Cura slicer

[Anguz]

So why caused it to not put a brim or a raft all the way round?
Skirt was the same shape...
The bottom is flat with just a fillet on the edges.
Turned support in but had to set angle to 0 to make it do a full brim

 

[Fred Trevvett]

Are you absolutely sure it's touching the whole face?

 

[Onoff]

Ask @Fred Trevvett 's brother maybe?

 

[tflnemesis]

Is the face completely flat? I have downloaded some models in past that have a very slight angle on what seems a flat face.
Otherwise I would say model is not flat to build plate.

 

[m_c]

As has been said, the part's likely not flat on the build plate.
If you rotate the view so you're looking at the bottom of the part (making sure you don't have raft selected - Cura may offset the part so it shows no contact due to the raft), any dark areas indicate that area isn't supported -

I've rotated this part up by 1deg to show the buildplate contact, which results in this raft -

 

[Anguz]

Are you absolutely sure it's touching the whole face?

Well it started as one extrusion.... agreed though it cant be flat
Dont really matter, cos i have decided to make the part from a bit of stainless, as not strong enough in plastic