Tech Tuesday - Cutting Carbon

Jan 3, 2012
by Mike Levy  
Cutting a carbon fiber handlebar, seat post, and especially a steerer tube, requires many of the same steps as trimming an aluminum component, although there are a few important points that can make this job stress free and smooth. You should approach cutting carbon fiber with the utmost care - the more time you take to do it, the higher the chance of making a nice, clean cut that doesn't require much (or any) attention afterwards. It's for this reason that we recommend using a saw guide, regardless of if you are trimming a bar or steerer tube, because it ensures that the cut will be straight. A saw guide isn't a tool that most riders will use that often, but the price of having to replace a carbon fiber steerer/crown assembly outweighs the initial buy-in of the tool. If you can't justify buying the guide or make your own (an old stem can be used), you're much better off having your local shop do the job for you.

Tech Tuesday
A saw guide and a hacksaw equipped with a fine 32 TPI blade are two important tools for this job.
Tech Tuesday
Don't want to buy a saw guide? You can use an old stem to help keep the saw in the correct place by cutting directly against the top of its clamping surface. No, it isn't nearly as good as a proper guide, but it will get the job done. Keep in mind that the blade will mar the finish on the stem.

What's needed:
Hacksaw with a 32 TPI blade
Saw guide
• Tape
• Marker
• File (optional)
• Vice (optional)

Some helpful pointers before you begin:
• A bit of water on the saw blade can help keep the dust down and the blade from clogging.
• Remember that a hacksaw will only cut in a forward direction. Applying hard pressure or trying to saw quickly will only make the job harder and your cut worse.
• Most hacksaws come equipped with a 24 TPI (teeth per inch) blade that will work for most jobs, including cutting a carbon fiber bar or steerer tube, but we highly recommend using a finer 32 TPI blade when sawing a carbon post or steerer. The finer blade will result in a cleaner cut that won't require as much attention after sawing.
Tech Tuesday
The difference between a coarse and fine saw blade is clear to see when you take a close look.

Tech Tuesday
Step 1 - The first step to this job is the most important - measure correctly! Any mistake that you make here will be very, very costly, so be sure that you are removing the correct amount of material. Use a felt marker to make a cut line completely around the tube, then double check your measurements once again. We used a black felt marker, but a white-out pen will make a cut line that is easier to see on the dark carbon tube.
Tech Tuesday
Step 2 - Wrapping the cut zone with a single layer of tape helps to keep the blade from causing the carbon to fray as you saw it. While this step isn't mandatory, you should approach this entire job with the goal of having the best possible cut that requires little to no post-sawing cleaning up from a file or sand paper.
Tech Tuesday
Step 3 - Clamp your saw guide into the vice and slide the steerer tube so that the cut line is aligned with the slot in the saw guide. Test the positioning before sawing by sliding the saw into the guide, being careful not to actually touch the carbon tube, and look to be sure that the blade lines up right on the cut mark. Snug down the steerer tube clamp once you're positive that the fork is position correctly.
Tech Tuesday
Step 4 - Now it's time to start cutting. Begin by applying light pressure in a controlled manner, trying to cut through the tube quickly will only result in an ugly cut. Remember that a hacksaw blade will only cut when pushing in a forward direction, and to use the entire length of the blade - think ''proper form before speed''. A few drops of water on the blade can help to keep the dust down and make the job easier.
Tech Tuesday
Step 5 - There is a good chance that you won't be required to clean the edges up if you've done the job correctly (the tube on the left hasn't been touch up at all), but you may need to smooth out the edges in order to have the stem slide on easily. If so, use a fine file in an upward motion to remove the burrs.

Do you have a trick or tip to add? Put 'em down below!

Past Tech Tuesdays:
TT #1 - How to change a tube.
TT #2 - How to set up your SRAM rear derailleur
TT #3 - How to remove and install pedals
T #4 - How To Bleed Your Avid Elixir Brakes
TT #5 - How To Check And Adjust Your Headset
TT #6 - How To Fix A Broken Chain
TT #7 - Tubeless Conversion
TT #8 - Chain Wear
TT #9 - SRAM Shift Cable Replacement
TT #10 - Removing And Installing a Headset
TT #11 - Chain Lube Explained
TT #12 - RockShox Totem and Lyric Mission Control Damper Mod
TT #13 - Shimano XT Crank and Bottom Bracket Installation
TT #14 - Straightening Your Derailleur Hanger
TT #15 - Setting Up Your Front Derailleur
TT #16 - Setting Up Your Cockpit
TT #17 - Suspension Basics
TT #18 - Adjusting The Fox DHX 5.0
TT #19 - Adjusting The RockShox BoXXer World Cup
TT #20 - Servicing Your Fox Float Shock
TT #21 - Wheel Truing Basics
TT #22 - Shimano Brake Pad Replacement
TT #23 - Shimano brake bleed
TT #24 - Fox Lower Leg Removal And Service
TT #25 - RockShox Motion Control Service
TT #26 - Avid BB7 Cable Disk Brake Setup
TT #27 - Manitou Dorado Fork Rebuild
TT #28 - Manitou Circus Fork Rebuild
TT #29 - MRP G2 SL Chain Guide Install
TT #30 - Cane Creek Angleset Installation
TT #31 - RockShox Maxle Lite DH
TT #32 - Find Your Tire Pressure Sweet Spot
TT #33 - Three Minute Bike Preflight Check
TT #34 - MRP XCG Install
TT #35 - Stem Choice and Cockpit Setup
TT #36 - Handlebars - How Wide Affects Your Ride
TT #37 - Repairing A Torn Tire
TT #38 - Coil spring swap
TT #39 - Trailside help: Broken Shift Cable
TT #40 - Installing a Fox Float Air-Volume Spacer
TT #41 - Replace the Seals on Your 2011 RockShox Boxxer World Cup Fork
TT #42 - Clean and Lubricate Your Fox F32 Dust Wiper Seals
TT #43 - Thread Locker Basics
TT #44 - Install a SRAM X.0 Two-By-Ten Crankset
TT #45 - VPP Suspension Bearing Service
TT #46 - Rotor Straightening
TeT #47 - Finding and fixing that creak
TT #48 - Bleed and Service Magura Marta Disc Brakes
TT #49 - Cup and Cone Hub Basics
TT #50 - Install and Adjust Pedal Cleats
TT #51 - Cup and Cone Hub Rebuild
TT #52 - Converting Mavic Crossmax SX Axles
TT #53 - Cassette Removal and Installation
TT #54 - Cane Creek AngleSet Installation
TT #55 Wider Rims Are Better and Why Tubeless Tires Burp Air
TT #56 - Bleed RockShox Reverb Remote Lines

Visit to see their entire lineup of tools and lubes

Author Info:
mikelevy avatar

Member since Oct 18, 2005
2,032 articles

  • 103 0
 Three Tech Tuesday suggestions;

1. Wheel building - perhaps done in several stages (ie rim, hub and spoke selection - taking into account flange length and spoke length calculation - lacing and finally correct tensioning)

2. Pedal bearing service - I actually know how to do this with shimano pedals and its quite easy; I'm just surprised that ML and RC haven't already done a guide for this at this stage, given as they've already done some pretty complex suspension servicing guides (stuff which i know mechanics who won't touch that stuff with a barge pole - but they can do pedal bearing servicing).

3.Perhaps a comprehensive bike building guide - for those who are about to embark on putting together their first custom built bike a (maybe) two part guide on things like different International Standards and Sizing to look out for - especially helpful with things like headsets, chain guides, front derailleurs, mixing sram and shimano - where best to start and what order to go about building in and then references back to relevant previous Tech Tuesdays.

just sayin'
  • 9 0
 sick! i agree Mr Levy. good work Jack.
  • 14 7
 Wheel building post would spawn a quadrojillion of nerd opinions how to do it properly... if I were Mike, I wouldn't do such tech tuesday, it's a political suicide apart from the fact that it would be a great way for people to screw up their good rims and spokes...
  • 4 0
 Amazing tools: Google & Youtube -
1. Wheel Building:
2. Pedal complete Service: (specific to SPD M520)
3. About to build a custom bike? No. 1 dont mix Sram and Shimano, No. 2 if your building a custom bike you better already know what you like by then. But just for people who cant turn a wrench:
  • 6 0
 @hankbrowne - well, yehhhh but...
its nice to have it all in one place, and ultimately the mountainbiker can refer to pinkbike for all their maintanence needs

but, good point
  • 7 1
 @WAKIdesigns I'm not sure that "nerds" giving their opinions is not a reason not to do something, you know, get off the fence! Wink but maybe you're right about people screwing up their rims and spokes but i suppose that comes down to personal experience (you won't try and build a wheel if you've never even trued one) and everyone learns through the mistakes they make.

@hankbrowne as RalieghVoid said its always good to have these tools in one place from a source that you trust, and somewhere, where we can discuss this sensibly (as we are now) unlike Google and youtube which are full of such spurious divergent rants, its difficult to know what to trust. These guides exist but it'd be good to see it here. Shimano and Sram have been known to mix, less so these days but its still within the realms of the possibility - for example Sram Chains and cassette on other shimano parts; we've all seen bikes with Shimano cranks and FR derailleurs on Sram shifters and RR derailleurs (before any one says "where?!?!" : just one example). AND perhaps warnings about things like compatibility with Shimano road with Shimano MTB - where it is and isn't. AND the differences between Long, Medium and Short derailleurs and where each is appropriate.

I know most of the answers to most of these questions but I've always built my own bikes since I've considered myself to be seriously into cycling but its taken me such a long time to learn things that there isn't an up-to-date data base for. Sheldon Brown's website is good but applies to a load of things that don't exist or aren't relevant anymore and misses out more up-to-date developments.

  • 1 0
 @hankbrowne Oh and thanks for the wheel truing video, it was good to have some of the basics laid down. Great for front wheels on 36 hole wheels!
  • 5 0
 We did do a TT on the basics of wheel truing:, but not an actual build article. Something for the future for sure. Thanks for the suggestions!
  • 1 0
 Surely every Tech Tuesday together will amount to some sort of comprehensive bike-building guide?

After my experiences as a mechanic I strongly feel if you're clueless as to how a bike is put together then don't attempt a full build, guide or not, just take it to your LBS and avoid yourself serious bike or bodily damage!
  • 1 0
 @bunkey I was suggesting it would be a good idea to outline compatibility issues which would then refer (maybe with hyper links) to previous TTs- kind of like a glossary or contents - including a guide as where it would be best to start with a building project. Maybe it would provide a more effective way of organising all of the TTs.

While we have a TT for setting up a RR der, we don't have one for eg selecting one and subsequent installation. I think that kind of rhetoric can prove to be massively esoteric and alienating - it can only perpetuate people being "clueless" and treat their bikes as if they're run by magic rather than a series of very simple rules. All of the TTs up to this point have been aimed at people who have a working (if basic) knowledge of bikes and their principles and turning that into something more practical, which is what i think a custom bike build would be as well.

Or maybe this is just something i should do! Wink
  • 1 0
 So in amoungst all those big words - What you're saying is produce a step-by-step guide, or checklist, to building a bike which outlines some sort of methodical way of doing it as opposed to how to do every individual task? Then link each step to the relevant Tech Tuesday to make it a bit more comprehensive? That would make sense yes. We have printouts on the walls at the shop which do just that and it does help you get stuff done quickly and efficiently when you're turning out 5 or 6 bikes per day.
  • 4 0
 jackclark89 - what I meant was:

Wheel-building is such a "sensitive" and broad subject that no matter what Mike or RC would write in such TT, there will be lots of ppl who:

#1 - will criticize him for showing "the wrong way"
#2 - will criticize him for not explaining well/broad enough

Wheel building is like sex - it's simple yet difficult and no matter how much movies you watch and illustrated stuff you read - you just have to get a good practice to be good at it - it takes many tries and disappointments to get it right. Aaa... and you need a mentor who actualy has done it many times not just spoke about it (a bitch to find...)
  • 21 0
 you forgot the most important tool... the high quality breathing protection! carbon dust is respirable and destroys your alveolus
  • 3 0
 Actually yes they did forget that part. It's very important because as you said, carbon dust is terrible for you. I usually just hold my breath. Eek
  • 5 0
 ^^ this

the current COSHH regulations we are issued as professional bike mechanics is to wear full PPE (personal protective equipment) including butyl gloves, workshop apron, eye protection and dust mask, and turn on the air extraction system, and ask other mechanics to leave the workshop - we also place a cloth around the vice (cut a slit in the middle so the vice is surrounded) and damp this cloth with parts cleaning spray to catch any carbon dust

here is an image showing my typical setup for CF cutting:

there is a lot of evidence coming to light that carbon fibre could be the "new asbestos" and we have been strictly told not to take any chances in the workshop
  • 1 0
 I assume thats its the resin dust that is more harmful? I know the carbon particles can lodge themselves in your lungs when inhaled but carbon itself is a harmless element. is this true?
  • 1 0
 Im pretty sure that solid particles of most substances becoming lodged in your lungs is going to be harmful. Anything that blocks the path of oxygen to the alveoli is going to reduce the efficiency of your lungs, surely?
  • 5 0
 When cutting with a hand saw I was taught to keep my shoulder, elbow and wrist in line with the cut - this way the path of the saw will always be in a straight line. Guides help too. You can also use stem spacers as guides, but tape them in place.
  • 6 0
 A quick tip if you're using a stem for your guide, use an old headset spacer too. I duct taped a 25mm spacer onto my stem and the stem is still in great shape, that way the spacer only gets mangled.
  • 2 0
 Nice! Great tip, thanks.
  • 9 0
 Hey mike! I cut my bars to length twice, and they're still too short!! what kind of glue/tape do you recommend?
  • 7 4
 If you really want to get technical you should be using a carbon blade (actually more of a grinder than blade) and oversized carbon-cutting guide. A saw blade is generally too aggressive and will often damage the carbon at the end of the cut, regardless of whether or not tape was used.
  • 88 0
 i recently invested in a light saber for just this sort of thing. you just have to watch out where you swing it in the shop.
  • 2 1
 Ha! Yes that would work too.
  • 3 11
flag czlenson (Jan 3, 2012 at 2:26) (Below Threshold)
 light saber emits to much heat I think, the end of the cut will be slightly burnt.
  • 16 0
 a simple karate chop works fine for me
  • 1 0
 ive got a powerfull laser that can cut stuff, this also runs the same burning issue?
  • 7 1
 i'll just give chuck norris a call
  • 5 0
 I thought chuck only did frame alignment...........or de-alignment !
  • 1 0
 Hip and spine alignment as well
  • 1 0
 id say more of de-alignment
  • 2 0
 I've never damaged carbon using a 32 tpi blade. I use a wrap of masking tape and cut nice and smooth
  • 1 1
 Fuck dis shit Imma buy a sledgehammer
  • 4 0
 I will agree with seraph.
If you're going to use such a blade, then applying a layer of thinned epoxy over the cut is a good idea (it will fill the tiny cracks created at the resin of the CF tube by the saw blade).
  • 4 1
 +1 on the breathing protection. Wear a mask and be especially careful with dust clean up. I usually lay an old rag down under the cutting surface to collect the dust and then roll it up and dispose of it in the trash...sometimes in a ziplock bag. Any fine particulate matter is bad for your lungs, but carbon fibers especially. If you work in a shop, remember that you're not just risking your health, but that of those around you when you're not careful with hazardous materials.
  • 1 0
 ^^good advise

see my post further above for the advice now given to professional bike mechanics in the UK
  • 5 0
 Don't want to be the grammar nazi, but it's "coarse" not "course".

It sticks out like a soar thumb....
  • 1 0
 Good eye, thanks!
  • 5 2
 hmm. mr grammer nazi, i hope that "soar thumb" was sarcasm, ha
  • 3 0
 Nah I'm pretty shore it's spelt like that Wink
  • 4 0
 ha thats rite, thats right how you spell it they're
  • 2 0
 I'm pretty curtain!
  • 2 0
 this hole series off comments makes me so happy haha
  • 5 1
 For cutting down handlebar length I use two spare lock on grip clamps as a guide.... works perfect
  • 1 0
 Just a tip...

When cutting a steerer tube, measure twice. Then slip the stem over the steerer tube and add that additional height before you cut.

Oh, and mark on the steerer tube cutting guide box "Add the width of the stem to your cut"

Or, slap your head and yell loudly "gosh darn it."

Don't ask me how I know.

  • 2 1
 I use safety scissors to cut my carbon, works like a charm. Not to mention time and energy efficient But this works too I guess
  • 10 0
 i still cant even use safety scissors
  • 2 0
 Step 6. Seal the cut end with some clear nail polish This will protect the carbon and finish the job nicely.
  • 1 0
 i want to see a crank replacement and how to set up crank spacers, p.s. for the more complicated jobs vids would be nice.
  • 1 0
 Why are you using metric? I thought you thick amerrycans/canadyans used overly complex imperial?
  • 2 1
 Nice tip, just cant afford any carbon parts.
  • 2 1
 sthil ms 880 works every time...
  • 1 0
 yes a sthil fan, i love the 880 its a freakin beast
  • 1 1
 ...and rinse off your tools, parts, hands, and work area afterwards so it doesn't get spread all over the shop.
  • 1 1
 I know someone with a laser cutter.
  • 1 1
 that saw guide is really a joy to work with
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