Hi jamie, yeah unfortunately inset is really pretty sensitive. It has a number of complex steps in it like a series of offsets, and also a merging process that involves merging coincident surfaces.

If you have your geometry to be as clean as possible it can help a lot.

In this case, you've got some surfaces in there that are planar, but they seem to be made up of sweeps or something like that rather than actual simple 4-point plane surfaces, like here:



If you simplify that piece by deleting the front and back faces, and then use the Construct > Planar command on it to cap off the front and back with simple planes, then Inset will work on it:



I've attached the updated 3DM file as well.

- Michael

Hi Jamie, also another quick thing you can try if something won't inset is to set up a keyboard shortcut with the ShrinkTrimmedSrf command on it, and run that on the object.

That shrinks the "underlying surface" of each face down to hug just the trim curves.

If you run that on this object, then Inset will work after that, even without replacing any surfaces with simple planes.

- Michael

Hi Michael

Thanks for taking a look. Indeed it was a sweep, good to know what to look for in the future.

Jamie