Introduction: The Blade Runner Multi-material Electric Knife

About: A long time Instructables lurker.. now pleased to be an Instructables worker, in; doing instead of doodling. This is easier now that I am 'semi' retired with more time to do stuff. My grandson is becom…

There are plenty of Instructables showing how to make hot cutters for foam but I have not seen one that uses this less smelly and more effective method.

This approach is definitely an unusual use for an ordinary thing, that gives EXTRAORDINARY results.

Step 1: It Started With a Cutting Need

I found some old foam sheets that had been used as camping mats or yoga mats.

I wanted to cut them into many different things but I wanted the best method.

I tried good old scissors, craft knives, carpet knives and hot knives but none were fast enough and gave a consistent cut.

Then I tried using an old electric carving knife and WOW what a great way to cut.

The remaining issue was controlling the cut and so I decided to build a mounting cradle.

I also decided that, instead of also building a bench or stand for it, I would build it to lock into a workmate type bench.

Step 2: Introducing the Blade Runner

I am extremely pleased with the way in which this has turned out and I have already used the new tool to create several useful items.

Here is how you can make your own:

Step 3: A Few Things You Will Need

As shown only a few basic tools and power tools were used.

Off cuts of white faced chip board, were already wide enough and so only needed cutting to length.

The electric carving knife was an ancient cracked remnant of the 70s but was still fully functional.

Of course it would look better in ply or an exotic wood, and I have no doubt that some readers will think that it could all be done with a CNC router, but it does a good job as built, and cost nothing to make.

I have not given precise sizes since so much depends upon the knife and workbench to be used, but the principles covered in this 'ible should enable anyone to adapt an old (or even new) electric knife into a very useful workshop tool.

Step 4: The Finished Project

Rather than put this image at the end I have inserted it here so that you can see what is going to be built.

You will need to adapt this basic plan to your own situation.

Step 5: The 'T' Shaped Mount

The two parts at each end sit upon the cross beams of the workmate and will need to be cut to suit your's.

Mounting this way save a lot extra work building a full frame. I have some other designs that I will share later that will be mounted on a workmate type bench.

Step 6: The Other Side

Here you see the electric knife mounted and ready for use.

Step 7: Bracket Close Up

I used a couple of metal brackets that I had in my box of bits. One of the brackets was not quite square but I compensated by off setting the mounting holes. This gives a strong support for the knife without obstructing the movement of the blade.

Step 8: Mounting the Knife

Having seen the finished item lets see how it was mounted.

The disassembly was done by removing one screw from the top and then pivoting the plastic body outwards.

Step 9: Marking Out

Having aligned the shell with the backing board and allowed ample room for the blade to be inserted, I drew a pencil line around the base.

Step 10: Marking the Holes

I drilled three holes in the case , spread out vertically. Then I marked the locations onto the back board. It might be have been possible to drill right through, but that would have needed holding in place which would have taken longer.

Step 11: Screw Down the Case

Three screws were sufficient to hold the case and the knife in position and there have been no problems in use.

Step 12: The Locking Screw Hole

Access to the locking screw would be required after the main body was returned onto the base shell. I solved this by drilling an access hole through the backing board.

Step 13: Wiring the Switch

The normal operation of the Knife is to have a momentary contact switch that needs to be held down during use.

For this application the knife needs to stay on, and so wires for an external switch were soldered across the terminals of the press switch.

Step 14: Wires Routed

The wires were fed down the sides out of the way of any moving parts and out through two drilled holes.

Step 15: All Together Now

Using the crafty access hole the retaining screw was inserted, locking the whole assembly together.

Step 16: The External Switch

A plastic switch box was fastened to the other side of the backing board.

Step 17: Wiring the Switch

The main switch was then wired up and the cover fastened on.

Step 18: A Safety Note

It is noted that there are available special power switches that will not suddenly start up again after a power outage.

If you are concerned that such a situation may arise, and you would not remember to switch off, then you may choose to add that type of switch to this project.

Step 19: Check Blade Alignment and Clearance

Conduct final all round checks to make sure all is in place correctly, and that there are no obstructions to the blades.

Step 20: Ready to Roll

Insert the assembly into your workmate and tighten up the jaws.

Adjust the surface of the knife board to be level with the surface of the vise. That will ensure smooth feeding of the material during cutting.

If smooth movement of the material is an issue, then consider adding a top surface that will extend out over the workmate top and provide a better sliding surface for handling larger pieces of material.

The Blade Runner is now ready to help you to create fantastic craft projects.

Step 21: Your Multi-material Cutting Electric Knife

The set up has been successfully used with many type of material.

These include; cardboard, Correx, leather, vinyl cloth, thin foam, thick foam, polystyrene, vinyl tiles and carpet.

I have not needed a permanent fence or guide but it is sometimes useful to clamp a guide bar to the workmate.

Step 22: Hey Careful Out There...


A reciprocating knife must be considered a potential hazard and so it is prudent to wear thick gloves of the type used by chain saw users. (Note: Sorry, this is definitely a, do as I suggest, not do as I do, type of note).

All domestic electric knives are only designed for short intermittent usage. Make sure that you do not use the machine for protracted sessions. Rest the motor for a few minutes every 10 minutes or so.

When not in use the machine should be unplugged.

A simple cover, such as the one that originally comes with the electric knife, should be placed over the blades between usage.

Take care....always.

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