How Do Prop Builders Make A Safe Chainsaw Bayonet Replica?

I love building props, and a chainsaw-bayonet replica is one of those builds that scratches both the cosplay and propmaker itches — loud design, mechanical-looking bits, and a lot of room to get creative while staying safe. The first rule I follow is: make it look intimidating without anything actually being able to cut, pierce, or whip. That means no exposed metal teeth, no sharpened edges, and no high-speed open chains. I usually start by sketching the silhouette and deciding which parts need rigidity (handle, mount) and which can be soft or flexible (the 'blade' and 'chain' faces). For cores I like lightweight aluminum or plywood spars for strength, or 3D-printed spine pieces in PETG if I need lots of detail. Over that, layers of EVA foam or high-density craft foam let me shape the profile safely and keep the whole piece light enough to carry for hours. Thermoplastics like Worbla are great for armored details, and Plasti Dip or flexible sealers protect foam from paint soak and give a more convincing finish without making anything sharp.

If you want movement — say a rotating-looking chain for effect — I favor an enclosed, low-speed solution that prevents fingers from ever reaching the teeth. A soft loop made from closed-cell foam or reinforced fabric can run over hidden polyurethane rollers inside a fully enclosed guide track. Use a small gear motor with a reduction gearbox (a worm gear is nice because it resists backdrive), keep RPMs slow, and limit torque so the chain can’t whip or bite. Always enclose the mechanism behind a rigid housing; any moving bits should be inaccessible behind screwed panels. Put in an emergency kill switch and a fuse inline with the battery, and locate the battery in a padded compartment so it won’t shift and break wiring if you bump the prop. For purely cosmetic vibration and sound I often ditch motion and install a little pager motor and a small speaker board that plays looped effects — it gives that chainsaw vibe without the mechanical risk.

Finishing is where the replica stops looking like foam and starts feeling real. After shaping, I seal all foam with contact cement or PVA then a couple coats of flexible sealer like Plasti Dip. Paint in layers: base metallic spray, darker washes in recesses, and dry-brushed highlights. For simulated teeth I cut thin wedges of craft foam or soft silicone, glue them to the outer face, and sand the tips to a rounded edge so they read like metal from a distance but are safe to touch. Rivets and bolts can be faux details made from epoxy or brass tubing — glued into place and weathered. Finally, test everything: drop tests, tug tests on the chain, and repeated on/off cycles for electronics. If this prop is intended for a con, double-check the event’s weapon rules — many require non-functioning props, no removable sharp bits, and a clear safety tag.

I always make a little safety checklist to pack: spare fuses, electrical tape, a wrist strap or harness to take weight from my hands, and a small toolkit to reseat fasteners. Seeing a chainsaw-bayonet come together — heavy-looking but harmless — is one of my favorite maker moments, and it’s a blast watching people do a double-take when they realize it’s built from foam and clever engineering.