Are replica non sprung loaded OTF knives even a plastic replica to use as a display visual prop.. for a full size joker display available
here in the UK I dont want to have something illegal in my possession.
I'm working on a 3d printed version of the prop based on the S&W Extractor 1600 which would be totally legal and safe. The way it's designed, everything works just as it does on the actual knife (safety lock, push switch activation, spring forward and retracting from the 'tab' protruding from the slit along the side) except that it doesn't lock when extended. This is so if you were to run into anything with the blade (whether by accident or on purpose, say for pretending to stab your friends) it would encounter only the resistance of the spring on the way in - kind of like those gag knives they sell at Halloween stores and costume shops (maybe even magic shops in their gags section).
Here are some renders of the 3D CAD model along with an exploded view to show the inside.
I opted for a "stainless" text imprint on the blade instead of the S&W brand to make it more generic but I kept the USA and # on the handle to add character.
The spring from the blade is taken directly from a cheap 'Spirit of Halloween' retracting gag knife which is such a generic model I'm sure any shop would carry the same one regardless of packaging. All that matters is it uses the same spring which has an outer diameter of 5/16".
For the push switch, just about any wire spring with a .23" or less outer diameter can be cut down to the proper length. I've peaked inside a few LCD devices with buttons to see if any had the right spring for the job but could only find those rubber pads, none of which provide the proper .06" give needed to release the blade. A number of other materials could work here as well, the first test for mine will be the inner 'tube' section from in-ear phones with the removable rubber buds. When cut down to the proper length, it should be thick enough to hold the switch up but provide enough give for release in the downward direction.
You'll notice that the slit running down the middle of the blade has no access point for installing the release switch - this is one bit of post-print labor required for proper assembly. A slice will be made along the back edge of the blade so that the blade can be pulled apart just enough to insert the switch from the back, then glue back together. The length of the blade should give the material enough flexibility to accomplish this but since the plastic is .1" thick, it's still durable enough to hold it's shape under pressure.
The best part is that the model is designed to be ready to work on right out of the printer, so people could order them directly from Shapeways once it's perfected. The parts are sprued together in concealed locations to cut back on labor costs for the print. Some sanding will be required on certain parts after cutting the sprues to ensure proper fit. This is how it's assembled for the 3d print:
The idea is that the parts are places as close together without risking fusing together, then sprues are added to connect them at locations that won't be visible in the final assembly. I have yet to print the parts and test the functionality but I'm pretty confident it'll work as I designed it. All that will be left after separating the parts is some sanding and paint/varnish to complete the look. Regular model paints work great, I'll be using Testor's enamel.
