Slipping seat post - will reaming help me?

[b_S]

The seat post keeps slipping on my old girly bike. It has a lugged clamp:

Unfortunately only the area at the lug makes contact with the post, the seat tube itself is a much larger diameter. With the QR lever cranked (so the clamp is almost closing on itself) hard it still creeps during use, which is getting annoying...

My plan is to ream it out to a bigger size, currently it's 26.8 but I'm thinking 27.2 is doable. I won't measure as such, but just keep slowly taking off metal until the 27.2 fits snugly.
Will this help me at all? I'm thinking so, and don't have much to lose besides a bit of time. Your thoughts please

 

[Tomas]

Tried liquid torque?

 

[Nerf Herder]

Me being a horder and tight arse ... I couldn't bear to think of throwing the post away ... so I'd rather add material then ream it.

Then again, you've prolly got a 27.2mm sitting around, just like I do, waiting for just this occasion.

Maybe

Tin Foil (or can o' black doctor) ??? folded over a few times ... and hammered down a little between two bits of wood ... not as satisfying as the dremel ... but there is hammering involved.

 

[smeck]

You could ream it, you'd just need to be really careful not to cut a taper into the tube, and ensure you get the step deep enough to give you enough insertion depth. If it's a steel frame with plenty of potential to bend, an option would be to run a hacksaw blade down throught the clamp lugs and the seat tube split, increase its width by 1mm or so. That would give you some increased crush to clamp your seat tube.

 

[b_S]

Tried liquid torque?

That's too simple a solution - didn't even consider it. Will give it a cleanup with a flapwheel or wire brush then see how liquid torque goes.
I've enough seatposts around, don't worry about that
As for getting the depth necessary, as said only the lugged area, which is only ~60mm tall, is on size - the tube it's brazed to has plenty of clearance which allows me to go much larger if need be.

Will have a play with it this weekend, the tape marks the height I ride at and you can see it's slipped ~7mm in an hour's riding.