Seat tube reamer tolerance

Hi, I want to ask what is proper tolerance for seat tube reamer, for seat post to slide nicely in?

I bought new 32mm hand helical reamer for a bargain and I want to let it regrind to size for 31.6 seat post, so I can choose the ideal tolerance.
My original idea was 31.65mm, but now I think a tiny bigger gap will be better, something like 31.7, maybe 31,75.
What do you think about this? Thank you, P.

Ream for size. Most posts are undersized in my experience.

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Thank you, this aspect didn’t cross my mind. I will let it grind it to 31.6H7 then.

I have a few thoughts

First- I was listening to Adam Prosise talk about having a reamer made for long dropper seat posts. He said that size varies drastically and that One Up droppers were considerably larger than others so he designed the tool based on the actual size of that post.

Second- Have you found someone to do it? I want to do the same thing and sharpen some HT reamers. Pretty curious on what it will cost vs buying new.


Hello yes, I found a guy who sharpen tools more than 20years. Total cost will be around 40€ (including the reamer).


Does anyone have experience using a reamer like this for seat tubes? I’m using an adjustable one now but would like to get the proper size.

I use a straight shank for reaming bar and steerer clamps for stems. I chuck the reamer in the lathe and push the clamp on with a bull nose live center in the tail stock. I rest the other end on a 3/4" thick plate of delrin that slides easily as it progresses onto the reamer and easily slides back off. Usually there is a ‘pucker’ moment there but haven’t had any issues to date.