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I began to feel a little knock in the left pedal on my old 10-speed and thought the bearings may have loosened.  But, when I examined it, I saw that the pedal shaft had begun to unscrew itself from the crank.  I have a suitable pedal wrench at home, but that bike is kept in another state for times when we visit there.  Because I have the necessary tools and scrap materials, I decided to make my own.

Step 1: Cut a Piece of Steel

I have a piece of scrap steel 5/32 inch (4 mm) thick.  It is a little harder than most steel and seemed ideal for making a pedal wrench.  It is thin enough to fit the narrowest flats on pedals and yet thick enough that it will not bend away.  

If it were a long bar, I could simply cut my wrench into one end of the bar.  I chose to cut off a piece of steel, form a wrench into it, and weld that to a bar for leverage.

I like to apply a piece of masking tape to steel and mark it with a fine point marker.  I am using a cutting wheel in an angle head grinder.  My steel is 2 7/16 inch wide.  I am cutting a 1 inch piece from it for my wrench.  Make it any size you like.

Step 2: Cut the Opening for the Flats

I applied a new piece of masking tape and marked the mid-point in the piece of steel.  Then I marked two vertical lines to define the sides of the wrench opening.  I cut two slots just under 15 mm apart at their outside edges.  Most pedal flats accept a 15 mm wrench.  Some are 9/16 inch.  9/16 inch is only 0.72 mm less than 15 mm.  In a pinch a 15 mm wrench can be used on a 9/16 pedal flat, or add a shim from a very thin piece of a can.

Step 3: Clear Between the Two Cuts

I clamped the portion of the steel I want to use in my vise.  I clamped a locking pliers to the part I want to remove and rocked it back and forth until it broke off.

Step 4: Fitting the Wrench to the Flats

My wrench piece was too tight to slide fully onto the pedal flats.  I would need to make the opening a little wider, but not by much.

Step 5: Grind Lightly on the Sides of the Opening

Although discouraged, I sometimes do a little light grinding on the side of an abrasive cutting wheel.  It made a good way to remove just a little material so I could fit the wrench for the pedal flats as in the previous step.  I also gave the bottom of the opening the shape of an arc so it better fits the rounded portion of the pedal shaft.

Step 6: Clamp in Place for Tack Welds

I had a piece of rod 7/16 inch in diameter and 11 inches long that would make a suitable wrench handle.  Holding a flat piece of steel in place for tack welding is much easier and more precise when a small spring clamp like the one here is used. 

Step 7: Finish the Wrench

After tack welding the wrench head to the steel rod, I removed the spring clamp and changed the wrench's position to make welding easier.  I welded both sides and removed the slag. 

The heat of welding did narrow the wrench opening just a little and I had to go back to step 5 to size the opening for the flats again. 

Step 8: In Use

You can customize your wrench by setting the wrench opening to an angle so the handle has a better mechanical advantage when removing a stubborn pedal.  Remember that as you face the outer end of a pedal, the pedal on the right side tightens when the wrench is turned in a clockwise direction, while the pedal on the left side of the bicycle tightens in a counter-clockwise direction.

The heat from welding seems to have softened my steel just a little.  Should the steel deform over time from pressure against the flats, I can always add a little weld bead on the affected area and grind it to size again as in step 5. 
Heat it up to dull red with a propane torch and dunk it in a bucket of old motor oil or water. Most steels available at hardware stores are either water hardening or oil hardening. Just don't quench with oil indoors, fire and houses usually don't mix well. :)
That would certainly be a good idea. I doubt I will use this wrench much. It is for emergencies. I did loosen the pedal shown in the photo by using this wrench. It was very, very tight. The wrench worked very well, but I could notice a very, very slight opening at the corners, indicating some softness. Thank you for the comment.

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Bio: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying ... More »
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