Bicycle frame - part 1

Time to bite the bullet and start making my bicycle. My first job was to cut up my precious Brown Oak and hope I had enough. I made a cutting list and prepped a stack, very much pushing my luck and minimising waste. Where the lamintes would be seen on the outside of the bike's top tube I made sure I cut the pieces from the same stock and numbered them so I could laminate them back in order to maintain grain pattern as much as possible.

timber stack

labelled timber

 

 

 

 

 

 

 

 

 

 A stack of Brown Oak and Maple to make the main bike frame parts, labelled up ready. I also cut and shaped some frame spacers for the inner cores. I used some scrap mahogany pieces to save the oak, as these would never be seen.

frame spacers

 

West Sytem 105

 

 

 

 

 

 

 

 

 

All my glueing would be done using West System epoxy. This should not only be super strong but also 100% waterproof. I used 105, 206 hardener and a 406 Colloidal filler for all the wood to wood bonding. Below is my first laminate to make up the bike's top tube. I realised I had sufficient Sycamore Maple to make a second frame, so I combined this with some normal English Oak and decided to make two bicycles at once. The setup was quite intensive, so I took the gamble the frames would work and decided the Maple bike would be my winter bike. The central core laminate below is made of 6 tapered lengths (as discussed) and three shaped spacers. As I had plenty of oak but no excess maple, I employed oak laminates in the centre, as these would not show. I did the same on my Brown oak bicycle to save the precious timber. To make one frame would require 6 of these curved forms (3 per half). I planned only to finger joint layers one and two, so made up the 8 forms necessary - lots of steaming followed by lots of glue ups. It seemed to take ages, but I got there.

 

First bicycle core

The down tube and seat tube did not need bending, so it was a simple case of cutting the blanks. I used 4" wide sections and laminated layers one and two, as these were the pair that would be finger jointed together. I used the MDF trial pieces I had made as  templates becasue I knew these fitted and I had worked out the finger jointing. I fixed the blank to the MDF jig and ran round with a flush cutting router bit.

finer jointing

down tube blank

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Using a guided finger jointer in my router table I cut the joints to join the three main bike tubes, but only layers one and two. Setting up the finger jointer bit is something of a trial and error pain, so once I had it set right I cut all the finger joints for both bicycles - 12 joints in all. The bit is quite large, so as I was relying on the guide bush, I added a starting pin to the router table to minimise kick back. This really helps feed in the work gently onto a fast spinning and quite large cutter. Below are pictures that show how the frame jig holds the three sections of bike frame in place, ready for glue up.

bicycle frame in jig 1

bicycle frame in jig 2

 

 

 

 

 

 

 

 

 

Using the index peg locations, I placed my bicycle frame shape jig and drew around it just to show how the frame would ultimately be cut out of the blanks. I clamped the two halves together to make sure everything was working and lining up accurately. This still only made up 4 of the six layers required. The final, outer layer lay up was slightly differently in order to overlap the finger joints and, hopefully, add strength. It was back to the steaming bag to prepare and lay up the 8 laminates needed for the bicycle top tube. Being the visible outside of the frame, these were the most crucial. 

bicycle frame halves

bike frame halves together

 

 

 

 

 

 

 

 

 

© Christopher Thompson