Five finishing mistakes that ruin a Polymer80 frame

Nearly every frame that fails to run was damaged during finishing, not made badly. These are the five mistakes we see most, and how to avoid each.

1. Cutting the rail tabs flush in one pass

Take the tabs down with the end mill in shallow passes, then finish with a file. One deep pass tears the polymer and leaves a ragged edge the slide drags on.

2. Drilling pin holes freehand

Drill through the jig guides, from both sides, to the middle. A pin hole drilled at an angle misaligns the locking block and the trigger housing and cannot be corrected.

3. Removing the barrel block too aggressively

Stop at the jig line. Going deeper leaves the barrel unsupported and causes erratic lockup.

4. Skipping the dry fit

Fit the slide before the rails are fully finished. If it drags, take a little more off the tabs; if it wobbles, stop, because material cannot be put back.

5. Letting the frame get hot

High drill speeds melt polymer instead of cutting it. Use a low speed, clear chips often and let the frame cool between steps.

Before the first shot

Function check unloaded: slide travel, trigger pull and reset, and that the striker does not release when the slide is closed hard. If anything is off, find it on the bench, not at the range.

This is general information, not legal advice. Laws on unfinished frames, receivers and firearms vary by state and city and change often. Check the current law where you live before ordering.