Support Free: Inverted Counterbores

Counterbores are often used in any assembly using fasteners, here is a trick to avoid the need to remove support material. It also works for slots as well:

This inverted slotted counterbore was printed without supports!

The key is the create two overlapping layers of bridging that create a square hole for the circular clearance hole to sit on top of.

Step 1: Start with your counterbore.

Step 2: Replicate the following sketch on the face your socket head screw would rest on.

Step 3: Extrude a slot into the part the thickness of one print layer, in this case 0.2mm.

Step 4: Extrude a square into the part the thickness of two print layers, in this case 0.4mm. Keep in mind we have only removed 0.2mm of material, but since we are reusing the previous sketch we must extrude 0.4mm.

Done! In the slicer we can see that the two bridged surfaces provide the perfect scaffold for the circular bore.