's Forum Archives - Components

Archive Home >> Components(1 2 3 4 5 6 7 8 9 10 )

Help: How to cut a carbon steer tube?(22 posts)

Help: How to cut a carbon steer tube?Tiger98
Sep 19, 2001 5:44 PM
My new Pinarello comes complete with a carbon fork. Yay! Unfortunately, it has a carbon steer tube that I need to trim. How do you cut a carbon steer tube? Anything I should be aware of? Is it easy? Advice greatly appreciated.
You take it to a bike shop :-) NM.nestorl
Sep 19, 2001 5:45 PM
How do I know the shop knows what they're doing?Tiger98
Sep 19, 2001 5:52 PM
Carbon steer tubes are not too do I know that they know what they're doing, and not just "winging it?"
How do I know the shop knows what they're doing?digger
Sep 27, 2001 4:47 AM
probably more common at a good LBS than any ol' joe's garage shop, no?

besides, if LBS blows it they owe you a new fork, if you blow it SOL.
How to cut a carbon steer tube.Atombomber
Sep 19, 2001 6:19 PM
Cut it the same way you would an aluminum one, but there is one more step. Wrap the steerer with masking or electrical tape where you plan to cut. This prevents fraying or tear off. Set the guide where you want, and grab the hack-saw with a medium fine blade (24teeth/inch). If you don't have a cutoff guide, use a mitre box.
How to cut a carbon steer tube--Thanks!Tiger98
Sep 19, 2001 6:24 PM
This bike is my new pride and joy. I mistakenly assumed that the steer tube would be Al-alloy, but instead it is solid carbon. BTW, I've heard that carbon steerers are problematic in terms of getting a tight headset fit. Anyway, I just don't want to ruin my new fork.
How to cut a carbon steer tube--Thanks!jawa
Sep 19, 2001 7:26 PM
I have been riding a Look HSC (full carbon fork) for 3 years now with any problems. I cut the steerer tube as described above and have a C.King headset. Works great.

re: Help: How to cut a carbon steer tube?Birddog
Sep 19, 2001 7:53 PM
I know how you feel. I just cut my new Reynolds Ouzo Pro last week. It was with much trepidation that I picked up the hacksaw and went at the $300.00 fork. Before you begin, make sure you have the correct length figured out. Add a few millimeters to the length by placing spacers at the top. It reminded me of when I was growing up and mom would buy my pants a little long so I could "grow into them". I used a plain old hacksaw, as I could not find the blade made for cutting composites. I even tried Sears. My LBS said they use a regular hacksaw blade all the time. I didn't bother with the tape, and all went well. Use a round file to de-burr the inside of the tube, and a flat file to square off the end and de-burr the top edge just a little.
Follow the instructions with the fork, and make sure you use the right type of stem. I have a Ritchey WCS and it is super. Generally, you can only have spacers of 25mm (1 inch)for a 1" steerer tube. I think it is about 35 mm for a 1 and1/8" steerer. The hardest part is sucking it up and making the first stroke. Take you time and it will be over in less than 5 minutes and you will be glad you did it on your own. Remember, measure twice, cut once!

Good Luck
re: WAIT !!!!!bikeman
Sep 19, 2001 10:09 PM
I've heard that you SHOULDN'T USE a regular hacksaw blade for cutting carbon steerer tubes.
Instead, use a tungsten carbide blades. I think they're meant to cut masonry tiles/bricks or something.
They fit into a regular hacksaw, but they have a round cross-section and they are much, much sharper.
This way you can actually cut through the tube cleanly without fraying it. Otherwise you may risk delamination or something else catastrophic like that.
re: WAIT !!!!!Pb
Sep 20, 2001 4:22 AM
I agree. Go to Sears and spend 5 bucks on a blade made to cut composites. It really makes a much cleaner cut than a blade with teeth.
go ahead!C-40
Sep 20, 2001 9:27 AM
No special blade is needed. A 24 or 32 tooth conventional blade works fine. Just use light pressure. Carbon-fiber cuts very easily.

Tungsten blades are made to cut hard brittle materials.
-----> DON'T DO IT!!! <----- (carbon fiber lesson number 1)Bikeman
Sep 22, 2001 11:33 PM
First let me ask you a question: Why is it that carbon fiber composites are so strong? Carbon like that found in charcoal is weak, right? Why then are the fibers strong? Answer: because they have a very small diameter. "What's that got to do with anything?" I hear you you ask. Well, if they have a small diameter, they contain less microstructural defects. Hence the crystal structure is more perfect and they are stronger.

What do you think you are doing to the carbon's microstructure when you start hacking into it with your rusty old saw blade bought from Kmart years ago? Destroying it, that's what. Sure it might not stuff up today or even tomorrow - but years down the track when the microcracks have grown big enough.

Why do I tell you to use a Tungsten Carbide blade - so you can cut through the fibers as cleanly as possible, plus not risk fraying the edges (like what happens to those people using a regular blade - then they tell you to wrap it in sticky tape and cut through that).

Look, how much is your fork worth anyway? Lots.
Just buy the proper blade for the job for a few dollars extra
- your fork would thank you if it could talk.

One more thing C-40, Carbon fiber may not be very hard, but it certainly can be brittle. Because a composite that is designed to be strong can not truly be tough, but that's another story.

Bikeman B.Sc (Materials Science - Hons 1)
Sep 25, 2001 9:02 AM
I've made many cuts in carbon fiber steering tubes with a standard blade. Never seen the slightest hint of any splintering, fraying or damage.
Sep 25, 2001 9:16 AM
Just b/c you can't see it with a naked eye doesn't mean it's not there. Listen to what the man said and if you don't believe him read the instructions from a Reynolds Ouz Pro. They warn several times not to use a standard hacksaw blade with teeth. But hey, what do these dopes know anyway? Just remember, when composites fail they do so suddenly and catastrauphicaly.

Happy descents....
any other brands with this warning?C-40
Sep 25, 2001 5:14 PM
No warning of this type is included with a LOOK or Colnago fork. LOOK instructions say to "cut with a metal saw". Maybe Reynolds products are more easily frayed. Either that, or the warning is included to guard against people not smart enough to use a sharp blade and light pressure.

I perform microscopic inspection of precision machined metal products on a regular basis. I've looked at cuts made in carbon fiber tubes by a standard 24T blade under a microscope. They are clean and sharp. I've put thousands of miles on my forks with no problem at all.
Sep 26, 2001 9:11 AM
Probably the operative concept is using "a sharp blade and light pressure." Given that we can't seem to legislate common sense the mfr.'s probably figure it's best to skip the whole issue. Using a finer tooth blade is always good unless you're in a hurry. I routinely cut and break all sorts of CF (building sailboard and boat related components) with any number of tools (from grinders to blunt rocks). The trick is to not pull the matrix apart and introduce a stress riser.
I agree with grzy (carbon fiber lesson number 2)Bikeman
Sep 26, 2001 9:44 PM
I agree with grzy, just because you can't see it, doesn't mean its not there.
Well unless you've got an electron microscope C-40, you probably won't see it! Do you know what the diameter of a single carbon fiber is? About 6 microns. Thats 6 thousands of a millimetre. And if you can barely see an individual carbon fiber with your naked eye, you aren't going to see a crack that WILL cause it to fail.
One again...take it to your LBS !davidl
Sep 20, 2001 4:29 AM
After reading all these posts, that should be enough to convince you. You are sure that you don't know how to cut the fork, at least there's a chance the LBS knows how [tounge in cheek]. If the LBS does it, at least you will have some recourse if something goes wrong. If you screw it up, who's at fault? Good luck with it!!
Following the advice of a LBS, I used a regular ol' hacksaw.bill
Sep 20, 2001 6:59 AM
I also did not bother to measure, take the fork apart, and cut with a miter box or a guide. I set it up on the bike, left a good cm or more for a margin for error (using spacers and the stem, built up, as a guide), and I cut it on the bike. It was one of the easier things I did in building up the bike.
Other tips -- I did use electrical tape to prevent fraying (which presented a little bit of an issue when I jammed stuff on over the tape in order to use the spacers as a guide, but it wasn't too bad). I also made sure to leave space beneath where the cap would go, so I actually cut the tube with about .25 cm of spacers less than I intended to use. I also used a fairly fine file to take off some burrs and a little unevenness. If I had used a miter box, the cut probably would have been that much more even, but I would have been petrified of having measured incorrectly.
Get a new bike shop.grzy
Sep 25, 2001 9:18 AM
That little "fraying problem" is the whole issue. One that you should avoid.
Sep 21, 2001 8:58 PM
Dremel. :D
Sep 26, 2001 5:20 AM
Agree with using a Dremel with a cutting wheel. Cuts like butter. Use masking tape around the steerer tube so you can aim the cutting wheel as you work the Dremel around the tube.

Measure twice, cut once.

BEWARE of Carbon DUST - Do this outside and not in the garage - or else wear a respirator/mask. Better yet do both. The Dremel makes an extremely clean cut but all the material it cuts becomes airborne - BEWARE!

I have done this in cutting down a Colnago Star fork tube.