Mate at work wanted something to cut thin films on microscope slides exactly vertically. So I came up with a guillotine-style rig…

There's also a remix of this with added fleur-de-lis (because, you know, it's a guillotine…) here…

Takes Wilkinson Sword classic-style double-edged razor blades. Other blades may or may not fit. You can edit the diameter and separation of the two flat pins holding the blade in place in the “moving arm back” part in the provided FreeCAD source file to fit other blades.

Other dimensions may also be adjusted in the FreeCAD source file, particularly the height of the whole contraption. The smooth rod length required for the supplied STLs is 72 mm but if you adjust the height of the contraption you will obviously have to also adjust what rod length is required. If you click on the “smooth rod” part under “props” in the FreeCAD file, you will be able to see the rod length in the “data” window (add forward and backward extrusion lengths).

You will need (for the STLs as supplied here):

• 1x Wilkinson Sword classic double-edged razor blade
• 8x M3x12 cap/socket head bolts for the base and cross beam
• 4x M3x6 cap/socket head bolts for the razor holder
• 4x LM3UU linear bearings (3 mm ID, 7 mm OD, 10 mm length) (e.g.,  from Amazon)
• 12x M3 nuts
• 2x linear rods 72 mm length, 3 mm diameter (e.g., from Amazon and cut to size)
• 2x compression springs, approx 5.7 mm OD, 39 mm length, 0.5 mm wire diameter - mine came from one of those spring assortment boxes you can get on Amazon. Exact dimensions not that important so long as the spring fits over the 3 mm rods and is long enough so the cutting jig is pushed against the cross beam when not in use.

Assembly should be pretty obvious if you look at the photos.

Some of the parts will need print supports, especially the “moving arm front” and “moving arm back” parts: supports are required for the semi-cylindrical depressions that take the bearings. Make sure to clear any artifacts out of them or else the bearings won't sit straight and the cutting jig won't move smoothly.

The base also needs supports where the bolts enter from the underside. There's a slight depression in the top of the base meant to fit a standard microscope slide so you can't just print the base inverted. The crossbeam and side beams print fine without supports.

Lubricate the bearings for smooth movement (I used 3-in-1 oil).

The springs are mounted below the cutting jig so that you need to push down (on the two sides that stick out past the side beams) to cut and the cutting jig returns to the top position when pressure is released. You could conceivably also mount the springs above the cutting jig so it's actually spring-loaded. Potentially more dangerous and more fun…