Print Anomalies: Weird tick in arcs and circles!

Hello!

I have this weird tick in arcs and circles and was wondering if anyone else is seeing this? My machine is a Taz Pro, Cura is 3.6.21. I have tried reverting back several versions on Cura and this still persists. I can’t see anything in the gcode. I use gcode viewers and there is no tick there so it has to be the interpreter on the Taz Pro.

Any ideas? Here are pictures of the problem; Google Photo Album of the tick

I’m thinking you are referring to the close-up examples you show in the last few photos.

It looks like this is where the print-head is starting & end each lap around the part as it generates the walls … and this may be an artifact over over vs under extruding at the start of a path vs. the end of a path.

Settings such as extra-priming after a retraction or coasting at the end of a printed path are meant to help deal with this. Other strategies such as wiping to infill can also help.

But you also have a little control over where Cura starts printed paths. In the “Shell” category, check the setting of your “Z-seam Alignment”. If you use “user-defined” then you can specify an x,y coordinate and it will find the location on your shell which is nearest to that coordinate and begin there. Or you can set “sharpest corner” and let Cura try to figure it out on it’s own. Or you can set “random” so it wont be in the same place on each layer (this somewhat hides the problem.)

But generally it is a result of uneven filament extruding. The printer has built-in “Linear Advance” to adjust filament flow based on changes in velocity … but while the firmware supports it, the default is that the printer doesn’t enable it.

I did do a Linear Advance test for both PLA and PETG on my TAZ Pro and found that a setting of right around 0.11 to 0.12 seemed to work best.

You can slice your model in Cura, then go into the “Layer” view menu… move up through the layers and click the animate button (the ‘play’ button) to watch how the nozzle plans to travel through that layer to determine if, in fact, the head is start and finishing the walls at that position and in which direction it travels. From this… you can tweak either some extra priming (to add more filament flow at the start of a path) or adjust coasting (to end filament flow just a tiny fraction before the end of a move).

So, this is the print head moving. You can literally see the print head jog over and then back on the opposite side. It is physical movement in the x and y axis together. No extruder involved as the start and ends are never in the same spot.

To clarify, I took the photos so that the tick is always orientated left to right. It manifests even in the skirts.

And no, the gcode has none of these movements present.

Since it isn’t showing up in the GCode, my guess would be something physical in the system or possibly the STL file. When you print, is it only at the start/stop seam locations or while it is in the middle of printing a perimeter? First, I would try random seam if it is only at the start/stop of the wall. Second, can you try creating a new file and saving the STL with more polygons?

John,

Thanks for the reply. It actually doesn’t have anything to do with start and stop. I let Cura chose that for me and it is never in the same place twice.

The defect is in the center of the arc or circle in line with the X axis. You can see this by the fact it does it in the skirt as well. Interestingly I was printing a 2GT Pulley and it starts off as a circle with the defect but once it got to the teeth the defect is not present BUT! it returns as it goes back to printing the circle towards the top.

Bolt holes all have this present inside the print. It is somehow a problem in the calculation of arcs in the gcode interpreter on the Taz Pro. So firmware.

Thanks again for the reply and questions.

–jb

Until you pointed it out, I didn’t notice it was also happening in the skirt.

This makes me wonder if there’s something blocking the machine. For example… if a bit of debris somehow got caught on the belt and that’s the spot where it gets pulled through the teeth on the motor. Or… is there some sticky point on the rods (are the rods damaged?) Or… is there something getting snagged?

Until you pointed it out, I didn’t notice it was also happening in the skirt.

This makes me wonder if there’s something blocking the machine. For example… if a bit of debris somehow got caught on the belt and that’s the spot where it gets pulled through the teeth on the motor. Or… is there some sticky point on the rods (are the rods damaged?) Or… is there something getting snagged?

The machine is clean. No damage. In fact!! If I replace the print head with the 0.8 HS and update the firmware the defect goes away. This is in the firmware for the dual extruder as far as I can tell.

When I put the dual extruder back on and update the firmware it comes right back.

OK, I have done my duty and asked the community. Time to open a ticket with the new owners and see if they are going to start updating the software any time soon.