Low Technology Institute

See yesterday’s post on the introduction and use of the broadfork, also from Matt Miles.

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If you possess some basic welding and metalworking skills, then you may find it worth your while to build your own broadfork at a fraction of the price that a commercially built version would typically cost.¹ This applies to an even greater extent if you already have the materials for construction readily available. If you don’t have materials on hand, they are almost certainly available at most metal supply shops and many good hardware stores. The project took me maybe one day of labor and cost me nothing, since I already had materials on hand. The available materials also drove my design, to a certain extent.

The broadfork I built is a modified version of the one Jeavons published plans for in his book. According to him, this design was based on one of two prototypes built for Ecology Action by two Stanford University engineering students. My design differs from Jeavons’s on a couple of major points. The tines on his are angled forward several degrees in relation to the handles, whereas mine follow a straight vertical line down from the handles. Jeavons’s design incorporates two triangular supports to further aid in levering the tines out of the ground. I omitted these, as have many other designs, as they would have added more overall weight.

As any search for “broadfork” will reveal, there are many design possibilities and customizable options available, depending on your preference. Ultimately, the broadfork you build should take into consideration the physical abilities of the user. For example, smaller users with less body mass will tire easily if they have to repeatedly lever and lift a broadfork constructed of all metal components.

Our ethos here at the reLuxe Ranch is to recycle and repurpose whatever we can whenever we can, especially when embarking on new projects or material improvements to our property. I cut the steel plate for the tines from an old bucket for a tractor that came with the property. We found little use for the tractor, which we eventually sold, however the bucket was too heavy to move. Likewise, the rectangular steel tubing for the handle stems and crossbar came from a trailer that used to go with the tractor. The wooden handles came from an old wheelbarrow.

Parts List

– 1 – 10”-×-20”-×-1/4” steel plate (for tines)
– 1 – 42 1/2”-×-1 1/2” rectangular steel tube (for crossbar and handle stems)
– 2 wooden or fiberglass wheelbarrow or shovel handles
– 6 – 2”-×-1/4” carriage bolts with lock nuts
– can of black spray paint and/or linseed oil (optional)

General Procedure

1. Cut five 18” tines from 1/4” steel plate.
2. Cut two 9” handle stems and one 24 1/2” crossbar from rectangular tube stock.
3. Weld handle stems to crossbar, leaving 1/4” to 1/2” reveal from each outside edge of crossbar.
4. Weld each tine to the crossbar, starting with the two outside tines, about 1” to 1 1/4” in from the outside edge of the crossbar. Evenly space the remaining three tines with about 5 3/4” between each.
5. Mill handles to fit into handle stems.
6. Drill holes on two axes through the handle stems.
7. Attach handles with 1/4” carriage bolts and lock nuts.

Tines

With a plasma cutter, I cut out the flat side sections of the aforementioned tractor bucket, one of which eventually ended up as doors on my cob-and-brick pizza oven and the firebox of my smokehouse. With a whole section of the plate steel left over and access to a CNC-driven plasma cutter, I decided to use this to construct the tines of my broadfork. You’ll need approximately a 20”-×-10” plate of 1/4” steel.

To cut my tines, I first prepared a scaled, two-dimensional drawing of all five tines, each placed next to the other but not quite touching in Adobe Illustrator. I then exported to a .dxf (AutoCAD) format that I knew could be loaded on the software that drives the CNC cutter. This can probably be accomplished with most drawing and materials design software; for example, Illustrator’s open-source cousin, Inkscape; or in SketchUp or Blender. In any case, the AutoCAD file is included here: Broadfork Assets.

I happened to be taking a welding class at the local community college when I decided to build this broadfork, so one of the instructors there graciously loaded my design and made the cuts from the steel plate for me on their shop’s CNC-driven plasma cutter. It took five or ten minutes at most to cut the tines from the plate stock, and they came out identical and much more accurately cut then I would have imagined.

Machine shops or hacker spaces may possibly provide these services, if you lack access to a CNC cutter. Other options would be to use a laser cutter or a manually operated plasma cutter to cut out the tines. With the manual plasma cutter, some grinding and finish work would probably be required. I do not think the tines would cut well with an oxy-acetylene torch, since in my experience it’s quite difficult to make accurate cuts with this tool, whereas a CNC-driven plasma cutter cuts within 1/16” accuracy, and a laser cutter is more accurate still. Another option entirely might be to use large-diameter rebar for the tines.

Crossbar and Handle Stems

With a metal cut wheel on my angle grinder, I cut a 42 1/2” length of rectangular tube. I then made two additional cuts, this time with a more accurate metal cut blade mounted on my chop saw to separate each 9” handle stem from the 24 1/2“ crossbar.

I currently own a “buzz box” type stick welder and a somewhat pricier MIG welder; however, I didn’t have a bottle of argon-carbon dioxide mix available at the time, which is required for MIG welding. On the other hand, I had a good supply of 7018 rod for stick welding, so that’s what I went with for the T joints for each handle stem.

To leave adequate space for a good bead between the crossbar and the perpendicular handle stem, I set each stem about 1/2” in from the outer edges of the crossbar. This allowed for a T-joint weld on both lateral sides of the stems where they attached to the crossbar. I also welded butt joints on the top and bottom where each stem attached to the crossbar.

Overall, the stick welds were probably satisfactory, but I had difficulty controlling the temperature, especially at the edges of the tube, where the electrodes tended to blow through the thin tube in a couple places.

Since I had access to a high-end MIG welder in my welding class, I opted to finish the piece using that equipment, and that’s also where I attached the tines. Some of the stick welds I ground down and went over with the MIG welder, which made nice, uniform joints and “bombproof” welds.

Attaching the Tines

With the main body of the broadfork assembled, MIG welding the tines was simple. I used a welder’s magnet to affix temporarily each tine perpendicularly to the bottom of the crossbar, starting with the outer tine on each edge. I welded both sides of each tine in T joints and managed to get a small butt weld on the top and bottom of the thin section of each tine where it attached to the crossbar, just for good measure.

For the two outer tines, I attached them directly beneath the handle stems, at the midpoint of the stem, about 1 1/4” in from the outside edge of the crossbar. I then attached the third tine in the middle of the crossbar, splitting the distance between the two outer tines.

With the last two tines, I split the remaining distance between the middle tine and the outer tine for each, and attached the tine there, at the midpoint. This works out to about 5 3/4” between each tine.

I did it in this order for several reasons. For one, it was easier to exactly position each tine this way. Another reason was, as opposed to welding each tine in series, this method dispersed the heat a little better throughout the length of the tube, without heating any one area too much and risking a blow through, as had happened with the stick welder.

Fitting and Attaching the Handles

The handles salvaged from the wheelbarrow were a little rough from sitting out in the weather for several years, and they did not quite fit into the tubing in their original state. To fix this, I gave them a good sanding with an abrasive disk on my grinder. This removed enough surface area at the bottom where they attached to the handle stems so that they could easily slide into the metal tubes of the stems all the way. I followed this up by rubbing the handles with linseed oil, which adds a nice finish to the wood and protects its surface from the weather.

The handles can be made from almost anything, but ideally, you will want something that will fit snugly into the handle stems and is lighter than the other parts of the broadfork, which are by necessity made of heavy materials. Here, fiberglass shovel or wheelbarrow handles might work, or perhaps even aluminum tubing or lighter steel pipe. You do want a material that will be able to handle the repeated stress of the user’s full body weight levering down on them to lift up on a large mass of compacted soil.

To physically attach the handles, which already had several holes in them where they previously attached to the body of the wheelbarrow, I used a titanium bit on a drill press to put two holes horizontally (front to back) and one hole laterally through the handle stems. I drilled the handle stems where there were existing holes in the wheelbarrow handles beneath, so as not to needlessly weaken the wood by drilling additional holes. The third lateral hole—necessary to vertically stabilize the handles—I drilled through the handle stems and the handles with a power drill. Where you drill your holes will depend on what material you choose for handles. Three bolts seemed to provide good contact between the handle stems and the handles. One side of the handles was somewhat narrower than the handle stems, so I hammered in a 1/8”-wide wooden shim to snug up the handles with the handle stems.

At this point, the steel parts—the crossbar with attached stems and tines—were ready to be painted. I sprayed on two coats of leftover black Rustoleum to cover all metal surfaces. This is necessary protection if any of the metal surfaces have begun to rust, as had the tube and tines in places.

I had six 1/4” stainless steel carriage bolts along with lock nuts readily available, so I used these to fasten the handles to the handle stems. This concluded the assembly process, and the broadfork was ready to use.

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¹Editor’s Note: We do not possess welding skills (yet), so we will create an experimental wood design and will post it to the blog if we can figure out how to make it take the strain of breaking up soil. Thanks to Matt for introducing us to this promising tool.