Building a new bike part 5

Hi

For the last few nights I have done some work getting ready to make the seat frame. This
will mostly be made from 12.7mm chromolly tube and will have 2 main support areas: it sits either
side of the main tube and is clamped in a seat clamp on 2 cantilever posts at the back.

A 2d cad sketch was used to work out the spacing of the seat frame rails. I find some bits of 40mm SHS and will be able to use that as seat jigging.

The spacing of the seat frame rails is set by the way the tubes will sit either side of the main tube and I will adjust the spacing at the seat post clamp using washers. So I make a few washers using a holesaw to cut bits out of a plastic tool caddy I'm no longer using. I think it was a sample from an engineering exhibition or something. These washers might come in useful in the suspension assembly as well.

One of the photos shows the finished, custom seat clamp with the frame tubes they will carry in place. I have brazed an 8mm tee nut into one of the plates, eventually this assembly will be able to be tightened by hand and it requires a captive nut on one side. Can't get much more captive than this! Quite pleased with progress, will be able to start on the seat itself now.