Last year, I installed carbon bars on one of my mountain bikes and I'm finding them too wide. I've been told that taping over the points you're going to cut at will prevent fraying/roughness, but what type of hacksaw blade should you use? Any other tips?
At the shop we generally use a "normal" hacksaw blade. I'd go with finer blade (more teeth per inch) if there's an option. Go slow and smooth (long low pressure strokes) and keep the blade perpendicular to the bars. The tape will probably help but do take care removing the tape or you might cause the fray you're trying to avoid.
There are special carbon cutting blades. We tried these and switched back to hacksaw.
Additionally: To cut at a perfect rightangle, I use two 'lock-on' collars (the sort that come with ODI MTB grips) next to eachother with a small gap between them as a guide for the hacksaw.
I've had better luck with the purpose made tungsten carbide blades. The teeth on a normal hacksaw blade tend to fray the carbon fibers more easily, especially with a low tooth count blade. The carbide blades are less apt to cause fraying, but you still have to be mindful as you cut. Let the blade do the work for you- don't bare down on the saw as you make your strokes.
The other big part to cutting carbon is your own personal safety. Carbon dust is nasty stuff that you don't want to inhale. A dust mask is one way mitigate the dust, but it still goes everywhere just to be knocked back up into the air later. Your best bet for keeping the dust out of the air is to spray water or rubbing alcohol (it dries quicker) onto the area you are cutting as you cut it. This traps the dust and keeps it in one place. Once you're done cutting you just wipe up the liquid and allow the area to dry. Much tidier and better for your lungs and the lungs of your shop mates.
I used a 32tpi hacksaw blade with a miter box from IKEA that they sell to cut their ceiling hanging curtain rail to keep my cut perpendicular to the bar.
It was a bit tougher cutting than I expected. But patience and no problems.
I'll echo the caution of carbon fiber dust. I sprayed the area with water and I still got "cotton" at the back of my throat.
But no fraying and some 150 grit sandpaper helped smooth the edges.