Hand Forged Wrench Knife Multi-tool: 10mm Carb Adjustment for Motorbikes




Introduction: Hand Forged Wrench Knife Multi-tool: 10mm Carb Adjustment for Motorbikes

About: I have too many projects going on to know where all the little cuts and scratches on my hands come from. Follow me here to catch up on my latest builds.

This instructable takes you through the process of making a wrench knife. Any size wrench will do but I chose 10mm since its the most common size hardware found on mopeds and motorcycles. The tip of the knife is also blunt and made into a flathead screwdriver which makes it ideal for adjusting carburetors on motorbikes.

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  • Anvil
  • Chisel Hardy
  • Hammer
  • Forge
  • Tongs
  • Belt Sander
  • Sewing Machine
  • Whet Stone


  • Wrench
  • Fuel for the Forge
  • Quenching Oil
  • Inner Tube

Step 1: Cutting the End Off

This step shows how I prepared the wrenches for shaping by cutting one end off. You need a forge, tongs, hammer, anvil, and a chisel hardy.

1. Prepare your work area and set the chisel hardy in the anvil

2. Heat up the metal till it's red hot and place it on the chisel hardy and hit it to cut it where desired

3/4. Hammer it! I like to do a big hit that gets most of the way through the piece then do a few small taps to finish the cut. The small taps prevent the freshly cut piece which is extremely hot from flying through the shop

5. Save the drops if you are doing multiple, you can weld them together and make an adorable baby wrench

Step 2: Shaping

The shaping of the knife is the biggest step uses a belt sander and all the forge equipment from the previous step except the chisel hardy.

1. Heat it up red hot and work it on the anvil. I need one hand for the tongs and one for the hammer so I don't have any hammering pics.

2. Hit it till you are pleased with the rough shape. Focusing your hitting on the side of the knife that you intend to sharpen will make it thinner and cause the steel to curve upward.

3. Use the belt sander to get a smooth curve and make any adjustment to its form. I made mine have a blunt tip the size of a medium flathead screw driver. This is so I can use it to adjust the carburetor on my mopeds and motorcycles but it has come in handy on several other occasions.

4. The knife must be thin at the sharp end and fat at the opposite end so I go over and refine the taper in the belt sander.

Step 3: Hardening and Sharpening

The knife will need to be hardened in order to hold a good edge, sadly wrenches are not the best steel for knife making razor sharp edges but they do good enough. This step requires a forge, tongs, a whet stone, and quenching oil (I used mineral oil).

1. Heat up the knife until it is red hot in the forge

2. Grab it with the tongs and dunk it in the oil. This will cause it to cool faster than normally and this produces a harder steel crystal structure.

3. Once cool take it out and sharpen on a whetstone.

Step 4: Sheathing

Sticking with the theme of motorbikes I made the sheath out of an old inner tube for one. It's so simple to make one this way it feels like cheating and you only need to sew one line.

1. Cut out a piece of inner tube long enough for you knife and sew a line just wide enough for it to fit in. This turns the single loop of the inner tube into two loops, one for the knife and one for the belt.

2. Put the sheath on your belt and you're good to go.

Step 5: Enjoy Your New Tool!

1. I made several iterations of this tool out of wrenches I got from a surplus hardware store that sold them individually.

2/3. While the blade is not the longest it fits nicely in my hand and does well when whittling small things.

4. The flathead tip I use for tuning my bikes and adjusting the carb for best performance.

5. The 10mm fits the handle bar mounts, exhaust nuts, head studs, and chain tensioner to name a few.

If you enjoyed this instructable or learned something from it please vote for me in the following contests, thanks!



Brave the Elements 2016

Second Prize in the
Brave the Elements 2016

Knives and Blades Challenge

Participated in the
Knives and Blades Challenge

Epilog Contest 8

Participated in the
Epilog Contest 8

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    3 Discussions


    3 years ago

    Great idea for a sheath using inner tube! The screwdriver tip is also clever.

    How well did the blade harden? I recently forged a knife out of an old Mossberg car wrench, but couldn't fully harden it (the file still digs into the blade when doing file test).


    3 years ago

    I like the idea. I am also very scared of slipping while using this tool :D


    Reply 3 years ago

    If you're scared of slipping, try to weld on a small handguard before the blade.