wsdnr tree drill and fill
TRANSCRIPT
Washington State Department of Natural Resources Tree Drill and Fill
Team Manager: Ethan Nelson
Max Flukey, Kevin Kruger
Advisor: S. Duan
Department of Mechanical Engineering
Hal and Inge Marcus School of Engineering
Saint Martin’s University
12/2/2015
Table ContentsAbstract............................................................................................................................................1
Introduction......................................................................................................................................1
Design..............................................................................................................................................3
Design Analysis.............................................................................................................................12
Design Results...............................................................................................................................19
Prototype Considerations...............................................................................................................22
Conclusion.....................................................................................................................................23
References......................................................................................................................................26
Appendices....................................................................................................................................27
Figures
Figure 1. Starting Drill Design........................................................................................................4
Figure 2. First Injector Iteration.......................................................................................................4
Figure 3. Second Iteration (Injector)...............................................................................................4
Figure 4. Third Injector Iteration.....................................................................................................5
Figure 5. Fourth Injector Iteration...................................................................................................5
Figure 6. Semi-Final Combination..................................................................................................5
Figure 7. Second Iteration Needle Extension..................................................................................6
Figure 8. PVC Extension................................................................................................................6
Figure 9. Delivery Shaft..................................................................................................................7
Figure 10. Injector...........................................................................................................................8
Figure 11. Expensive Injector..........................................................................................................8
Figure 12. Injector Handle...............................................................................................................9
Figure 13. Unformed Injector Mount..............................................................................................9
Figure 14. Measurement Dial........................................................................................................10
Figure 15. Fluid Chamber..............................................................................................................10
Figure 16. Drill Bit Extension.......................................................................................................14
Figure 17. Drill Bit........................................................................................................................15
Figure 18. Janka Hardness Scale [4]..............................................................................................21
Tables
Table 1. Shedule 40 Pricing...........................................................................................................16
Table 2. Schedule 80 Pricing.........................................................................................................16
Table 3. Drill costs.........................................................................................................................17
Table 4. Miscellaneous and Total Costs........................................................................................17
Table 5. Drill Specifications..........................................................................................................18
Table 6. Drill and Drill Bit Extension...........................................................................................18
Equations
( 1 ).................................................................................................................................................13
( 2 ).................................................................................................................................................13
( 3 ).................................................................................................................................................14
( 4 ).................................................................................................................................................14
Abstract
The purpose of this project is to develop a set of devices that will ease the application of
growth hormone to small Douglas Fir trees. The devices will need an extended reach to remove
the need to kneel and crawl underneath small trees; Allowing the work to be done from a
standing position in a shorter period of time.
With collaboration with Washington State Department of Natural Resources’ employees,
a suitable design has been found and will be produced before there next application in the spring
of 2016.
Introduction
The ultimate goal of this design project is to save the WSDNR money and the current predictions
support this to be true.
Our design was limited by the project manager with a few constraints, the materials must be
available at a hardware store or online, our design cannot involve tools outside of his shop, and it
must be modular and repairable in house. The design reflects this as it is made from mostly PVC
pipe and fittings, and can be made only with access to simple power tools. The prototype is
centered around a three foot drill extension, with the injector mounted on the end. The extension
is connected to a cordless drill to power it, and the injector functions by pressing it against the
hole.
Washington State Department of Natural Resources is a multi-faceted government
organization. We have worked with the Douglas Fir seed orchard in Lacey. The goal for the seed
orchard, as well as how they make money, is by harvesting and selling seed cones. Natural tree
stands only flower periodically and inconstantly, anywhere from 3 to 7 or more years and in a
seed orchard, this performance is unacceptable and hard to plan for [1]. The WSDNR uses three
methods to encourage constant and fruitful harvests at manageable amounts every year.
To understand the use and need of the drill and injector, the process that the WSDNR
does should be explained in more detail. The first step is partial girdling of the trees. Two
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overlapping half circumference saw cuts are made through the bark and cambium layers of the
wood. The cut is extended only until the saw teeth begin to reach xylem, the center of the tree we
simply call wood. The cuts are made below all of the branches and relatively low on the trunk,
with the second cut about 1.5 times the stem diameter apart from the first [1]. The girdle is done
a few weeks before the injections in mid-April, but this time varies from orchard to orchard. In a
similar fashion to the drilling, an employee on either side of the row of trees will girdle the tree
on their side of the tree and the second will place the next cut at the proper distance either above
or below the first. Partial Girdling is considered a safe, low cost, and predictable technique for
stimulating consistent flower crops [1].
The next step is drilling, done in mid-April, and is where the first of our two devises will
come into play. The sole purpose of drilling holes is to create a reservoir to hold the growth
hormone. This allows the tree to absorb the fluid at its own pace. The hole is drilled at
approximately 45degrees down so the fluid doesn’t drain out. As well as 1 inch deep so as to
only penetrate into the portion of the wood that is alive and pumping sap throughout the tree.
Multiple holes are drilled evenly about the circumference of the trunk depending on the dose of
hormone administered to that specific tree [2]. Our second devise will be used to inject the
growth hormone into the reservoir in measured amounts. A minimum of .2 ml is injected into
each hole with a maximum of .4 ml until the total does is administered. This is done at the same
time as the drilling to ensure the holes do not fill with sap.
The third method is to gather, mix and re-disperse the pollen as to insure a good amount
of cross breading between all the families of trees, of which there are approximately 60. Without
this method, natural wind pollination is the only way trees are pollinated. Crosspollination allows
WSDNR to genetically manipulate the trees in order to produce seeds adequate for the terrain
they wish to reforest. By crossing a tree that is good in one geological location and a tree that
does well in another, WSDNR can create a tree that is suitable in both geological locations or in
an entirely different location. The re-dispersal is also more affective at pollinating the trees than
natural wind pollination. Once the cones have reached maturity the pollen is collected with a
vacuum system developed by Rocky the project manager at the WSDNR. The pollen is then
collectively mixed and re-dispersed during that breeding season or is saved for following years.
This process is done the year following the girdling and injections. In the late summer of this
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same year once the cones have been harvested, the trees are pruned back to keep them at
manageable sizes.
Each field of Douglas Fir trees are divided into three sections, so that each section is on a
different step. The first set being girdling and injections. The second is pollination and
harvesting. And the third block is in a rest period of recovery and growth [2].
Another method to administer the growth hormone is to hydraulically force it into the
trunk. A needle can be hammered into the stem, connected to a press and then a dose of hormone
is forced into the wood. This will split the wood apart and often does excess damage to the tree,
leaving it susceptible to diseases and pests for a longer period of time them a few small holes.
Only a small volume of wood is removed so by the time the growth hormone is absorbed, the
hole begins to fill with sap, like a scab. The hydraulic split is a much larger wound and as such is
much more difficult for the tree to heal.
The fluid put into the trees is Gibberellic acid or GA. This acid is dissolved in an ethyl
alcohol solution [1]. By placing this acid in the tree, it stimulates flowering. The girdling and GA
are both intended to produce more seed cones, but they do this in very different ways. Girdling
stress the tree and forces it into a survival mode allowing it to focus more energy on growing
seed cones vs growing itself. This is a common trait in many species of plants, when they are
threatened or injured more energy is put into reproducing. The original plant may die, but it may
have successfully reproduced and thus continued its lineage. The GA stimulates growth by
artificially introducing a larger than normal amount of growth hormone into the system. The
dosage of GA must be controlled because it can harm the tree in large concentrations. It will
shock the tree causing it to lose most or all of its needles at too high of a dose. Inhibiting its
ability to photosynthesize and grow in any way.
This process is done in an assembly line fashion. First, an employee measures the base of
the tree getting its rough diameter. That diameter determines how large a dosage of GA the tree
can sustain as well as how many holes to drill to allow that dosage. An employee who oversees
the application of the fluid can deny the injection of the fluid if the tree is deemed unfit. Next,
employees, half on each side, drill the holes into the tree one inch deep equidistant from each
other around the circumference of the trunk. Next, the team with injectors fills the holes to the
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desired amount. This occurs on every tree in the block being worked (approximately 200 trees
per year). Typically it takes three days of work to finish this task. With the introduction of the
designed tool, it would hopefully cut down the time of this task to save the WSDNR time and
money.
Design
Over the course of the semester we went through many design iterations while working with
Rocky. He had a few requirements for the design of the device or devices, which often changed
from meeting to meeting as we realized something wouldn’t work or he decided he didn’t like
some feature. This was not necessarily a difficult process but it made us think outside of the box.
The outside look from Rocky was also helpful, especially when we were stumped on where to go
next or how to improve something. His input was vital and truly helpful. But there were also
times where we would surprise him with something, which is the reason for getting help from
engineering students.
When we first chose this project we had some rather extravagant ideas for our device.
The first was for the drill and it involved making a way to mount the drill to the user’s shin with
the trigger rewired to a long cord to hold in the hand. This accomplished the first requirement of
not having to bend over to use the drill and injector. But we later found out that the hole had to
be drilled at a downward angle making this design nonfunctioning. Not to mention ridiculous
and slightly dangerous to the user. There was a likely possibility that the drill could twist and
injure the users other leg. Another preliminary design involved designing and manufacturing a
drill bit with a needle tube through the center. Giving the ability to rout the fluid through the drill
bit so that a hole could be drilled and then the GA could be immediately injected into the tree.
But we immediately realized that finding a way to route the fluid into the drill bit would be
extensive and difficult to design and likely to manufacture. When we mentioned this design to
Rocky we realized that he wanted to be able to make these devises by himself. So we got a big
limitation at this point that all the parts we used needed to be custom ordered or made with only
simple modifications that could be done at the WSDNR shop with mostly hand tools.
Through the iterations there is significant change in the design process. Rather than
complicating the system as more design parameters appeared, the design got simpler as time
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went on as depicted in figures 1 through 6.
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Figure 1. Starting Drill DesignFigure 2. First Injector Iteration
Figure 3. Second Iteration (Injector)
Figure 4. Third Injector Iteration
This then became our number one design parameter and we refocused our designs to use
stock parts and easily purchasable materials. Rocky also around this time presented us with his
idea for the drill. It would be a long drill bit extension housed inside a PVC tube with a handle
for added control and support. We later adjusted this slightly by adding a prong at the end to
stabilize it to the tree so that the drill bit wouldn’t walk across the bark and damage it
unintentionally. The drill extension would also need to be longer then the tube by about an inch
to allow the tube to be secured to the tree and then push the center rod into the tree drilling the
hole. At the time we accepted this as our current model for the drill and began to work more on
the Injector as it was the more difficult of the two.
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Figure 5. Fourth Injector IterationFigure 6. Semi-Final Combination
Figure 7. Second Iteration Needle Extension
We came up with two basic designs and would expand on both of them over time. They
were both good options and Rocky couldn’t pick what he more preferred at first. So we
continued on with the dual designs. The first was simply adding an extension to the needle so it
would reach the hole without bending over. But we would have needed to use a very small tube
so that it would act like a needle and the fluid wouldn’t fall out while walking around. So it
would have to be supported in some sort of shroud. This option dismissed fairly quickly because
of the expense of tube and the likelihood that the tube could bend. So this was redesigned to add
another silicone tube between the injector and the needle and supporting it inside a pipe. This
would make it easier to replace the needle if or when it bends. Also silicone tubing is much
cheaper then small metal tubes.
The other design was a handle and trigger extension. Instead of modifying the needle, we
started to modify the trigger. Our first design was to bracket on an extension, probably PVC or
some sort of metal rod, with a handle and trigger near the back. We would link the handle trigger
to the injector with a wire to translate the motion down to the injector. For a while this was our
preferred design and we began updating it and figuring out the details. Like the bracket that
would connect the injector to the handle. At first it was just a statement that we’d find a way to
do it later because we were focusing on the more general overall design and mechanics. But
included with every injector was a bracket that mounted to the top of the injector to connect a
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Figure 8. PVC Extension
small vial of medicine to. We were going to use that as the bracket. It was already designed to
attach to the injector, so we would just have to modify it to attach to the rod. The problem was
making sure that it could support the weight in a way it wasn’t design for.
Next running from the previous design, we wanted to slip down the injector and remove
the handle and remake the trigger mechanism. We were having trouble finding an open enough
space inside the mechanism to place the spring. We eventually decided that if we ground down a
part of the internal mechanism we could add a spring, this would however limit the functionality
of the injector to only 1 ml instead of 2 ml. Rocky was okay with this however because they
never used more than 1 ml at a time. This would require modifying the delivery shaft featured in
the figure below.
Rocky also showed us another injector they had used in the past. It was more expensive
but because of its design we were able to come up with a rather simple mounting bracket and
triggering mechanism. Later Rocky and Jeff decided that they would rather use the cheaper
injectors they are currently using. But we had made a few revelations with this design that
allowed us to simplify our other designs.
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Figure 9. Delivery Shaft
Figure 10 depicts the first injector that was described and Figure 11 depicts the more
expensive and easily modified injector that we were shown. The reason why the expensive
injector was favorable in modification was due to its linear spring system that already existed so
there would be less work to do, unlike the NJ Phillips injector.
It was at this time we made a rather useful discovery about how the injector worked. If
you simply push on the back with the front tip pressed against something, like the tree, then you
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Figure 10. Injector
Figure 11. Expensive Injector
could operate it. Without pulling the trigger at all we could operate the injector. This is due to the
spring structure in the handle seen in Figure 12 below.
This meant that we could simplify the design and not have to add secondary trigger with
a connecting wire. It also allowed no modification to the delivery shaft so no limitations could be
put on the measurement dial, seen in Figure 14.
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Figure 12. Injector Handle
Figure 13. Unformed Injector Mount
By not modifying the measurement dial, the fluid chamber can act as normal, seen in
Figure 15.
So we began working on how to attach the handle to the injector in a fortified way
because we would be pushing on it to make it function. The first thought was to cut a groove into
a PVC tube and slide the injector in back end first, then place a cap with a hole in the center over
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Figure 14. Measurement Dial
Figure 15. Fluid Chamber
the end to hold the injector in. The groove would push forward on the back of the injector
pressing the tip into the tree and compressing the spring. The next step was to just add a simple
handle and support which would be easier to hold then just a rod. While talking to Rocky we
came about an idea to form the PVC around the injector. In a fashion similar to a kydex gun
holster. These holsters use heated plastic that is pressed over both sides of a pistol to take on its
shape. But when the plastic cools and hardens it allows the holster to retain the gun while the
person moves about. We can do a similar thing with the PVC. Instead of cutting a groove, a slit
can just be cut to the depth needed, about halfway up the nozzle end. PVC has a max temperature
of somewhere between 40 and 80 degrees Celsius, so if we boil water and submerge the end it
should become malleable enough to form over the injector. If more temperature is needed then a
flame can be used to slowly bake the PVC until it will form.
At this same meeting we also discussed the possibility of making both the drilling and
injection doable by a single person. Drilling the hole then immediately injecting it with the GA.
Rocky said this would speed up the process because the hole can be hard to see, so when the
second person comes up they have to search for it. Our first proposal was to simply modify the
handles of both devices so they can be wielded with one hand each. Holding the drill in one hand
with some sort of arm support similar to crutches for long term use. And the same for the
injector. This could become quite awkward to handle because it leaves both hands full and
unable to do anything else. The next was to combine the devices in such a way that you would
hold a single tool, but it would have a split end, with the drill bit on one and the injector needle
on the other. We had a preliminary proposal for this at the time, but with some brainstorming
during a meeting, and a bit of on the spot research, we made a very plausible design.
The main body would essentially be the drill extension we had planned to use; Basically
a long pipe with the extension running through the center, and a handle attached to the pipe for
your other hand to use for more control. Then at the bottom we would add a wye bracket. This is
a T bracket that instead of coming off at 90 degrees splits at some angle in between. We decided
that 22 degrees would be a good option. First it was a standard angle used, being half of 45, and
the small angle felt good to allow to pressing force to be transmitted more linearly into the
injector. Off of the wye we would put our formed piece of PVC for the injector hanging from the
bottom of the long rod and twisted so the handle will point to the left or right instead of straight
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down. The offset handle allows for more clearance from the ground. And by hanging the injector
down instead of to the left or right, the user could easily twist the whole device to one side or the
other to use the injector giving an ambidextrous use.
This design also minimized the work Rocky would have to do while making and
maintaining these devices. They have very little moving parts and can be easily constructed in
his shop with simple hand tools. The device also satisfies many of his other requirements. It
allows the user to operate from a standing position, no needing to crawl under the tree to do the
job. Use parts that are easy to obtain and easier to make. And we combined a two person process
into a single person job. Also Rocky wanted a design that was modular, or easily repairable in
the event that something broke while being used.
Our next steps are to begin refining this design. We’d like to make an ergonomic handle,
and we still have to figure out the exact routing and mounting for the bottle of GA that feeds the
injector. They currently simply hang the bottle from there belt and run a tube to the injector. This
is still a viable option but we are going to look into mounting the bottle to the handle somehow.
The relatively large weight could make it unwieldly if placed poorly. Many kinks will come out
once we begin the prototyping next semester. It’s possible that the pipe may flex too much and
will rub on the drill extension. Or that by pressing into the handle we flex the pipe too much. We
are confident that our design will allow for simple modifications to be made in the event of a
failure during prototyping.
Design Analysis
The design analysis mainly consists of the methodology of the designing process. Once a
final design was agreed upon a structural analysis can be applied. With this structural design,
there are assumptions that are made. The first assumption is that the system can be modeled as a
cantilever beam due to the operator’s strength greater than the total weight of the system, causing
the handhold to appear as a wall. The second assumption is that the pipe’s weight is negligible
due to it being the beam and its low total weight. This creates a model of a cantilever beam with
a point load. For the pipe the maximum deflection can be modeled as,
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δmax=P l4
3 EI( 1 )
Where δ max is the maximum deflection, in inches, P is the loading at the end point (can be
considered the total weight of the injector), l is the total length of the pipe, E is Young’s Modulus
of Elasticity, and I is the moment of inertia. P, l, and E are properties that are known. I is a
derived property that can be shown as,
I=0.0491(Do4−Di
4)
( 2 )
Where Do is the outer diameter of the pipe and Di is the inner diameter of the pipe.
There is another analysis to be done in the way of deflection and that is for the drill bit
extension. There was no information on the drill extension, so it is assumed to be carbon steel.
This analysis is similar to the previous one except instead of a point load it is a weight distributed
load. The weight per unit volume of the drill can be found using table A-51 [3]. To find the total
weight of the drill, multiply the volume by the weight per unit volume. A distributed load has a
different maximum deflection and moment of inertia equation which are,
I=12
M R2
( 3 )
Where M is the mass of the drill extension and R is the radius of the drill extension.
δ max=ωl 4
8 EI( 4 )
Where ω is the weight distribution of the drill which is the total weight per unit length.
There are other analyses that could have been done, such as the torque in the drill and
drill bit extension (seen in figure 16 and figure 17), the hoop stress of the fluid flowing through
the tube, and the chemical decomposition of the internal chamber. Sound assumptions can be
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made on all of these analyses. The torque in the drill and drill bit can be negligible because the
drill bit extension is designed to handle the stresses that is put on it, by the manufacturer. Fluid
flowing through the channels is 0.2 mL per squirt. That little fluid flow will do next to nothing to
the tube’s inner wall. There are not even concerns about the path tube being suctioned to itself
because Rocky2 already took care of that. There is no plausible way to analyze why the fluid
chamber of the injector deteriorates with use of the GA. The chamber is made up of a known and
tested material, some clear plastic, but the GA makers have a patent on their chemical
combination and won’t provide even a glimpse of what the chemicals are in it. All we know
about the GA is, it is in an alcohol solution.
The drill bit extension’s importance cannot be downplayed. It allows the extension of the
drilling mechanism. However, its deflection can determine whether or not the PVC piping will
wear down. Its torque will determine whether or not the entire system will hold or break.
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Figure 16. Drill Bit Extension
With this analysis, there are design considerations such as cost. Depending on the
schedule of PVC pipe used a different cost will be associated with it.
There are different costs for schedule 40 and schedule 80 piping which will provide
different strengths. The strength of schedule 40 PVC piping is that it will be a low costing,
relatively strong material with little deflection. The strength of schedule 80 PVC piping is that it
provides a higher moment of inertia, causing it to have less deflection than schedule 40 piping.
The downside is that schedule 80 piping is more expensive than schedule 40 piping. The
difference in cost can be seen in the tables below.
Table 1. Schedule 40 Pricing
Schedule 40
Item Cost
3/4" Wye-22.5 Degree $ 3.50
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Figure 17. Drill Bit
3/4" T $ 0.37
2 (3/4") Caps $ 1.58
Adapter (3/4"-1") Bushing $ 0.49
3' (3/4") $ 1.38
6" (1") $ 0.39
Total $ 7.71
Table 2. Schedule 80 Pricing
Schedule 80
Item Cost
3/4" Wye-22.5 Degree $ 3.50
3/4" T $ 0.37
2 (3/4") Caps $ 1.58
Adapter (3/4"-1") Bushing $ 0.49
3' (3/4") $ 5.10
6" (1") $ 0.39
Total $ 11.43
The drill has also been priced with two different variations, two foot drill extension and
three foot drill extension. The two foot drill extension has the set screws desired by the client,
however, it might not provide a long enough reach to sate the requirements. The price difference
can be seen in the table below.
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Table 3. Drill costs
Drill
Item Cost
2'X.25" $ 22.99
3' Quick Change $ 29.99
Drill Bit $ 2.38
2' (Total) $ 25.37
3'(Total) $ 32.37
Then is a miscellaneous purchase of PVC cement that may be needed depending if
threaded pipe is used. Its cost and the totals for each design can be seen in the table below.
Table 4. Miscellaneous and Total Costs
Misc.
PVC Cement $ 4.94
Totals
Total Per Unit (2,40) $ 38.02
Total Per Unit (3,40) $ 41.74
Total Per Unit (2,80) $ 41.74
Total Per Unit (3,80) $ 48.74
To understand the table, (2,40) means the two foot extension with schedule 40 PVC pipe
and (3,80) means the three foot extension with schedule 80 PVC pipe.
There are also specifications designated by the manufacturers of the PVC pipe and Ryobi
Drill, listed in the tables below.
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Table 5. Drill Specifications
Drill
Motor 18 V DC
No Load Speed 0-440/0-1600/min (RPM)
Clutch 24 Positions
Torque 340 in.lb. or 38.4 Nm
18-Volt ONE+ Lithium-Ion Battery 1.3 hours of use
Weight 7.2 lb
Depth 7.1 in.
Height 9.8 in.
Width 11 in.
Table 6. Drill Bit Extension
Length 36”
Shaft Diameter 3/16”
Material Carbon Steel
Flexible Yes
Knowing the material of the drill and the drill bit, the life of the tool can be determined
by the use of fatigue theory. Mainly the Maximum Shear Stress Theory. This theory states that
the factor of safety is,
n=S y
2 τ max(1)
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Where n is the factor of safety, Sy is the yield strength in either tension or compression, and τ max
is the maximum shear stress applied to the system. For this particular case, however, τ max is
going to be the shear below,
τ=TrJ T
(2)
Where τ is the shear stress, T is the torque applied due to the reaction force from the tree, r is the
radius, and JT is the torsion constant of a cylinder.
Table 7. PVC Pipe Specs
Schedule 40
Nominal Size 3/8”
Outer Diameter 0.675”
Inner Diameter 0.473”
Min. Wall 0.091”
Nom. Wt/Ft 0.115
Max W.P. PSI 620 PSI
Schedule 80
Nominal Size 3/8”
Outer Diameter 0.675”
Inner Diameter 0.403”
Min. Wall 0.126”
Nom. Wt/Ft 0.146
Max W.P. PSI 920
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Design Results
The results from δmax are 0.554 inches, 0.482 inches, and 0.0028 inches for schedule 40,
schedule 80, and the drill, respectively. This shows that the deflection of the pipe is greater than
the deflection of the drill. By having this result, the drill will support the pipe to an extent.
In Figure 18, schedule 40 (the material that was selected for the prototype due to its light
weight) PVC pipe has a 25 pound load attached to the end of it. The deflection calculated by the
simulation was found to be approximately 0.404 inches which is significantly less than it was
previously calculated. In Figure 19, schedule 80 PVC pipe was tested in order to show its
capabilities in case of schedule 40 failing. Its deflection was found to be approximately 0.321
inches which, similar to the schedule 40, is significantly lower than estimated.
Considering the drill as a support, the pipe won’t deflect nearly anywhere near what was
stated because the drill will act like a support along the entire length of the pipe. Therefore, the
deflection in the pipe is negligible. This means, however, that the drill is rubbing up against the
pipe. The only section that should be rubbing up against the pipe should be the extension rod.
The pipes deterioration by heat or wear should be negligible.
Using carbon steel’s tensile yield strength of 60,200 psi, a radius of 0.09375 inches, and a
torsional constant of 1.213 E-4 inches4, the safety factor can be derived if the counter torque is
known.
The factor of safety is dependent on the amount of torque that counters the torque
provided to the drill. Since this ‘counter’ torque was not provided in the classes and unavailable
to find as a resource, a look at the Janka Hardness scale, figure18, will determine whether or not
the torque against is reasonable. Each line in figure 18 represents 500 pounds force required to
indent a steel ball half its diameter into the wood. With this scale, it can be assumed that pine
trees have a relatively low hardness because the Janka Hardness Scale goes to 5000 and most
pines land within 1250.
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Figure 18: ANSYS Mechanical APDL Analysis Schedule 40
22
Figure 19: ANSYS Mechanical APDL Analysis Schedule 80
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Assuming the counter torque is a direct correlation with respect to the trees hardness, the
torque placed through the drill, and the speed of the drill, a defined torque can be backed out. For
all intents and purposes, it will be assumed that the counter torque will be a ratio of 1:100 with
its hardness. This means the effective counter torque is one-hundredth of the tree’s hardness,
ergo the counter torque is averaged to be 12.5. Since there is genetic manipulation at the
WSDNR tree farm, this number will vary depending on the pine and its original location.
Assuming only positive hardness increase, the new hardness will be set to 1500 giving a new
counter torque of 15. Table 7 shows that 15 in. lb. of counter torque is optimal for a safety factor
of 2.4.
Table 7. Factor of Safety
T (Torque due to drilling) n (factor of safety)
1 in. lb. 19.5
5 in. lb. 6.5
10 in. lb. 3.5
15 in. lb. 2.4
20 in. lb. 1.85
25 in. lb. 1.5
30 in. lb. 1.26
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Figure 18. Janka Hardness Scale [4]
Prototype Considerations
Due to the lack of equations and supporting data, the counter torque due to the drilling of
the tree, a proper factor of safety cannot be truly determined. This lack of knowledge will force
testing of the drill bit extension using safety measures in order to prevent injury if failure occurs.
If failure occurs, further research will be done to ensure that an appropriate drill bit extension is
used and change the design if required to use the new drill bit extension.
The potential rubbing of the drill bit extension and the PVC piping, could prove to be a
hindrance for the design. If schedule 40 is used rather than schedule 80 piping, the deflection is
greater causing a greater chance for the drill bit extension to rub against the
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The major proponent for our considerations is the cost. As seen in Table 1 through 4, the
cost varies albeit not significantly but they differ. Those tables show the cost per unit, WSDNR
has six units. That difference between (2,40) and (3,80) can be $64.08, for all 6 units, when the
final design is achieved and produced. This is something to think about since the PVC pipe is
cheap and easy to manufacture.
If the prototype has a major flaw, when it is produced, there should be time to modify it
before WSDNR does the annual tree injections. If the combined design fails consistently and
there is no solution before WSDNR does their annual injection, the previous iterations of the
design can be implemented in place of the combined device.
Once a design is fully actualized and meets the requirements given by WSDNR, detailed
production-grade CAD drawings will be provided to WSDNR, showing detailed and step by step
construction steps. Allowing more devices to be made easily in the future.
A fully operational model of our current design should be up and running by February.
From there, wear from the rubbing between the drill bit extension and the piping will be
determined negligible or not. As well as if the bending from pressing on the injector will cause
significant trouble.
Prototype Fabrication and Assembly
The device was made by cutting Schedule 40 PVC to 18”, 1’, 4¼”, and two 6” segments,
drilling a ¼” hole in a flat cap and a 7/32” hole in another. Two small pilot holes are drilled for
the screws to screw into on the ¼” hole cap. They are placed roughly halfway between the wall
and the outer edge of the center hole. A ½” hole has to be drilled at the base of the 22˚ wye for
the silicone tube to pass through from the bottle to the injector.
The 4¼” piece becomes the injector mount. Measured from one end, a ¾” hole should be drilled
1¾” from the end. On the opposite side of the tube a 1” hole is drilled measuring 3 ½” from the
edge to the back of the hole. Then using a small saw cut the large hole straight to the edge. Place
the injector piece into boiling water and using leather gloves and tongs, pull it out and wrap it
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over the injector holding down until cool. The small hole is to pass the notch on the injector, and
the larger hole acts as the backstop for the injector.
Roadblocks and Updates:
A few issues showed up during testing. The first was that the extension could easily be
pulled out the back leaving the drill bit inside the pipe and not usable. We fixed this onsite by
adding a temporary drill stop made of tape, with the intent of buying a set screw drill stop to use
as a permanent solution. Using the drill stop doesn’t cause any assembly issues. The whole
device can still be deconstructed and reconstructed without removing it.
Rocky also expressed concern about the injector mount. He would like to be able to see
the indicator showing how much fluid was being pumped in each press. As well as being able to
adjust it if need be. I believe this can be a simple fix. A small hole can be drilled above the
indicator to allow it to be seen. But the adjustments may be hard to expose. Our idea is to place a
small cut out on either side of the front of the mount. This should allow the adjustment without
harming the retention of the mount. We also zip tied it in place to allow for extra security. We
could use Velcro straps in the future to keep from having to cut and replace the zip ties.
The screws we placed in the cap to prevent the drill from walking where not functioning
well in our first tests. They were two wide set and the drill bit was too far forward so they didn’t
engage the tree at all. We tried re-drilling the pilot holes for the screws at a better angle but the
head of the screw would tilt when pressed against the cap. But they make flat caps for PVC
instead of just rounded caps. Rocky had one on hand so we re-dilled the drill hole and the pilot
holes so the screws sit parallel with the drill. We also recessed the drill bit a little behind the
screws to allow them to engage the tree first.
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Our last major issue was the drill bit wearing away at the cap. The sides of the drill bit
acted as a mill bit and created an oval hole nearly twice as large as it started. This made the drill
bit wobble and often just scraped the tree. We haven’t implemented our fix for this yet. But we
will use a design rocky has used previously to solve a different issue. He uses ¼ inch aluminum
tubing placed over the drill bit and hammered in place to hold itself down. This was to keep only
1 inch of drill exposed as to not drill to deep. But now this sleeve will act as a bearing surface to
the cap to prevent the drill bit from eating the cap away.
Physical Prototype Testing
0 2 4 6 8 1 0 1 20
5
10
15
20
25
30
Time Trial (10-minute Trial)Two Prototype
Time (Minutes)
Tree
s Do
ne
Figure 17: 10-min Time Trial
The above figures are data gathered during the field test conducted on 2/24/2016. It was
conducted with the current method of WSDNR where one drills and another fills and the
prototype, which requires only an individual rather than a pair.
Figure 17 shows explicitly the efficiency of the prototype compared to the current
method. The current method is capable of doing 24 trees in a 10-minute span. The prototype is
capable of 20 trees in 10 minutes. When thinking about the current method, the fact that it
requires two people already halves its efficiency. In essence, the current method with an
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individual could approximately drill and fill 12 trees compared to the prototype’s 20. This means
the prototype in itself is 66.6% more efficient in drilling and filling than the current method.
Within the field test other factors of the prototype were assessed such as the comfort,
fatigue on person, fatigue on machine, and overall performance. By having inexperienced users
of the machines, actual conditions were replicated. This inexperience is due to the outside help
WSDNR requires in order to perform the drilling and filling operation.
Those who worked with the previous method of being close to the ground with a hand
drill and an injector complained of sore knees, back stiffness, overall exhausting. Those who
worked with the prototype complained only of exhaustion of their left arm which is their support
arm for the prototype. When testing the prototype with bottle meant for the Gibberellic Acid was
filled with water and hoisted onto the grip. By moving the bottle onto the waist or onto the back,
weight can be removed from the prototype, thus lessening the strain on the support arm.
If the complaints from both groups are taken into account, it can be extrapolated that the
current way of drilling and filling will exhaust the operators more so than the operators of the
prototype. This means that the operators of the prototype will be able to persist longer and
maintain a stronger work pace throughout the day compared to those of the current method.
The drilling and filling operations of the prototype worked well, however the drill wore
through the cap and did not center well. An onsite fixed the latter problem and another was
proposed by Rocky to eliminate the former.
Overall, the testing was a success, knowledge of major issues of the prototype were
acquired, and minor issues were resolved on site.
Conclusion
From the design methodology, it is apparent that as certain criteria was given our design
changed. It did not only change to meet the parameters, but in its complexity. As new parameters
where introduced, the design got more complicated, only to be refined to an even simpler
construction.
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The only non-negligible analysis is the deflection of the drill bit extension. Since its
deflection is little the PVC piping will rub up against the drill bit extension. This rubbing will be
determined as a minor or major problem when encountered. One solution is to reinforce the PVC
pipe so it doesn’t bend, and another is to add a bearing surface between the extension and pipe to
eliminate rubbing.
With the unknown counter torque provided by the tree, a full understanding of whether or
not failure will occur did not happen. Instead, the assumptions made should predict what should
happen. The assumptions, however, are not based off of any equations or supportable data.
Therefore, the only way to determine whether or not the drill bit extension will fail is by testing
only.
The entire length of the main piping should not exceed three feet. Its piping will be three-
quarter inch PVC pipe, depending on the testing, schedule 40 or schedule 80. The wye joint that
will split from the main section will be at 22.5º angle. Piping from the wye will expand out to
one inch in diameter in order to press fit the injector’s back end. A T joint will be placed around
six inches away from the open end, on operator’s side to act as a handle and support. The piping
from the T joint will be three or four inches of length, depending on the testing of ergonomics.
Goals from WSDNR were: made of simple parts with minimal or no machining required,
extend the reach of the tools, and have the two tools combined. Clearly, the design uses only
simple parts as it is almost solely constructed from PVC. PVC piping is widely available at any
hardware store, large or small. Its assembly is also easy, it can either threaded together or fit and
glued. The drill extension requires no machining on the WSDNR end as it will be custom
ordered to the exact length needed. The specialty PVC wye is also widely available from online
vendors.
The design requires little machining. Cutting the pipe to length is one of the most
pertinent machining requirements. It requires a hole to be drilled in the two end caps of the main
piping for the drill to rest in. It also requires sawing off the top half of the wye joint so it can be
glued on the bottom of the main piping. The connector for the injector needs to be heated to a
certain temperature so that it can press fit onto the injector itself. Those instructions are the only
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machining requirements for the design. Construction instructions will be included with the final
design to allow the WSDNR to make more of these in the future.
All the goals set forth by WSDNR were met. This does not mean they were done to the
best of their ability. One way to improve the design is that the wye joint can be incorporated into
main piping; however, this requires more cutting of pipe. Other than that, there are no
foreseeable improvements on the design at this time. There is a possibility that improvements
may be made during the prototyping and testing phase.
Table 8. Total Specifications for Three Foot
Three Foot Drill
Total Length ~ 47 inches
Total Height ~ 10 inches
Total Width ~ 7.1 inches
Total Weight ~ 7.66 Pounds
Energy Input Required 18 Volts DC
Estimated Life per Charge 1.3 Hours
Nominal Counter Torque in. lb.
Total Cost $48.74
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References
[1] L. K. Miller and J. DeBell, "Current Seed Orchard Techniques and Innovations," USDA
Forest Service Proceedings, 2013.
[2] R. Oster, Interviewee, [Interview].
[3] R. G. Budynas and J. K. Nisbett, Shigley's Mechanical Engineering Design, New York:
McGraw-Hill Education, 2015.
[4] "wikipedia," 30 November 2015. [Online]. Available:
https://en.wikipedia.org/wiki/Janka_hardness_test. [Accessed 1 December 2015].
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