And the oven was created

So we decided not go with a hexagonal base but instead went with a very simple yet complicated design. We took two pieces of plywood and made slots on both of them to house them perpendicular and inside each other. This is one of the most structurally sound and minimalistic design that we came across. We also made the base of the oven tapered (narrow at the top and wide at the bottom) so that we won’t have any turning problems. We mounted the oven on a lazy Susan. The whole structure was still heavy on the back (the end with the window and mirrors) so we used four wheels on the front to balance the weight out. We also added two more wheels on the front at the base of the window as a support and also for mobility purposes. We also added two more mirrors, one in the bottom and one in the front, for more sunlight concentration inside the convection chamber. 

The feat and epitome of recycled engineering

We also tested the oven one moderately sunny day and the oven reached a max temperature of 85°C when the atmospheric temperature was 25°C. The temperature inside the oven rose by about 10°C every 10 minutes until 60°C and then 10°C rise by every 25 minutes until it reached 85°C. After the point the sun decided to disappear behind the clouds. We also did another round of test on a slightly sunny day (atmospheric temperature: 21°C) and the results were similar. The sun again was lost after getting the temperature to about 68°C. We did a calorimeter test with a insulated coffee cup and the water received 3.6KJ in 8 mins. It was an error on our part because we should have used a conductive container to house the water instead of using an insulated cup. We also tried cooking some makkara. They were done, not well done, but they did smoke and were tasty (on the other hand makkara are tasty even when they are raw). 

Enhanced for mobility

The oven really depends on sunlight (surprise, surprise) and we are not having so much of it anymore so we haven't seen good temperatures. The contraption could still be used as a cooker when the sun is at its fullest and it can doubled as a food dehydrator when it can't be used as an oven. Just for fun we put 100ml of algae sludge from another students project to test the dehydration capabilities of the oven and after an hour 25ml of water was dehydrated. It was not a bad result, considering there is not fan installed in the oven to draw out the moisture.

So with the final days of summer drawing to an end, we reflected on what we had accomplished and how well we did. In the final post we will discuss what we would have done differently if we could start over again.

Summer in Finland is the last 2 weeks of July

We mounted the window with some screws and instantly we saw a flaw on our design. The bottom of the chamber was unreachable and in any case if something fell in there it would lost and unrecoverable. So we dismounted it and put it back together with some nuts and bolts. We almost broke the window too but fortunately we missed it by a hair. As the saying goes luck favors the bold (more like luck favors the fool and the dumb). In the end it turned out swell and although its a pain to remove the very overweight (lets call it chubby so we won’t hurt its feelings from henceforth) window, its do-able. We also scrapped the idea of gluing the mirror and instead held the window in the place with some rubber stoppers. We felt very proud about this one. The mirrors were mounted too with some door hinges and we will be adjusting it with an adjustable window hook to set in place.

Oven with the mirrors and windows attached

The temperature test on the other hand seems like a lost cause now. It seems that the summer is over and the day we could have actually done the test, we spent it indoors in magical Biltema. We will have to wait for a sunny day in August which doesn't seem to be happening in weekdays on august then after that its about 2-3 weeks of rainy autumn and then frigid winter for about 7-8 months. Attaching hot plate with batteries to make it work in the winter sounds more and more promising. At least the oven is done and we can hope that someday there will be some solid hours of sunshine and we will boil a container full of water on it. We’d hate it if we have to wait until next summer.

The base however is a different and perilous story. We have tried different approaches. We gave cutting an angle on the base to mount the oven a thought. It would solve the balance problem but we wouldn't be able to rotate it. After much brainstorming we decided to go with a hexagonal base.

More bad news and a Silver lining

Still shaken by the findings of the last week, we get to the workstation to find out that the magic seal is a great seal but a very bad adhesive when it came to attaching heavy object like mirrors to the plywood it was pretty much useless. At least the sauna foil turned out fine. We decided that we need to get stronger adhesive to glue the mirrors. The magic seal when in the tube looks like mixture of ferrous clay and water. When it dries it turns out like ceramic and is very resistance to heat and fire which we found out after some testing (we basically tried to light it in fire, under monitored conditions and with all the safety precaution in mind). It didn’t catch on fire. It did heat up at the point of contact with fire but it could still be held while it was being burnt which was some positive news which we really needed. We also managed to finish the oven and got it ready for testing. We did some preliminary testing of the oven (we let it sit on the sun when it was out. This also yielded a good result and after all the insulation and sealing it did heat up a bit. We still hadn’t attached the windows and the mirrors. 
 

Ceramic inner coating

Window clamped on to the base for testing

Not a very sunny day

We still had all the other problems to worry about and hopefully fix. We decided to go on a journey to seek answers to our problems so we headed to Biltema one sunny day. It was possible the sunniest in the history of our residence in Finland which is about 3 - 4 years for both of us (yes there’s only two of us now to think of it we never mentioned). Biltema was another wonderful place the possibilities there were almost infinite. Of all the time we were there, most of the time was spent running around being amazed by the place. If we have money we would probably buy a lot of stuff and build many little projects. We did find some useful stuff while we were there. We found a strong hollow rod with a base plate that we could fit inside the base and rotate the whole base. We also thought of using an axle which didn’t come cheap and the possibility to get one from the salvage yard. We concluded that we will cut our base into half and rotate half of it while the bottom half would be fixed. We’d achieve this with nothing other than a lazy susan.

Trash to treasure

Since the beginning of the project we had an issue about the angle of incidence. According to the geographical location of Tampere, the theoretical angle of incidence was calculated to be about 72°. This seemed pretty steep but we decided not to argue with the calculation. When we were shaping the frame to house the convection chamber, we did mock mounts to see what it looks like and apparently it is very steep. We had to check and recheck the calculation again to see we hadn't made a blunder. We even thought of getting a new oven and cut it to a more horizontal looking mounting angle. But we again decided to settle with the theoretical angle with some self explanation to make ourselves feel better.

Is it going to work?

I hope so!!

We also needed something to glue and seal everything so we made a trip to Bauhaus. We amazingly found this magic product which acted as a glue and a heat resistant seal which could resist temperature up to 1500°C and which was also not so expensive in Biltema. We got two tubes of the magic seal (that’s what we’re calling it) Courtesy of the department of Erkki, we also got a Pop Rivet gun and a lots of Rivets to play with. We used it to make the oven itself more sturdier and we fashioned a lot parts out of the oven spare parts. When we started with the project we didn’t think we’d be smithing a lot of parts. So the whole week was smithing trash to fit our build. 

We tried to use the bits of the oven we cut off. It didn't work well.

Well, I guess we make our own parts then!

I always thought fabrication would be fun, but my thumb may disagree. :)
But it did work!

The whole inner body of the convection chamber was lined with a coat of magic seal mix which acted as the thermal seal which was left to dry and another coat was applied on top of it to glue the sauna foil. The whole setup was effective and it was hard to stare at when the sun was bright. We even tested the mirrors by holding it and concentrating the sunlight and the result was very pleasing to say the least. The mirrors we had also were cut with a very old glass cutter. We managed to ruin a piece of mirror because of our incompetence with an old glass cutter. We did have some extra piece and all was saved. The cut mirror was glued to a piece of plywood and left to dry. We are now waiting for all the seals to dry which according to the instructions require about 24 hours to set properly and we have decided to allow more time to set.

We also worked on the mounting and rotating mechanism. We found a very heavy, flat circular piece of metal plate with a bearing inside. We attached another aluminium plate on top with a big nut and washers which will be attached at the base of the oven. We then attached the oven on the mount and the window with clamps and did some stability and rotation tests. This did provide us with new insights. First of all our oven weighed like a overfed hippo, it squeaked like the glorious song of thousand mice and wobbled like a poorly trained circus bear on a unicycle. 

This brought on about a whole lot of concern. Furthermore the oven touched the corners of the base and it was front heavy and was tilting a bit at the back. Structurally speaking, aluminum panels as reflectors and acrylic window is how it should’ve been done but beggars can’t be choosers so we used an old window with the frame intact which weighed about 7-10 kg as the (umm..) window and solid glass mirrors, 4 of them, which weighed about 1-2 kg each. This made our whole oven about 8-10 kg heavier than it should be. This changed things. We would have to think about the whole design of the oven. We now are discussing our next course of action. We have decided to finish the oven and then think about the base, rotation and mounting after that. The oven now is mounted on a table and we can perfectly run some temperature tests as it is after we finish insulating of the oven. The week ended on a rather depressing mode.

Bodywork, birthday and a visit from the stork.

The working hours were very much limited because of birthdays and arrival of a new person. The Finnish midsummer had to be observed too so the work on the oven took a halt. When all the auspicious occasion had passed and when we finally got back to work. We decided we also need to work on the weekends when possible to catch up on the work we slacked on. We then started debating among ourselves on how should we proceed further. We still had no solid clue on how were we actually building the body of the oven. 

Visualize it

 

Yay! Power tools! (Cutting open the oven was tense.
If we calculated the angle wrong, it's going to be a bad day..)

A bit of the oven frame

We cut the oven at an angle and we decided the convection chamber would be long and made out of plywood. We’d have to insulate the oven, especially the convection chamber. We did get some new insulating material, rock wool, which would stand up to 700°C thanks to Kevin’s father-in-law, Erkki,  who was quite a savior in time of material shortages and design issues. We certainly made use of his knowledge of carpentry.

We also got some sauna foil which we decided would insulate the convection chamber and also act as  a reflective surface. We also got very good used mirrors which we decided to use to concentrate the sunlight into the chamber thanks to Erkki. We decided to build a frame around the oven and use the frame to attach the convection chamber and also use the gap between the frame and oven as the insulating zone. We will insert the rock wools there and  cover it up with plywood. 

The convection chamber itself was built with plywood held together with some angle brackets. Then we saw the gap between the plywood boards. The gap cannot be seen but it is there and that will radiate all the heat out. We then decided we would build another chamber outside it and fill the gap between those two chambers more insulating materials.

Promise of summer

We are provided with a shed near the dumpsters in the rear of TAMK by the parking lot, which is a perfect place for us. Its literally couple of steps to the trash which is like a treasure chest for us. It was a bit like Scrooge McDuck swimming through gold. Going with the spirit of recycling, we salvaged a pair of undamaged auditorium speakers which has been helping us get through the work hours. Not that they are dreary its more like icing on the cake. 

 

Salvaged work bench with salvaged speakers :D

We salvaged a pallet for the base where the oven will be mounted, we guessed we build the bottom first and build our way to the top. We also don’t have all the required materials to fashion an oven yet so base was the logical choice so we can at least get some work done. We decided to go with the classic four pillars and horizontal dark brown wood boards (thanks to the city of Tampere) on each four sides. It’s to achieve a Nordic look or that’s what we tell people. We are just using what we can get and that is what we could find.
 

Sizing things up

Measure twice, cut once, right?

The four pillars of doom

We got the planks cut to the size we needed in the construction engineering labs which is like the candy store for us. The equipment there makes every grown man’s/woman's eyes glisten with the world of possibilities... or its just us. We also got some insulation which was rated to about 70°C thanks to Eeva-Lisa Viskari head of the Environmental Engineering programme and also the person who commissioned the project. We had already stripped down the oven (with helping hands of one Mr. Gerbrand Grobler) to its bare bones and separated the main oven part (which we will use as the main body of the oven) and the hot plates.

 As a joke, we are still hanging on to the plates because we want to mount it under the oven with some car batteries to make a new wonder :- a solar oven that works in winter in Finland.

Small Beginnings

Most solar oven cook food by concentrating sunlight. There are different designs and most of them can be fashioned in very short amount of time with cardboard boxes and aluminium foil. The Solar Oven we chose to build is the design of an Arizona based - award winning tracking solar oven design which can be found here: solarcooking.org/plans/cookerbo.pdf. It works on amalgamation of different principle like; convection i.e. warm air rises up and is replaced by cool air, greenhouse effect and concentration of solar radiation. We will be making appropriate changes to the design as required.

Theoretically, if an airtight, insulated hollow box is heated, the temperature inside the box should rise up infinitely. But we cannot totally isolate the system and some heat loss will always be prevalent regardless of the insulation. With proper shape, insulation and angle of incidence, our aim is to reach about 250°C (optimistically). We also have a challenge of spending little to no money on this project so we’re building it all out of predominantly discarded materials. Almost everything we use in this project will be trash (technically). We got the together around the end of may and spent the rest of the month on planning. Since we are only using trash, our design options are very limited. We can only build our oven according to the trash we find. Until now we have found pieces of board wood, wooden beams, an old discarded oven and window all thanks to the city of Tampere and TAMK.

Disassembly of the oven

The meat and potatoes

We have a pallet to start with as a base. Our basic design is to mount the oven into a base and fitting a window in the rear end with reflectors to concentrate the sunlight. A chamber will also be mounted between the oven and the window which will give the set-up some room for convection. We are still not quite sure about the insulation. There are few options we are thinking about. The easiest material to obtain would be the insulation (rock wool) that is used to insulate buildings. There was also the option of using the air conditioner thermal insulator. We thought that might be available to us since the school was also under renovation and we might get the extra they ones that they don’t need or the old ones they want to dispose of. For now we will continue to gather materials to design and build with.

As it stands now we have aquired the following:

an old Upo oven
a number of 4cm x 4cm lengths of wood
about 40 lengths of reclaimed fence wood that had been stained brown
a reclaimed wooden loading pallet ( this would act as our base )
a number of different screws and bolts
clamps, saws, screwdrivers, etc... many tools