Cutting a carbon seatpost

Discuss light weight issues concerning road bikes & parts.
MattSparkes
Posts: 11
Joined: Tue Mar 29, 2016 11:23 am

by MattSparkes

Can I get away with cutting to the red line, or maybe even orange? Is it a good idea to put a slant in there, like the Fizik posts? Also, what should I coat a carbon post with in an alloy frame? It's a very tight fit and only just came or after a few weeks use. Some lacquer seems to have worn off and left an irregular surface on the post - there was much wiggling to get it out, so it's probably from that...

by Weenie


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Frankie - B
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by Frankie - B

Moved to Road by me. Please let us know if this is the wrong forum.

May I suggest that you post a picture of the seatpost, or mention the brand at least?
A rule of thumb for cutting seat posts is that you let it at least extend 1.5 cm past the bottom side of the top tube. slanting means that you can cut it shorter. Roll tape around the place where you want to cut and saw, with a sharp blade through the tape afterwards, finish the cut with nail polish or varnish.
'Tape was made to wrap your GF's gifts, NOT hold a freakin tire on.'
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vanmatthew
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Joined: Thu Jul 14, 2016 5:20 am

by vanmatthew

What do you mean finish the cut with nail polish or varnish? To remove the paint?

If you want to be safe, just measure the distance of the current safe line and just make sure that much is available after the cut. You can get more material off with a slant cut but I don't know if it will work with carbon. Fizik may have added extra carbon to shape it that way.

Raccooningtanuki
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Joined: Mon Aug 22, 2016 7:30 am

by Raccooningtanuki

Frankie - B wrote:Moved to Road by me. Please let us know if this is the wrong forum.

May I suggest that you post a picture of the seatpost, or mention the brand at least?
A rule of thumb for cutting seat posts is that you let it at least extend 1.5 cm past the bottom side of the top tube. slanting means that you can cut it shorter. Roll tape around the place where you want to cut and saw, with a sharp blade through the tape afterwards, finish the cut with nail polish or varnish.

Should the nail polish color match your frame or accents? Is glitter ok?

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Frankie - B
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by Frankie - B

The nailpolish needs to glitter and be bright pink.

No, you need to nail polish to bind the strands of the carbon on the face that you cut together again.

@vanmatthew, this is weight weenies, not keep it within standard weenies ;) I have cut a couple of seat posts and it always works.
'Tape was made to wrap your GF's gifts, NOT hold a freakin tire on.'
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Marin
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Location: Vienna Austria

by Marin

Or just cut it with a saw or dremel, insert and ride. Noone is going to see the bottom end, and you don't really need to seal or finish the cut. That's the way I do it with my steerers and seatposts.

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Juanmoretime
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by Juanmoretime

I just use a proper cutting guide with a brand new hacksaw 32 tooth blade every time I cut a post or steer tube. I wrap the area to be cut with a layer or two of masking tape. Mark my spot to be cut after measuring it a bunch of times to be sure I'm cutting it in the right place, can be pretty expensive cutting it in the wrong place. I alway like a 100mm of post to be inside the frame. Once cutting I cut 1/2 way thru and rotate then cut from the other direction. Then I lightly sand the cut area and tend to put a slight bevel in the clear coat to make insertion a bit easier. Add carbon paste with a seatpost and properly toque.
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F45
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by F45

I balance it on my knee and hit it with my battery powered sawzall. When you ram it in the bike, any carbon shavings will get knocked off. Pretty easy.

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cyclespeed
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by cyclespeed

F45 wrote:I balance it on my knee and hit it with my battery powered sawzall. When you ram it in the bike, any carbon shavings will get knocked off. Pretty easy.


What is a sawzall?! Like a chainsaw?! I'm sure that's a very fast way to do it!

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F45
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by F45

I guess they call it a Hackzall. I use the Milwaukee M12 model with the metal cutting blade. You can zip tie the vacuum hose to the underside of the metal guard and catch 99% of the carbon dust. So cash.

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pdlpsher1
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Location: CO

by pdlpsher1

I use a chop saw with a carbide blade designed to cut wood. No taping of the post is needed and the finished cut is as good as the factory cut. No splinting or fraying. I also use the same carbide blade to cut aluminum and it goes through aluminum like butter.


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dpkinard
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Joined: Tue Oct 11, 2016 11:31 pm

by dpkinard

I've used a pipe cutter before, with the small wheel that you tighten one turn and spin around the fork, tighten, spin repeat. It's always going to be straight and 90 degrees.

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kkibbler
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by kkibbler

dpkinard wrote:I've used a pipe cutter before, with the small wheel that you tighten one turn and spin around the fork, tighten, spin repeat. It's always going to be straight and 90 degrees.

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This is bad for carbon. You want to cut the fibers, not crush them until they break.

by Weenie


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