Introduction: Rotating Turbine Fire Pit Cover
After a brief nightmare spell with a housemate from hell, I was trying to help the homeowner (and my now-housemate as she decided to move back in again) clean things up. One of the things that was left in a horrible condition was one of those small 'bowl' style patio fire pits that the other tenant had use and left full of ash and char, which quickly clogged up it's spillway so it filled with water and rusted up considerably.
I started by trying to weld over some of the rusted spots on the bottom, but that quickly spun out of control as there was far more rust than I had first guessed. Even trying to stabilize it with special sprays and paints turned into an uphill battle. So I instead ended up deciding to try to refurbish it from the bottom up and in the process wanted to add some kind of a fancy touch that would be dynamic in nature.
After considering a number of possibilities, I was sitting in my office looking out the back window one evening when I noticed the rotating turbine vent cover on the shed out back. And inspiration was born. I decided not only to try to make a cover for the new pit that would work like the roof vent, but ultimately wanted to try to make it work kind of like a merry go round. (the second part is still pending ideas, but the first part is complete and is neat enough by itself)
The first step would be to get a patio pit of some kind. To help re-enforce her's, I was able to pick one up around $50 at Sears that I fit inside the old one (shown in the first pic after priming) and chased down some scrap to work with for the cover. I welded the smaller one inside but this could just as easily be added to a single bowl. A few sketches later and I had an idea where to start.
Before I started, rather than spending a lot of time doing complex math, I knew that I would want to come up with a blade length that could be inserted at approximately a 45 degree angle, but also be curved somewhat. To prototype this out, I just got some poster board and worked with it until I got the length and curvature I would want. I also had a limited amount of scrap sheet to work with, so I also wanted to be able to create the blades in such a way that I could alternate them on the sheet to get as many as possible. I ended up settling on 24 blades total as my final number that would best cover the whole surface with the width of metal I would have to work with.
The scrap I ended up picking up from some of the guys next door to where I work who often toss out old metal drawers and rolling drawer units that provide some nice working material for my projects. There were some nice stainless bottoms to some of the drawers and shelves and I was able to get three sheets of them that would fit the size blades I wanted to use for a 24" circular cover that would fit over the sears fire bowl (inside the rim of the older one)
I have nothing but a little portable band saw that I created a vertical stand for and it can only cut out about 5" width segments so I couldn't split the sheets and stack them. I had to cut each pair the hard way and thus could only make sure one cut was uniform. For anyone with a full size band saw, they would probably have a much easier time cutting the blades uniform, I instead had to burn out 2 1/2 wheels and a set of commutator brushes on my angle grinder shaping them all to exactly the same size. (I put a small welding bead down one corner once I had them all lined up as closely as possible. The amount of material I had to take off was only about a sixteenth of an inch on any given side, but all 24 sheets stuck together was over 2" thick!)
Once I was satisfied the shape was even and close to my pattern, I ground off the bead holding them together and separated the end result. (pictured) I used a couple of pieces of 3/8" iron rod and shaped them (by eye mostly) into a circular shape based on the 24" diameter I needed (2*pi*r or pi*24 length). Welding the two pieces together into the loop, I then took a short piece of plain old 1 1/4" plumber's pipe with a screw on cap. Cut it long enough to fit the inner portion of the blades and drilled a small indent inside the center of the cap for the pin to eventually rest into. I hit some quick spot welds on the edge of the cap after screwing it on to keep it from un'screwing itself.
I then started manually shaping the first blade based on my prototype, then used it as a form to shape all of the others to the same curvature. Making sure the curve was such that I could angle it at the 45 degrees I wanted and have it reach from the center hub to so the corner of the blade would just rest on the metal ring. (also pictured). When I had finished using the plastic/rubber mallet to get them all to the same curve, then the only thing left at that point was to weld them all onto the ring.
For fun, I threw out a problem to my friends on facebook to see if anyone could figure out the curve that I would need on the inner edge to get them to line up well on the inner piece of pipe. In the end, I ultimately ended up just eyeballing the first one then clamped them together again with a c-clamp to curve the rest of them all at once to approximately the same curve. I subdivided both the inner pipe and the outer ring and then offset a second set of marks on the bottom part of the inner pipe so I could maintain approximate spacing and the proper angle all the way around.
Then started welding! It took a couple of hours to go all the way around and get all the pieces together, but eventually I got the whole thing together. For the pin I just used a piece of threaded 3/8" rod and actually used the two bowls initially to hold it up. (later I built a frame for it by making a second circle with some square stock I had and just did a simple '+' shape with two arced pieces and put a second threaded hole down the middle as it made it easier to pull the whole unit off)
After all of the welding was complete, my initial test I had decided by then to instead try a high heat bearing instead of the balancing pin thinking it would be more stable. But the initial test was a complete flop as the bearing would quickly slow to a stop if I spun it and wouldn't spin at all above the fire. But I had already put a point on the threaded piece it was balanced upon and as mentioned earlier, I had already put the indentation in the cap to let the pin point rest into. So I whipped out the screwdriver, pulled out the bearing and tried just resting it on the pin to see what would happen. I had barely let go when it already started spinning around on it's own and I shot the attached video a few seconds later, I was so excited.
(warning, a wee bit of adult language at the start there, but as I say, I was quite excited it worked so well!)
Step 3: Horses Are the Final Touch, But Not Yet.
Since my housemate is also into horses, the other thought was to make it the merry go round. I may post those changes later if I find a way to finally make it work. My initial thought was just to weld horses around the outside and I found a place in Oklahoma that made me some really nice silhouettes, but I really want to make them go up and down. (the balance concept is very low friction and every attempt at using a contact point to move the horses has failed. I'm trying tests now with magnets, but neodymium breaks down with heat. I'll beat it yet, but still haven't come up with a satisfactory solution so that instructable will have to wait for another day)