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PostPosted: Sun Nov 27, 2016 2:07 pm 
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That makes sense, it did work better on metal than carbon.

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PostPosted: Sun Nov 27, 2016 3:08 pm 
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kkibbler wrote:
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.


It does not crush the carbon.

The cutting wheel is very sharp hardened steel and slices through carbon fibre.

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Posted: Sun Nov 27, 2016 3:08 pm 


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PostPosted: Sun Nov 27, 2016 5:23 pm 
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Nope. It doesn't slice at all. The cutting wheel always applies a cutting force that is perpendicular to the tangent of the tube circumference. As opposed to a sawing motion which doesn't apply force in that direction at all; instead it's more like sanding a thin line through the tube.

Pipe cutters also tend to leave a flared end so if that's what you like on your tubes, be my guest.


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PostPosted: Sun Nov 27, 2016 6:11 pm 
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kkibbler wrote:
Nope. It doesn't slice at all. The cutting wheel always applies a cutting force that is perpendicular to the tangent of the tube circumference. As opposed to a sawing motion which doesn't apply force in that direction at all; instead it's more like sanding a thin line through the tube.

Pipe cutters also tend to leave a flared end so if that's what you like on your tubes, be my guest.


I use a pipe cutter to scribe a thin cut around the tube - I keep the pressure extremely low. The blade is sharp enough to cut cleanly, and I then have a 'groove' that the saw can follow for the final cut. I've used this method for at least 20 tube cuts over 10 years with no issues.

And when you saw, you have to apply some downward pressure or it won't cut at all.

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PostPosted: Mon Dec 19, 2016 4:02 pm 
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I measure Mark and tape then cut with a jeweler so it's like a ultra thin ultrafine hacksaw. It works really really well


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PostPosted: Mon Dec 19, 2016 6:19 pm 
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Joined: Tue May 23, 2006 9:39 pm
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i use 3M magic tape where i'm cutting. this keeps the carbon strands from splintering. after cutting, i remove the tape and touch up the freshly cut rough surface with sandpaper or a single cut file away from the edge, not towards it. makes for a clean edge that won't mar the insides of the seat tube.

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PostPosted: Fri Jul 07, 2017 12:22 pm 
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You can use a short metal tube and pull over, then tape it so it's fixed.
Just a bit larger diameter than the seatpost itself
The use a http://www.parktool.com/product/carbon-saw-blade-csb-1
Finally, use some fine grit sandpaper to smoothen the edge.

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PostPosted: Fri Jul 07, 2017 2:53 pm 
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Joined: Sat Dec 13, 2003 2:25 am
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Location: Canada
Carbon posts are so over-engineered it isn't funny (obviously, to resist compressive forces from the binder). I think it would be pretty hard for you to mess that up. I will wrap the area I am cutting with a turn of tape, though, and cut it with as fine a saw blade as I can find (hand saw, please). Cut it half way, then rotate the piece and finish the cut in the other direction (to prevent a 'green-tree' split). The only 'finishing' required is to bevel-in the cut with a fine file.

On the subject of files, some would have you believe that you need to use an escapement file, or something. Not true. As I say, a seatpost is really overbuilt and a nice, fine mill file is perfect. Just be sure to draw it toward the centre of the post so as not to pull-out fibres from the resin.


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PostPosted: Fri Jul 07, 2017 3:47 pm 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 435
Location: Madison, WI USA
Carbon seatposts are not sweaters; they won't unravel if you fail to apply nail polish. I mean, there's no harm in doing so, but there's also no need as long as you have a reasonably clean cut. There are places where you'd want to prevent any cutting-induced cracks from propagating, but the ends of seatposts aren't very highly stressed. Most of those stresses are in circumferential compression anyway, and cracks tend to spread in tension, not compression.

People seem to want a little magic to be required when cutting carbon fiber, but many of these same people have no such concerns about cutting wood. They're both composites; a clean cut is a clean cut.

I personally use a dremel tool with a cutoff wheel to cut carbon parts (mostly steerers and seatposts). "Cutoff wheel" is actually a misleading name for those discs...they're just very narrow grinding wheels; they don't actually cut. Of course, that's also true for abrasive hacksaw blades marketed for cutting carbon fiber.

I do agree, however, that pipe cutters are a bad idea for carbon. Even if you just barely tighten them, their wheels make point contact with the post-steerer and the contact pressure is enormous. Using a pipe cutter for the entire cut tends to encourage "greenstick" delamination on the inner circumference.

Besides, if you're a weight weenie, you really want to cut at a ~45-degree angle, with the longer bit in front. Cutting seatposts at an angle is more structurally efficient (which is one reason Ritchey posts are cut this way). Cutting at an angle also allows the tip to deform a bit in contact with the seat tube, spreading the load and reducing the stress concentration in the seat tube.

Apply clear nail polish to the cut if you feel like it. But a clean cut on a post shouldn't require nail polish.



Edit: typos.


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