DIY CONE WRENCH TUTORIAL
When you need to service your front or rear wheel, you will no doubt need to remove the cone nuts in order to remove the axle and get access to the bearings. In order to remove cone nuts, you will need a special "slim" wrench designed to catch the flat faces on the cone nuts. This special wrench is of course called, a cone wrench. You can purchase a cone wrench at most bicycle shops, but if you are a all about DIY, then you can also make your own using nothing but an angle grinder and an old box wrench like the one shown in this photo.
A bicycle axle cone nut is actually a threaded bearing race. This race supports the weight of the bicycle through the axle and onto the ball bearings in the wheel hub. The cone nut is made of very hard steel, and also includes a dust cap that helps keep water and dirt from entering the bearings.
To make your own DIY cone wench, you will need a box wrench that fits onto the flat sections on your cone nut. Well, you can actually use a smaller wrench like I did, and open it up to fit, but it is easier to start with a wrench that fits if you have one you are willing to "hack" for the cause. As shown here, a normal wrench is much too thick to fit on the cone nut when there is another nut installed over the top of the cone nut. What we will do here is simply grind down the wrench until it is about half as thick as it is now. I choose a wrench that was slightly too small to fit, so I will also be opening up the slot in the wrench to fit the cone nut.
This photo shows two kinds of grinding discs; a sanding disc (flap disc) shown on the left and a thin grinding disc shown on the right. if you choose a donor wrench that already fits into the cone nut, then all you will need is the flap disc, but if you need to open up the wrench to fit onto the cone nut, then you will need the regular grinding disc as well.
A flap disc is a disc that contains multiple flaps of sandpaper, making it great for removing material a little bit at a time. Don't get me wrong, you can easily remove a lot of metal with a flap disc, but you can do it in a more controlled manner than a regular grinding disc, and it does a nice job of making the final grind nice and smooth.
The flap disc will be used to "machine" down the thickness of the wrench to about half of what it currently is. The idea is to hold the disc flat onto the face of the wrench, and work it back and forth at the same angle in order to remove an equal amount of material over the entire area to be ground. You only need to grind down the box section of the wrench, as this is the section that needs to slip between the done nut and the top nut.
The thin grinding disc will be used to open up the width of the wrench if you choose one that was slightly too small for the cone nut. I had a spare old wrench in my toolbox, and it was only one size too small for the cone nut, so it shall get new life as one of my custom DIY bicycle tools.
The thin grinding disc will be used to open up the box section by using the edge to evenly grind out material. Don't use a "zip disc" for this procedure, as they are too thin, and really better suited for cutting. This grinding disc is about 3/16" in thickness, so it can be used at the angle shown here without worry of it shattering from wearing too thin at the sides.
To open the width of the wrench, use the thin grinding disc to carefully remove material from the inside of the wrench as shown here. Come in at an angle of about 30-40 degrees so that you are not grinding on the face of the disc. Thin discs like this, should be used on the edge, not the face as they could break apart if they are worn too thin. Try to take off material evenly, moving the disc up and down along the entire distance to be machined. After 2 or 3 passes, flip over the wrench and then grind the same amount from the opposite side.
After a bit of grinding, check the wrench on the cone nut to see where you are at. It's better to take out a little material at a time, checking the fit as you work. in this photo, I took out enough material to get the end of the wrench to slide onto the cone nut, but it needed a little more work on the inside of the wrench to fit on all the way.
Repeat the process, taking off material where necessary until the wrench fits snuggly onto the cone nut.
The wrench should fit snuggly onto the cone with minimal play. A little slack is ok, but if the wrench is too loose, then you may round off the corners of the cone nut when you are removing or tightening the locking nut.
This photo shows the adjusted wrench fit onto the cone nut. Notice how the wrench is almost twice as thick as the flat sections on the cone nut, something that will now be adjusted using the flap disc.
Using the flap disc, remove material from the box section of the wrench, keeping the disc even as you work it up and down the section to be thinned down. Even though the disc is made of nothing more than overlapping sheets of sandpaper, it can easily take down the metal, so don't push too hard on the grinder, and try to work around the entire face evenly.
Once you have made a few passes with the flap disc, the wrench will probably be getting a bit warm. If the wrench is turning blue, then you are pressing too hard, so ease off and work a little slower. The ground face should look smooth and even as shown here. The goal is to remove an even amount of material to maintain the flat sides of the wrench.
Continue the process, taking off the same amount of material on the other side of the wrench. Try to machine the face evenly so the wrench maintains its original flat shape.
When you have taken a little material off both sides of the wrench, place it on the cone nut for a quick fitting test. You want to take off enough material so that the wrench is only slightly thinner than the height of the cone nuts flat sections. As shown in this photo, my wrench is now a perfect fit on the cone nut.
Once you have thinned your wrench so that it fits onto the cone nut properly, you can then clean up the sharp edges. The edges of the wrench are razor sharp due to the grinding process, so a little smoothing out with the flap disc will easily remove the sharp edges. lightly run the disc at a 45 degree angle along the outer edges and inner edges of the wrench until it is smooth to the touch.
Your DIY bicycle cone wrench is now complete. With a little clean up, the finished product looks almost store bought. Actually, this DIY cone wrench is of higher quality than the store bought units I own, as they are only made of stamped mild steel whereas this one is hardened polished steel. Not bad for 10 minutes of work with an angle grinder!
This photo shows how the cone wrench fits between the top face of the cone nut and underneath the locking nut. The reason the cone nut has such a minimal profile is because wider axle hardware would require a wider spread on the frame tubing or front fork tubing, which would just be a waste of material.
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