Som Project Paper

8/11/2019 Som Project Paper

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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

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