Step 10: Aligning the frame for brazing/welding
*Place the main frame on a flat fire-proof surface. Paint flux on the ends of the tubes and inside of the coupling, and slip the two tubes inside the coupling as far as they will go, ensuring that there is flux at the edge of the joint. If the tubes spring back out, bend them in.
*Measure 19" from the back end of the main frame. Use a square to get even measures on each side of the frame. Mark on the side of the tube, so the mark is visible when a tube is placed on top.
*Place one of the ribs between the two marks. Check to see if the miters fit well. If the tube does not fit, bend by hand until it does. Support this rib with bricks, magnets, or other metal scraps, but not right in the center, where the spine will be.
*Mark for the front rib 16 1/2" in front of the marks for the center rib. This positioning is not exact, but should be right where the bends start on the main frame. The front rib needs to stay out of the way of the wheel well. Adjust to fit, and support this rib as well. Do the same for the back rib.
*Mark the center of the front and back ends of the main frame by marking half-way points on the table where the sides are parallel, then by drawing a line through those points to the main frame end pieces. Lay the spine over the ribs.
*Once the pieces are centered, vertical, aligned, plumb, flush, or otherwise how you want them to be, take them all off and coat each surface that will be brazed with flux. Replace all the pieces.
*Read the brazing information on the following pages. Braze the frame together, starting with the ribs. If the spine does not sit perfectly on the ribs, tilt the ribs towards the curve of the spine until there is contact, or bend the spine down to make contact.
Creating the dropout jig
Note: These measurements assume that you are using 2 front wheels from bikes, with 4" distance between the outside surfaces of the locknuts. If you are using rear hubs or hubs with a different spacing make an appropriate adjustment in the jig.
*If you are lucky enough to find 20" wheels, measure the axle width, adjust the dropout jig, make the wheel wells shorter by 6 inches or so, and take off 3 inches off of each side of the ribs and spine to keep the same clearance. (Axle height on a 26" wheel is 13", and on a 20" wheel it's 10".) If your wheels are strong, the cart with 20" wheels should be more stable and stronger than a cart with larger wheels. Move the wheel wells and center rib back by 6 inches to stabilize the cart. If you are going to be making several trailers, I suggest using nylon nuts for this jig. If you are making just one trailer, you could make a cheaper jig from wood or metal rod. As an alternative to nylon nuts, use 2 regular nuts tightened together.
*Measure the width of the center rib from the outside of the one mitered end to the outside of the other end. Center to center will be about 22, and outside to outside will be about 22 3/4". Take your measurement, and subtract 1/4" (to allow the dropouts to sit well against the tube). It will be about 22 1/2".
*Thread on a wing nut on each side, with the flat side of the nut facing out. Slide on two 3/8" washers on each side.
*Thread 2 nylon nuts onto the threaded rod, one from each end. (The side without the nylon has to go on first.) To hold the rod while threading, you can thread two regular nuts onto the opposite end of the rod and tighten them together. Hold this end in a vice or another wrench.
*Thread the first nylon nut 6" onto the end of the rod. Thread the other nylon nut on the other far enough so the distance from the outside of the two washers is the same as the distance measured along the center rib, minus 1/4" (see above, probably 22 1/2" or so).
*Thread another nylon nut onto each side, so that the distance between the two nylon nuts and two of the washers is the same as the spacing for your wheels. For 26" mountain bike wheels, this distance is 4". For road bike wheels, the distance may be less, down to 3 7/8". If you're using rear wheels, it might be 4 3/4" or more.
*Slide on two more washers on each side. Thread on one more wing nut.
Adding wheel wells and dropouts
*Turn the frame right side up. It will rest on just the spine. Place 4 bricks under the front and back ribs to make the main frame parallel to the ground.
*Place a dropout between each set of washers on the dropout jig(4 sets). Align them on a flat surface with all the slots in the same direction. Tighten the wing nuts.
*Use 4 rubber bands or string to get the wheel wells snug against the main frame.
*Find and mark the centers of the wheel wells (about 16" from each side).
*Place the dropout jig with dropouts on bricks/metal scraps, etc, just behind the center rib. It should be at such a height so that when the wheel wells come down to rest on the outside dropouts, the inside edge of the tube rests
with the dropouts. Note: if the dropouts are centered on the tubes, or too far from the wheel-side of the tube, there could be clearance issues with the spokes hitting the tubes, especially on 700c and 27" wheels. See diagrams.
*When everything is aligned nicely, apply flux, and braze the wheel wells onto the main frame.
*Make a small tack braze on each dropout. Remove the jig before brazing the dropouts completely, or the nylon in the washers will melt or the nuts could get brazed to the dropouts. Brazing the dropouts to the rib will require much more heat than brazing two tubes together because of the wall thickness. To keep from burning through the tubes, aim the flame mostly at the dropout.each side, so that the flat sides of the nuts are facing the washers.