What might cause gaps in the shell?

[rob 0]

I've printed a few different objects recently and noticed a line/gap in the shell on the back of the objects (only the back surface) I've printed where there is plastic missing, It seems to be in the same place on all of the objects, any idea what might be causing this?

 

I'm using 3mm Earl Grey filament from Faberdashery and Cura 13.06

 

 

[snowygrouch 1]

By "same place", do you mean just "the back"...or its the same Z height level as well ?

 

[thingster 0]

Obviously the z-level. Strange problem. It doesn't look like under-extrusion but to verify I'd need to see the objects from top. For the moment I'd assume it's bad mesh geometry mixing the slicer up or a problem with the z-carriage, maybe a rod with a defect exactly at that point or something like that.

[snowygrouch 1]

Its not at all obvious Trion, if it was 100% a z level problem there would be no reason for it to only

occur at the back only without showing any other sign of interlayer mismatch on sides or front.

The Z screw is not moving during a single layer (unless the new CURA has "jump" feature). Therfore any layer offset

from the Z stage must be reflected in the alignment of the entire layer in question.

So I think its important to get more info. What happens on the outside is also strongly

influenced by whats inside the model. So if you have some infill happening on a certain level

and so on, this (depending alot also on the slicer) is having an effect on outer shape.

I would suggest to post STL file, and details about what slicer settings you are using.

 

 

[Daid 306]

How thick are those layers?

 

[pablobell 0]

Daid has a good point. A layer size thicker than 80% the nozzle size is too much, as you wil be close to dropping the melted plastic in mid air. That means not more than 0.32mm for the UM nozzle.

If that is not the issue, then try rotating the object, slicing again and printing. Did the hole move with the object?

Then cut a slice from the bottom of the object with your CAD/NetFabb, so that the object gets thinner. Slice and print. Did the hole move?