Sometimes you need to change your forks. Maybe you broke one or you just want to try something new. When you buy a fork in the shop it may not be the correct length for your bike and you'll need to cut it down. Here's what to do:
Step 1: Measure twice cut once
The first thing to do is insert the fork into the headtube with the headset and stem so you know how much extra steer tube there is. You can also measure the steer tube from the old fork and the steer tube from the new fork then mark a spot on the new fork at the correct position to cut.
Step 2: Punch it
Most stems these days connect to star nut inside the steer tube. If possible we want to reuse this nut. To do so we will get a punch with a diameter larger than the threaded portion of the steer nut. It's best if it is the size of the center piece. Secure the fork in a vice or use cushions under the fork blades and then hammer the punch into the star nut to move it to the new desired location. If you punch it too far you won't get it back, if you don't punch it far enough you will cut through it with the saw.
Step 3: Cut it
put the fork in the horizontal band saw so the mark from the first step lines up with the blade and make your cut
Step 4: Finish it
the fork will be rough and a little jagged after cutting. get some files and file off the top and the outside and inside edges.
install the fork and go