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I've got to cut the steerer tube on a new build shortly, it's carbon. Have never cut the steerer tube myself before, is it going to involve more than a hacksaw and a pipe cutting guide to get it straight?

Are there any pitfalls I should be aware of?

23 comments

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spongebob [277 posts] 5 years ago
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just cut mine using a pen and a hack saw. Just go for it bro

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trikeman [309 posts] 5 years ago
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Hi, I have always used a wide masking tape slowly wrapped around the tube once you know where the cut is to be made. Being wide and used with little tension it will keep the tape line straight. If both ends meet perfect then your cut guide line will be correct.
I use junior type hacksaws on carbon, but don't just go from one point, slowly revolve the tube lightly sawing as you go. Once you have a good guide line it is just a matter of folowing this carefully around making the cut deeper as you go. Finaly finish with a light file. Sometimes just sawing straight through with a large hacksaw CAN splinter the carbon and send a sliver down the tube - you don't want this. Take your time and you will be OK.
There are special 'clamps' that can be bought, but if its only the one the above method works well.
I have used this for 'donkeys' on carbon, aluminium and steel without issues.
Hope this helps.
Regards

Trikeman.  3

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spongebob [277 posts] 5 years ago
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I'm glad I didnt know that before I went to town on my steerer trikeman as it would have taken forever!

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dave atkinson [6330 posts] 5 years ago
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Park do a specific hacksaw blade (CSB-1) for carbon steerers, it has a grinding surface instead of teeth so it's kinder to the carbon. trikeman's advice about starting the cut all the way around the steerer first is well worth following too.

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garyh [34 posts] 5 years ago
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Buy a Carbide Grit Hacksaw Blade for your normal hacksaw - much cheaper than buying the Park one.

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thereandbackagain [173 posts] 5 years ago
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Yep - good advice in here. I was a bit anxious about it initially, but tbh it was pretty easy.

When I cut mine down I used masking tape, drew the cut line on that and made a shallow cut all the way around with a jnr hacksaw blade. Once the shallow groove was there I used light pressure and made the cut. It went fine.

Use a fine grade of wet & dry paper to put a small 45 degree chamfer on the new top edge. That looks neat, and helps the stem & spacers to slide on easily. Use a mask or keep your head away from the carbon dust.

Make sure when you measure you cut it low enough for the top cap of the aheadset to have a couple of mm of free space to tighten down on the headset stack. Last thing you want is a lovely neat cut that doesn't let you adjust it properly.

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matt637 [47 posts] 5 years ago
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dont get too worried. A junior hacksaw with a high TPI, a cutting guide and some tape round the steerer where you are going to cut. I have done 2 successfully and have always cut straight through. The carbon will split badly if you don't put the tape on. Just take your time, and slam that stem!

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lazyusername [105 posts] 5 years ago
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Thanks everyone

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Amos [33 posts] 5 years ago
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Just cut my steerer, as suggested here I used a high TPI blade. As a guide I used and old defunct stem seem to work perfectly.

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SideBurn [890 posts] 5 years ago
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Just a word of warning don't be too keen to cut your steerer. After cutting mine down I rode the bike for a while and thought it was a bit too low. Which is a bit tough after you have cut it! On my other bike I cut it longer and left some spacers on top of the stem to get used to it before deciding to cut to size.

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02curtisb [63 posts] 5 years ago
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Having just given this a go i would add two points which may/may not be useful or obvious!

1. A new fork is really long so have a practice further up!
2. If you cut from one point all the way through its very hard to not cut at an angle. So the shallow cut all the way around and Trikeman's point about revolving the tube as you cut is definately helpful

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bikeylikey [228 posts] 3 years ago
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You can avoid cutting at an angle by installing two Jubilee clips on the steerer a few mm apart to allow the cutting blade through. I've done this successfully, it seems to work as well as a steerer cutting guide.

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StraelGuy [1095 posts] 4 months ago
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Sorry for the serious thread revival but my Strael arrived today. I've just done a preliminary steerer trim of the carbon forks so I could get the thing together and a normal fine toothed hacksaw blade worked perfectly. I used a Planet X cutting guide and held the blade by hand rather than fitted to the handle and took my time and didn't exert much pressure. it took a while but the cut is absolutely perfect, no feathering or splitting or anything - exactly like cutting metal. I just knocked the edges off with some dry wet'n'dry and it's absolutely spot-on. It does leave a large pile of what feels like gritty soot though so might be worth having some Swarfega handy...

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Jack Osbourne snr [680 posts] 4 months ago
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Hope you were wearing a decent dust mask...

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CXR94Di2 [1856 posts] 4 months ago
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I use masking tape to give a line to cut down. Then big file to smooth edge, vacuum to extract dust.

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Scoob_84 [435 posts] 4 months ago
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One thing i may add, for the benefit of those who may read this thread in future, its not terribly important to cut the steerer tube straight or square. There will always be a slight gap between the top of the steerer and the upper surface of your top spacer (the surface in contact with your stem cap, so don't beat yourself up if your cut is slighlty wonky. 

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StraelGuy [1095 posts] 4 months ago
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Just a heads up - I used one these. They're very well made and currently selling for £7.99 at Planet X. I've used it quite a few times and it'll probably see me out.

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antigee [451 posts] 4 months ago
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cut many a steerer by hand - they don't actually need to be dead straight - remember for the stem bolts to be equally loaded then a spacer above the stem should be the norm and will sort a mil' or so of sloppy cutting, having said that I picked up a similar product to the planet X one in a bargain bin and find it doubles up for cutting ice hockey sticks to length by junior antigee - which is now a job I don't have to do mail

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LastBoyScout [329 posts] 4 months ago
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You can get the Park blade Dave mentioned quite cheap if you shop around online - I bought one and it works really well. Fine wet and dry sandpaper for finishing off.

Used an old alloy spacer taped into place as a cutting guide.

Measure twice, cut once and definitely don't cut too much off at a time. Allow for at least a 5mm spacer on top of the stem to move the stem clamp away from the end of the steerer - the hoop strength is better that way.

I've cut my steerer twice and it's still got about 20mm of spacers above the stem!

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Lincolndave [34 posts] 4 months ago
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I just use an ordinary 32tpi hacksaw blade, I mark the steerer fix it securely and cut, then go around the cut with a fine file

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kil0ran [594 posts] 4 months ago
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This is one where bunging your LBS a tenner would seem to be the best option. Get them to whack the star fangled nut in whilst you're there. Some might baulk at installing parts you've bought off eBay but this stuff is bread and butter to most. Cake often helps  1

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StraelGuy [1095 posts] 4 months ago
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Carbon steeres can't use a SFN, they're only for metal steerers. They use a sort of expandable bung type of thing that are quite annoying to work with (ask me how I know).

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Jimmy Ray Will [814 posts] 4 months ago
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I've used an old stem clamped on the steerer below the cut to provide both a guid, and also support for the steerer. Never been a problem.

I would also highlight that carbon dust is not the best thing in the world to be inhaling, so I'd advise a dust mask whilst cutting.