Almost Perfect Parts, but…

120918 Manga  Retract Problem

I’ve been able to fine tuning my tool chain and Tantillus printer to the point that parts come off the printer looking almost perfect. The dimensions are close to spot-on, though my first layer is still a bit squashed. The surface finish when I print PLA with 150 micron layers looks almost like satin.

Therein lies the problem. The surface finish is so good that any defect is immediately noticeable. And I’m getting what I call ‘zits’ on the surface at some locations during the print. The ‘zits’ are small protrusions of extra plastic that stick out from the surface. My best guess is that it’s a retraction problem that occurs at z-axis transitions and other spots where the extruder has to quickly retract the filament.

Of course the same zits must be occurring within the part, but since I can’t see them they don’t bother me. And, as long as the parts are fairly simple – like cubes, cylinders, and the like, the zits don’t show up very much. However, as soon as the part gets a little complex, especially when I use infill, the zits pop up like a high school student addicted to chocolate bars and quarts of ice cream.

Going back to the Slic3r initial settings that were developed for Tantillus doesn’t eliminate or minimise the problem. Researching the problem online has helped a bit, and convinced me that it is a retract related problem. But, since Tantillus is a Bowden based system, unlike most of the RepRap printers out there, the retract settings have to be considerably different.

So, to try and debug the problem, I’ve started to print multiple copies of the same part – initially a simple ring, while varying the retract settings. Hopefully I’ll be able to see which setting(s) make the problem better (or worse), and home in on a solution.

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Avid technologist with a passion for 3D printing, RepRap, and robots of all types and sizes.

Comments (5)

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  1. Mark Voevodin says:

    This is exact same problem, with same settings, on my Printrbot LC. Let us know if you have any success.
    I like the reference to ‘zits’, as I explain 3D extrusion as “like popping a zit”!

  2. Are you printing directly from a SD card?

    • 3DPrinter says:

      Yes. I rarely print from the PC, though I sometimes have it connected to monitor the printer. Even when the PC (Macbook Air) is connected running Pronterface, the printer is grabbing the gcode data from the built-in SD card.

  3. Sublime says:

    Have you followed the retraction calibration on the tutorial page of Tantillus.org? Once you get the retraction speed as high as it will go you can then try increasing or decreasing the retraction distance in slic3r. The key is to retract as much as possible within the time it takes for the ooze to reach the layer. If you are in any spot too long regardless of retract distance you will get a zit. If you do not retract enough you will get a zit. It is a fine balance of speed vs. distance. But it all comes down to how long it is at one particular spot and how log it takes to travel to the next spot. If the travel speed is too low it will ooze while travelling and leave the zit where it travels too. If it leaves the zit where it leaves from it is a retraction speed or distance problem. For Tantillus the retraction distance should be between 4mm and 6mm. Another helpful setting is the temperature. If it is too hot it will ooze more. Also if the plastic has absorbed moisture it will ooze a lot as it converts to steam. You can dry it in an oven at a low temp if you think this could be the issue. One last thing that it could be is your flow is too high. This results in there being extra pressure in the cable which is hard to deal with in retraction. Try following the flow calibration on Tantillus.org and see if it helps reduce the zits.

    • 3DPrinter says:

      Thanks Sublime.

      Yes, I’ve gone through the retraction calibration process. I may have set it too low and will go back and redo it again. We reduced it in the firmware before when I was having other problems.

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