Rear pivot welding and frame assembly

I cut the rear frame as marked and welded the rear pivot plate.  The plate distorted.  The front pivot plate had also distorted when welded before.  The result was that the rod-end bearings did not align properly and would not turn when tightened.  I realigned the front plate by tightening some nuts on a threaded rod passed through the holes.  I bent the rear plate in a vise until the alignment was perfect.

I am very pleased with the assembled frame - the front boom is still very long, I will cut this when I am happy with the reach to the pedals.  There are many things still to do - seat mount next.  I have a carbon fibre seat from Germany.

Pivot angle measurement and marking of rear frame cut

I have a platform for painting ceilings.  The underside has strengthening steel angles.  I used this as a straight edge to clamp the front and rear frames in line and used some threaded rod through the pivot to set the steering angle of 63 degrees (with the invaluable help of Sarah, seen holding the protractor in the picture).  I used a magnet to fix the rear frame in the correct place and drew a line at the place where I needed to cut.  

You will notice that the rear frame is upside down in the photos.  Thankfully I noticed my mistake before cutting and went through the whole process again to make the correct cutting marks.

Rear frame welding

The design of the rear frame has changed from the original plan.  I decided to have a crosspiece so that the part of the frame under the seat is now in the centre line of the bike.  This adds a bit of weight, but should increase rigidity (twisting) and make mounting the pivot and the seat easier.

When welding, the crosspiece distorted, leaving the two long pieces not parallel.  This was expected.  My plan was to bend the long section by hand / vise using my body weight.  This did not work as the tubing is too strong (on reflection, a good thing).  I therefore welded some dummy beads on the outside of the tube to deliberately distort it in the direction needed.  I used low power and needed 4 beads before the desired distortion occurred.  Pretty pleased that I managed to figure this out.

Tomorrow, I plan to lay out the bike in a parallel frame to finalise the angle and length to cut the rear frame end to mount the pivot plate.  I will also use the opportunity to think about a seat position and mounting.

Rear wheel and rear disc brake mounts

I drilled the hole for the rear wheel in the 40x20 tubing using a cheap stepped cone drill.  This worked very well, much better than a standard drill which leaves a ragged hole in 1.5mm steel.  I have an M12 clearance, 17mm spacer inside the tube to prevent it being crushed when the wheel nut and bolt is tightened.

With the wheel fitted, I measured for the brake mount.  I made an IS caliper mount using information from this excellent site:

http://www.peterverdone.com/disc-brake-mounting-systems/

 Cutting out the recess where the caliper protrudes was the most challenging part of the build so far.  I couldn't get an angle grinder into the recess and a Dremel was too flimsy.  It took me a long time with a hacksaw and a file - the end result is functional but ugly.

Drivetrain test

I have an old 9-speed drivetrain from another bike - today I installed it to check the chainline and clearances. 

I found that I had to shorten the drive side dropout tab in order to mount the wheel with the mech installed.  I also had to add a washer to the mech as the hanger was too thin (5mm) and the chain was hitting the screw.  After this it was all fine.

Front frame assembly and welding

I've spent the last couple of weekends welding the front frame.  I have no jig, so I've had to align the various pieces using careful measurement, magnets and temporary spacers TIG tacked on. 

As usual, the distortions from welding have required a certain amount of bending and adjustment after welding, but I'm very happy with the final alignment and rigidity.

The front boom / BB mount and the 40x20 cross pieces are still too long and need to be trimmed.  I will also add brake mounts at some point - I'm still not sure if I will use a disc or v-brake as I had the wheels built to be able to use either.