Fork Stem Shorten - Page 1 of 2


Figure 1

When making your own human powered vehicle, it is often necessary to shorten a head tube and fork for reasons such as under seat steering clearance, making a matching fork set, or simply for aesthetic purposes. Cutting a head tube down in size is as simple as marking and cutting, but to shorten the fork hardware to match requires cutting and welding with careful alignment. Now, let me get this out of the way before we continue: the section above the fork is technically called "the steerer tube", not the "fork stem", but since the term fork stem is more often used, I will use it as well. No point dwelling on grammatical inexactitudes when the time would be better spent on building something!

This tutorial assumes you have already cut your head tube to the desired length or have one you are planning to use that is too short for the fork stem. Install both bearing cups into the head tube and then install the top hardware on the threaded fork stem (including the top bearing) as shown here. While pressing the head tube up into the top hardware, measure the distance from the underside of the lower cup to the widest part of the fork bearing race. This measurement will represent the amount of material that needs to be taken away from your fork stem. Shown here is a measurement of 3 and one eighth of an inch to be removed.

Figure 2

Mark your fork stem using you measurement about an inch above the bearing race so that the welded area will not end up inside the bearing cup where the clearance is minimal. There are two methods that can be used to trim cut the head tube stem: freehand cutting with a hacksaw or zip disc and a tubing cutter. If you don't have a tubing cutter, you can make a cutting guide by wrapping some tape around the fork stem so that it makes a straight line around the circumference of the fork stem tubing.

Figure 3

A tubing cutter is an inexpensive hand tool that will make a perfect cut by running a sharp disc around the tube much like a guided pizza cutter. The benefit to using a tube cutter is that the joint will be perfect when you place the two pieces back together for welding. To use the tubing cutter, place the cutting wheel on the marked line, tighten the clamp wheel, and then turn the tool around the tubing until it there is little friction. Repeat this process until the cutting wheel has made it completely through the tubing. Cutting a fork stem will take about 30 seconds using this tool.

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