Reaming a seattube - Rounding at 27mm then up sizing to 27.2. Who is good in London?

I'm building up a beater and I'm having the classic problem of seat post fit.

Internal tube measures 26.8, but won't clamp tight on a 26.8 post.
Shimmed up to 27.0 it works ok, but not great.

My plan is to run a 27.0 reamer in and get the tube round and clean again. Test fit a 27.0 post. If that's loose and there is enough material on the seattube, then ream to 27.2.

What shops in London can anyone recommend specifically for this or who on the forum has the tools to do it?

Thanks for any pointers

I'd go and buy one of these
https://www.rdgtools.co.uk/acatalog/ADJUSTABLE-REAMER--RANGE-1-1-16----1-3-16---H12--MEDIUM-SET--83465.html
And a cheap set of digital calipers and have at it yourself, any shop with the tools is probably going to want more than the cost of buying the tools and doing it yourself

Here's a repeat of my post from 'Seat pin slot pinching' 22 days ago.

If you don't want to bother with Clive's solution, you might try simply removing some material from the sides of the slot with a file or a hacksaw.

Hot Melt Glue

Here is a radical but simple solution to the seat post problem - forget the clamp, just use hot melt glue.

Clive Bonavia (google him) was an eccentric but excellent frame builder who used this method on all his later frames. He said it had three benefits: it saved him the trouble of making any kind of clamp, it saved the weight of the clamp and, most importantly, it prevented any water getting into the frame past the clamp (a common problem, causing corrosion).

Clive's main business was joinery, so he knew all about glue. Although I think this material was intended for wood, it seems to work perfectly for this purpose. It can be reheated any number of times to adjust the seat post, and the amount of heat required to free the glue does not damage the paint.

You should be aware that I'm just quoting Clive here, I'm not writing from personal experience, but in my experience he was always right about these technical matters.

So I suggest you google 'hot melt glue', and don't forget to clean and degrease everything before assembly!

It’s a frame building task that should be performed before assembly- typically the frame is clamped in a vice at the bottom bracket, although some frame builders clamp the ream and then lower the frame onto it, using the frame for leverage.

Can the bottom bracket be removed and or is it stuck in place?

Reaming can be performed when the bike is assembled/painted, but clamping it in such a way that you don’t deform the tube you are reaming is key, and also using a proper, long team that won’t tip- if you go in at an angle you’ve fucked it and won’t be able to recover the situation.

Proceed with caution!