Cutting of carbon steerer

Discuss light weight issues concerning road bikes & parts.
Posts: 65
Joined: Mon Jun 28, 2010 3:28 pm

by ianeverton

I am in the middle of tweaking my stem/bar position and so removing, changing out spacers etc, when I have found the best position for me i will be looking to cut down my carbon forks.

Any advice on best techniques, tools, length I need to leave etc in advance please ??


User avatar
in the industry
Posts: 3085
Joined: Sun Nov 21, 2004 2:45 pm
Location: London, UK

by ultimobici

A cutting guide like the one Park do is handy for a good 90 degree cut. A carbon friendly blade, which is more like a file than a serrated blade coupled with some electrical tape.

When you cut, cut from one side to the halfway point then rotate 180 degrees and cut the rest. This avoids damage at the end of the cut.

by Weenie

User avatar
Posts: 5072
Joined: Mon Jan 23, 2006 6:35 am
Location: New York

by stella-azzurra

It's advisable to remove the fork from the frame.

You need a guide and a cutting blade, some tape if you like and some sand paper.

Use this cutting guide Threadless Saw Guide - #SG-6 or make one yourself. You can also use a miter box
Use a 32T cutting blade.
Use some tape to wrap around the area you will cut through to avoid any splintering of the carbon.

Cut slowly with even straight strokes.
Do not force the blade while cutting. Let it cut.
Do not force the steer tube just let it fall off as you cut.

Use the sand paper to plane the top if needed and remove any burs.
I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree

Posts: 131
Joined: Wed Jun 06, 2007 5:50 am
Location: Pacific NW

by roadrider22

Mark the top of the steer tube at the top of the stem with the proper amount of spacers underneath. It is often a good idea to leave enough stem to place a 5 or 10mm spacer above the stem (some manaufacturers, like Trek, require this on thin walled carbon steer tubes). Regardless of whether you leave a spacer on top of the stem, your mark to cut must be a couple of mm below the top of the stem or spacer on top to accomodate the top cap. Once I have my mark I wrap a couple of layers of clear tape over the cut mark to eliminate any fraying of the carbon. Source a steer tube cutting guide to assist in the cut and always use a minimum of a 32 tooth SHARP hacksaw blade. Good luck.

Posts: 361
Joined: Sun Mar 23, 2008 7:31 pm

by Camilo

All the advice given above is good. I have just a couple of minor things to add.

A very fine hacksaw blade works as well as anything, the best thing I've found.

I've used a miter guide twice and neither time was the cut perfectly square. Next time I'll either buy a cutting guide or fashion one out of hose clamps.

The times the cut didn't come out square, it was easy enough to square it up with a flat file -slowly, checking w/ a square on two different axes, etc. Took about 5-10 minutes. It really wasn't a big deal, but the cut wasn't too far off to begin with.

It's really not a technically tough thing, but if you mess it up, it's a high price to pay. I recommend doing a practice cut (i.e. cut the tube long just to practice).

Measure twice cut once - use the method described above (actual installed length with spacers and stem). Follow the fork and/or plug manufacturer's recommendations as to length. Some require a couple mm below the stem, some recommend cutting it 3 mm longer than the top of the stem so you can put a 5 mm spacer on top of the stem and the tube will be about 2 mm shorter than that. There is no "standard" way of doing this, it depends on how the plug interacts with the stem. I've had both types of instructions.

Posts: 1651
Joined: Wed Mar 28, 2007 12:49 pm
Location: Near Horgen, Switzerland

by mrfish

My technique:

1) Put tape on the tube. Mark off the height all the way round the tube. This is critical as if the hacksaw wanders off you need to be able to see it and stop cutting.

2) Clamp the tube so it doesn't move. It's impossible to make an accurate cut if the fork is wiggling around on a desk.

3) Use a seat clamp, stem, fork brake hanger or similar as a cutting guide. Clamp it near the cut line then add a cheap stem spacer to guide the blade. Of course a Park tool version is better, but not worthwhile if you only use it every 3 years.

4) Cut slowy. If it goes a bit off line, stop and start from another position. Cut right through without attempting to snap off the last piece. As it's all fixed down, this is easy.

5) Leave the stem spacer where it is or move it down 0.5mm. Use it as a guide to file the top completely square.

Posts: 576
Joined: Wed Jul 08, 2009 9:19 pm

by Doolop

Okay, I know this will be considered crazy by many, but after hundreds of carbon posts, forks and bars this is the best I have found.

A cut off saw. The kind made for metal. It seriously leaves the best cut I have ever seen. Go slow and it practically melts through the back side.

Other then that wrap the tube with electrical tape and cut away. Cut a bit in from the backside to avoid splintering.

Posts: 86
Joined: Thu Jun 03, 2010 8:28 pm

by bikerboy337

Make sure you use a guide... i always sand lightly when done as well...

also, be careful of the carbon dust... dotn want to breath that in...

Posts: 41
Joined: Fri Jul 15, 2011 9:32 pm

by ajz07

I love that it took how many posts before someone noted that he needed either do this in a well ventilated area, or better yet, to wear a ventilator/ mask.

I agree with pretty much all of the above, but please wear a mask!

User avatar
Posts: 2035
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

My top choice is my electric miter saw with a fine-blade intended for thin plywood and veneers.
Even cutting "slowly" it is increadibly fast and leaves a perfect 90° cut with no splintering.

But I have also used a fine-blade metal blade in a hack saw. This is much slower and effort-intensive, but works.

I always smooth the cut end with fine (400-600 grit) sandpaper and make sure therre are no delaminations or chips .

Yes, wear a dust mask.

User avatar
Gold Knight
Posts: 553
Joined: Mon Nov 07, 2005 4:27 pm
Location: Santa Barbara, CA

by Gold Knight

i see no reason to wear a mask while cutting a little tube like a fork or seatpost. make a nick on the tube and just align it and cut the thing through the Park guide and brush off the dust with your hands to throw away and wash up.
:smartass: DO NOT RIDE AN AX-LIGHTNESS FORK :smartass:

User avatar
in the industry
Posts: 680
Joined: Mon Aug 14, 2006 4:58 pm
Location: Detroit, MI

by bigskyTi

I use a guide, a fine blade and a Sawzall. Seriously. I've done it by hand but the cut tends to wander more and it does take a while. I suppose a diamond blade would be best since it is better to 'sand' instead of cut, but I can't be bothered.

As far as the mask it is a pretty good idea. I usually have black snot for a day if I don't wear one. evidence enough that there fine airborne particulate you probably don't want in your lungs. well anymore than following a city bus i guess. It's not like we are mining coal for 10hrs.

Posts: 219
Joined: Sat May 09, 2009 3:03 am
Location: Maryland

by JN2Wheels

I have cut many steerers, with never a problem. Always use a cutting guide and a carbide blade. I recently made a final cut on my fork, and decided to use the sawzall for a beautiful cut. It was going great until the end, when to my horror, a little bit of lamination peeled away. It is directly in my clamping area, and seems to effect maybe 25% of the steerer depth.

So, fair warning, slow waaaay down at the end, or flip the steerer 180 degrees at mid cut. This is something I've always done when cutting with the hack saw, but thought it wouldn't be necessary with the sawzall.

Anyway, my question is two-fold...

1. Ride it? Repair it? Bin it?
2. Repair tips for epoxy resin in this type of job?


by Weenie

Shop Owner
Posts: 850
Joined: Sun Jan 03, 2010 4:58 am

by Butcher

One good thing about you using a sawzall, is that we can all see what happens when you have no control over your cutting.

Inject epoxy, clamp, and reuse.

Post Reply
  • Similar Topics
    Last post