Sanding a seatpost to size?

[Gartenmeister]

I would like to reduce the size of a 27.2 carbon seatpost to 27.0. Anyone tried this? Tips? Recommendations?

I was thinking to start with a razor blade "scraping" (commonly used to remove clearcoat/logos) and then just hand sand it. Not sure what grit to start with.

Any better ideas?

[bikerboy337]

I'd buy the correct size post.

I dont take any chances on parts that will cause me to crash if/when they fail. Contact point, wheels, not areas i'd modify personally...

[palincss]

I reduced the size of an aluminum post by a small amount. It took a lot of patience, and an assortment of grades of sand paper, from 80 to I think 400. In my case there was no "correct size" option: I learned from the previous owner there had been an issue with the size from the day the bike had been delivered, and on account of something that happened in the build process (I'm vague on the details) it ended up being between official sizes. The "correct" size slipped and the next one up was extremely difficult to adjust.

I don't think I'd try it with carbon.

[cnighbor1]

are you sure frame takes 27.0 mm
Maybe it needs reaming to 27.2 mm

[notsew]

Seems like a massive PITA.

If you do, make sure you wear gloves and a mask.

[Corso]

True tale: Back in the early 90s, I bought a cheap 1/18 aluminum quill stem-for a 1” headset bike. Doh, My mistake.

Because I didn’t pay a lot of money for it, I went to work with a file, and hand ground that sucker to fit. Heck-the quill wall was pretty thick--Looked just fine!

After everything was all together, and a few test rides, I was feeling good with myself.

The I "woke up", took it off and threw it away. The thought of that stem snapping while racing made me realize of how stupid I was.

I think this is the first time I’ve admitted to doing this foolish thing...

Do you really want to compromise that seat posts strength? I’ve seen a few carbon posts break.

[charliedid]

I would like to reduce the size of a 27.2 carbon seatpost to 27.0. Anyone tried this? Tips? Recommendations?

I was thinking to start with a razor blade "scraping" (commonly used to remove clearcoat/logos) and then just hand sand it. Not sure what grit to start with.

Any better ideas?

I recommend no.

[mtechnica]

I seriously doubt .2mm sanded off a seatpost will compromise its integrity. Could take a while to sand it though. Also, in the past, I've fit a greasy 27.2 post in a 27.0 frame without even doing anything to it but YMMV

[JAGI410]

Are you out of your damned mind? NO!!! It seems like an insignificant amount to remove, but it's not worth the risk. But if you're willing to test the sensation of a sharp broken Carbon tube colliding with your genitals, go for it.

[dem]

Dissenter here.. if it is an even color (ie, you cannot see the weave of the carbon - it is a uniform black) it likely has a cosmetic top layer to even it all up.

Try the razor blade method and see if it comes off, totally fine. If anything, you'll be able to see any future cracks better!

(Disclaimer: I've ridden a cracked carbon seatpost for 10,000 miles, so I am maybe not the best person to take advice from. In this case it was the reverse problem, the post was slightly undersized, so the clamp cracked it a bit. I just kept an eye on it and it never moved.)

[Peter P.]

If it's a carbon seatpost, then don't do it. If you think you can reduce the clearcoat by a mere 0.2mm then you know more than I do. If you cut through any of the carbon fibers, then throw the post away.

If it's an aluminum post you're referring to, then I suppose it's possible but extremely time consuming. I'm inclined to think all aluminum posts from manufacturer X are created from the same blank and only the O.D. is machined to the correct diameter. If my theory is correct, then there is sufficient material to turn a 27.2mm post down to 27.0.

A problem I see is trying to sand an aluminum post. Sanding aluminum will gum up sandpaper pretty quickly, rendering it useless. You would be better off cutting it down with a lathe.

[kingpin75s]

Regardless of other considerations discussed, I would be concerned about the ability to keep it truly round as it is sanded leaving uneven contact with the seat tube.

I would fall in the not recommend category if there is a count ;)

[FlashUNC]

Just sand the point into a spear. Save you the trouble from the inevitable breaking.

[cachagua]

Second on getting the frame reamed.


Oh, wait -- it's a carbon frame?

[ripvanrando]

Just use more KY

[Gartenmeister]

I've fit a greasy 27.2 post in a 27.0 frame without even doing anything to it but YMMV

Well, believe it or not this is actually the correct answer. Turns out the height markings on the post are a really thick paint, and the clampy part of the seat tube shaved this (paint) a bit, but otherwise its good to go.

Thanks to all.

[fogrider]

Well, believe it or not this is actually the correct answer. Turns out the height markings on the post are a really thick paint, and the clampy part of the seat tube shaved this (paint) a bit, but otherwise its good to go.

Thanks to all.

Typically, a greasy carbon seatpost is not a good idea as it tends to slip. carbon paste is a good idea all the time, http://www.velonews.com/2014/12/video/ask-mechanic-use-carbon-friction-paste_355755

Additionally the idea of sanding a carbon seatpost is such a bad idea, I just don't know what to say.

[spinarelli]

On carbon I would not do it. It cannot end well.
Just buy a new post and sell the old one in the classifieds.
Maybe on aluminum post if you had access to a lathe, maybe, if you are in a pinch.

[onekgguy]

Not related necessarily but interesting nonetheless.

https://youtu.be/4TkjA41tJ78

Kevin g

[David Kirk]

I apologize if i missed it but........what material is the frame?

dave

[Gartenmeister]

It's steel, an old Bridgestone RB-2.

Question is answered and the post is in guys, thanks. It went into place with no sanding or scraping required. Did not grease it either, although there was a light coating in the tube. It is very, very snug- not exactly easily adjustable- but it should work fine. If it slips I'll add paste later- quite familiar with its use.

It is interesting that I got this carbon post in w/o modification as the frame in question will absolutely not accept any alloy 27.2 post (with good reason, its a 27.0 tube).

[ultraman6970]

Erased.

[Gartenmeister]

Erased.

Too bad; good comments-I can see the original in my e-mail. Thanks.

[FriarQuade]

The biggest problem is keeping the seatpost round and a consistent OD throughout it's length. Best to do this kind of a thing on a lathe.

[jumphigher]

I'm planning on doing the exact same thing in the next day or two, OP - 27.2 to 27. Will post my results. I think done carefully it will work just fine. :)

[ultraman6970]

Sorry, noticed the dude fixed the problem so why to left it there hehehe... either way it can be done but depends a lot of the seatpost, and since carbon seatposts are never 100% accurate to wet sand 0.1 out of the clear coat is not like a lot, the other way is just sand the seat tube using a exhaust pipe expander or a car cyclinder reamer tool thingy, 3 blades and not super expensive either... well gonna stop right there.

Too bad; good comments-I can see the original in my e-mail. Thanks.

[Red Tornado]

I once had my LBS ream a seat tube out 0,1mm (0.004") so I could go from 30,8 to 30,9. I wanted a certain make/model but the mfr didn't have 30,8 available at the time and didn't want to force an oversized post in there. Seems like you got it figured out, but if the shop has a reamer or a hone it's easier to go that route than removing material from the post provided you're not opening it up too much to. Maybe 0,1 to 0,3mm IMO.

[firemanj92]

I've sanded a seat post as it was just a shy larger than the I.D. of the seat tube. It took a lot of trial and error to finally get it right. As someone else stated, "patience". But in the end it was a feeling of accomplishment.

-J

[jumphigher]

Well as promised I'm updating how my own seat post sanding project went. I did it this evening on an older Richey carbon (:eek:) post I had. Basically I took several sheets of med grit sandpaper and sanded the post in a circular motion, below the portion that sticks out of the frame. It worked well, after I reached the required size I greased the post and inserted it into the frame. Alls good so far. I'll be riding the bike tomorrow and will report if anything gets weird.

[JWDR]

I'll be riding the bike tomorrow and will report if anything gets weird.

Good luck and be careful sitting on that ticking time bomb. Why wont you just listen to all the experts here that this will end badly? I advise calling ahead to your local hospital to ensure they have your blood type on hand.

[jumphigher]

Good luck and be careful sitting on that ticking time bomb. Why wont you just listen to all the experts here that this will end badly? I advise calling ahead to your local hospital to ensure they have your blood type on hand.

Well it survived 40 miles today with no issues. I'll be pulling it out and checking it periodically, though. I'm confident the small amount of material I removed is not gonna cause it to fail, but time will tell. :beer: