When you have gathered all the materials needed, we are ready to begin the destruction.  Carefully cut the frames of the two bicycles forward of the seat tube. 

File down any protruding stubs of tubing, leaving a smooth surface.  Now you will need the local bike shop.  Take the rear wheel assemblies you just freed to the bike shop to have them “remove the crank”.  You’ll want it taken down to a “bare bottom bracket tube”.  Ask them to measure the I.D. of the bottom bracket tubing, and write it down.  When they’re done scratching their heads, you will have two frame sections with wheels; after removing the seat and seat post there will be nothing else that can be removed except the wheels.  If there is seat retention hardware, hold on to it, you can use it later.

Now you can shop for and buy the large diameter tube to join the frames together.  You want to buy the largest size that will fit into the bottom bracket tubes of the frames you have.  Thinner wall is better, I’d look for 1mm (.040”) or .050” thickness.  1/8” will weigh a figurative TON!  4130 is the best alloy, any 4xxx series will suffice.  1010 steel will also contribute to a porcine aspect to your cart.  Remember, although your dog is pulling it, you’ll be lifting it in and out of the car.  “Simplicate, and add more lightness” as per William Stout is our motto.

The length of the tube you buy will be determined by the distance between the wheels desired (the “track”).  Set the two frame sections on the floor, resting on the tires and the bottom bracket tubes.  Sit between them to get a feel for the correct distance.  Then measure from the OUTSIDE of one bottom bracket tube to the OUTSIDE of the other.  You should get a number within a couple of inches either side of thirty inches.

At this point we have two ways to proceed.  One we will follow if we wish to be able to break down the cart for easier transportation, the other will yield a non-collapsible cart.  The non-collapsible cart will be more rigid, but the other will hold up to anything short of Mr. Toad’s Wild Ride.

For the take-down style cart: Lay the frames out as you did before, only this time slide the bottom bracket tubes over the large diameter tube.  Place one frame section at each end of the large diameter tube.  The large diameter tube must extend all the way through the bottom bracket tubes, and be flush with them on the ends.  Now drill a ¼” hole through both tubes in the middle of the bottom bracket tube, flip the assembly over and drill a corresponding hole opposite the first.  Two ¼” bolts, 3” long, Grade 8; with nuts, washers and lock washers will complete the assembly.  By removing these bolts you can effect the disassembly for storage or transportation.

The alternative is a rigid assembly.  Weld the large diameter tube in place as described above.  The local bike shop can assist you in having this done.  At this point you should have something that looks like this. Take this opportunity to paint your cart.

Finally, we need to have a way to hitch our dog to the cart.  We will use the two shovel handles for this purpose.  Measure the I.D. of the seat tube where the seat post fit.  Turn down the handle for a length of three inches to a diameter that will fit inside the seat tube.  The clamping method used to secure the seat posts will suffice to hold the traces; should you wish for a more secure mounting method, the tubes and traces can be cross-drilled and #10 hardware used to secure them together