I've been looking at the extrusion width setting after going through pages and pages of people moaning on the S3D forums.

    I measured the fin thickness at around 0.33mm and tried setting the width at 0.16 and it came out much better on a tiny test piece. I'm now in the process of printing a part with those settings to see what happens.

    I'll post a picture when it's done (3 hours).

    One thing I don't understand, how can you print a 0.15mm line with a 0.25mm nozzle? Stretching the filament as it oozes out?
     
    #4 Jasons_BigBox, Oct 18, 2016
    Last edited: Oct 18, 2016
  5. Alex9779

    Alex9779 Moderator
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    Who says you can?
    You can set the values but physics won't let you get the result you expect. The slicer calculates that the extruded amount will match the theoretic line at that width but what will be printed is different...
     
  6. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Ah, salesmen! I didn't think it possible either. BUT.......... When I printed the piece with a smaller width I got much better results. I think if you want a 0.3mm line to print it will do one at 0.25mm's worth of extrusion and one at 0.05mm's worth and what happened for we was the second pass just spread and smudged the surface. When I made the width 0.15, the result was far better. It simply performs two runs 0.15 apart and extrudes much less for each pass. Some of the effect is still there but it's very minor now:

    DSCF1296.JPG


    Comparison:

    DSCF1297.JPG
    What's not clear is that the yellow one is actually 1:7 scale where the silver is 1:6 so the fins are even smaller. It looks odd because the silver one is only about a quarter of the head while the yellow one is a full half.

    I should be able to clean them up much better now.

    Thanks for the pointers

    Jason
     

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