Shadco 

If you wanted to remove 1 to 2mm from a carbon fiber steerer tube how would you do it?

Would you bevel the edges down to where you wanted to end up?

.

nomadmax 

Disk sander, not a handheld model.

Shadco 

right but what to hold the fork true to the platter?

.

shelbyfv

It doesn't need to be particularly true. Longer lengths are usually cut with a hacksaw, not precise.

Andrew R Stewart 

Since the top of a threadless steerer doesn't need to be particularly square with the axis a simple and quick "eyeball" approach is all that's needed. One trick is to wrap a bit of masking tape around the steerer and use the upper edge as a visual guide while grinding away. Remove the tape and deburr by hand with fine emery cloth. Andy

FBinNY 

As noted by others, it doesn't have to be perfect because nothing ever rests on the top and relies on it for squareness, nor is it ever seen.

However, if you're finicky, throw a hose clamp around it as a reference guide, and trim down with a file, or cut down with a hacksaw. While a bevel isn't necessary, I bevel all cuts out of habit.

wheelreason

We have a dedicated miter saw with a crazy fine blade and a jig to hold the fork (or seatpost) cause time is money, but a sacrificial hose clamp or old stem and a disk sander (hand held or otherwise) works well too. This is another "i gotta shoot the s***t with the mechanic for a bit" scenario, otherwise folks ***** about the rate per minute on the service. I usually tell em to get a coffee or such, and "it should be ready" when they get back...

FBinNY 

One hint for those using a hacksaw to cut CF steerers.

One of the general rules of using saws counts double with CF, namely, Let the saw do the work. People have a tendency bear down when sawing, which is fine on wood, kind of OK with steel or other metals, but a definite NoNo with CF. You want a sharp blade, and want to let it do the work. Bearing down causes it to bite too hard and tear rather than make a smooth cut.

Same with a file, light but firm pressure, not force.

Shadco 

brilliant, hose clamp and I tend to bevel. Hose clamp, mill file, mask and goggles don’t like cf dust.

SoSmellyAir

I would just add a 2 mm spacer, but maybe I am too risk-adverse when it comes to non-reversible changes.

Kontact

Don't grind it. That will damage the matrix. Use a diamond saw or a well worn metal hack saw.

FBinNY 

For that amount, I wouldn't bother either. However the OP asked how can I, not should I.

Steve B.

That was my thought. Why bother for a millimeter or two.

Andrew R Stewart 

The amount wanted to be removed (the reason and some of our opinions are unknown) is pretty much the cutting width of a common metal hack saw blade and much less than those carbide glued to a wire ones. So in this specific case I sort of suggested using a bench grinder or belt sander. The key, as I learned it by doing, is a fast cutting speed and a maximum grit count (fine cutting) stone/belt. The feed should be pretty slow and I have held the steerer's end against the grinder so the cutting force is tangential and the fibers support each other better. The usual time to do this is after cutting down the factory length to fit a bike and one does want to deliver the bike with a close to square and smooth top of steerer, so only minor removal is done. But taking off another mm or so should be no big deal if one doesn't use a hand held sawing tool. Andy

grumpus

I'd use one of these https://www.amazon.com/Zona-SA35-35-...dp/B0006N736A/ and just cut it as square as I could. Truthfully I wouldn't bother with 2 mm, but I do find those saws useful for precise cuts. CF pros use rotary tools with carbide grit discs for trimming, I'm not sure how useful that would be with such a fine cut.

Shadco 

The reason would be I have a custom spacer stack coming for this bike, it should work out just fine allowing me to simply replace the existing spacer stack while keeping the flush top cap.. if there is a couple mm difference from the current spacer set I want to reduce the height enough to use the stock cap. I know I could use a small spacer on top.





.