the fluted laprade post for my super le tour has got some gouges i'd like to clean up, if possible. it came that way. it's a 26.4 and would like to keep it vs just getting something else. but, how much is too much before getting "too thin" on the wall thickness? .1mm maybe .2mm max? i've got some new digital calipers so i can keep an eye on how much i'm taking off. i don't expect i'll get it perfect, but as good as possible is fine

thanks!

ps. would someone have a most expedient method that would also help prevent flat spots?

You can rig up a jamb nut on threaded rod to chuck in a drill or press that can be secured inside the post to spin it and sand or grind. It can be a bit tricky so you have to work with it to get it secure but it can be done.

Or you can find a machine shop that will turn it on a lathe.

I don't think it is about how thin but how much diameter are you losing. Too small and you start compromising the seat post clamp on the frame.

Sorry I can't help with measurements, too many variables, your weight, extension out of the frame (lever arm), etc. I did one fluted Laprade from the early '80s, the gouges where localized at the rear of the post a few inches above min insertion. I used a 1 1/2" emory cloth rolls like I was shinning the toe of a shoe, only at the area of the gouges with the post secure in a vice. After finer grit it is impossible to see any change in the post, very smooth transitions. Did not need to take much off and was not worried as the material resisting bending on the sides of the post rather than the front and rear are more important. High tech posts like the Thomson Elite have elliptical bores with thinner sections in the front and rear of the seat posts to save weight.

Ive taken .2mm off a seat post before. Sanded down from 27.2 to 27.0 because I needed it at 27.0 for fit and also because there were some gouges originally. That isnt going to in any way negatively affect the seatpost- they are simply too thick for .1mm around to compromise safety. It did smooth out the gouges though.

As mentioned- taking a seatpost that fits a bike and then sanding it will make it smaller than what you need for the bike. I would instead buy a seatpost that fits and is in good condition, or is .2mm too big for the seattube right now and will fit once sanded.

The emery cloth and shoe polish method is the way I go, also. The trick is to do a wee bit and move, do a wee bit and move, ensuring that you do your best to do the entire post as close as the same amount as you can. During the process, use your calipers to check diameter in several places. It is important to avoid flat spots or out of round. Area of contact is what holds the post in place, not just clamp pressure.

So, once you have cleaned and polished the post to a uniform thickness, you should be good to go. However...

As others have mentioned, if you have to remove too much, then the post will slip and you will, most likely, distort the seat lug by over tightening the seat post clamp bolt.

Anyway, this has worked for me many times, over the years.

thanks for all the input. given all that, i think i'll start with some emery cloth and keep removable to a minimum. i have read .1-.2mm difference in diameter isn't a big deal. otoh, i do have a couple of other 26.4 posts from mtb's. they're just black and i'd have to cut the length down. and, they aren't original, of course

the current post insertion leaves probably 90mm exposed. iow's, wall strength and material removal i don't believe would be much of the concern. but, like ya'll said it's the seat lug issue. i'll see how it goes!

wait...i do have a silver zero offset post that's 26.8. and, it's the right/shorter length. do you think sanding it down to 26.4 is going too far?

I've chucked one up in a lathe and took off way more than 0.2mm deep gouges before. Naturally this is going to compromise strength.. use it accordingly. Think about how much stress is on one of those at maximum extension with a heavy rider. Just don't go there.

thook-

You can sand and polish scored seatposts into a very presentable form. Check here: https://peugeotcoursepb12.wordpress....g/sr-seatpost/ Be sure to hone the seat tube, file back the points on the seat lug and file or sand back the upper edge of the seat lug to avoid re-scoring the post.

Before:




After:



Be sure to go just the minimum in the area which will be clamped in the seat tube to avoid undersizing the post.

i'm not a heavy rider, though i am overweight for my height. i hadn't weighed myself in a while, but i'm sure i'm just over 170lb. need to drop about 30lbs. at any rate, i went out and measured and have, as i guessed, 90mm of post from the seat lug to the clamp. the gouges aren't as bad as the post seen above. that is they're not as prolific and wide. more etched as they'd have been done with the point of a knife. hard to say how deep, though. supposed it's a bit moot on the portion submerged. just smooth it out there and clean up around the seat lug as suggested

i have a friend that used to have access to a lathe, but he doesn't have that job, anymore. so, it'll be by hand. maybe with an orbital sander to keep it simple vs rigging up to a drill/press.

more than helpful, gentlemen! thanks!