Can the difference in print dimensions in the X,Y plane when using fine Low Quality to Super Quality be accommodated in the software.

[TimBL 0]

I have been satisfied user of Cura for a number of years but there is one issue that I have not been able to resolve.

 

When I print a model the external dimension are always model dimension plus the thickness of the print laid down i.e. less for super quality and more for lower quality. Likewise inner dimensions such as holes are model dimensions minus the print lay down thickness. It seems the Cura software centres the printer on the edge rather than offsetting to take account of the change in print thickness. This is a problem when making parts that mate together. I can accommodate this by taking account of this extra material in model dimensions but that is almost impossible to manage if I want to print in a low quality and then fine.

 

Is there some switch I shpuld beawre of? Scale is not an option as it will make any holes smaller than they should be.

[GregValiant 1,330]

If you slice a 25 x 25 x 25 cube at 0.4 line width you will find that the toolpath in the gcode is 24.6 x 24.6 x 25.  Adding 1/2 line width all around gives a final dimension of 25 x 25 and the height will also be 25 as that is the height of the bottom of the nozzle off the build plate (provided leveling went well).  (Just for reference - my prints are typically +/- .04mm.)

That can be changed with the setting "Horizontal Expansion" and also (I think) with the Experimental "Slicing Tolerance" ("Middle" is the default).  The "Flow%" will also have an effect.
There may be some difference in "Quality" definitions between your printer and mine, but for my Ender 3 Pro there is no difference (regarding tolerancing) between "Fine" and "Draft".  The Layer Height changes but the line width is the same for both and so the toolpath (24.6 x 24.6) would be the same for both.

If the "Flow%" is different then the outer dimensions will be different.  There is no change in layer height or extrusion length so any difference in the volume of plastic only affects the line width and consequently the dimensions.

So the comment "Cura software centres the printer on the edge" would be incorrect.  With no Horizontal Expansion and with the Slicing Tolerance as Middle - Cura puts the path 1/2 line width from the part wall.  The "Variable" line width capability means it might be 1/2 the Calculated Line Width rather than the Line Width you entered into the setting box, but it's going to be 1/2 line width.

[TimBL 0]

Thanks this is what I have been looking for.