eldrick

There is a setting - Shell/Horizontal Expansion - which can make your walls thinner, by using a negative value. For example, a -.3 setting would make the cutter .6mm thinner, by shaving .3mm off both inner and outer walls. Use Preview to determine how many walls would result, and adjust to get the number of wall lines that would result.

https://www.mcmaster.com/threaded-inserts/

In Portland, Oregon with LOTS of spare parts. Make offer?

If the material is flexible, it will almost certainly be be too stretchy for a precision drive belt.

" I was after a slow incremental increase option? If there is one." Yes, there is, such a setting. It is found at the bottom of Cura's settings, under Experimental, and is called Use Adaptive Layers..

The only virtue of Sketchup for 3D printing is that it is free. Unfortunately it is worth the price.

Worse yet, when the printer reverses direction, it will result in blobby corners, because you have laid a new hot layer on top of the first layer without allowing time for the first layer to cool. All of the slicers that I know of have removed this feature, which was implemented to reduce print time, but had bad side effects.

Try Variable Layer Height.

Or try slightly thinner, like .38mm.

All the external surfaces are inside-out, i.e. not normalized. Run it through https://service.netfabb.com/login.php and it might be able to correct the errors.

The .stl is a mess - it has lots of errors. Run it through https://service.netfabb.com/login.php and it MAY correct the problems.

Small ABS parts can often benefit from fan cooling.

Right-click any STL file and choose Get Info. On the info panel note the "Open with:" item halfway down – choose Cura, then click Change All button. Done.

For several years I have heated the bed up to the target temp, while heating the extruder to about 50C less than its target. This avoids the possibility of overheating the material in the nozzle, and doesn't heat both at the same time for nearly as long. I've never had any sort of issue from doing so. I usually do this manually, rather than in starting gcode.

Adjust the Line Width by a a few hundredths of a mm up or down until you see the long gap vanish, for a start, and it will reduce the triangles size.