uncle uncle

So, I'm rehabbing a vintage seat post, which on Velo Base, has a finish of "satin" listed in the description. The seat post had the ubiquitous 'zig-zag' scratches that you so often seen. My OCD personality wouldn't let me reinstall a seat post with those on it, but, even though I've done the minimum sanding to diminish the scars, my sanded area doesn't match the original, unsanded areas. Anyone have some tricks they've found for simulating the original finish? Thanks in advance...

P!N20

No expert, but you'll probably have to sand the entire seat post to achieve a uniform finish.

Some pictures may help so we can see what finish you're trying to replicate. Is your post anodised?

I was playing around with a seat post the other day and polished a section that had only had a 400 grit sand and the result was what I would call satin.

randyjawa 

Sand wet with wet and dry sand paper. Work from a coarser grit, say 600, then 1000, then ... checking frequently until you like what you see. I have done this many times. NOTE: Avoid over sanding to the point of significantly reducing the diameter of the post.

Kabuki12

After sanding the scratches out, the alloy should be media blasted(usually talc) and then clear anodized. That will give the alloy a satin silver finish like some Campagnolo brakes when they are new. All blemishes and scratches should be removed prior to media blast or the anodize will make them show up more.

uncle uncle

Here's a picture of the seat post... sorry, it's not a very good one (picture that is). We are experiencing some gloomy, snowy, overcast weather... and getting good light was impossible. This is a pre-sanding photo. With it blown up, it looks more like a "ribbed" finish than "satin"; it does have a small amount of that "ribbed" texture... well, not anymore, at least in the area that I sanded.

P!N20

^ Almost looks like a machined finish. Going to be impossible to replicate with sandpaper.

scarlson 

Yeah, those are tool marks from a lathe. The post was turned to diameter and that's all. I'd polish it.

repechage

and not beyond the exposed portion
to remove those scratches it will probably decrease .1-.2mm

TPL

Have a friend with a lathe ?

Chuck it in a lathe and wrap it with a scotch brite pad ....voila !, smooth finish

That's a rather inexpensive seatpost ....you could just buy a replacement with a nicer finish

xiaoman1 

^^^^^^ Scratches are too deep and getting them all the way out will change the dia. of the post, so stay above your insertion line, otherwise you will need to use a shim.
Best, Ben

uncle uncle

It's a budget build... every part going on the bike has some sort of cosmetic issue or two, and none of them are special. Trying to replicate the finish is just a learning goal... if I can't/don't, no big loss.

Roger M 

I had a similar problem with a Campagnolo seatpost recently. I wasn't going for a factory original finish, so mine turned out a bit overdone.

I think if you clamp the post in a vise, and sand with the 'grain' of the machining, you should be able to get good results. I would finish with 400-500 grit and see what that gets you(you can always go finer if it's not good enough)

Good luck!

Here's the link for my project

Seatpost Rehab Thread?

oneclick 

Those scratches are deep enough that if you remove enough of the post to get to the bottom of them the seatpost will likely be a different size.

And if you don't get to the bottom they will show - especially as you likely have that part of the post exposed.

Worry about something else; there must be *something*, surely...

BTinNYC

Imperfect solution, but you can blend the different areas with Scotchbright pads. Start with red, I think grey will be too fine but YMMV.

Mr. 66

I would clean up the seat lug so it won't mark the surface, and I would lightly sand the high spots above the inserted area, if I was to keep the post.

Chombi1 

Replicating the original finish on scratched up anodized aluminum components is difficult.
Short of sanding, polishing and re-anodizing the compondnt.
Sanding and polishing out all the scratches is tedious, especially as you have to tke off the hard layer of anodizing protecting the surface. And it's easy to go too far and end up polishing off too much material, badly affecting the appearance of the part. But once you get it all polished out, you have to restore the satin finish of the aluminum.
I use the finest grit Scotchbrite scouring pad I call find to knock down the mirror finish to a satin finish by ever so lightly rubbing down the part in careful, directional strokes to reintroduce the "grain" of the satin finish, and stop when I think I got it to the right amount of satin look.
This method has worked for me when I restored badly scratched up crsnksets, stems and seatposts on my bike.
Thing is, it leaves the aluminum raw, and unprotected from the elements because the original anodizing is eliminated in the process.
I use car wax to then protect the part from corrosion after the restoration.

xiaoman1 

If you want more practice I have one that needs help.
Nice work.
Best, Ben

uncle uncle

So, an update. This was about 20 minutes worth of careful sanding, after reading everyone's suggestions, and going thru the linked, previous thread, along the same issue. I'm not sure if I'm completely done, but I'm much happier with this than with the zig-zags. I measured it, and it's mostly comes out at the stamped diameter value (no spots less than .1 mm than the stated diameter, and there were some "under" values that existed in places before I started). No seat post was hurt (sanded) below the theoretical insertion line.

Oh, for prosperity, this was done with 320 wet sanding, low pressure, always going with the original direction of the lathe marks (aka, 90 degrees to the flutes) and just a quick hit with Mother's Mag Polish, to finish. This seat post didn't have an anodized finish (which probably made things easier) and it isn't the seat post that was installed on the bike in question (that seat post is making the jump to another, higher pedigree, bicycle.)

uncle uncle

Thanks for the link Roger. I tried to look through older posts for "inspiration". Somehow, I didn't come across this one. It's content was very helpful.

The Golden Boy 

There's nothing like that beautiful satin sheen on the high end components like Gran Compe.