Group Three Sauna Bench Project Toni Lahti, Chris Morris, Tomoyo Nakamura, Taeho Noh March 23, 2016 CONTENTS PROJECT DESCRIPTION Task description Background to the project DESIGN PROCESS CUBE ­ Shape of the cubes ­ High Humidity and High Temperature Test STRUCTURE ­ Strings, Net, Beams ­ Beam Structure ­ Shower Test of Beam Structure COATING ­ Untreated MANUFACTURING PROCESS CUBE STRUCTURE APPLICATION REFLECTION & CONCLUSION PROJECT DESCRIPTION Task description The aim of the task was to create a wooden surface or element that could be used in a wet space like toilet, shower, spa or sauna and would present the positive aspects of the material to said space. Part of the task was to study the properties of wood and different wood species in detail through literary sources and by tests performed by groups. The aim of these tests was to find out how wood behaves when in contact with water and moisture in general, and to understand why and in what situations water and moisture causes problems with wood. The findings of these studies and tests were used to further develop the designs, so that the inherent weakness wood has against water and moisture could be handled, and wouldn't cause issues in the final product proposal. The task was planned to be executed as a joint project between architecture and engineer students, so that knowledge and skills of each team member could be used to improve the final product. In our group the engineering student had to leave the team after first meeting, and that lead to more design oriented approach in the process. Background to the project In a situation dealing with sauna, the surface of the wood is directly touched by the user, however there isn’t much variation in types of benches. The most conventional type of sauna bench is simply just wood planks with small gaps in between. Thus, as a team we decided to create a different, more tactile sauna bench that is more design friendly and variable. The main idea of a “melting wooden cube” consists of small wooden cubes with sanded edges to create a soft, comfortable surface. The gentle feeling of wood on skin and ergonomical design is meant for textural irregularity and interest. Small pieces give way for flexibility in both shape for variation, in size, and in replaceability of bench pieces. Fig: Concept model As a result, we decided to make 600mm x 600mm wooden surface with 40mm x 40mm wooden cube. Wooden cubes sit on the wooden lattice which has an undulation in the middle of structure. It affords comfortable sitting place to guest and gives interesting appearance. This report shows how we decided the shape, species and grain direction of cube, joint between cubes, and manufacturing process of whole structure. DESIGN PROCESS CUBE Shape of the Cube The aim of designing the shape of the cube is to fulfill both a visual and welcoming, haptic experience, which can be found in nature. The shape of the ice cube has rounded edges with a smooth feeling and, when a number of cubes are repeated, they turn into an interesting surface. To build a panel type surface, the size of individual has to be decided. This decision not only dictates the total number of cubes in 600 x 600mm size of panel, meaning that the load of work can differ depending on how big each cube is, but also the appearance of the panel. Three different size of the cube were suggested with simple 1:1 mock ups, 30 x 30 x 30 mm, 40 x 40 x 40mm and 50 x 50 x 50mm. Among these options, a cube of 40 x 40 x 40mm size was chosen because of its good appearance and reasonable amount of workload. To shape a cube into a ‘melting ice cube,’ edges and corners have to be carved or sanded into a certain radius. Therefore, several test pieces with different radiuses were built to decide the shape of the cube everyone agree on. There are 3 different cubes with 3 different radii. From the right hand side, first one is the one with 8 mm radius, second one is the one with 10mm radius, and the last one is the one with 15mm radius. Fig. : The test pieces with different radii The main factor considered in making our design decision is how comfortable the bench is when users sit on it without compromising the aesthetics of a sculptural shape of ice cube. As a result, the one with 15mm radius was chosen for the final shape of the cube, which is to be seen the most suitable. High Humidity and High Temperature Test To choose wood species and grain direction, different four species of wood have been selected as specimen. They were put on wooden structure with three type of grain direction. Fig. shows that dimension and mass of each species and direction. Fig.: Test piece for public sauna environment Wood Species Grain direction 1 Grain direction 2 Grain direction 3 Aspen R: 40.09 T: 39.66 M: 23.62 L: 40.12 T: 39.72 M: 23.84 L: 39.6 R:39.79 M: 24.88 Alder R: 40.70 T: 39.87 M: 28.35 L: 40.33 T: 39.91 M: 28.34 L: 39.77 R:39.95 M: 26.98 Spruce R: 39.99 T: 39.97 M: 29.01 L: 40.76 T: 40.05 M: 23.95 L: 40.68 R: 40.02 M: 24.51 Maple R: 40.76 T: 39.46 M: 37.36 L: 39.86 T: 39.53 M: 38.81 L: 39.94 R: 39.46 M: 38.97 L: Longitudinal (mm), R: Radial (mm), T: Tangential (mm), M: Mass (g) Fig.: Dimensions before experiment The expected environment is public sauna with everyday use. We assumed public sauna situation as 8 hours in use of one day. The experiment was carried out in steam oven to create a public sauna environment. It was scheduled so that eight hours at 100 degree celsius and 100 percent humidity immitated the sauna environment, while the off hours were set to 16 hours at 25 degrees celsius and 60 percent humidity as normal condition. After five days, the cubes changed in surface and dimension. There were many cracks on surface in wood piece of “Grain direction 1” especially maple. The cracks on surface causes to get water in wood piece. Spruce was changed in mass and secreted some resins. Aspen and alder didn’t show much change. Grain direction 1 has many cracks on the surface and the change in tangential dimension is quite big, causing irregular dimensioning of gaps between cubes. Aspen is more reasonable because of material limitation in the workshop, and grain direction 3 is the best to keep cubes straight position. Fig.: Test piece after steam oven Wood Species Grain direction 1 Grain direction 2 Grain direction 3 Aspen R: 40.91 T: 42.10 M: 26.9 L: 40.29 T: 42.28 M: 27.40 L: 39.93 R: 40.65 M: 28.57 Alder R: 42.08 T: 41.38 M: 32.89 L: 40.51 T: 41.48 M: 32.79 L: 40.12 R: 41.18 M: 31.11 Spruce R: 41.19 T: 41.50 M: 39.41 L: 40.90 T: 41.30 M: 27.55 L: 40.89 R: 41.18 M: 31.11 Maple R: 42.38 L: 40.01 L: 40.14 T: 42.80 M: 43.01 T: 42.56 M: 44.58 R: 40.94 M: 44.35 L: Longitudinal (mm), R: Radial (mm), T: Tangential (mm), M: Mass (g) Fig.: Dimensions after steam oven STRUCTURE Strings, Net, Beams It is necessary to have an additional element to connect cubes one another. There must be many ways to connect them, however, proposed ideas are either 1) using string, or 2)net fabric, or 3)wooden lattice structure with half lap joint. Firstly, weaving cubes with a certain type of string such as fishing line or metal wire is suggested. Simple principles and techniques used for bead craft can be applied to weave them into one panel. Even though it may sound simple and easy, this technique requires many detailed works on each cube to firmly tighten wire up and make sure that each cube has comparatively the same distances to the other 4 cubes around it. When mock­ups were built with the idea, both, fishing line and metal wire, were used. There are two different ways used to weave cubes with the strings. First idea is to cut the cubes into half and lay string on the bottom half and glue the top half on the other. The other idea is to drill a hole on the cubes and interweave them one another with string. Unfortunately, it was not successfully fabricated to have a stable structure. The first idea, cutting the cubes into half, made inevitable imperfection due to glue in­between and gap made by thickness of string. The other method, making holes in cubes, was hard to assure to make the same distance of gaps between cubes since tightening up string was very challenging. Fig : mock­ups with string structure(left : metal wire, right : fishing line) Another way to connect cubes is using net fabric. This idea is simple and intuitive to come up with. To make a mock up, cubes are cut into half and lay all the bottom halves of cubes with the same distances one another, making a grid pattern. The net fabric, supposedly made of plastic or metal, is glued and laid on the cubes and the other halves of the cubes are glued on the top. Even though it only requires really a simple and easy way of fabrication, it is hard to predict how plastic or metal net fabric will behavior in a humid and hot space like sauna. Lastly, wooden lattice structure is suggested to fit cubes on it. Basically, half lap joint is used to build lattice without using any glue to fix. The structure guarantees the stability and makes sure the cubes have the even distances one another. However, it lacks of flexibility which connecting methods with string or net fabric have. Therefore, using fixed structure may compromise a certain kind of experience which users can obtain. In addition to this, designers should consider dimensional change of wood due to moisture in sauna. Beam Structure The structure is designed in lattice, in which wooden boards with half lap joints meet orthogonally. The width of the board and size of the joint are vital parts in design, therefore, several mock­ups were built in 1:1 scale to investigate stability and how much of weight the structure can support. Fig. : mock­up of the structure In the end it was decided that the structure would consist of two different types of pieces with slightly different dimensions. First pieces were the structural pieces spanning 600 mm and holding the weight of the person sitting on the bench. These pieces had the dimensions of 600 x 65 x 6,7 mm and the notch that was cut to it was 35mm deep and 7mm wide. This left for structural purposes 30 x 6,7 mm of material, as the top part of the was cut every 40mm and had no structural significance. The second pieces are the ones running in the direction in which the bench can be expanded to seat several persons. These pieces bind the structural pieces together, help out by dividing the load between those, and give sideways support to resist twisting. The dimensions of the second pieces are 600 x 55 x 6,7 mm and the notches that were cut to it were 25mm deep and 7mm wide. The width (6,7mm) of the pieces was determined by the width of the table saw we had available. The blade of the table saw is 3,5 mm wide, so with 2 perfect cuts we can make a notch that is 7 mm wide. The wider the cut that we can make, the thicker pieces we can use, and the more stable the whole structure will be. As we need to take the tolerances in consideration in the manufacturing phase the actual pieces were 0.3 mm thinner that this gap where they were meant to fit. This created a nice fit, so that it was possible to assemble the structure without using too much force, but still the pieces fitted nicely without any “loose” connections. For the 600 x 600 mm final product total of 26 pieces were needed (13 + 13). And these pieces were placed at the distance on 40 mm from each other. Fig.: Some broken test pieces for the structural members The structure was tested by creating mock­ups with different sized structural pieces, and then by bending and twisting those and by suspending them between two tables it was tested if they would hold the weight of a person. Shower Test of Beam Structure The chosen structural system relies on small tolerances (0.1mm) to create a supporting grid of thin(6.7mm) wooden beams for the wood cubes. Wood usually has quite low moisture content when worked with, but in this case the final product will be used so that it’s moisture content might be quite high at times. This will lead to moisture movement, that when in combination with low tolerances and the varying grain directions might cause cracking. At the joints we always have exposed end grains and this is always the point where the most of the moisture will enter the timber pieces. At the same time in wood the smallest amount(<1%) of swelling happens in the direction of the grains/fibres. So according to this even if the tolerances were low, the group assumed that this wouldn't cause issues for the structure. Fig. : exposed end grains at the joints of the supporting structure But to be sure the group conducted tests with 1:1 scale mock­up structure made of spruce. In the test the structure was made wet under a typical shower for 10­15 minutes, and then dried for 2 hours. This cycle was repeated 4 times. In actual use scenario the structure should never face this kinds of moisture spikes, as in typical use it will be used as a bench in sauna where the humidity comes mainly from the moist air. After the test the structure felt moist to touch but no signs of cracks or other problems could be found. Fig. : mock up of the supporting structure during the shower cycle As an extra test some empty “squares” of the structure were filled with typical paper towels, and these paper towels were soaked in the shower. These soaked paper towels were left there for 24 hours, and then removed. The places around these soaked paper towels clearly felt wet/moist, but no signs of cracks could be seen even after the structure dried again. Based on these tests the group concluded that the structure should be safe to use in the planned environment, and it should be able to handle the moisture movement caused from the exposure to water. COATING Untreated As the proposed use for our groups product was sauna bench, it made the group lean towards the option of untreated surface from the beginning. Even when no tests had been conducted the intuitive reaction to the idea of “treated” surface against the skin felt to many as unpleasing. Some more “light” ways of treating like waxing or oils were considered, to guard against moisture so that it wouldn't affect the touch sensation too much. Aspen was selected to be used as the material, and it has long traditions in Finland as both bench and wall material in saunas. Based on common knowledge and experiences from use in sauna we could expect that it could be used in saunas as untreated. The untreated Aspen turns a bit darker with time and might experience some discoloration, but this could be accepted in our sauna bench concept. The group did a test where one of the cubes was treated with paraffin oil (sold as saunasuoja) to test its effect on visual and haptic properties of the piece. Paraffin oil is recommended by the manufacturers of industrially mady sauna benches made of aspen. The test piece turned noticeably yellow, and even when dried had slightly oily sensation when touched. Based on these facts and experiences the group decided to leave the structure and the cubes untreated. Fig.: Paraffin oil treated test piece(to left), untreated test piece (middle) and the test piece that went through the steam own(sauna simulation)(on right). On the last lecture of integrated interior wooden surfaces held by Katja Vahtikari, the topic of how people perceive the treated and/or untreated wooden surfaced in general. Based on the findings of the presented study it seemed clear that people perceive the untreated “natural” surface as the most pleasing, and this reflected our own findings too. MANUFACTURING PROCESS Cube To manufacture cubes, aspen was chosen among many different wood species. From sawn timber, long beams of wood with 40 x 40 mm of cross section are made. At this moment, first notch along a longitudinal direction can be cut off with a table saw. After cutting off the first notch in the middle of the beams, 40 x 40 x 40 mm cubes are made by cutting the beams with the table saw again. To make the other notch which orthogonally meets the first notch at the center, one guide structure is necessary to accomplish an accurate size of notches on a number of cubes on the same fixed part. For this reason, the one guide piece was suggested and used to make the notch. Fig. : guide structure for making notch The next step is to round off 4 edges of one surface of a cube to make it look like a shape of an ice cube. First, a router can make this work really efficiently, however, another guide structure is needed to do a work with accuracy. The guide piece has a space where only one cube can tightly fit so that all the edges can be rounded off while the cube does not move without having workers hands close to a blade of the router. Fig. : guide structure for rounding­off edges of the cube Even after rounding off the edges, it was necessary to sand corners of the cube since the router still leaves an unnatural shape of corner with a less welcoming haptic experience to users. This sanding work was all done by hand with a sanding machine. 1.
Make a mark 2. Round a corner 3. Make a corner smooth After sanding with a machine, more sanding work was done by a sanding paper. Despite the delicate work with the sanding machine, it left surfaces with angles. To make all the pieces sleek and smooth, hand­working was able to complement for the details. Through this process, 169 pieces of the cubes were produced for the whole structure. Fig. : the process of producing a cube Structure The structure was manufactured by sawing and planing pieces of solid wood to dimensions of 600 x 65/55 x XXX mm. From this bigger solid wood piece 9mm wide pieces were saw with table saw. These pieces were planed in two steps down to 6,7mm. Six of these pieces were taped together to speed up the manufacturing process. If more than six pieces would have been cut at the same time it could have affected to the accuracy of the cuts. The cuts were made to these taped pieces with a table saw. The depth of the cuts was 35mm for the taller structural pieces and 25mm for the “binding” pieces that gives sideways support for the structural pieces. There was always two cuts right next to each other and that created 7mm wide notch. The accuracy of the cuts was essential at this phase, as a miscut of 0.1mm played significant role when the structure was assembled. 0.1mm too little and the pieces wouldnt fit, and 0.1mm too much and the joint would be noticeably loose. Fig.: Places of the cuts on a 600mm piece (with 3,5 blade) After the cuts were done the sharp corners of the cuts were sanded to make sure the pieces would fit as smoothly as possible, and that none of the sharp corners would break any of the other pieces. After this the tapes holding the pieces together for the time of sawing were removed and the structure was assembled. After the structure was assembled it was sanded down with an hand held belt sander to give it a more ergonomic shape. After sanding the ready made wooden cubes were placed on the structure. The cubes sit on place by force of gravity and friction, and no glue or screws were used. It was essential to manufacture both the structure and the cubes with extremely low tolerance of 0.1mm to achieve a fit that is loose enough that it would be possible to assemble it easily, but still tight enough so that the pieces wouldn't wobble or come off unintentionally. After assembly the cubes can still be taken away and replaced if needed simply by lifting them off by hand. APPLICATION This wooden surface can span 600mm easily. For public sauna situation, 600mm x 600mm surfaces can be connected next to each other and get a large surface. REFLECTION & CONCLUSION The goal of designing a new type of a sauna bench was to overcome a conventional appearance which can be easily seen anywhere. For this reason, block­type seating was suggested and an idea to solve a structural part of the seating was needed. There were many proposals to resolve the structure, however, we thought that the stability as a seating is the most important factor to be considered. Therefore, the lattice structure was selected to fit more than one hundred of wooden cubes. When there are many elements and components which have to be assembled one another, high level of accuracy is essential to make a perfect model. Moreover, since the idea of this sauna bench is aiming to provide users with a favorable haptic experience, delicate work was required. The condition that the task is to build a surface which is to be used in a wet space, many things we can do were restricted. However, through many tests including steaming and drying in the oven, shower test and so on, we were able to make the most reasonable decision to achieve our design. Building mock­ups always helped proceed the process for designing and manufacturing whenever we confront unclear moments along the project. Consequently, our group built a sauna bench with elegant a curved surface which has a sense of inviting users to sit on. Wooden blocks nicely shaped into a shape of ice­cube give people a unique haptic experience. Not only does this surface give users a pleasure of touching it, the appearance also corresponds to it functional purpose as well. It was a good opportunity to look deeply into properties of wood in a wet space and challenge ourselves as designers to overcome constraints of wood with moisture and wood to design and build a useful product which fulfill both, function and aesthetics.