som project paper
TRANSCRIPT
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Newtons Log Cutter
Ainslie Campbell Angus MorineBeth Faulkner Gerry PetrashJames Lapido
Design Team: Newtons Log Cutter ENGN 3006, Strength of MaterialsDepartment of Engineering, Dalhousie University
Submitted to: Dr. Peter HavardDepartment of EngineeringDalhousie UniversityMarch 21, 2014
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Contents
Abstract 3
Introduction 4
Design Concept 5
Data and Methods 6
Estimated Budget 7
Discussion 7
Conclusions 9
References 10
3-D Sketches 11-16
Hand Drawn Sketches 17~
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Abstract
The purpose of this design project is to address ways in which a homeowner may
prepare his or her own firewood: a common practice in rural Nova Scotia and beyond. The
process of transforming large logs into manageable, split firewood is inarguably labor-intensive
and potentially dangerous. One person who prepares his own firewood will have to bend or stoop
over many thousands of times, wield a heavy chainsaw and stack and restack the same pieces
of wood repeatedly. The wear and tear on the body is obvious, but this study will attempt to
calculate and quantify the amount of work done and to come up with solutions to reduce the
amount of energy required to perform such a task. This study proposes a two-fold solution toreduce the amount of energy expended by one person preparing his own firewood:
1. manipulate the wood at waist-level with ramps and a custom designed table
2. eliminate the lifting of the chainsaw by bolting it to a moving stand
The proposal includes ideas that employ gravity, since many of the logs are already
elevated on top of a large pile. We also advocate the use of some inexpensive off-the-rack
accessories to facilitate the task of man-handling the logs and eliminate the need to invent new
tools. To eliminate the repetitive chainsaw movement, we conceptualized a device that looks
similar to a lawnmower: a chainsaw is bolted to a kind of wheeled cart with the blade extending
vertically upright. This chainsaw mower can be pushed back and forth relatively easily while the
logs remain stationary on a table.
We approached the project by using as our case study the situation of a certain Dr. Peter
Havard, the avuncular Strength of Materials instructor at Dal-AC. Through meetings and lectures,
we learned that his current process involves having 8 cords of uncut logs delivered to his
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property once a year. He cuts them himself with a chainsaw, splits them with an electric wood
splitter and stacks them. With the data and anecdotal information that he provided, we were able
to come up with some ideas on how to improve on his current methods.
It can be concluded that our rethinking of the wood-splitting process by using strategically
placed ramps and a table is possible and worth trying. The chainsaw mower idea needs to be
subjected to a far more rigorous examination than can be provided here. It represents a major
design project in and of itself and would require many man-hours just to produce a working
prototype. It is not likely that this idea will make it to the drawing table anytime soon.
Introduction
At the heart of our project is the fact that we live in one of the coldest countries in the
world. Despite what anyone says or believes about climate change (aka global warming ), the
winter of 2013-14 has been colder than usual. The Earth may be heating up, but it is far too soon
to stop thinking about how we are going to stay warm during the long Canadian winters. From
sealskin boots to igloos, from hi-tech sportswear to building insulation systems, Canadian
engineers, designers and lovers-of-the-great-outdoors are always on the look-out for innovative
solutions to living comfortably, safely, economically and sustainably in such extreme cold.
Canadians pride themselves on self-reliance, problem-solving and a can-do pioneering spirit and
when it comes to home-heating, many people are not satisfied with burning oil. Providing ones
own firewood by hand and with hand-held machines, is an attractive, albeit non-mainstream
alternative to burning fossil fuels.
The design objectives for this research are to reduce strain on the workers body by
reducing the number of times needed to bend over and pick up each piece of wood and by
eliminating the need to lift the chainsaw up and down by hand. Not only will this potentially
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decrease the workload, it will also be safer due to the decrease in repetitive tasks and the
physical distance from the chainsaw.
Design Concept
In order to meet our objectives, we propose the design of two main components...
1. custom-built wooden table
2. custom-built chainsaw mower
...and the purchase of some new tools:
3. two arched aluminum loading ramps (USD 180.00)
4. two Woodchuck log mover tools (USD 89.00)
5. two Hookaroon log moving tools (USD 55.00)
The table has three gaps that run its entire length. The chainsaw blade can move through
these gaps in order to cut through the logs without inflicting major damage to the table itself.
The log-cutting machine resembles a lawnmower, but instead of a spinning blade on the
bottom, a chainsaw is bolted on top with its blade protruding upwards. The handle of the
machine is not attached to the back like a conventional mower, but rather to the side. The legs of
the table are built to allow passage of the cutting machine.
Here is a step by step guide on how the system would be implemented.:
1. The table is positioned at one end of the wood pile.
2. The splitter is positioned at the end of the table that is opposite the woodpile.
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3. The loading ramps are installed between the table and the wood pile by just setting them
in place. One end of the ramps is connected to the table. The opposite end rests on the top of
the wood pile.
4. Using the Hookaroons, the user can pull the logs and roll them down the ramp and line
them up on the table. The table will support up to about 4 logs at a time.
5. The user starts the chainsaw and then pushes it through one gap the entire length of the
table to make the first cut through all of the logs on the table.
6. Back up and push the rig through the second gap and make the second cut through each
log. This will reduce each log to four smaller logs.
7. Switch off the chainsaw, turn on the woodsplitter and transfer each log directly to the
splitter to be split and then drop them into a waiting wheelbarrow.
8. Transport the split wood to the stacking area.
9. Reload the table with a new load of logs and repeat the process until completion.
Data and Methods
We will denote half of the length and width for the table top as a and b respectively (for
purposes of calculations). These distances, paired with the Pythagorean Theorem can be used
to compute the distances from the legs to the center of the table, where the load vector is
located for the logs. Note that it does not matter if we interchange a and b; our calculations
will not change. By taking the sum of the torques about one of the legs as being equal to zero,
the following equation can be derived: F leg= (F )logs(a2 + b
2)
/(a + b + (a
2 + b
2)
).
Normal stress in the table legs was also analyzed and calculated using: = F/A , where F
is the axial load and A is the cross-sectional area of the table leg.
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For buckling of the legs, the equation: P cr = 2EI/KL2 was used for the critical axial load,
where E is the modulus of elasticity, I is the moment of inertia of the leg, K is a constant
corresponding to the type of beam and L is the leg length.
Estimated Budget
Wooden Frame Table $300.00
Arched aluminum loading ramps $180.00
Woodchuck log mover tools (2) $89.00
Hookaroon log moving tools (2) $55.00
Chainsaw $250.00
Chainsaw Mower $500.00
TOTAL $1518.00
Discussion
The design that we decided upon through a selection of ideas for a solution of lessening
the stress on a persons back from cutting logs, was a table that would allow a cart with a
chainsaw to roll underneath it. The table was the main focus of the design concept, since the
table would be the element that would elevate the logs. The elevation would prevent the bending
of the back which could harm the worker.
In order to assess the torques in the table, we first consider the type of loading. The logs
are a distributed load whose resultant force is at the middle of the table top (the centroid). In
order for the table to remain in equilibrium, the torque vectors about any point must have a sum
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of zero. The load is in the center of the table, meaning that the loads in each table leg are equal.
Note that the F leg variable represents the force required in a single table leg.
The force of the logs is equal to approximately 18000 newtons. This equation can be used to
size our table top. We choose a length and width and realizing that the selected values
correspond to 2a and 2b in the above equation, we divide them by two to put them in our
equation. The equation will generate the minimum force required in each leg for rotational
equilibrium of all points.
The design of the table began with legs needing to be able to hold the weight of 1000 lb in
compression from the logs on the table. The area calculated for the legs when they were under
compression was 1.7 cm^2 which was rounded to 2 cm^2. under further investigation of the
legs, the legs were very susceptible to buckling. Since the legs at this size would start buckling
with less than one-sixth of the weight that would be applied from the weight of the logs that the
table would need to hold. The legs would have to be resized to at least a area of five square
centimeters, which was doubled for safety reasons of preventing heavy logs from falling and
causing injury.
If we want a table with dimensions of 1.5 3 meters, we put 0.75 and 1.5 into our
equation to solve the minimum force in each leg for rotational equilibrium, which is approximately
3850 newtons. This is much lower than the critical loading value of 6700 newtons. We did not
need to calculate a safety factor, since the table can easily handle such loads.
The construction and design of the cart that would move and hold the chainsaw is a very
complex structure, that would need to be hold the trigger and safety guard in position, and have
an emergency shut off triggers and button. The design would also need to account for the force
of pushing and pulling the cart, the weight of the chainsaw, and forces such as cutting through
the logs and kickback caused by the saw biting into the wood to far. These calculations are far
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beyond the abilities of us at this time. Another problem with the cart is finding a viable way to
push or pull the cart safely under the table. The attachment would not be able to have a handle
like a lawnmower since the would only be a small gap created from the chainsaw through the
logs and it could not come out the side of the table because of the legs of the table. Pulling the
cart with a cord is another option but it could also cause safety hazards since the logs could roll
forward or the cord could snap if it became frayed or wasnt strong enough to withstand the
tension caused by the cart. There are also safety concerns with having the chainsaw pointing
straight up without anything to keep people from knocking into it, which could cause serious
injury or even death. It is evident that a lot of further analysis would need to be placed in the
design of the cart, which at the level we are at we are unable to do at this time in our studies.
Conclusions
From the analysis of the design of the table it can withstand the amount of weight needed
to hold the logs. The legs of the table are able to withstand the force that put the legs in
compression, but after further analysis the legs had to be modified to keep from bucklingunderneath the weight. The design of the cart that would hold the chainsaw was far beyond our
knowledge to calculate the forces to correctly design structure that would need to safely support
the chainsaw. Without the knowledge about the cart it was hard to tell it it would be enough force
to pull the cart with a cord, or tell if that force would mark the cart tip over. Even though most of
the components of the design are acceptable, there are more things that could be added to the
components to help with safety features. To see if the design is plausible more work and
calculations would need to be done with the design of the cart.
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References
Baileys.com, Baileys Outdoor Work Equipment
Canadian Centre for Occupational Health and Safety
Forestry Safety Society of Nova Scotia
Husqvarna: Buying Guide for Chainsaws
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Sketches
Figure 1: General design concept
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Figure 2: Preliminary idea: fixed inverted chainsaw with adjustable ramp
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Figure 3: Preliminary idea: fixed inverted chainsaw on permanent ramp
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Figure 4: Preliminary idea: guillotine log cutter
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Figure 5: Preliminary idea: triple guillotine log cutter
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Figure 6: Preliminary idea: giant chainsaw mounted on pick-up truck