how do you get the drive tube the right length other than with spacers? is it ok to cut down the drive tube on a carbon fork if its way too long? and do you know if you could clamp a threadless stem onto a threaded fork? or if its a long one then cut the threaded portion off the drive tube then treat it like a threadless?

First, a little terminology: it's called a steerer or sterrer tube, not a drive tube.

Yes, it's perfectly normal to cut the steerer to the proper length for your frame and desired handlebar position. In fact, new forks come with the steerer intentionally much longer than almost any rider needs and are expected to be custom cut to the desired length.

You can clamp a threadless stem to a threaded fork if the steerer is long enough to allow all of the threaded section to be cut off. There are those who say you can leave a little bit of the threads and still be ok but I wouldn't do it for myself.

hmm... i wonder if it is unsafe to sandblast carbon fiber to get the paint off.. just because i know carbon fiber can be funny..
is there a special thing you need instead of a star fangled nut or expander bolt for carbon fiber, or is it all the same?

If you cut the carbon steerer tube, be sure to use a fine blade or you will cause carbon splinters to start. consider wrapping the steer tube with masking tape first to decrease splintering of carbon.

"Sterrer tube"?; what the hell is that?

Use an expander bolt for carbon, never a star nut.

Easton has a good article about cutting carbor fiber which can be found here:
https://www.eastonbike.com/downloadab...-05-Carbon.pdf

As rmfnla pointed out, you need an expander bolt for a carbon steerer tube.

When cutting, sanding, or sandblasting(why would you do this?) CF, be VERY careful. You need to use a ventilator mask and gloves. The dust is toxic.

Here are two references for cutting carbon steerer tubes:

https://www.eastonbike.com/downloada...D-05-Carbon.pdf
https://www.parktool.com/repair/readhowto.asp?id=111

It's important to use a cutting guide, or mitre, to keep the tube end square. This is just as important as having the top and bottom head tube faces perfectly parallel. If they are not, your bearings will not get equal loading all the way around and the bearing races will wear faster on one side. Having the top cap, or expander, installed perfectly square does the same thing. It preloads the bearing surfaces before you tighten up the stem clamp bolts. No matter what kind of bearings you have in your headset, it's important to have equal loading on them all the way around. The same is true for BBs as well. It's the same principal.

Unless its a Cannondale, they all use star nuts in the carbon steerers.

I can't see how this is possible. The top cap rests on the stem, not the steerer tube. The top cap is what adjusts tension. Unless your stem is sitting crooked somehow, its not going to affect bearing tension in any way that I can conceive.

Yes, if the steerer tube is cut to the correct length, you are correct. I have seen a couple where the top cap is just making contact with the top of the steerer tube and then it does make a difference - if it's square, you can get away with it. If it's not square, then it's the same result as having an improperly faced head tube (i.e. not parallel) That's what happens when someone tries to cut the tube to exactly the length for clearance rather than to miss the top of the stem by 2-3mm (which, of course, is what you should).

If the cap is crooked (for whatever reason), isn't it going to transfer this crookedness to the stem (as you pointed out) and cause uneven loading on the bearing? I have seen a lot of people state that they just pound in the star nut without a proper tool. If you think this through and the star nut is not aligned correctly, then you end up with a crooked top cap which will put more pressure on one side of the stem which will put more pressure on one side of the bearing. Right? If stems were an interference fit over the steerer tube, then I would have no argurment here. But, they do have some slop until they are tightened up and they are affected, to some extent, by the top cap. My point is that if your head tube faces are not parallel, and your top cap is crooked, or, the steerer tube was not cut to the correct length, then you are wasting your money on a good headset. How many people do you think go out and buy a CK headset and don't bother checking the facing of the head tube and getting it done (although if you're going to check it, you might as well get it faced), or, just pound that star nut in without considering how important it is to get it in perfectly straight?

One tip for cutting CF steerers is to use nail polish on the cut end after you're done. This helps prevent fraying and moisture contamination of the laminates.

A typo.

The instructions that came with my Kestrel EMS forks (all carbon except the steerer and dropouts) very specifically say "DO NOT sandblast, beadblast, or blast with any other media."

Also, DO NOT clamp a threadless stem to a threaded steerer, as someone above told you. Yes, you CAN do it, but you will never be able to remove the fork, as clamping a threadless stem will damage the threads on the steerer, so you will never be able to get the top nut or headset off again, common sense here..

Maybe he speaks my native dialect of redneck.

What? First, I recommended cutting off all the threaded portion of the steerer before using a threadless stem. You don't want to clamp the stem over the threads as they are a weak point and not intended to take the bending stresses imposed by the stem.

Second, since you will have to use a threadless headset, you do not thread the top nut of the headset onto the steerer so damaging the threads is not a problem. The threads aren't there and aren't needed.