Introduction: Build a Shopping Cart Cargo Bike
Build a cargo bike out of an old mountain bike, a metal shopping cart, miscellaneous bike parts, a variety of scrap metal, and a willingness to hack things apart!
I am currently living a car-free life and need a means of transporting supplies for those larger projects. Constructed at UPland.
To start off, I daydreamed a bit, searched around on the internet to see what other folks have created, talked to friends about what they use, and looked at some manufactured cargo bikes for ideas.
I landed on placing the cargo hold in front of the main bike with a 20" wheel out in front of the shopping cart for constructability, ridability, and stability reasons. I used a shopping cart for the cargo bed because it acts as a box truss between the front wheel and the rest of the bike, adding stiffness and strength, and is ready built. And it looks cool. This construction process can probably be adapted to any cargo bike configuration. I didn't worry too much about making sure the frame was perfectly straight and aligned as this it is as heavy as a tank and built for rough hauling purposes, not high performance racing.
Costs should be minimal with careful craigslisting and keeping an eye out for useful parts.
If you venture down this path, good luck! And please post pictures of your reinterpretations.
Step 1: Collecting the Bits & Pieces
All of these parts should be steel to allow basic welding. Avoid aluminum, carbon, or titanium bikes.
- Steel Mountain Bike [acquired on craigslist for ~$20]
- Metal Shopping Cart [can usually be found on the street in my neighborhood]
- Head tube, fork, and 20" wheel from a kids bike [a friend had cut a bike apart for another project and had these parts left over]
It is just a coincidence that all the parts I found are some shade of red. I wish that was intentional. Also, as everyone knows, red goes faster.
Scrap Steel for Frame:
I dug around in another friend's scrap metal pile to find these parts, so dimensions are not exact. Just a rough guide, other shapes and sizes will work fine.
- 6' of steel 3/4" square tube stock
- 3' of steel 1/2" square tube stock
- 8' of 3/4" metal conduit/EMT
- 4" x 1-1/2" piece of 1/8" steel sheet/bar stock
- (3) 2" x 1/4" bolts with locknuts
- 3' of steel 1/2" round tube stock
- Small piece of 3/16" steel plate
- 2' of 1" steel angle stock
6' of 3/4" metal conduit/EMT
Tools & Consumables:
These are the tools I used, although substitutions can easily be made depending on what you have available.
- Angle grinder with cutting disk
- Angle grinder with abrasive grinding wheel
- Metal cutoff saw
- Flux core wire feed welder setup [no shield gas required]
- Miscellaneous spring and bar clamps and stock for clamping jigs [use whatever is around] for welding
- Anvil [made from a train rail] & 3 pound sledge
- Metal vise
- Soapstone marker
- Drill with various bit sizes
For safety, I wore a face shield, heavy gloves, double respirator, and ear muffs [ear plugs] when grinding or cutting and an autodarking welding mask, welding gloves, and double respirator when welding. I also worked primarily outdoors [that is, in a very well ventilated area] because of the fumes created during the process. Make sure the area on the piece your welding has been ground clear of paint and other contaminants. I also wore natural fibers which don't melt and made sure none of my clothing was baggy.
Step 2: Layout and Disassembly
Remove the wheels from the shopping cart by by separating the wheel supports from the cage with the cutoff wheel on the angle grinder. I was able to cut along the welds and pry the legs off right against the cage for a clean cut. Quickly grind the cut area with the abrasive wheel to eliminate any sharp edges.
The 20" wheel I found had already been separated from the rest of the frame, but if you still have the whole bike you will need to cut just behind the steering headset to remove the top tube and down tube. The turning mechanism should still work.
Layout the bike, shopping cart and front fork on the ground to determine proportions and make sure everything will fit. The image shows the rough layout for the bike I built [although I hadn't removed the lets of the shopping cart, which just made things more difficult]. I used an expansion join in the concrete as a reference line to get the location of the shopping cart and front wheel correct relative to the rest of the frame. This reference line acts as the groundline when the bike is on its side. The rear wheel of the bike should rest on this line with the chainstay parallel to the line. The bottom of the shopping cart should be parallel to this line as well. The front wheel also rests on the line, but the fork can be tilted slightly to the back to shorten the bike. The front fork should remain nearly upright to ensure the steering works.
The whole project was done essentially without absolute measurements and just taking measurements directly off of the various parts. This ensures that everything fits well and doesn't require any drawings. The bike will be laid out multiple times throughout the process to take measurements and make sure everything is in the right place.
Step 3: Building the Frame
The Long Tube
While the bike is laid out, mark the length of the tube stock that runs underneath the cage. This should be about the distance from connection point on the bike frame to the front of the shopping cart plus 1 or 2 inches. Measure it again, making sure you have the shopping cart in the right place relative to the bike. Mark the angle that the tube stock meets the frame and cut the tube stock to length with one square end and one end angled to match the bike frame. The angle will not be perfect, correct the angle with the saw or grinder until it is close enough. Grind the angled end to match the curvature of the bike frame [see image]. Remove the paint from the bike frame in the area that you will be welding with the grinder to make a cleaner weld [and avoid toxic fumes].
Create a jig to hold the tube in place while you weld it to the frame. I used a short board and a long board clamped to either side of the frame to create a stable surface to clamp to [see image]. Weld the tube on and you now have a one wheeled jousting bike.
The Short Tube
The short tube connects the long tube that runs under the shopping cart to the head tube of the front fork. Lay out the bike on the ground again, position the short tube, and mark for cutting. The short tube should terminate on the top on the long tube [see image] leaving enough space for the shopping cart to fit between the bike and the short tube. The 1 to 2 inches of extra length on the long tube allows this distance to be adjusted. The front fork should be slightly angled back with enough clearance between the short tube so that the wheel turns freely. Measure again and cut the tube with the angle to match the top and bottom where it meets the other tubes. Clamp and weld to the long tube. The two bars now create a bent 'L' projecting from the front of the bike. [see image]
The Front Fork
Take the front fork and grind flat the stubs of the frame that stick out of the head tube. Cut a piece of flat plate steel/flat bar to the same width and length as the head tube. Clamp this against the flattened frame tube stumps and weld in place [see image]. This creates a strong flat surface that can be welded to the short tube.
Lay out the bike yet again and position the front fork against the short tube, checking the height and angle. The angle of the end of the short tube may need to be corrected [by cutting or grinding]. Clamp and weld! [see image]
The Frame Brace
To prevent the bike from folding up on itself, add a tube between the top of the down tube of the bike and the long tube. Lay out the bike [one last time, I promise] and mark the angle to cut [see image]. I set the angle of the bar to match the angle of the head tube purely for aesthetic reasons. Cut, fit, grind and weld.
The main spine of the bike is now complete!
Step 4: Mounting and Bracing the Cart Cage
Drop the cage into place on the spine, making sure to center it from side to side.This was the only time I used a tape measure. Depending on the quality of your shopping cart, the wire lines of the cage may not be square and thus look skewed. Tack weld the shopping cart cage to the bike frame at regular intervals, especially where the larger shopping cart members cross the bike frame [see images].
Take a length of EMT and bend into a shallow 'V' shape to bridge the distance between the shopping cart frame and the back of the front head tube [see image]. To do this, a large vise is very helpful for both flattening the EMT where it will connect to the bike and as a brace for bending against. The make the EMT brace, use the following steps, checking the brace dimensions regularly against the bike:
- Flatten 3" of one end of the EMT in the vise [see image]
- Bend the EMT to nearly 90 degrees so that the flat part of the EMT runs along the side of the cart and the body of the tube points towards the front head tube.
- Where the EMT intersects the head tube, flatten the EMT and bend parallel to the plate welded to the head tube [see image]
- Bend the remainder of the tube back towards the opposite side of the shopping cart cage.
- Where the EMT touches the side of the card, create another 3" flat section of EMT and bend parallel to the side of the cage
- Cut to length
You should now have a brace that ties the top of the shopping cart cage to the front of the bike.
Weld the brace in place, know that WELDING EMT/GALVANIZED METAL IS DANGEROUS. Do what this guy says: https://www.instructables.com/id/Welding-EMT-Condui... And wear a good respirator.
Create another brace for the rear of the shopping cart to connect it to the head tube of the bike. Same process, different location, the second one is easier. Weld this into place [see image]. It now looks like a cargo bike!
Step 5: The Steering Linkage
Create a steering column that reaches from the handlebars to below the shopping cart cage by extending the headset. First cut a small plate about 2" by 4" and drill a hole that matches the diameter of the tube you will be using as a steering column to extend the headset [see images]. Weld this plate to the long tube to hold the steering column from flopping around at the bottom. Place the end of the steering column in the center of the cutoff fork and align steering column parallel to the head tube to determine the placement of the plate [see image].
The fork from the bike I used had a hole through the bottom of the center [probably to mount fenders]. This allowed me to drill a hole in the end of the steering column and bolt it in place in the fork [see image]. Depending on the angle the steering column intersects with the plate, the hole may need to be enlarged slightly. I used a tapered drill bit to get the fit right, while still keeping it snug.
Cut the steering column to length, a few inches below the small plate with the hole. Cut a 10" piece of angle stock and drill a 1/4" hole ~1" from one end, centered on the right end, bottom of the "L" when facing forward. This hole will be used as a pivot to for the connecting bar. Weld the left end of the angle stock to the steering column, making sure that when the handlebars are straight, the angle stock is perpendicular to the bike frame. Position the angle stock with the "L" facing forward and the hole in the end parallel to the ground [see image].
The Front Fork
Take another piece of 8" angle stock and position it perpendicular to the top of the right side of the front fork with the "L" facing downwards and backwards. Drill a 1/4" hole in the top of the right end of the angle stock, which will act as the pivot for the other end of the linking bar. Grind the end of the angle stock to match the curvature of the front fork and weld in place [see image]. The angle stock acts as the lever for the front steering.
Bend a 6' length of EMT into a connecting bar between the angle stock steering levers. Bending conduit without a proper tool is ugly, but can be done. I used the vise, but instead of gripping the material, I bent the tube into a soft curve by pushing down on the tube against the vise in small increments, constantly changing position so as to avoid getting a kink. Constantly check the connecting bar against the bike to ensure they shape is correct. It will need to run below the cage and then curve up to meet the angle stock welded to the front fork [see image]. Once the shape is correct, cut the tube to length and flatten both ends. Bend the front end to match the face of the angle stock with the hole in it. Drill holes in the conduit to mirror the holes in the angle stock at both ends, while ensure that the handlebars are facing forward and the front wheel is aligned. The at the back can be re-drilled in a new position to correct the alignment, if necessary [which I assure you it was for my bike]. Bolt the conduit into place, liberally sprinkling the joint with washers to ease rotation.
Everything should be working, take it out for a spin!
Step 6: Metal Edits
Test rides revealed a few problems that can be rectified with the addition of a few key pieces of scrap.
Fork to Steering Column Connection
Where the trimmed forks connects to the steering column is a little bit loose and needs a way to be clamped down. To do this, take a 6" length of 1/8" x 1" flat bar. Drill a 1/4" hole in one end for the bolt that travels through the fork. Bolt the flat bar to the front fork and clamp the lower section in place against the steering column. Weld the flat bar to the steering column along each side. The fork and steering column should now be firmly bolted together through this flange without any slippage when turned [see image]. The steering column can still be removed if necessary by removing the bolt from the front fork and pulling the steering column straight down.
Rear Steering Lever Extension
When the handlebars are turned, the front wheel does not turn enough making it necessary to turn the handlebars very far to corner. To rectify this, the steering linkage connection point at the front can be moved towards the center of the bike or the connection at the back can be moved outwards from the center. Drilling a hole closer to the fork in the front bar would be easier, but them some leverage is lost. It is better to extend the angle stock welded to the steering column, which will increase the steering leverage. Take a short length (~4") of angle iron and weld it to the end of the existing angle iron welded to the steering column [see image]. Drill a hole in the end to reconnect the steering linkage rod [see image]. Small adjustments in the handlebars now correspond to larger wheel movement. The additional holes in the bottom angle stock allows the attachment point for the connecting linkage to be fine tuned, if necessary.
Strengthening the Front Fork
There is some concern that the front fork may fold away from the rest of the frame if heavily loaded or a sharp shock is applied (which happens regularly with the potholed roads in the area). To strengthen the front fork connection, take a 14" long 3/16" by 2" piece of flat bar and bend into a U shape [see image]. I used a length of pipe that was approximately the same diameter as the headset of the front fork as a bending form. Take the U shaped length of stock and clamp in place around the front fork, overlapping with the frame that runs under the cart. Weld in place [see image]. This piece firmly connects the front fork to the rest of the frame.
The frame should now be sufficiently strengthened, most of the slop removed from the steering, and the metal ready for painting.
Step 7: Buff and Polish
This is a rough job, so buffing and polishing may be something of an exaggeration. These last few changes really make it spiffy though:
For the base coat, hit all of the rusted metal with a wire metal brush to clean off all loose material. Follow this with a few coats of exposed rusted metal with "rust converter" to stabilize the rust [see image]. Apply a top coat that matches the color approximately, in this case a nice glossy red.
The steering system still had a little slop, so I used a stack of washers to replace the front and rear steering connections. I placed two washers on the outside, with a stack of four between the steering column and connecting rod and tightened the locknut fairly hard [see image]. This removed most of the wiggle in the handle bars.
A bit of basic bike maintenance made the bike generally more ride-able and I replaced the shifter cables, adjusted the rear brake (you'll need all the stopping power you can get when fully loaded), and adjusted the seat.
That's all folks. Start hauling.