Tech Tuesday - Cutting Carbon
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.
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A saw guide and a hacksaw equipped with a fine 32 TPI blade are two important tools for this job.
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.
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. |
The difference between a coarse and fine saw blade is clear to see when you take a close look.
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.
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.
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.
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.
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.
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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'
1. Wheel Building: www.youtube.com/watch?v=qTb3x5VO69Y
2. Pedal complete Service: www.youtube.com/watch?v=OXfrmkOTicM (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: www.youtube.com/watch?v=OXfrmkOTicM
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
@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?!?!" :http://en.wikipedia.org/wiki/File:MtbEpic2007MarathonCarbon.jpg 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.
Rant....!
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!
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!
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...)
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:
lp1.pinkbike.org/p4pb7457039/p4pb7457039.jpg
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
Carbon blade ? WTF ?
Marketing ?
www.eastoncycling.com/bike/wp-content/uploads/2010/04/RD-05-Carbon.pdf
www.parktool.com/blog/repair-help/fork-steering-column-length-and-sizing
but,
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).
see my post further above for the advice now given to professional bike mechanics in the UK
lp1.pinkbike.org/p4pb7457039/p4pb7457039.jpg
It sticks out like a soar thumb....
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.
Twice.