Homebrew Laser Cutter made by Zach Radding

Step 8 Mirror and Lens

That's it, the whole optical system.

In this photo Zach's fingers are twisting a lead screw that raises and lowers the focusing lens. This is necessary to deal with materials of different thickness. This brings the hottest part of the beam to bear on the surface of the workpiece. Commercial machines typically raise and lower the platform supporting the workpiece instead.

The black triangular dingus contains a front-surface mirror angled at 45 degrees. The thumbscrews push the mirror around to aim the laser beam in the right direction, which is straight down through the focusing lens.

The focusing lens is a single piece of glass housed in the aluminum block attached to the leadscrew mechanism by two 4-40 capscrews. The lens housing came as a unit with a 45degree mirror attached for ~$600. For this machine the mirror was in the wrong place so Zach cut it off.

Below that are some nylon wireties. They ordinarily hold a hose that sucks smoky air away from the lens.
This is important. Without air flow smoke prevents good cutting. Also it gets on the optics and they burn up which is a tragedy except to those people who sell expensive lenses.