Almost jigless bicycle frame building

Step 5 Joining the Bottom Bracket and Seat Tube

Usually the first step is to join the bottom bracket to the seat tube. I won't go into all the details such as mitering and drilling vent holes. Get the Paterek Manual if you need to find out more about that part of fabrication.

With a big C-clamp and some flat bar stock (not shown), clamp the bottom bracket to the jig table. Then using the appropriate sized tube lifts (also clamped to the jig as shown), line up the seat tube against the bottom bracket over the vent hole. Welder's magnets will hold it place for you to tack the tube. You also might be able to use those big spring clamps (the ones that look like big metal clothespins) to hold the tubes against the lifts.

Of course, before you tack the tube, double-check that the seat tube is parallel to both the jig face and to a straightedge lined up against the face of the bottom bracket.

After you tack it, check for parallelism again.