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 ...
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.