Test Fit, 3mm Machine Screw in to Boss

[ForrestErickson]

Test fit a Machine Screw into 3D Printed Boss

Using a Prusa 3i printer with a 0.4mm print nozzle and 1.78mm PLA filament, Lee printed the file "BOSS_ONLY_FILE.stl" as of 20250208 in blue PLA on about 20250210.

Test setup

Tape the boss to a table top.

Measure the OD of the boss and found 4.63mm

Measure the ID of the hole and found 1.86mm

Measure the ID of the counter bore and found 2.57mm

Try with 2.5mm screw

Not able to get the screw to make threads.

Reference

The openSCAD design called for
Hole ID of 2.4mm
Counter bore ID of 3mm

[samoyin]

There is approximately an 0.5mm difference between the expected and actual (2.4-1.86 = 0.54) Hole ID and the same difference is seen in the Counterbore ID (3- 2.57 = 0.43 difference.) This means the 3D printer is printer thinner walls for the Bosses. The actual outer diameter was 4.53mm and the expected was 4.8mm (4.8 - 4.53 = 0.27 mm difference.)

[ForrestErickson]

Lee testing with a plastite like screw taken from a multimeter. The major diameter is 2.63mm and the minor of 2.30mm.

I was able to get some thread engagement but

[nk25719]

3D print of the Boss

Trying to fit in a 3 mm Screw

Trying to fit in a 3.5 mm Screw

Outer diameter of the screw

hole diameter

counter bore diameter

[ForrestErickson]

Testing Rev2 Boss

File name: BOSS_ONLY_FILE_REV2.3mf
Lee Printed out of PLA.
Boss OD is 4.79mm
Boss length is 12.76mm
Hole ID is 2.54 mm
Counter Bore ID is 3.09 mm

Fit to Screw

A 3 mm machine screw fit into the counter bore.

Turning the machine screw it began to cut threads with some considerable force.

Turned in about three revolutions.