Human-Powered Band-Saw in Woodcraft Industry - Report Example

Mechanism Development Report (MDR) Design of a Human-Powered Band-Saw for Use in the Woodcraft Industry Name Institution Date 1. Developing the Brief This report expounds on the design of a human – powered band – saw that is meant to be used in the woodcraft industry for the purpose of roughing out wooden blanks for skilled carvers of ornaments. What a band saw is defined as a cutting device that consists of a circular blade that is made up of a continuous band of teeth and is mainly used in woodworking, metal cutting and also in lumbering process. For this particular project, a pedal operated a circular band saw machine was designed. Pedal power is a form of energy generated by human beings and is transmitted through a crank system, and the working principle of the pedal power circular saw will be to change circular motion into linear motion (Callens and Bignonnet, 2012). Also, the band saw will consist of a larger wheel connected to a smaller wheel by a belt, and the smaller wheel will be supported by the shaft and bearing support. A circular saw will be mounted on the same shaft with the small wheel, and as the shaft rotates, then it will be possible to cut a piece of wood. Therefore, the user is expected to seat of a bicycle seat and then pedal the machine while the workpiece is firmly fixed. It is expected that the machine will reduce human effort four times and the cutting time will be determined by the thickness of the workpiece to be cut. Although this device reduces human effort, it will face competition from the electric powered band saws (Callens and Bignonnet, 2012). However, this design seems more favourable since the project is meant to be used in developing countries. Thus, it will be able to be used in areas without electricity, and its prices will be low. Since used bicycles can be turned into pedal powered band saws. Also, it is worth to mention that if a dynamo is fitted into the system, then it can be used to generate light to the company. This project will face constraints when determining the right materials that will be able to withstand the working environment of the machine. 2. Mechanical analysis a. Calculation of the total load Total load = =Pt + Pc + Ps Pt = tangential force Ps = tension due to sagging Pc = centrifugal tension Pt = power / angular velocity Power = 200 watts σ = stress = 18.15*10^6 N/mm2 Bearing Area A = 7*10^-5 m2, obtained from available hand book Chain velocity = pitch * number of teeth of the smaller sprocket * number of revolution / 60 Pitch = 15.875 mm Number of teeth of the smaller sprocket = 25 Chain velocity = 8 m/s Service factor Ks = 1.25 Tangential Force Pt= 200/8= Pt = 25 N Tension due to sagging of the chain; Ps = K*w*a Coefficient of Sag K= 6 a = 0.56 obtained from available handbooks w = Weight per meter = 0.9 N Ps = 3 N Pc = w*v2/g = 0.9 * 82 / 9.81 = 5.8 N Total Load Σp= Pt + Ps + Pc = 25 + 3 + 5.8 = 33.8 N b. Calculation of the design load Design laod = Σp*Ks = 33.8 * 1.25 = 42.25 N c. Calculation of the factor of safety FSw = Breaking Load/Design Load Breaking load = 21 N, obtained from PSG handbook FSw = 21 / 42.25 = 0.49 d. Calculation of the σ roller σroller = Σp*KS/A = 42.25 N * 1.25 / 7 * 10^-5 = 754465 N/m2 e. Design of the ball bearings Axial Load Fa = 1000 N Radial Load Fr = 1500 N Speed N = 1500 rpm Life in hours = 15000 hrs F Design of Shaft Load of Sprocket = 250 N Load of Blade = 600 N Length between Bearing = 1240 mm Length between Sprocket and Bearing = 620 mm Length from Blade to Sprocket = 310 mm Figure1. Free body diagram RAV+RBV = 250+600 RAV+575 = 850 N RAV = 275 N Bending Moment at B = 0 Nmm Bending Moment at D = 575*310 = 1.75*10^5 Nmm Bending Moment at C = (575*620)-(620*310) = 1.70*10^5 Nmm Bending Moment at A = 0 Nmm Maximum Bending Moment = 1.78*10^5 Nmm me = (Л/32)*σb*d3 1.78*10^5 = (Л/32)*2*40*d3 d = 28.22 mm d = 30 mm (approximately) 3. Concept design The device consists of a larger wheel connected to a wheel. The pedals are connected to the larger wheel which transmits power to the smaller one. The mechanism is in such a way that it rotates a shaft that is connected to the small wheel. The shaft carries a circular saw and is supported by bearings. As the user rotates the pedal, the circular saw then cuts the workpiece at the much-reduced effort. Figure2. 3 D representation of the designed pedal powered sprocket 4. Subsystem Interaction The mechanism as mentioned earlier, will consist of a set of subsystems. The mechanism applied in this system involves the use of a belt and wheels where motion and power is transmitted from the large wheel to the smaller wheel. The smaller wheel needs to be aligned to the shaft which has the cutting saws. Of the wheel and the shaft are not aligned then, the reliability and the smooth operation of the device will be influenced. Therefore, the problem of alignment between the smaller wheel and the shaft bearing the cutting saw can be achieved by use achieved by use of a flexible coupling so as to avoid failure of the machine in the future. 5. Component search and selection The following components shall be needed for the fabrication of the designed device; power circular saw blade, pedal, small wheel, large wheel, frame, bicycle seat, shaft, bearings, belt. Components such as the frame and the shaft can be fabricated in the workshop (Callens and Bignonnet, 2012). However, the other mentioned components can be bought off the shelves. Some of the components to be used in this design are as shown below; Figure 3. Bearings Figure4. Pedal Figure 5. Bicycle seat Figure 6. The stand Figure7. The chain Figure 8. Circular saw Figure 9. Shaft 6. Geometrical Stability The device will be subjected to tremendous cutting forces and moments; it will be very crucial then, to ensure that the stability of the machine is guaranteed. For this particular project, the saw was made stable by the construction of a frame of four stands. Two stands were used to support the seat and the bigger wheel while the other two stands were used to support the smaller wheel and the cutting saw as shown in the diagram below; The stand was made stable in that they were designed such that their base surface area was sufficient enough to prevent the machine from tumbling during the cutting operation. The stands were held together by welding. Bolts and nuts could also be used. 7. Environmental Robustness The machine will be made from mild steel which is susceptible to wear and tear as a result of corrosion. Therefore to prevent the menace of rusting the device has to be painted. The machine does not need enclosure since the wood particles and dirt will not affect its operations. However, the moving components need to be covered so as to avoid accidents. 8. Operational Reliability As mentioned earlier, this machine is subjected to tremendous cutting forces and moments. Therefore mild steel will be used for the fabrication purposes so as to ensure that the system meets the expected strength, operational lifetime and reliability. Mild steel will be preferable because apart from being strong, it is also cheaper compared to other fabrication material such as stainless steel. 9. Serviceability One of the design consideration of this system was to ensure that the machine was easy to service. Therefore, if any of the components fails such as the bearings, cutting blade, wheels or the belt, they are located in a position that makes them easy to remove. Also, different subsystems are independent such that if one of them fails, then it can be removed and be replaced or be repaired without disassembling the entire system. For example, the pedal system and the belt system are independent but are connected by use of couplings. Also, in an effort to reduce periodic maintenance of the system, the number of moving parts has been reduced to greater extend. 10. Sustainability During the design of the device, it was taken into consideration that, the device will need to be disposed of after its lifetime in such a way that it will cause minimal or zero environmental pollution. Due to that reason, the materials used can be recycled and be moulded into something else which can be useful. Recycling helps in reduction of pollution by eliminating deposition of solid waste. Therefore, the entire project can be termed as a sustainable design and all engineering projects should take into consideration how to dispose of the project once it has reached its life span. Conclusion This project sought to design a bicycle powered band saw. The design parameters considered include the expected loading conditions as well as the ergonometric aspect of the user. As such, a detailed loading conditions were set and the expected forces and moments calculated. The next stage entailed a 3D modelling of the individual parts of the bicycle, which was done in Solidworks. Finally, an analysis of the design was conducted to suit the expectations and powering parameters. Here, the comfort of the user as well as the sustainability of the system was considered. It can, therefore, be concluded that the project was a success. Reference list Callens, A. and Bignonnet, A., 2012. Fatigue design of welded bicycle frames using a multiaxial criterion. Procedia Engineering, 34, pp.640-645. Read More

Therefore, the problem of alignment between the smaller wheel and the shaft bearing the cutting saw can be achieved by use achieved by use of a flexible coupling so as to avoid failure of the machine in the future. 5. Component search and selection The following components shall be needed for the fabrication of the designed device; power circular saw blade, pedal, small wheel, large wheel, frame, bicycle seat, shaft, bearings, belt. Components such as the frame and the shaft can be fabricated in the workshop (Callens and Bignonnet, 2012).

However, the other mentioned components can be bought off the shelves. Some of the components to be used in this design are as shown below; Figure 3. Bearings Figure4. Pedal Figure 5. Bicycle seat Figure 6. The stand Figure7. The chain Figure 8. Circular saw Figure 9. Shaft 6. Geometrical Stability The device will be subjected to tremendous cutting forces and moments; it will be very crucial then, to ensure that the stability of the machine is guaranteed. For this particular project, the saw was made stable by the construction of a frame of four stands.

Two stands were used to support the seat and the bigger wheel while the other two stands were used to support the smaller wheel and the cutting saw as shown in the diagram below; The stand was made stable in that they were designed such that their base surface area was sufficient enough to prevent the machine from tumbling during the cutting operation. The stands were held together by welding. Bolts and nuts could also be used. 7. Environmental Robustness The machine will be made from mild steel which is susceptible to wear and tear as a result of corrosion.

Therefore to prevent the menace of rusting the device has to be painted. The machine does not need enclosure since the wood particles and dirt will not affect its operations. However, the moving components need to be covered so as to avoid accidents. 8. Operational Reliability As mentioned earlier, this machine is subjected to tremendous cutting forces and moments. Therefore mild steel will be used for the fabrication purposes so as to ensure that the system meets the expected strength, operational lifetime and reliability.

Mild steel will be preferable because apart from being strong, it is also cheaper compared to other fabrication material such as stainless steel. 9. Serviceability One of the design consideration of this system was to ensure that the machine was easy to service. Therefore, if any of the components fails such as the bearings, cutting blade, wheels or the belt, they are located in a position that makes them easy to remove. Also, different subsystems are independent such that if one of them fails, then it can be removed and be replaced or be repaired without disassembling the entire system.

For example, the pedal system and the belt system are independent but are connected by use of couplings. Also, in an effort to reduce periodic maintenance of the system, the number of moving parts has been reduced to greater extend. 10. Sustainability During the design of the device, it was taken into consideration that, the device will need to be disposed of after its lifetime in such a way that it will cause minimal or zero environmental pollution. Due to that reason, the materials used can be recycled and be moulded into something else which can be useful.

Recycling helps in reduction of pollution by eliminating deposition of solid waste. Therefore, the entire project can be termed as a sustainable design and all engineering projects should take into consideration how to dispose of the project once it has reached its life span. Conclusion This project sought to design a bicycle powered band saw. The design parameters considered include the expected loading conditions as well as the ergonometric aspect of the user. As such, a detailed loading conditions were set and the expected forces and moments calculated.

The next stage entailed a 3D modelling of the individual parts of the bicycle, which was done in Solidworks.

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