Constrcution lines - spoiling look and feel of model

[jimmyd 0]

Design query

I’m building my models in AutoCAD 3D 2013. I’m currently working on an item that requires raised font to be detailed upon the objects surface. Im producing the desired results from CAD but once I input the design into Cura it is producing very annoying ‘construction lines’?. Lines of PLA that zig and zagg across the surface and join with each item of lettering? It’s spoiling the look at the object.

Does anyone have experience of this? And can I mitigate the issue within Cura settings? We’re currently in the process of purchasing Sketchup (mainly for our architectural design requirements) but was wondering If said software would produce better models V's AutoCAD 2013?

J

 

[IRobertI 520]

Have you printed the model or are you looking at the preview in cura? The lines you're seeing could just be lines indicating where the head is moving. If that's not it make sure that you have enabled retraction.

 

[Daid 306]

Most likely you are having strings. Making sure retraction is enabled, and lowering the temperature a bit usually does wonders.

 

[jimmyd 0]

^{Yep models are printed and the enable retraction is selected. It almost appears as if its a trail as the nozzle moves around the printed item? im studiously watching the print to try to understand the prcess and it appears that as the nozzle moves around the model it leaves a tiny amount of PLA as it moves and over the course of the print and many layers it has the effect of appearing as if its part of the model?}

^{What temp would you recommend is set it at? im running at 210 currently?}

^J

 

[IRobertI 520]

In my experience it's a bit of black magic to find the sweet spot sometimes. The behaviour of the plastic can vary a bit depending on colour/batch/manufacturer. For example I have a roll of black that seems almost impossible to stop from stringing. I have a red roll that needs higher temperature than the others to stick to the bed. And then I have others that print very cleanly.

So I'd say experiment a bit, with both higher and lower temps. Personally I'm usually printing at around 220 but I have printed as low as 185.

Also, check if the edges of your print are curling up so that the nozzle is dragging through them and picking up plastic. You might need a bit more cooling if that's happening.

 

[gr5 2,173]

In general, the slower you print and the colder you print the less stringing you get but some types of PLA will string slightly no matter what you do. Here is an experiment I have repeated with a few colors and brands of PLA now that demonstrates the affect:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

 

If the lettering is near the top of the object I would just slow down print speed to 50% (with cura print window or with ulticontroller) and also lower the print temp to 195C and then once it settles, down to 190C. Once the lettering area is done I would raise the temp back and gradually, as temp is back to normal put speed back to 100%. This can all be done with the Ulticontroller or Cura print window.

In Cura settings, it's good to have the movement speed nice and fast - I like 150mm/sec which is the speed the head moves when not extruding.

Be careful not to accidentally go below 170C as Marlin will stop extruding if that happens.