Fork Steerer Cutting Anxiety

tl;dr Cut it a tiny bit longer and file it down to the correct length. Cover your fork with an old bed sheet to keep metal shavings off the stanchions. Make sure you're not going to cut into the star nut! Steerer should be 3mm below stem for top cap clearance. Measure top cap clearance after stem is tightened.

I read several posts on mtbr of folks using pipe cutters. They seem to work fine but roll the edge a bit. I was going to try this but my pipe cutter is for copper 1/2" and was too small. So hacksaw it is. First I drew a circle around the steerer at the top of the stem with a sharp pencil. Then I removed the stem and measured 3mm down for top cap clearance.

Next I wrapped a piece of painters tape at the top of the line. The hacksaw blade I had cuts a little over 1mm in width (kerf), so positioned it accordingly. The cut wasn't perfect but it veered out rather than in so that's fine. Next I filed it down so it'd be even with the tape. I recommend wearing gloves when filing since it can get really sharp and you need your fingers to ride your bike. Now I tapped the star nut down to the correct position.

This filing created a huge mess of metal shavings which stuck to my fork, so I spent the next 5-10 minutes cleaning shavings off. I put the stem back and tightened down on the top cap but nope it was still too tall (the compression washer in the stem moves about a 1mm as it is tightened). So back to the filing. This time I wrapped the fork with a cover. Now I could get the headset tight. It did loosen slightly on the first ride which is typical.

Top of stem marked

Measured 3mm down from top and taped

Final length

Lastly, after you preload the headset and tighen the stem, remove the top cap and measure again. The preload compresses the washer and brings the stem down a bit, such that it may be less than 3mm now and bottoming out. If it is, file it down some more