Hi Scott, probably the easiest way would be to use sweep for constructing that rather than doing 2 extrudes.

To get it done with your current objects you would probably have to use Trim to cut them with each other and then carefully select the pieces you want to discard.

If you use Sweep it has a mitering mechanism built into it when sweeping along a rail curve that has corners in it, where it automatically extends and trims pieces with each other without you needing to do any extra work.

To do the sweep method, make just one profile curve and then have a path curve made up of 2 lines joined together (either draw a polyline or draw 2 lines and then use Edit > Join to glue them together into one curve).

So that should look something like this (curves contained in attached 3DM file miter_sweep_example.3dm):



Then to do the sweep, select just the profile curve like this:



Then run Construct > Sweep, and at the prompt select the joined line curve for the rail path, then push "Done" or right-click in a viewport to finish the sweep, and you'll get this kind of result:




That tends to be the best way to build something like this using the least amount of curves and modeling operations, it's built into Sweep that it handles doing the corner miters for you for these kinds of paths.


It is possible to form a joint by intersecting the 2 extruded pieces as in your original question but it's a kind of more fiddly method. You could use either Trim or Booleans to do it. Trim and booleans are similar in that they cut things up, the difference is that Trim is a surface level operation that just cuts up the outer skins of things (then you usually follow it by Join to glue things together), while booleans are more oriented towards working with solid volumes and decide which pieces of things to keep and discard by which volume they are contained inside of. If your extrudes are solid closed volumes you could select both of the pieces, and then run Construct > Boolean > Merge which will intersect the pieces with each other and divide them up into smaller solid chunks at every crossing. Then select the excess pieces and delete them. That will leave you with 2 long pieces and a corner piece, select all those 3 remaining pieces and use Construct > Boolean > Union to unify them back into one solid again.

I'd recommend using the sweep method though so that you have a mitered result right from the initial construction though.

Hope this helps!

- Michael