The Retractable Precision Knife v2

Stop losing your safety caps and worrying about exposed blades on your workbench. This 3D-printed precision knife features a fully retractable mechanism with two locking positions, designed for standard #11 hobby blades. The sleek, screw-together assembly ensures the blade stays secure during use and concealed during storage.

⚠ Safety Warning

• Handle with Care: Hobby blades are surgically sharp. Never touch the cutting edge.

• Material Limits: This is a 3D-printed tool and should be treated as more fragile than a metal equivalent. Do not apply excessive pressure.

• Inspection: Regularly inspect the plastic for stress fractures or white stress marks. If the slider becomes loose or the plastic cracks, discard and reprint immediately.

3D Printing

3D Print Settings

• Filament: PETG Highly Recommended Avoid standard PLA for this build. In testing, PLA proved too brittle and prone to wobbling. PETG provides the necessary flexibility and snug fit.

• Layer Height: 0.10mm – Critical for functional threads and internal tolerances.

• Seam Position: Rear – Keeps the internal sliding track smooth.

• Infill: Concentric (Top/Bottom) – for a professional finish.

• Supports: Paint-on supports required under the shaft slider notches and the top of the slider slot. Ensure supports do not enter the internal shaft.

• Brim: 5mm recommended for the Shaft and Grip components to ensure vertical stability.

Orientation, brim, and support details

Post-print Processing

1. Remove any brim and support material and burs from the shaft and grip edges.

2. Ensure the notches on the shaft for the latch are square.

3. File, sand, or trim, lumps or imperfections from slider part.

Assembly Instructions

Fit Check

1. Smooth Slide: Before installing the blade, test the slider inside the shaft. It should move freely.

2. Firm Threads: Screw the grip onto the shaft to "chase" the threads and ensure a smooth fit.

3. Dry Run: Follow assembly instructions first with no blade or optional printed blade to ensure the mechanisms fit into place.

The Slider Assembly

1. Install Latch: Slide the latch into the dovetail groove on the slider located below the handle. Center it so it protrudes equally on both sides.

1. Seat the Blade: Place a #11 blade onto the mounting pin of the slider. Ensure it sits perfectly flush.

1. Secure the Cover: Snap the blade cover onto the slider using the guide pins. The ends of the pins will protrude slightly from the sides—this is intentional.

Final Integration

1. Insert Slider: Insert the completed assembly inline into the shaft, backside first, handle facing up. Gently spread the tips of the shaft to allow the latch and cover pins to enter. (Similarly for disassembly, gently spread open the tips of the shaft, while depressing the handle and sliding forward.)

1. Align: Depress the handle and slide it back, ensuring the cover pins seat inline to the internal channels on each side of the shaft.

1. Test: Cycle the slider action several times to check for smoothness. Retract the slider fully when complete.

1. Attach Grip: Screw the grip onto the shaft until snug. Do not overtighten.

Retraction Action

• To Extend: Depress the handle and slide forward to your desired locking notch.

• To Retract: Depress the handle and slide all the way back until the blade is fully concealed.

Repeat a to break it in. Some initial friction is normal. Use discretion and do not force. If the mechanism does not loosen after several cycles, carefully disassemble and check for uneven surfaces or obstructions.