How to trim a carbon fibre steerer tube in 5 easy steps

IceToolz make a really nice tool for deburring the inside and outside edges of the cut. It works brilliantly http://www.icetoolz.com/ec99/rwd1111/product.asp?prodid=16B1.

Re the specialist carbon saw blade, any ceramic tile style hacksaw blade works. These are preferable to regular blades because the teeth of a regular blade hook the carbon strands and try to pull them out of the resin as they cut. Much better for the overall integrity of the carbon to abrade your way through with the tile saw style blade. You can shim the cheaper saw guides out with a bit of coke can or the like to make the gap wide enough for such a blade.

2 jubilee clips set a hacksaw-width apart, and a fine-toothed hacksaw. Works every time 

I've done a few now - new forks in used frames. I mark around the steerer and cut with the cut off disc on my angle grinder, usually while still on the bike. Glasses only (incredibly little dust created) worn. Never had a problem

So.... It's a tube. Plumbers deal with tubes all day. They use pipe cutting tools. They are deadly accurate, cut cleanly and you can be as gentle as you like. 
I have no idea why saws as used on steerer tubes. That's the way I was taught - makes no sense to me. 

I've done a few carbon steerer tubes and just use a fine toothed hacksaw and the Planet-X cutting guide. Does a perfect job every time, just avoid the dust.

For all those vacuuming carbon dust, make sure the vacuum has a HEPA filter on it otherwise a lot of the finest (and nastiest) dust will find its way back out of the vacuum.

This is listed as suitable for fibreglass and looks identical to the more expensive supposedly "bike" specific blades. 

https://www.toolstation.com/tungsten-carbide-grit-hacksaw/p48146?utm_sou...

I got a new stem last week and it has a 5mm stack height taller than my previous stem, which means to fit it there's no space for a spacer above it. It fits perfectly and looks totally flush, but I'm not sure if that's safe or not. Anyone have any idea? The new stem is a Zipp Sl course and has it's own top cap. All seems to fit fine. Haven't ridden it yet. Have visions of the front end exploding 

Worth checking what is advised by your fork manufacturer in terms of max number of spacers under the stem, as well as including a 5mm one above, as mentioned previously.

There's nothing wrong with wetting the saw blade to reduce dust production either.

aluminium tube- angle grinder+ file

Carbon tube- angle grinder, vacuum+ file

Using aluminium as a cutting guide (old stem, spacer, etc) may lead to the saw chewing up the guide and the cut not being straight. I'd go for something made of steel, eg the proper tool.

Good call about the gloves, mask and glasses.

I have found that a 10mm spacer taped into place makes a usedful guide.

Mask, gloves and glasses. Extra careful if you wear contacts, I knew someone who had some quite nasty eye problems after accidental exposure to fibreglass dust in their office.

The steerer tube that came on my new fork was crazy long - I'm sure no-one has a head tube that long!

A bike shop took 2" off it for me when they fitted the crown race, but now I've had it for a while, I'm confident it can lose another 15-20mm and still leave me with a bit to play with. Not ideal, but I really don't mind a bit sticking up on a road bike.

Unfortunately, because of the health issues with cutting carbon, my local bike shop seems to have a policy of once they have enough bookings, they'll start the extractors up. As the only person I'd trust to do it for me is fully booked, I've bought a carbon cutting blade - £8 online from Ribble - and will chop it myself with the hoover turned on.

Couple of jubilee clips should do the job as a guide.

FFS! Any sharp fine tooth mitre saw will do the job ! Why do folks these days over spec everything  !

Planet-X do something like this Park Tool guide (Jobsworth Fork Steerer Tube Saw Guide) for £14.99. Not sure if it has a guide wide enough for carbon specific blade though, might just be for usual steel blade.

Have also seen one for aero seat posts/steerers.

Only needed it done twice and both times I've been charged a mere £15. Cheap for peace of mind, no tools needed and have comeback against someone if they cock it up. It's the only job I won't do.

They haven't been around that long? 1963? 

Blimey.  New hacksaw blade and an old stem clamped to steerer as a guide to cut against.

That, probably expensive, blade looks like an ordinary tile cutting blade.

I don't know where park tools came from but they haven't been around that long and there's nothing special about most of their stuff.  I'm used to every US site plugging them but it's getting a bit much here doing it over here too.

I have a new carbon fork on order from my local shop (idiot pedestrian, busted fork), and they offered to cut it to size. Foolishly declined the offer; I'll be beavering away with a tape measure tonight, and back in tomorrow to eat some humble pie and ask pretty please if they could take a little off the top.

Some things are best left to the experts, or people more expert than me anyway.

Also, depending what stem you have, if it is completely flush and you decide to change brand you may be limited by the stack height. Not an issue for all people as well but if you decided to change your position in the future you may benefit from the adjustment

You should always have a small, usually 5mm, spacer above the stem, so the shop did it correctly. The reason is that there is less likelihood of crushing the top of the steerer with the stem clamp if you are not clamping right on the end of it.