The “Onebone” cement mixer uses a five gallon plastic bucket, a powerful portable drill, and the mixer blade.

Caution: this mixer will burn up most mortal drills very quickly. Either use the recommended drill or try an air-powered drill (those little suckers are incredibly torguey and usually long- lived IF you keep them oiled properly). I have a nice 1/2″ Makita which certainly has a lot of power but I bought it new and I wouldn’t risk destroying it to mix concrete. Air-powered drills are reasonably priced and lower RPM — like an air-powered lug nut driver — MIGHT be an improvement.

In Onebone’s words, here’s how he makes the mixer blade:

There’s the driveshaft, which is just a piece of allthread, 1/2″X13 and about 30 or 32 inches long. Best to start off a little too long, so that you can cut a bit off, if necessary—it’s easier than trying to make a short one longer. I file or grind three flat spots at the top end for the drill chuck to get hold of.

Then there are the two blades. They’re made of steel, 1/4″ thick, 1″wide, and 10″ long. They have the ends slightly rounded, so they don’t tear up the inside of your mixing buckets too quickly. These two blades are drilled and tapped (drilled 7/16″ and then tapped with a 1/2″X13 thread tap, at the center of each blade. On the bottom end of the allthread drive shaft you first put a nut, 1/2″X13 thread. Then you screw on one of the blades, and run the nut and blade an inch or two up the shaft. Then you put on another nut, and then the second blade. This blade goes onto the shaft ONLY until the bottom of the blade is flush with the bottom of the shaft. Now you use a wrench to jam the lower nut down tight against the lower blade. This will lock the blade onto the shaft so it does not spin in use.

Next, you rotate the upper blade so that it is at 90 degrees to the lower blade, and run the jamnut down against it to lock it also into position on the shaft.

As I mentioned, too much aggressiveness on the blade is a no-no. You want it to be able to slice thru the mix without too much resistance, and if 1/4 seems to be too thick, you might be able to grind the outer end of the blade down a bit thinner. Say, start halfway out on the blade, and taper it down to 1/8 or less at the tip. You must retain the sweep diameter (length of the blade) in order to sweep the corner of the bucket and keep the stuff from compacting and hardening in the corner, but the blade does not have to be thick out there to do that.

The expensive Hole Hawg with a Milwaukee motor I use is a two-speed, 300 or 1200 RPM, and to tell the truth, even the 300 RPM is a little faster than I consider optimum. Due to the length of the blade, 10 inches+, which is necessary to sweep the corner of the bucket, the tip speed gets kind of high, and tends to splash the mud at 300 RPM. I’d like it better if it were a bit slower, like 250 or even 200.

Lesser drills have not been as successful with this mixer. It will be necessary to restrain the buckets from spinning. I ducktaped a chip of wood to the side of the buckets, at the bottom, and built a frame out of a scrap of plywood and some scrap 2×4. When the buckets start to spin the wooden wedge jams itself against the frame and restrains the bucket from spinning. The frame holds two buckets at a time: the weight of the one helps to keep the other from spinning, and taking the frame with it.

I fill the buckets a bit more than half-full (as much as I want to carry) and give each bucket 8 to 10 seconds of mixing time, which is plenty.

There are several nice things about the way this works: Mostly, it’s that, when you are thru mixing, the mix is already in the bucket and handily ready to dump into the form, or onto the mortar board, or hoisted up to the scaffold. There’s no dumping it out of the mixer, shaking the handle of the mixer, and screwing around trying to get the mix out of the barrel and into a wheelbarrow, or trying to dump it into buckets: it’s already in buckets. Next, cleaning up afterward is a cinch. You dump a gallon of water into the buckets and run the mixer in it for a few seconds.

As I said in a previous rant, THIS MIXER CAN GO TO ANY JOBSITE IN THE SADDLEBAG OF A MOTORCYCLE! Also as I said before, I’ll bet any reasonable amount of money that a five-man crew can place more concrete in an hour with a Onebone mixer than the same crew can place with a barrel mixer.

END OF ONEBONE’S INSTRUCTIONS.

In reviewing those instructions I posted, I thought there were a few construction details he missed but in RE-reading it, I see they were NOT missed. One does have to read the instructions carefully to realize the bottom face of the lower blade is FLUSH with the bottom end of the driveshaft. Don’t let even a burr on the driveshaft stick out beyond the bottom face of the lower blade — a few licks with a file will make sure — and I would definitely round- over those outside corners on the blade so they don’t dig into the plastic bucket. All in all, a GREAT idea and a good set of instructions for how to bild-yer-own.

One thing I’ve learned which helps a bunch is to measure ingredients accurately and keep track of how much water is added to get the ideal consistency. Make a mark on a clear plastic milk jug at that magic level and you can duplicate the recipe time and again — leaving the actual mixing to someone on your crew who is just getting started and doesn’t know that much about concrete YET.

Another thing is to keep all your tools and buckets CLEAN. Don’t let concrete harden on them or you’ll never get them clean again. I fill a bucket or trash can with water and ANY tools, shovels, rakes that aren’t actually being used at that time go IN the water immediately so they can be cleaned later. Watch your helpers and pick up unused tools for them and toss ’em in the water (them too at some point if they don’t catch on – smiles). Any buckets which aren’t being re- used immediately should be rinsed and scrubbed clean OR filled with water to clean later. Even buckets which ARE being re-used immediately should be rinsed clean down below the “water line” – (that area which will be quickly covered with new mix).

Rinse water can be poured into trash cans and used to make concrete so it’s not really “wasted.” If you’re done making concrete and all the tools are clean, let the rinse water settle out overnight and siphon off the “clean” water for outdoor plants and trees.

Most importantly — have LOTS of cold water, cold beer and pizza or good food on hand for your helpers — AND a place to go to the bathroom. (If it’s cold outside, hot coffee and donuts.) No matter if they are volunteers or paid labor, you WILL get your money’s worth and everyone’s attitude will be better if you set the example by having the BEST one.