Since I'm fresh from finishing my first trike, and just cutting up the tubing for the second one, I made myself a simple Jig made of some plywood and pieces of hardwood. Since I made the cross part of the frame from four pieces (boom 2pcs and crossmember 2pcs) and welding with CO2 (MIG), I weld the crossmember tubes together first, because they form a very open "V" letter, and after that I weld the crossmember to the main boom tube under the proper angle (watch out for the castor angle!), and at last, the remaining boom tube part with the BB... Letting your angles float away "here and there" can transform a trike to a suicide machine. My trike goes in a straight line when I ride it without keeping my hands on the handlebar, and so should every well made trike (At least I think so) Playing with your life, or the customers is not a joke. And as they say if you're gonna do it, than do it as it is supposed to be done, correct. So, the 8 degree angle should be 8 degrees, not 7 or 9... 1mm mistake on the other end of the frame can be 2cm off the proper position! So, take your time and a few pieces of hardwood, cut it out to hold your tubes, you won't regret it... Making the final measurements, I found that if any sliding away happened, it was when I needed to re-do my castor angle from 4 to 8, and it slipped away to 9, and that is just because I had to cut out a piece off the frame on the boom and bend it... Otherways, all the mistakes are under measurable limits (much less than 1mm on lengths over 1000mm)
Take care and good luck,
Robert Stein "Bike-R-Plus" Designer of the first Yu Trike
From: Brent & Maryann
Carter I build custom furniture for a living, so wood was the obvious choice for my jigs. The first thing I did was make up several feet of v-block from some 3" wide strips of 3/4" MDF. Plywood would also suffice. I used pieces of this to hold the tubes in place for brazing.
You need some means of cutting the pieces to which these v-blocks will be attached (again 3/4" MDF or ply). A jigsaw would be the minimum, but a bandsaw and tablesaw certainly helped. Measure everything very carefully and attach the sections of v-block to the supporting board using drywall screws. I used washers and index cards where necessary to shim the v-block into the proper position in all three dimensions. You can cut notches in the backing board where necessary to allow the flame to pass for brazing.
To clamp the tubes where you can't get a spring or screw clamp, cut another short section of the v-block and screw it upside down over the tube into the lower block. The other jig device that I used was a piece of v-block attached to a long section of 3/4" x 3" ply. The v-block had one screw through it's centerline so it could be swivelled to adjust for any angle I needed. You can clamp the long pieces to another board to hold frame pieces when the frame has gotten too unwieldy to work flat on the bench.
The other tool that really came in handy was a sort of wooden protractor. I could set it to a particular angle, rest one leg of it on the tube and check the other leg of it for level using a torpedo (8") level. Other than that a good 2' level and a miter gauge are pretty important.
>Bending and mitering the tubing.
The only tubes I bent were the seat tubes. These I did
with a conduit bender. Not easy and not fun but possible.
I had the handlebars bent by a local guy with a racecar
shop. You could do these too but if possible find one and
have him do all the bending or buy the bent stuff from
Ian when you get the kingpins. Make sure you have a
source for the bronze bushings (automotive starter shop)
or get them too.
Straight mitering was easy. I used a carborundum blade in
my tablesaw. I have a homemade sliding table for it so all
I had to do was cut a wedge of 3/4" material at the
proper angle, set the tube against it and slide the table
slowly across the blade. This could also be done with a
the blade in a miter saw. Check for max rpm rating on the
blade though.
If you don't have either of these you can do it by hand
with a wooden measuring jig. Attach 2 strips of 3/4"
x 3" board together to make one strip with an
L-section. Do this twice. Now you can clamp the two
sections to a backing board so that you have two 3"
high vertical fences with the tube's miter angle between
them. Start grinding on the end of the tube. Test fit it
to your jig and grind until the side and end of the tube
fits flat against the fences.
I found it easiest to do the birdsmouths with a bench
grinder and a small round file.