When the device is done, this is where documentation for the open source hardware stencil printer will live.

Here's a picture of the incomplete first prototype.

List of parts used from McMaster-Carr so far

97345A206 Type 316 Stainless Steel Shoulder Screw, 5/16" Dia X 7/8" Lg Shoulder, 1/4"-20 Thread
2397A11 Shoulder-style Removable Locating Pin, Round, 0.1245" Diameter, 1-3/16" Overall Length
9435K75 302 SS Precision Compression Spring, .875" Length, .36" Od, .032" Wire
90145A553 18-8 Stainless Steel Dowel Pin, 1/4" Diameter, 3" Length
9513K42 Color-coded Plastic Shim Stock, 15 Pieces, Assortment Of 5" X 20"
8982K58 Multipurpose 6061 Aluminum, 90 Deg Angle, 1/4" Thick, 2" X 4" Legs, 2' Long
1865K2 Quick-access Base Mount Shaft Support, For 3/8" Shaft Od
6061K325 Hardened Precision Steel Shaft, 3/8" Diameter, 15" Length
8600N5 Miniature Alum Base-mnt Ss Ball Brng--abec-3, For 3/8" Shaft Diameter
1630T32 Multipurpose 6061 Aluminum, U-channel, 3" Base X 1-3/4" Legs, 1' Length
5125K63 Brass Knob, Knurled Rim, 1/4"-20 X 1-3/4" Ss Stud, 1" Diameter
89585A8 Stainless Steel Swivel Pad, W/acetal Pad, 5/8" Dia, 5/8" H, 1/4"-20 Thread
94648A370 18-8 Ss Broach Style Captive Nut, 1/4"-20 Thread Size, .060" Minimum Panel Thickness

Optical breadboard is Newport SA2-08X08.

Press-fit holes for 0.250" pins in HDPE used size C drill, which is 0.242 nominal diameter. The pins pressed in nicely with an arbor press.

Positioning bolts thread into PEM nuts KFS2-0420, also known as McMaster 94648A370. In HDPE, these nuts press nicely into a nominal 0.328" hole, which is a 21/64" drill. I use the nuts because threads in HDPE don't last very long (or at least I fear they would get gummed up).