This is what I have come up to de-rust some of the tools i'm lucky to live with. 
I find it to be very effective and it doesn't touch any of the good metal.
I've taken a cheap but large enough waste bin. Its size determines how large of a tool you can fit in it. Since I wanted to do my no 8 plane I surely needed a large one.
Inside the bin there has to be an anode (positive pole) that acts as a donor metal. I used 4 rods of 12mm rebar firmly secured with metal strips normally used in construction.
I bent the metal strips to roughly follow the outline of the bin corners. And I drilled 2 holes in each corner as high as possible but not so high it would cause you to pull out your hair when trying to put the bolts through.
For drilling to holes I used my Famag self centring pilot hole drill bit.
Each rebar mounting bracket consist of a metal strip, the rebar and a second strip. With two M5 bolts I Firmly pulled the metal strips together.
These M5 bolts also connect the wiring to the rebars. After firmly tightening them I loosened them again to mount the wires. I use a washer, the wire, a washer ad the nut for reassembly. Because the wires are held between the washers they aren't mechanically damaged and make good contact.
The wireing seems a bit complex but it isn't. All the rebars are simply connected with each other. To even out the amount of current per rebars I ran a wire between all rebars. From each rebar a wire runs to its 2 neighbouring rebars and two wires (a round the left and one around the right) to the opposite rebar. Its not necessary to do this but I liked to create a ballanced current loop.
Next I drilled two 12mm holes across the lid to fit a rebar. I use this rebar to hang the toll from. I also drilled a 5mm hole in the end. This way I can ty a wire to the toll, hang the toll from this wire and fasten the wire with theM5 bolt.
I use an old car battery charger. The negative clamp is placed on the rebar in the lid and thus to the tool hanging from it. The positive clamp is placed on one of the bolts of the brackets in the corners.
From now on its a de-rusting station instead of a garbage bin. The de-rusting station is filled with tap water. We hang a test piece of metal in the water and connect the battery charger. Almost no current will flow (pure water is not conductive). We add about 3 to 5 spoons of Na2CO3 sodium carbonate aka washing soda to the water until about 3 to 6 amps of current flows.
You will notice small bubbles come out of the fluid. This is oxygen and hydrogen. Both are not hazardous to you or your surroundings as long as you have some ventilation going on.
A few warnings:
Don't use stainless steel instead of normal metal, iron or steel for the anode. I used rebars because their ordinary steel and very cheap. Stainless stell contains chromium which is not very good for your health.
Don't use salt instead of washing soda. Although it works instead of oxygen and hydrogen chloride is formed. Which is a very poisonous gas.
Disposal
When the washing soda / water soluation becomes very polluted with a thick layer of rust floating on top you can scoop it off. The fluid itself is not harmful for the environment and can be disposed down a drain without problem. I would however advise again using it to give it to your flowers. Th fluid contains both iron and sodium carbonate which is a salt. Most flowers will not like such a fertilizer altough some do.
I find it to be very effective and it doesn't touch any of the good metal.I've taken a cheap but large enough waste bin. Its size determines how large of a tool you can fit in it. Since I wanted to do my no 8 plane I surely needed a large one.
Inside the bin there has to be an anode (positive pole) that acts as a donor metal. I used 4 rods of 12mm rebar firmly secured with metal strips normally used in construction.
I bent the metal strips to roughly follow the outline of the bin corners. And I drilled 2 holes in each corner as high as possible but not so high it would cause you to pull out your hair when trying to put the bolts through.
For drilling to holes I used my Famag self centring pilot hole drill bit.
Each rebar mounting bracket consist of a metal strip, the rebar and a second strip. With two M5 bolts I Firmly pulled the metal strips together.
These M5 bolts also connect the wiring to the rebars. After firmly tightening them I loosened them again to mount the wires. I use a washer, the wire, a washer ad the nut for reassembly. Because the wires are held between the washers they aren't mechanically damaged and make good contact.
The wireing seems a bit complex but it isn't. All the rebars are simply connected with each other. To even out the amount of current per rebars I ran a wire between all rebars. From each rebar a wire runs to its 2 neighbouring rebars and two wires (a round the left and one around the right) to the opposite rebar. Its not necessary to do this but I liked to create a ballanced current loop.
Next I drilled two 12mm holes across the lid to fit a rebar. I use this rebar to hang the toll from. I also drilled a 5mm hole in the end. This way I can ty a wire to the toll, hang the toll from this wire and fasten the wire with theM5 bolt.
I use an old car battery charger. The negative clamp is placed on the rebar in the lid and thus to the tool hanging from it. The positive clamp is placed on one of the bolts of the brackets in the corners.
From now on its a de-rusting station instead of a garbage bin. The de-rusting station is filled with tap water. We hang a test piece of metal in the water and connect the battery charger. Almost no current will flow (pure water is not conductive). We add about 3 to 5 spoons of Na2CO3 sodium carbonate aka washing soda to the water until about 3 to 6 amps of current flows.
You will notice small bubbles come out of the fluid. This is oxygen and hydrogen. Both are not hazardous to you or your surroundings as long as you have some ventilation going on.
A few warnings:
Don't use stainless steel instead of normal metal, iron or steel for the anode. I used rebars because their ordinary steel and very cheap. Stainless stell contains chromium which is not very good for your health.
Don't use salt instead of washing soda. Although it works instead of oxygen and hydrogen chloride is formed. Which is a very poisonous gas.
Disposal
When the washing soda / water soluation becomes very polluted with a thick layer of rust floating on top you can scoop it off. The fluid itself is not harmful for the environment and can be disposed down a drain without problem. I would however advise again using it to give it to your flowers. Th fluid contains both iron and sodium carbonate which is a salt. Most flowers will not like such a fertilizer altough some do.
