Guillotine Wire Cutter with NEMA 17 Screw Drive

A wire cutter that pinches the wire and spits it back instead of shearing it is the failure this guillotine is built around. Two 8 mm screws, one down each side, move a split carriage whose two V blades pass each other with no face gap, so the cut closes from the sides toward the middle instead of trapping the wire. The base and the bottom blade holder print as one piece, so nothing loosens or pries up under the cutting load, and each flanged nut is captive inside the split carriage, so nothing sticks up into the switch area and the carriage is pulled down as well as lifted.

Fit and print numbers

• Cutting height: the bottom blade's V bottom sits exactly 53 mm above the base underside, set to line up with a feeder. The holder stands 42 mm tall and grips 18 mm of the blade; the blade bolt head is open at the front, so a blade change needs no channel cut into the base.
• Base and blade holder: one piece, 132 × 45 × 42 mm overall, with a 6 mm base that sits just around the motors.
• Split carriage: lower half 128 × 28 × 16 mm, upper half 128 × 28 × 8 mm. Four M3 × 10 mm bolts clamp the halves, with the nuts trapped in the lower half. Each flange sits in a 22.8 mm round pocket, 3.5 mm deep, at the joint, and the 2 mm stub rises into a relief in the upper half. No bolts go through the flange holes.
• Drive: two NEMA 17 motors, 41 × 41 × 37 mm, bolted down with four M3 screws on the standard 31 mm pattern — 3.4 mm clear holes with 6.2 mm counterbores underneath. The two 8 mm screws are 100 mm long, joined to the motor shafts by 25 mm couplers (12.5 mm on the 5 mm shaft, 12.5 mm on the screw).
• Top plate: 130 × 42 × 10 mm in one piece, with no bearing in it. Each screw passes through a plain 8.6 mm hole, and the plate is sandwiched between two 8 mm clamping shaft collars (about 16 mm OD, with set screws) — one under the plate, one on top. A flat M8 washer on each side cuts friction. The collars clamp anywhere on the screw, so the screw ends can be trimmed; they currently stand about 15 mm above the plate. T8 nuts above and below the plate are the alternative if you would rather not use collars.
• Blades: each V blade is 10 × 2.5 × 34 mm, standing upright, with a 5 mm deep V notch — 29 mm to the V bottom at the centre — and a 3.3 mm hole centred 3 mm from the held end. The top blade sits 2.5 mm behind the bottom one, one blade thickness, so the faces touch. At the open position the blade tips are 8 mm apart and the V bottoms are 18 mm apart vertically. A 6 mm wire clears only if it sits centred side to side. An M3 bolt enters from the front through the hole into a hex nut trap in the back face of the holder, so a blade can be changed without splitting the carriage.
• Limit switch: 20 × 6 × 10 mm body with a roller underneath. The body sits in a 20.4 × 6.4 mm slot in the top plate, wires running out the top. The slot sits at X = -22, clear of the screw hole and the collars. The roller hangs below the plate directly over the flat top of the carriage, and the carriage itself trips it after about 8.5 mm of upward travel — no trigger post to print or lose.

Tolerances already in the model

• Blade pockets: 10.6 × 3.1 mm for the 10 × 2.5 mm blade, about 0.3 mm of play per side.
• Blade bolt holes: 3.6 mm for M3.
• Flange pockets: 22.8 mm for the 22 mm flange.
• Barrel holes: 11 mm for the 10.2 mm barrel.
• Screw holes: 8.6 mm for the 8 mm screw.

Fitting the flanged nuts

The carriage splits at the flange, so the nut drops in rather than being pushed through anything.

1. Lay the lower half with its joint face up.
2. Drop the nut in barrel first — the barrel goes down through the 11 mm hole until the flange sits in its pocket.
3. The 2 mm stub points up out of the pocket.
4. Set the upper half on top; its relief takes the stub and the flange is clamped between the halves.
5. Fit the four M3 bolts.

Print layout

The model comes as four parts, each flat on the bed with no supports, in a footprint of about 132 × 167 mm:

• Base and blade holder in one piece, standing upright.
• Top plate, flat on its bottom face.
• Carriage lower half, flipped so its joint face is on the bed and the blade pocket opens upward.
• Carriage upper half, joint face down.

At 0.2 mm layers and 15% infill the set is roughly 11 hours and 85–90 g: about 3.5 h for the base and holder, 3 h for the top plate, 3 h for the carriage lower half and 1.5 h for the upper half. Four perimeters, 10–15% gyroid infill and 4–5 top and bottom layers keep the strength where it matters — the perimeters carry the load in these parts, so slicer settings save more plastic than extra cut-outs would.

Split carriage and captive nuts

The split lets the flanged nuts sit inside the carriage instead of on top of it, so nothing sticks up into the switch area and the carriage can be pulled down as well as lifted. The bolts only clamp the halves; the flange presses on the printed halves in compression, not on the bolts.

• Print each half with its split face on the bed — both faces are flat, so no supports are needed.
• The lower half's blade pocket opens upward, so it prints cleanly.
• Layer lines run parallel to the joint; use extra perimeters around the bolt holes.
• The split also lets you change a nut without reprinting the whole carriage.

Before running it

• Set the lower end stop in your motor control. The V bottoms cross once the carriage bottom drops below about 70 mm, and the couplers stop it at about 58 mm, so there is roughly 12 mm of overlap. That is the only margin — do not rely on the hardware to end the stroke.
• Wire both motors to the same driver output, or to two drivers sharing step and direction. With no guide rods and no rear column, screws that drift out of step will twist the carriage and make it bind.
• The blades are modelled touching exactly. Two real faces with zero gap will rub, and printed pockets carry tolerance. If they bind, leave about 0.1 mm of clearance or a slight spring preload.
• Confirm the nut fit. The model uses a 15.5 mm overall nut: 10 mm threaded body, 3.5 mm flange and a 2 mm stub above the flange. If your 2 mm offset is meant to sit inside a 15 mm overall length, resize the pockets.
• Check the switch trips before the carriage reaches the top plate, and move the switch to the other side of the plate if your wire runs through on the left.
• Add side stiffness if the cut loads the frame. The top plate is held only by the screws and collars; two thin printed side rails from the base to the plate will resist flex better than extra plastic in the plate.
• Print the carriage and blade holder with layers running along their length, and use extra perimeters around the bolt holes and blade pocket.