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Is it okay to cut down a carbon seatpost?(10 posts)

Is it okay to cut down a carbon seatpost?eciofi18
Apr 22, 2003 7:17 AM
I was wondering if it was okay to cut down a carbon seatpost so that it will fit in my Kestrel Frame with is also carbon. If it is okay, what is the best way to go about doing this? Thanks.
re: Is it okay to cut down a carbon seatpost?russw19
Apr 22, 2003 7:52 AM
First a question... do you need to cut it? Will it not go into the frame far enough for your seat hieght to be correct? If so cut it. If you are trying to save a few grams.. don't cut it. It's not worth the potential risk.

If you are going to cut it, use a NEW hacksaw blade. Figure out where you are going to make the cut and put a piece of masking tape aroung the post there. Cut the post thru the tape. It will keep the splintering down. And then lightly file the carbon smooth at the cut. Watch out for cabon splinters if you get one in your finger, you will have to cut a huge chunk out of your skin to get it out. (ask me how I found that out) but make sure you don't nick your post anywhere else in the cutting process. It could cause problems later on.

But if it is not 100% necessary, don't cut it. Too much hassle and potential screw ups that could cost you a nice carbon post.

I have only done this once so hopefully someone with some more experience can elaborate more on this.

re: Is it okay to cut down a carbon seatpost?boyd2
Apr 22, 2003 8:12 AM
I have never done this for my bike, but I am an engineer that works for a composites company. I would guess that you really are not going to buy much by doing this, and you could generate some problems that I can't forsee. If you do this I would not cut any closer then about 2" from the binder bolt beacuse the tube could become buckling critical. Tape is a good idea, but I would not use a hack saw. The reason is that a hacksaw could damage the fibers by pulling them when it does not cut them cleanly. This damage will propagate up the tube away from the cut and could reach the binder bolt and cause you big problems. I would use a Dremmel tool with a cutoff wheel, or better yet a diamond tipped tile saw. We use a Makita tile saw here and it would be the best tool for the job. Let the saw do the work, do not push it or you risk damage like I described above. Use a stream of water to cool the blade and keep the kerf free of carbon dust. If the dust builds up it will dramatically decrease your cutting efficency. Make sure that you seal the cut ends with a 5-minute epoxy to prevent any delamination. After the 5-minute cures you can sand it on the outside so that it fits back in the seat tube. Make sure that you do not sand into the fiber!!

It is really not that hard if you have the proper tools and techniques, but think about the concequeces of a screwup.
carbon fork manufacturer's don't agree...C-40
Apr 22, 2003 8:38 AM
I've made dozens of cuts in CF steering tubes and seatposts with a 24TPI or 32TPI hacksaw blade. Never saw any indication of splintering or damgage of any sort near the cut.

The instructions provided by the manufacturers of CF forks with CF steering tubes make no recommendation to seal the cut end of a CF steering tube, nor do they specify specialty saws to make the cut.

I've taken the scrap cutoff from a CF steering tube and sawed through it repeatedly with heavy pressure in an attmept to creat such damage, but couldn't do it. I would be suspicious of the quality of a CF product that splintered when cut. The fibers should be totally saturated with epoxy resin and not prone to this damage, if made properly.
yes, but always the bottom end nmDougSloan
Apr 22, 2003 8:52 AM
And be sure to measure twice before you cut a carbon part ; -) nmStraightblock
Apr 22, 2003 2:52 PM
that was just evil ... :) (nm)weiwentg
Apr 22, 2003 5:06 PM
Apr 22, 2003 9:01 AM
You will void the warranty, but it will not hurt the strength of the post if you still leave plenty of length.

Some do have a aluminum insert or a thicker area that is reinforced for clamping. It should have a min and max insertion clearly marked on the post if that is the case.
Apr 22, 2003 9:28 AM
Hey C-40 I agree with you 100% you will most likely be OK. I am looking at it from a different perspective. The aerospace composite structures that I work with have razor thin margins and we have to think about problems like creating damage while cutting. I think your experience with actual bike hardware is more valuable beacuse you have done the work. Also you comment about better wetout of fiber is important, but I was considering that there is quite a bit of variability in wetout of composite layups in our buisness, and we have really, really tight controls. I imagine that in the commercial world you could get some very dry parts and some very wet parts. I figured that the worst case dry part could give some trouble with delamination.
re: Is it okay to cut down a carbon seatpost?MR_GRUMPY
Apr 22, 2003 11:29 AM
Check out the website for the Easton seatposts. They have full instructions.
Ps. Don't use a cross cut saw.