Axles – How to Flat-Spot
Most axles are retained in a strut using a small set screw. Since the axle is round, a small flat spot should be made where the set screw contacts the axle to maximize the surface area. Here is the suggested method for flat-spotting axles on Pro-Link brand struts.
Pro-Link axles are supplied long to fit a variety of wheel sizes and brands. They must be removed from the strut and cut to the required length. Simplest method is to insert the axle through all the wheel components and mount the assembly onto strut. Measure the excess length between the head of the axle and the face of the wheel bushing. This measurement is what you will remove from the axle length. Mark you cutline with a sharpie.
Using a cut-off wheel (air or dremel), cut the end of the axle off at your mark. Use a belt sander or sanding drum to remove any burs and create a slight bevel to the axle end.
Slide the assembly back together over the axle and install the axle into the strut. Make sure the axle is fully inserted but not binding the assembly. Tighten the setscrew down fairly secure to create a mark on the axle where the screw makes contact.
Here the mark made from the set screw is visible. As you can see, the set screw, without a flat-spot, will only make contact with the high points of the radius. We want to make sure the screw has full contact with the axle surface.
There are numerous methods to create the flat, here I am using a Dremel with three cutoff wheels stacked to make the cut in on pass. A small file would work just as well. The key is not cutting to deep and making sure the flat is parallel with the axle.
Here is the flat-spot you want to achieve. Don’t cut too deep or at an angle! You only want to create a flat large enough for the screw to rest against. Do not flat all the way to the axle end, this tends to wedge the axle in the hole and can cause binding. Cut too deep and you weaken the strength of the axle! We don’t thread-lock these set-screws in our shop but should you prefer, we suggest blue only; and when removing, heat the set-screw with a soldering iron before removal to avoid the risk of rounding out the hex.