What to do with Star Nut when Cutting Steerer Tube
 

When cutting a steerer tube to its final length, should the star nut be driven to final position with a punch or does it have to be replaced?

I just push them a little further down the steer tube. They are too hard to replace.

I had a similar situation the other day and checked with my LBS.. they charged me $5 to put a new one in. It took them like 5 minutes max. I'm guessing that just pushing it down on your own would work as well, but it was nice knowing (or expecting) that it was done right by the LBS. I figured $5 is worth that peace of mind. :)

It's better to cut the fork before fitting the star nut, but if you're cutting a fork with the star nut already in, there are two possibilities.

1- star nut is above the cut, in which you can make the cut below it, then push it out of the scrap and reuse it.
2- star nut is at the cut in which case you'll have to push it down deeper, since they're difficult if not impossible to pull back up. If you improvise a depth gauge you can push it to just below the cut, then maybe a bit more to final position after cutting.

If you push the star nut in too far, don't try to pull it back, either get a longer top cap screw to reach it, or push it down out of the way and fit a new nut in the right place.

Or saw right through the star nut, mumbling and wondering all the while why it's so darn hard to cut a steerer tube. Don't ask me how I know of this option. ;)

Star nut in steel ..maybe not in aluminum, no in Carbon.
compression expanders better then,
+ they are easily removed , and make No marks inside the tube .
scratches can = cracks over time.
the nut is aluminum on the one I had , so it breaks ,
leaving the stars, to turn and remove .
sus fork crown casting wouldn't allow me to shove the star nut out thru the bottom.

I fitted a BBB BHP 21 a Quill stem raiser for 9/8" threadless steerers
so no star nut was not needed again.

their design can go fully into a steerer, reinforcing it .. or stick up. and has keyed shims to clamp to the stem and the stem compresse the shims to the quill.
I needed more steerer not less..
the bolt tightening the wedge is threaded internally at the top,
for the other bolt for the headset adjustment.

Since it needs to be driven in further so that it is straight it's best to use a tool for the job. Just using a screw is a good way to end up with it misaligned unless you're both careful and a bit lucky.

The biggest problem with star nuts in aluminium steerer tubes is the typically thicker wall that makes it so hard to drive the nut in without scoring the snot out of the inside. In one case the wall was thick enough that I was able to use a 1 inch star nut. Another time it was thinner so that wasn't an option but the one sized for steel was too big. In that case I mounted the steel sized nut in my drill press and using an angle grinder "turned" the ears down a little and then smoothened out the sharp corners and edges to make for a nice fit which didn't scar things up badly at all but still gave a good grip. Sometimes you gotta improvise. In another case with an oddball inside diameter the fork came with the right size nut to fit the aluminium steerer tube.

Would pulling it from the crown with a long bolt give me better alignment?

Possibly, but no guarantee at all. A bolt that long will be pretty darn flexible and if one of the ears on the star is dug in more than the other it'll want to kick it to an angle.

Driving the star nut down further while keeping it straight is no more difficult than driving it in straight the first time.

Assuming it is in reasonably straight but too far up, get a longer bolt with the proper threading and use the headset's top cap as a centering guide while you drive the star nut deeper. Make a witness mark (a dot of nail polish works well) on the bolt above the top cap to guide how far down it should go.

Head set pre load adjustment is not needing much force at all to accomplish.
that bolt doesn't do much, after you tighten the stem clamps around the fork steerer,
it's just along for the ride..

Seems we should forget about bloody PITA star nuts and just go with compression plugs.

Starnuts are cheap and light, compression plugs are neither. So the star nut prevails as OEM and compression plugs are sold separately.