How to Make Human-Powered Tools: Bike-Frame Cultivator

Human-powered tools are not only better for the environment than their gas and electric counterparts, they serve as an act of self-sufficiency, too. Learn how to build a bike-frame cultivator, and discover the difference human-powered tools can make.
February 15, 2013
"The Human-Powered Home," by Tamara Dean, is your complete guide to modern pedal-powered, treadled and hand-cranked devices for the home. 

Cover Courtesy New Society Publishers

What if I could harness some of all this energy my own body produces? An unusual question, to be sure — yet human power is a very old, practical and empowering alternative to fossil fuels.The Human-Powered Home (New Society Publishers, 2008), a MOTHER EARTH NEWS Book for Wiser Living, is a one-of-a-kind guide to human-powered tools gathered from a unique collection of experts. This book discusses the science and history of human power and examines the common elements of human-powered devices. For those who are beginning to understand the importance of a life of reduced dependency on fossil fuels, this book can be a catalyst for change. 

Buy this book in the MOTHER EARTH NEWS store: The Human-Powered Home.

Read more from The Human-Powered Home:
How to Make Human-Powered Tools: Treadle Sewing Machine 

The joy of working outdoors lies in appreciating nature. But birdsong and blossom-scented breezes are too often extinguished by the racket and smell of gasoline engines. Peace is the reason, many have told me, that they opt for human-powered lawn and garden tools. Others add that many human-powered tools work just as well, if not better, and as quickly as their motorized counterparts. Watch how long it takes someone to blow leaves off a sidewalk. Could sweeping them really take longer? Not only that, but human-powered tools are often more durable. In his book Homesteading: How to Find New Independence on the Land Gene Logsdon writes, “The [hand-pushed] cultivator makes no noise, always starts, never breaks down..., needs no gasoline, can be controlled easily to avoid plowing out vegetables — and mine is at least fifty years old.”

How to Make a Bike-Frame Cultivator 

Home gardeners might be familiar with the twisted back and cramped hands that result from hours of loosening dirt with a handheld cultivator. A cultivator attached to a modified bike frame, however, affords the gardener greater power and a more comfortable, ergonomic position. It also covers more ground in less time.

This plan is inspired by a bicycle cultivator mentioned in a 1981 issue of MOTHER EARTH NEWS magazine, though I’ve created a modified version that’s more durable in some ways and simpler to construct. The plan doesn’t call for welding skills or supplies, but if you have them, you could make your cultivator sturdier.

At the time this was written, commercially available versions of similar wheeled cultivators sold for $85 to $130.

Ease of construction: Fairly easy; it involves minimal knowledge of (or willingness to learn) basic bike mechanics. For some steps, it’s helpful to have two sets of hands. Depending on the bike, it might require special bike repair tools.

Time to make: 4 to 6 hours

Cost to make: $15 to $30, using scrounged parts

Ease of operation: Very simple

Following is an overview of the steps in this plan:
• First, you’ll disassemble most of an adult bike by removing the seat, shifters, brake levers, brakes, crankset, chain, derailleurs and front wheel and sawing off the top tube and down tube.
• Next, you’ll separate the front fork and steerer tube from the head tube and reattach the front fork to the part of the frame you saved. This creates the cultivator’s long handle.
• Finally, you’ll attach a cultivator head to the seat tube in your modified bike frame.

• One adult-sized, steel-framed, single (not tandem) road bike, salvaged. A bike with a wheel size between 20" and 27" will work. It’s okay if the frame is slightly bent or banged up. A lower-quality bike can often be dismantled with standard shop tools, whereas a high-quality bike is more apt to require custom bike tools. You probably wouldn’t want to ruin a high-quality bike for this project, anyway.
• One old, long-handled cultivator, as shown in Figure 2 in the Image Gallery. In rural or exurban areas these are common antique-store finds, usually costing less than $10. (In fact, if the handle is broken or missing, which is fine for this project, you could get an even better bargain.) However, if you can’t find an old cultivator, you can substitute a modern long-handled cultivator, given some modifications to this plan. See the “Variations and Considerations” section at the end of this plan for ideas.
• Four 1/4"-diameter carriage bolts, 1-1/2." long, plus matching washers and nuts
• One 1/4"-diameter carriage bolt, 6" long, plus matching nut
• At least six fender washers which are at least 2" in diameter and whose center holes are least 1/4" in diameter
• One 6" hose clamp
• One 3/4"-diameter galvanized steel pipe nipple, 5-1/2" long* (if you’re short, choose a slightly shorter one, or if you’re tall, a longer one)
• One 3/4" galvanized steel floor flange*
• One 3/4" galvanized steel 45-degree street elbow (male-to-female)*
*The size of these parts — all of which can be found in the plumbing department of your local hardware store — depends on your seat tube’s inside diameter being roughly 1"; this is almost always the case, but check yours to verify its size before buying these materials. 

• Safety goggles
• Permanent marker (in a color that contrasts with your bike frame)
• Set of wrenches (sizes will vary to match the sizes of nuts on your bicycle; they are almost always metric), including open-ended wrenches, socket wrenches and allen wrenches
• Pipe wrench
• Phillip’s head and flathead screwdrivers
• Hacksaw
• Drill press with 1/4" drill bit and cutting oil
• Clamps
• Cable cutter
• Bolt cutter or chain link tool to sever and remove bike chain
• A bike repair stand or other method of locking bike into place (a workbench and clamps could suffice)
• Lockring tool or pipe wrench
• Optional, if your bike requires it: Crank extractor tool (or crank puller)
• Optional, if your bike requires it: Bottom bracket tool
• Optional, if you might want to re-use the chain: Chain link tool

Steps for Making a Bike-frame Cultivator

1. If you have a bike repair stand, mount the bike on the stand and clamp it securely. If not, try finding a way to clamp it tightly to the edge of a workbench, vertical post or shelf support. If you have no way of fixing the bike in place, it’s best to have another person help you steady it during some of the following steps.

2. Remove the bike’s seat, or saddle. Seats are attached to the seat post with a saddle clamp. Saddle clamps differ from one bike to another. However, in most cases removing the seat is a simple matter of removing one or two nuts and bolts or a screw.

3. Next, remove the seat post from the seat tube. The seat post is the metal tube that fits snugly within the seat tube and allows you to adjust the height of your seat. Most seat posts are fixed in place by a binder clamp. Loosen the binder clamp (often this entails turning one screw) and pull out the seat tube.

4. If the bike has a kickstand, remove it. Most kickstands are attached to the chainstay, either near the bottom bracket or near the rear hub. Removing a kickstand might be a simple matter of removing one nut and bolt that hold the kickstand to the frame.

In some cases, though, kickstands (for example, those on old Schwinn bikes) require a special tool to remove them or they might be welded onto the chainstay. If your kickstand isn’t bolted on, you can either leave it attached (it won’t hamper the cultivator’s functioning) or use a more drastic removal tool — for example, a hacksaw or an acetylene torch.

5. If the bike has an attached bottle cage, take that off by removing the nuts and bolts that hold it to the frame.

6. Cut the chain with a bolt cutter and remove it. If you don’t want to ruin it, use a chain tool to remove a link pin and free the chain.

7. Next, using a cable cutter, sever the front and rear gear cables both near the shifters and the derailleurs and slide them out of their braze-on cable guides to remove them from the frame.

8. Also use a cable cutter to sever the front and rear brake cables, both near the brake levers and near the brakes. Slide them out of their cable guides and remove them from the frame.

9. Take off the shifters and brake levers. These might be connected to the handlebars, the stem (just below the handlebars), or on older bikes, the down tube. No matter where, they’re affixed to the frame with a clamp that’s tightened using screws. In some cases the screws are hidden under rubber covers. Use the appropriate screwdriver or Allen wrench to loosen the clamp and then remove the shifter or brake lever. If the handlebar end grips prevent sliding off the shifters or brake levers, remove the grips (they’re normally held on with friction). If the grips are stuck, try holding a wrench snugly around the handlebar just before the grip, then hitting the side of the wrench with a mallet to nudge the grip off the end of the handlebar.

10. Next, you’ll release the tension in the rear brake and remove it. Depending on the type of brake, releasing the tension might involve flipping a lever, loosening a small screw or bolt, or squeezing the calipers, then pulling up on the cable that spans the two calipers. After releasing the tension, remove the brake and attached cable, if any, by threading the nut off the end and removing the bolt that holds the rear brake assembly to the top of the seat stays.

11. Repeat Step 10 for releasing the tension in and removing the front brake from the top of the front fork.

12. Remove the rear derailleur and any remaining length of the gear cable by removing the lug that holds the derailleur to the rear drop-outs (the metal ends of the rear fork, where the seat stays and chain stays intersect). It’s okay to leave the cogset in place.

13. The front derailleur is attached to the bottom of the seat tube or a nearby braze-on with a bolt and nut. Remove the bolt and nut to remove the front derailleur and any remaining gear cable.

14. Remove the pedals where they attach to the cranks using the appropriate open-ended wrench. On nearly all bikes, the right-hand pedal is removed by turning the wrench counterclockwise while the left-hand pedal is removed by turning the wrench clockwise. In other words, in both cases, you would turn the wrench toward the back of the bike to loosen and remove the pedals.

15. Next, you need to remove the crank arms, chain rings and spindle — that is, everything that’s left at the intersection of the seat tube and down tube. Crank arms are attached to the bike’s frame via a spindle that goes through the bottom bracket. However, the attachment can take one of a few different forms depending on the bike. On many inexpensive bikes, crank arms are made of one S-shaped piece of metal, also known as a one-piece crank.

These are the simplest type to disassemble, requiring only the use of wrenches and a flathead screwdriver. If you do not have a one-piece crank — that is, if your crank is attached in a more complex manner, consult a bike repair manual, such as Todd Downs’ Bicycle Maintenance & Repairfor Road & Mountain Bikes or Lennard Zinn’s Zinn and the Art of Road BikeMaintenance to find out how to remove it. You might need to purchase a crank extractor tool (or crank puller) and bottom bracket tool to accomplish this (unless you want to try a brute force method, which might involve a pipe wrench).

16. Now the bottom bracket should be hollow. Next, you’ll remove the front wheel. Since you took off the front brake earlier, you can easily remove the wheel by loosening the axle nuts on either side of the wheel and slipping the wheel off the front fork. Or, if your bike has a quick-release mechanism on the wheel — that is, a lever on one side and a cap nut on the other — loosen the nut and pull the lever outward to release the wheel.

17. Clamp the frame, by the seat tube, in a repair stand or workbench. Then use a hacksaw to cut off the top tube close to where it intersects with the seat tube.

18. Also using a hacksaw, cut off the down tube close to where it intersects with the seat tube. You should be left with a modified bike that consists of the rear tire, seat tube, seat stays and chain stays, similar to the one pictured in Figure 3 in the Image Gallery.

19. Remove the handlebar tube and front fork from the head post on the part of the frame that you cut off in steps 17 and 18.

20. Flip the remaining bike frame so that the bottom bracket shell is on top. Secure the frame on a bike repair stand or workbench.

21. Next, you’ll attach the front fork and handlebar tube to the chain stays to create a handle. Hold the fork and handlebar tube in front of you in the same position it would be if you were riding the bike. Now rotate it 180 degrees. With its “wrong” side facing up, slide the fork over the seat stays and hold it so that the fork arms line up with the seat stays. The fork arms should also bisect the bottom bracket shell. (As shown in Figure 4 in the Image Gallery.)

22. On each side of the fork, use the permanent marker to place a dot where an imaginary line through the center of the bottom bracket shell would intersect the fork. This is where you’ll drill and insert a bolt. (If you’re welding, weld the fork in place at the bottom bracket and against the seat stays. This will probably require adding some material between each arm of the fork and the bottom bracket’s rim. Then skip to Step 27.)

23. On the drill press, drill a 1/4" hole through the fork in each place where you made a mark in Step 22. For safety’s sake, wear protective goggles while doing this and use cutting oil. To keep it steady while you drill, clamp the fork to the drill press table. Because forks are tapered, it’s helpful to use a shim between the fork and the table so that it’s level. Be sure to drill in the center of the fork arm, since drilling closer to the edges might compromise the strength of the arm. Also, aim to make the hole perpendicular to the face of the fork.

24. Line up the fork so that the holes you just drilled match the center of the bottom bracket. Notice the space between the fork’s edges and the outer rim of the bottom bracket. Insert enough 2"-diameter or larger fender washers on either side of the bottom bracket to fill this space. Try to position them flat against the rim of the bottom bracket shell.

25. Insert the 6"-long carriage bolt through one side of the fork, the fender washers, the bottom bracket shell, the fender washers on the other side, and then the other side of the fork.

26. Add a nut to the end of the bolt and tighten securely.

27. To doubly fasten the handle in position, bind the front fork to the seat stays by wrapping a 6" hose clamp around both. Tighten securely with a screwdriver. (If you’re welding, weld each side of the fork to its respective chain stay.) The forkhandle attachment should look similar to

28. Now you’re ready to insert the handlebars back into the head tube. You probably want them to face the same way when you operate the cultivator as they would face if you were riding the bike, which means inserting them into the head tube 180 degrees opposite of the direction in which they were originally installed.

29. If you removed grips from the handlebars earlier, replace them now.

30. Setting the bike frame aside for a while, next you’ll disassemble the long-handled cultivator and prepare it to be attached to the bike frame. Clamp the cultivator head onto your workbench. Using a hacksaw, cut off the metal bracket that connects the head to the wooden handle so that the remaining cultivator head has as near to a flat top as you can make it.

31. If you are indeed using an old long-handled cultivator, the tines will be bolted tight between two metal plates. In the cultivators I’ve picked up, there are four bolts, and the two outside bolts are spaced 2-3/8" apart on center. This happens to match exactly the distance between opposite holes in the pipe flange. If the bolts on your cultivator head do not line up, or if you are using a cultivator head whose tines are fastened in a different manner, you’ll have to make your own bracket from two steel plates, measuring where best to put bolts and drilling holes for the bolts to go through.

32. Remove two bolts and nuts on the exterior of old cultivator head plates.

33. Attach the floor flange to the top of the cultivator head by inserting new 1-1/2"- long 1/4"-diameter carriage bolts through the holes on the exterior. Add matching washers and nuts and tighten firmly.

34. Now screw the 45-degree pipe elbow onto end of the floor flange. Use a pipe wrench to screw it in so that it’s tight.

35. Next, screw the 5-1/2" pipe nipple into the 45-degree elbow. Use a pipe wrench to screw it in so that it’s tight. The cultivator head and its attachments should look like Figure 5 in the Image Gallery.

36. Unfasten the bike frame from its stand or workbench and flip it over, so that the seat tube is facing up and the handlebars are resting on the floor. Insert the end of the 5-1/2" pipe nipple (and the attached, modified cultivator head) into the seat tube. Tighten with a pipe wrench. The curved ends of the tines should be pointing toward the wheel and away from the handlebars.

37. Flip the bike-frame cultivator over and try it out.

Variations and Considerations

• If you can’t find an old-fashioned, long-handled cultivator to dismantle for this project, you can buy new five-tine cultivator heads manufactured by Beaver Manufacturing (for attachment to their push garden plows) for about $25. Because these are designed differently than the antique types, you’ll have to adjust the means of attaching the head to the floor flange at the bottom of the bike frame cultivator.
• Rather than using an old cultivator head, one variation on this plan uses recycled bike forks as cultivator tines.

This excerpt has been reprinted with permission from The Human-Powered Home: Choosing Muscles Over Motors, published by New Society Publishers, 2008. Buy this book from our store: The Human-Powered Home.