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loopy prints

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Why are my prints not smooth? The filament creates a loop design instead. I don't know if the problem is with the filament or the extruder or with a setting in Cura. The problem has occurred with multiple files, but not every file. We have tried changing filament spools and will have success for a while, then the problem reoccurs. This question is coming from a novice, so thank you in advance for your help.

3d.thumb.jpg.7698c4c8a7cdd00975d26067b509a69f.jpg

3d.thumb.jpg.7698c4c8a7cdd00975d26067b509a69f.jpg

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It looks like the nozzle isn't touching the print bed when you start the print. Is it? If it is then it looks like pretty soon (second or 3rd layer) the nozzle is *above* the print instead of touching it on future layers.

So the nozzle should be touching the glass when Z=0. There syhould be some kind of calibration procedure for this. What kind of printer is it?

Or you Z screw is moving much to fast such that when it should separate the nozzle and glass by an adittional .2mm it is instead moving maybe 2mm. If you think it's this second problem then move the Z 10mm and see if it actually moves about 10mm with some kind of ruler. Again - what kind of printer is this? Please put your printer type in your settings. It's okay if it's not an Ultimaker printer.

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Thank you for your response.  After investigating further, it does seem the nozzle is not touching the print bed when the print begins.  The distance from the glass differs on each print file.  Would that indicate a problem with a Cura setting on the files or a calibration problem with the printer?

I am using an Ultimaker 2, Cura 15.02.1, and Ultimaker brand PLA.

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I doubt it's cura but you could open the gcode file and search for the letter Z. It should typically be setting Z to 0.3 (0.3mm above the glass) on the bottom layer. If not you might have some cura settings messed up.

How much does this distance differ? Did you calibrate the Z? Did you use the paper method? You can calibrate it such that the nozzle is touching the glass also - that's how I usually calibrate.

I still don't know if your problem is that your calibration is a bit off, or if your z axis is moving 2X as far as it is supposed to. There are many causes for each of these issues.

If you are good with computers then I recommend you install pronterface to help sort this out:

http://koti.kapsi.fi/~kliment/printrun/

(do you have a pc? I think pronterface might not work on mac) After installing and launching it, connect your computer to the printer with the USB cable. Connect to the computer with pronterface (that's the hardest part sometimes - there are many possible com ports - maybe look in device manager and a com port should appear when you plug in the computer).

Try homing Z using pronterface. Check that the nozzle is just touching the glass. Then move to Z=10mm and measure that the nozzle is roughly 10mm from the glass. Doing those two operations will let us know if you have a Z home position error, or a Z steps/mm scaling error.

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Actually I don't think you need pronterface. In the advanced menu I think you can home the Z axis and check that the nozzle is just barely touching the glass. Then I think you can move the Z axis also in those menus somewhere. The tinker firmware is better though in that it shows you exactly how far you have moved. I think the standard firmware might not tell you that. So maybe you *do* need pronterface. Or tinkerMarlin.

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