Seatpost slipping down no matter what

[bikeworkshop]

Two pages in and not a single mention of using a Coke can as a shim. This site has gone

Coke can?
You mean
"Euroshopper energy drink"
Retrobikers have "moved on"

@Splatter Paint did mention a drinks can, but has yet to finalise his "product placement" contract...

This, if the seat post wobbles in the frame or drops rapidly down without the clamp present then you can be pretty sure the post is too small for the frame.

Your average aluminium drinks can is 0.1mm thick. So you very carefully cut one up and make a shim 100mm long