Been given a request by a friend who is doing an engineering course in
college. Currently his project entails strength of materials and he has
been asked to aquire 4 boxes made of 4 different materials, his choice.
They are to be tested to destruction. How I don't know, neither does my
friend.
Well he's asked me to make a box out of wood and I've been told to make
it strong. Box has to be hollow for equipment. 6 inches inside space,
exterior no more than 12 inches. No foreign material, i.e screws, nails
etc etc but epoxies and glues are. I was thinking of getting something
like a roof joist, 6inches thick/ 12inches wide cutting two squares out
of it, carving out the centre and gluing the two halves together with
long wooden dowels or biscuits.
Well what do you think? Is there another way? What would you do
different?
TR
You may want to consider a laminate sytem.
The box will only be as strong as its joints.
By building up smaller pieces laminated on top of each other in different
directions you will have more overall strength.
"TrailRat" <[email protected]> wrote in message
news:[email protected]...
> Been given a request by a friend who is doing an engineering course in
> college. Currently his project entails strength of materials and he has
> been asked to aquire 4 boxes made of 4 different materials, his choice.
> They are to be tested to destruction. How I don't know, neither does my
> friend.
> Well he's asked me to make a box out of wood and I've been told to make
> it strong. Box has to be hollow for equipment. 6 inches inside space,
> exterior no more than 12 inches. No foreign material, i.e screws, nails
> etc etc but epoxies and glues are. I was thinking of getting something
> like a roof joist, 6inches thick/ 12inches wide cutting two squares out
> of it, carving out the centre and gluing the two halves together with
> long wooden dowels or biscuits.
>
> Well what do you think? Is there another way? What would you do
> different?
>
> TR
>
Tom H wrote:
> You may want to consider a laminate sytem.
> The box will only be as strong as its joints.
> By building up smaller pieces laminated on top of each other in different
> directions you will have more overall strength.
You mean sealing in the sensor equipment as I go? Sounds like a lot
less hardwork too.
There are probably more design parameters than you have been given. I
would expect weight to factor into the scoring in a negative way
(weight counts against you). When I was in engineering school, lo
these many years ago, we had a contest to design a carrier that would
deliver a grade A medium hen's egg safely to the ground from a free
fall of 30 feet. Weight of the container was multiplied by time spent
falling with the lowest score winning (if the egg survived). The heavy
containers and the parachutes didn't score very well.
DonkeyHody
"We should be careful to get out of an experience only the wisdom
that is in it - and stop there; lest we be like the cat that sits down
on a hot stove-lid. She will never sit down on a hot stove-lid
again---and that is well; but also she will never sit down on a cold
one anymore." - Mark Twain
Wood Butcher wrote:
> Much better but don't stop there. Try and find a student that
> has already taken the class and go for anything you can get.
>
> Also, start speculating about the tests.
> 1. Water may be a soaking which would weaken some glues.
> 2. Heat will weaken epoxy glues and most plastics.
> 3. Pressure may be internal pressure(via a water balloon type device)
> to test the ability to contain expansion.
This isn't it. The box is sealed with equipment inside. No holes for an
air line and I can't see a gas canister in the little polystyrene box
of gizmos my friend gave me. Theres a whole range of little sensor,
i've determined one is for measuring heat and another for moisture. I
might be having a stab but the other might be a g-reader.
> 4. The car may be a deadweight compression test or an impact test.
>
Wood Butcher wrote:
<snip>
> Part of an engineering course is to test the students and find
> out which ones are too stupid to ask questions. These ones
> usually flunk out and transfer to liberal arts.
...who then flunk out of the liberal arts when asked to learn a few
languages, or Plato's theory of forms, or what have you...then they
turn to what, Wood Butchering?
Smirking at a good jab,
H
> "Water and pressure" suggests an immersion to some depth (possibly
> bottom of the local pool, possibly something more strenuous with a
> pressure chamber). Heat is just heat; probably an oven, possibly a
> ceramic kiln. As for the car, my guess is "thrown out of".
>
> Is the objective explicitly to build the box that's hardest to destroy?
> Or is that just something everyone's assuming? Given the description
> of "four boxes", I'd be tempted to make one out of corrugated cardboard,
> maybe with saran wrap duct-taped to the outside for waterproofing. :)
>
> (Actually, three-inch-thick slabs of corrugated cardboard laminated
> together would probably be reasonably sturdy, as such things go.)
>
> If he's got the instrumentation and can build it inside the box, that's
> definitely the way to go, whatever you're building.
>
The assumption is toughest to destroy, they ain't been told a lot i've
seen the paper work given to the pupils.
Did as you instructed and found a student who has had the same teacher.
This teacher is smart. The parameters are different. Either the teacher
lied to his students or changes his tests.
Same parameters for the boxes but the conditions don't sound the same.
No water, no car.
Six tests are as follows.
1: Squeeze press 50 ton load, 10 minute - Check for damage/shape change
2: Dropped out a window, 6th floor, time the ascent. Check for
damage/shape change
3: Ball bearing blast (equivalaint to a sandblasting) 5 minutes one
surface. Check for damage/shape change.
4: Intense heat with flame, (blow lamp) One face 5 Minute. Check for
damage/shape change
5: Sledgehammer, narrow 15lb head one hit each face. Check for
damage/shape change
6: 10ft drop onto 1inch steel plate. Check for damage/shape change
Then they had to examine what was left and say how the structure of the
chosen materials had changed.
Wood Butcher wrote:
> Much better but don't stop there. Try and find a student that
> has already taken the class and go for anything you can get.
> >
alexy wrote:
> "TrailRat" <[email protected]> wrote:
>
> >Same parameters for the boxes but the conditions don't sound the same.
> >No water, no car.
> >Six tests are as follows.
> >1: Squeeze press 50 ton load, 10 minute - Check for damage/shape change
> >2: Dropped out a window, 6th floor, time the ascent.
> Wow, they really are different. Nothing in the current one about the
> box needing to be lighter than air! <G,D,&R>
I did that on purpose honestly. The award for spot the typo goes to
Alexy.
I meant descent honestly.
TrailRat wrote:
> Been given a request by a friend who is doing an engineering course in
> college. Currently his project entails strength of materials and he has
> been asked to aquire 4 boxes made of 4 different materials, his choice.
> They are to be tested to destruction.
Then each box will undergo only one test, right?
The variable to be measured is the material. All other factors should
be held constant. Therefore, build four boxes of different materials
but the same dimensions.
> Sounds like fun! I think I'd opt to build from a pair of 12x12x9
> slabs. If the instrumentation allowed, I'd begin by routing out a
> 3"-radius hemisphere from the center of both. Next (6" from the
> outside bottom) I'd rout out a centered 4-1/2"-radius circle. Finally,
> I'd rout radial crenelations with sloped sides (imagine gear teeth).
>
> Both top and bottom are routed the same, except that one is started
> with the grain running side-to-side and one with the grain
> front-to-back - for cross grain strength.
>
> It isn't easy to visualize, so I'll post a sketch to ABPW. It
> shouldn't be much more difficult to lay out and cut than a full-blind
> dovetail joint. :-D
Many thanks got the picture now. Looks interesting to try any way.
TR
All sounds like a great ideas.
Mr Doveys design in white oak. Errm what would you use to glue the the
two halves together with?
Without ruining a good design I was also thinking of a peg system.
Using 1x1 square pegs from corner to corner going through the
crenallations on two sides to hold it together.
Nice idea about the fire retardent paint. Two things, No foreign
materials and no fire, just intense heat.
TR
"TrailRat" <[email protected]> wrote in message
news:[email protected]...
> Been given a request by a friend who is doing an engineering course in
> college. Currently his project entails strength of materials and he has
> been asked to aquire 4 boxes made of 4 different materials, his choice.
> They are to be tested to destruction. How I don't know, neither does my
> friend.
> Well he's asked me to make a box out of wood and I've been told to make
> it strong. Box has to be hollow for equipment. 6 inches inside space,
> exterior no more than 12 inches. No foreign material, i.e screws, nails
> etc etc but epoxies and glues are. I was thinking of getting something
> like a roof joist, 6inches thick/ 12inches wide cutting two squares out
> of it, carving out the centre and gluing the two halves together with
> long wooden dowels or biscuits.
>
> Well what do you think? Is there another way? What would you do
> different?
>
> TR
>
I'd be inclined to use laminated 3/8" white oak with epoxy for glue. Leave a
void that meets the minimum cavity requirements and alternate the grain
direction. White oak is tough to crush...
John
Wood Butcher wrote:
> "TrailRat" <[email protected]> wrote in message
> news:[email protected]...
>>Ok after emailing my mate, I have managed to get three things out of
>>him that he has managed to get out of his teacher. One, there will will
>>be water and pressure involved. Two, intense heat but not fire. Three,
>>a car. And there will be six tests.
>>
>>That is all the teach will give him.
>
> Much better but don't stop there. Try and find a student that
> has already taken the class and go for anything you can get.
>
> Also, start speculating about the tests.
> 1. Water may be a soaking which would weaken some glues.
> 2. Heat will weaken epoxy glues and most plastics.
> 3. Pressure may be internal pressure(via a water balloon type device)
> to test the ability to contain expansion.
> 4. The car may be a deadweight compression test or an impact test.
"Water and pressure" suggests an immersion to some depth (possibly
bottom of the local pool, possibly something more strenuous with a
pressure chamber). Heat is just heat; probably an oven, possibly a
ceramic kiln. As for the car, my guess is "thrown out of".
Is the objective explicitly to build the box that's hardest to destroy?
Or is that just something everyone's assuming? Given the description
of "four boxes", I'd be tempted to make one out of corrugated cardboard,
maybe with saran wrap duct-taped to the outside for waterproofing. :)
(Actually, three-inch-thick slabs of corrugated cardboard laminated
together would probably be reasonably sturdy, as such things go.)
If he's got the instrumentation and can build it inside the box, that's
definitely the way to go, whatever you're building.
- Brooks
--
The "bmoses-nospam" address is valid; no unmunging needed.
TrailRat wrote:
> Did as you instructed and found a student who has had the same teacher.
> This teacher is smart. The parameters are different. Either the teacher
> lied to his students or changes his tests.
I presume he changes his tests. Even if it's only because each year he
thinks of something new and interesting to try, or discovered last year
that one of the tests didn't work out like he'd hoped.
> Same parameters for the boxes but the conditions don't sound the same.
> No water, no car.
> Six tests are as follows.
> 1: Squeeze press 50 ton load, 10 minute - Check for damage/shape change
> 2: Dropped out a window, 6th floor, time the ascent. Check for
> damage/shape change
> 3: Ball bearing blast (equivalaint to a sandblasting) 5 minutes one
> surface. Check for damage/shape change.
> 4: Intense heat with flame, (blow lamp) One face 5 Minute. Check for
> damage/shape change
> 5: Sledgehammer, narrow 15lb head one hit each face. Check for
> damage/shape change
> 6: 10ft drop onto 1inch steel plate. Check for damage/shape change
>
> Then they had to examine what was left and say how the structure of the
> chosen materials had changed.
Ah! I was right about questioning whether the real objective was to
have the strongest box! (Well, sorta.) Sounds like to me that the
_real_ objective of this experiment is to produce interesting results to
describe, and for the students to get some experience in how different
materials respond to various damaging things.
Just build something tough. Have fun. :)
And, for extra fun, I'd suggest giving the engineering student a list of
the suggestions and possibilities, and have them make all the final
decisions about how to build it.
- Brooks
--
The "bmoses-nospam" address is valid; no unmunging needed.
Morris Dovey wrote:
> Morris Dovey (in [email protected]) said:
> | TrailRat (in [email protected])
> | said:
> |
> || 4: Intense heat with flame, (blow lamp) One face 5 Minute. Check
> || for damage/shape change
>
> Hmm. I didn't handle this part very well. You might want to drill a
> tiny hole from each corner to the internal cavity and plug it with a
> small amount of wax to relieve pressure that builds up during this
> test...
Huh? You handled it perfectly fine by ignoring it, I'd say.
Let's assume, for the sake of absurd argument, that this heats up the
interior cavity to 300C. That's twice atmospheric temperature, so by
the ideal gas law it's going to be at twice atmospheric pressure. A six
inch square face is 36 inches square, times 15 psi, is about 500 pounds.
Yeah, that's a fair bit, but the box should certainly handle. Besides
which, if it does yield a little, it will thereby immediately develop a
leak and relieve the pressure, preventing failure.
This is completely aside from the fact that heating the interior up to
300C means that the sensors inside are toast and the box has failed
anyway regardless of whether it remains structurally sound.
And it's also completely aside from the fact that I would be very
surprised if the back side of three inches of oak would even get _warm_
after only five minutes. There's a reason the Chinese use the stuff for
heat shields on some of their space capsules....
- Brooks
--
The "bmoses-nospam" address is valid; no unmunging needed.
TrailRat <[email protected]> wrote:
> Been given a request by a friend who is doing an engineering course in
> college. Currently his project entails strength of materials and he has
> been asked to aquire 4 boxes made of 4 different materials, his choice.
> They are to be tested to destruction. How I don't know, neither does my
> friend.
> Well he's asked me to make a box out of wood and I've been told to make
> it strong. Box has to be hollow for equipment. 6 inches inside space,
> exterior no more than 12 inches. No foreign material, i.e screws, nails
> etc etc but epoxies and glues are. I was thinking of getting something
> like a roof joist, 6inches thick/ 12inches wide cutting two squares out
> of it, carving out the centre and gluing the two halves together with
> long wooden dowels or biscuits.
> Well what do you think? Is there another way? What would you do
> different?
I would start with a 4x8 sheet of 3/8" plywood. I'd then cut it into 32
squares of equal size (slightly less than 1' squares). You won't use one of
the squares.
I would take a router or scroll saw and cut 8" circles out of the center of
21 of the squares.
Using resorcinol glue, create a laminate of 5 full size squares and 21
hollow squares. Create a second laminate of 5 full size squares. You now
have a box with an 8" diameter x 7 7/8" tall cylinder in it. Put the
equipment in the cylinder and glue the lid on the box. You've now got a
slightly less than 1' cube of laminated wood. To remove the equipment cut
the top 5 layers off the box.
IMHO, that design should be waterproof, insulated, and able to support the
weight of a car.
Morris Dovey (in [email protected]) said:
| I think I'd opt to build from a pair of 12x12x9 slabs.
Better make that 12x12x7.5 slabs.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto
TrailRat (in [email protected])
said:
| Did as you instructed and found a student who has had the same
| teacher. This teacher is smart. The parameters are different.
| Either the teacher lied to his students or changes his tests.
|
| Same parameters for the boxes but the conditions don't sound the
| same. No water, no car.
| Six tests are as follows.
| 1: Squeeze press 50 ton load, 10 minute - Check for damage/shape
| change 2: Dropped out a window, 6th floor, time the ascent. Check
| for damage/shape change
| 3: Ball bearing blast (equivalaint to a sandblasting) 5 minutes one
| surface. Check for damage/shape change.
| 4: Intense heat with flame, (blow lamp) One face 5 Minute. Check for
| damage/shape change
| 5: Sledgehammer, narrow 15lb head one hit each face. Check for
| damage/shape change
| 6: 10ft drop onto 1inch steel plate. Check for damage/shape change
|
| Then they had to examine what was left and say how the structure of
| the chosen materials had changed.
Sounds like fun! I think I'd opt to build from a pair of 12x12x9
slabs. If the instrumentation allowed, I'd begin by routing out a
3"-radius hemisphere from the center of both. Next (6" from the
outside bottom) I'd rout out a centered 4-1/2"-radius circle. Finally,
I'd rout radial crenelations with sloped sides (imagine gear teeth).
Both top and bottom are routed the same, except that one is started
with the grain running side-to-side and one with the grain
front-to-back - for cross grain strength.
It isn't easy to visualize, so I'll post a sketch to ABPW. It
shouldn't be much more difficult to lay out and cut than a full-blind
dovetail joint. :-D
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto
How about MASSIVE??
Massive blocks of wood - selections from a post and beam structure.
Massive mortise and tenon with massive dowel pins - as in post and beam.
Massive dove tail - may not be a strong as above but will not pull apart =
easily.
IMO the biscuits will be the weakest link if going for strength.
--=20
PDQ
--
"TrailRat" <[email protected]> wrote in message =
news:[email protected]...
| Been given a request by a friend who is doing an engineering course in
| college. Currently his project entails strength of materials and he =
has
| been asked to aquire 4 boxes made of 4 different materials, his =
choice.
| They are to be tested to destruction. How I don't know, neither does =
my
| friend.
| Well he's asked me to make a box out of wood and I've been told to =
make
| it strong. Box has to be hollow for equipment. 6 inches inside space,
| exterior no more than 12 inches. No foreign material, i.e screws, =
nails
| etc etc but epoxies and glues are. I was thinking of getting something
| like a roof joist, 6inches thick/ 12inches wide cutting two squares =
out
| of it, carving out the centre and gluing the two halves together with
| long wooden dowels or biscuits.
|=20
| Well what do you think? Is there another way? What would you do
| different?=20
|=20
| TR
|
Much better but don't stop there. Try and find a student that
has already taken the class and go for anything you can get.
Also, start speculating about the tests.
1. Water may be a soaking which would weaken some glues.
2. Heat will weaken epoxy glues and most plastics.
3. Pressure may be internal pressure(via a water balloon type device)
to test the ability to contain expansion.
4. The car may be a deadweight compression test or an impact test.
Art
"TrailRat" <[email protected]> wrote in message
news:[email protected]...
> Ok after emailing my mate, I have managed to get three things out of
> him that he has managed to get out of his teacher. One, there will will
> be water and pressure involved. Two, intense heat but not fire. Three,
> a car. And there will be six tests.
>
> That is all the teach will give him.
>
> TR
>
Then find out how the box will be tested. All engineering
projects(especially student ones) will have criteria to be
met, including how testing will be done. Lacking this info
it is nearly impossible to do a good design.
Part of an engineering course is to test the students and find
out which ones are too stupid to ask questions. These ones
usually flunk out and transfer to liberal arts.
Art
"TrailRat" <[email protected]> wrote in message
news:[email protected]...
> Been given a request by a friend who is doing an engineering course in
> college. Currently his project entails strength of materials and he has
> been asked to aquire 4 boxes made of 4 different materials, his choice.
> They are to be tested to destruction. How I don't know, neither does my
> friend.
> Well he's asked me to make a box out of wood and I've been told to make
> it strong. Box has to be hollow for equipment. 6 inches inside space,
> exterior no more than 12 inches. No foreign material, i.e screws, nails
> etc etc but epoxies and glues are. I was thinking of getting something
> like a roof joist, 6inches thick/ 12inches wide cutting two squares out
> of it, carving out the centre and gluing the two halves together with
> long wooden dowels or biscuits.
>
> Well what do you think? Is there another way? What would you do
> different?
>
> TR
>
Morris Dovey (in [email protected]) said:
| TrailRat (in [email protected])
| said:
|
|| 4: Intense heat with flame, (blow lamp) One face 5 Minute. Check
|| for damage/shape change
Hmm. I didn't handle this part very well. You might want to drill a
tiny hole from each corner to the internal cavity and plug it with a
small amount of wax to relieve pressure that builds up during this
test...
Drilling from the corner should help prevent high temperature gasses
from being blown directly into the cavity by the torch. The meltable
wax seal /may/ help to prevent or retard flooding if there is a
subsequent water test.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto
W Canaday (in [email protected]) said:
| We'll let the test, itself, provide the sealing, eh? ;-)
I like the way you think. :-)
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto
On Tue, 24 Jan 2006 10:24:14 -0600, Morris Dovey wrote:
> Morris Dovey (in [email protected]) said:
>
> | TrailRat (in [email protected]) |
> said:
> |
> || 4: Intense heat with flame, (blow lamp) One face 5 Minute. Check for
> || damage/shape change
>
> Hmm. I didn't handle this part very well. You might want to drill a tiny
> hole from each corner to the internal cavity and plug it with a small
> amount of wax to relieve pressure that builds up during this test...
>
> Drilling from the corner should help prevent high temperature gasses
> from being blown directly into the cavity by the torch. The meltable wax
> seal /may/ help to prevent or retard flooding if there is a subsequent
> water test.
Nope. As a proto-type machinist / die-maker, I recognize the reflexive
desire for symmetry .. but symmetry (that doesn't look like it's spelled
right) is no advantage here and 'pretty' is not a design constraint /
tested value.
Only drill from one corner. That will restrict the ability of liquid to
flow into the cavity. Air is only about 1/16 as dense as water: make the
hole tiny ... mebbe a #60 or so. Or. better yet, route / carve a WAAAAY
shallow groove that curves 180 deg or more several times in a switchback
pattern. The air under pressure will escape just fine (the test is for
just a few minutes and all the designs so far provide for an insulating
mass.) Incoming liquid will pressurize the compartment, slowing the flow
of the liquid and allowing the fibers time to swell.
In fact, come to think of it, don't take the groove all the way to the
cavity. Stop just a few thousandths short of it. The gasses will penetrate
the cells but the liquid will not. If you overshoot the mark, glue a piece
of craft paper over the oopsie. Same net result.
Paint the thing with fire-retardent paint such as used in restaurants. If
the fire test comes first the swelling of the paint will give us bonus
protection from the liquid. It might also shield the adhesives from heat
failure.
We'll let the test, itself, provide the sealing, eh? ;-)
Bill
I had to do this too. The winning design (not mine) was a rocket
shaped aluminum tube with holes in the body. Rings of larger
holes near the tail progressed to rings of ever smaller holes near
the nose. The tube was filled with shaving cream and the egg
inserted near the tail. When it hit the ground the obvious happened
and the egg survived perfectly. The real stroke of genius was the
realization that there was no specification (or limit) on the initial
velocity. This allowed launching the tube via bungee cord launch
mechanism and reduced the free fall time to less than what gravity
alone would produce.
Art
"DonkeyHody" <[email protected]> wrote in message
news:[email protected]...
> There are probably more design parameters than you have been given. I
> would expect weight to factor into the scoring in a negative way
> (weight counts against you). When I was in engineering school, lo
> these many years ago, we had a contest to design a carrier that would
> deliver a grade A medium hen's egg safely to the ground from a free
> fall of 30 feet. Weight of the container was multiplied by time spent
> falling with the lowest score winning (if the egg survived). The heavy
> containers and the parachutes didn't score very well.
>
> DonkeyHody
"TrailRat" <[email protected]> wrote:
>Same parameters for the boxes but the conditions don't sound the same.
>No water, no car.
>Six tests are as follows.
>1: Squeeze press 50 ton load, 10 minute - Check for damage/shape change
>2: Dropped out a window, 6th floor, time the ascent.
Wow, they really are different. Nothing in the current one about the
box needing to be lighter than air! <G,D,&R>
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.
"TrailRat" <[email protected]> writes:
> alexy wrote:
>> "TrailRat" <[email protected]> wrote:
[...]
>> >2: Dropped out a window, 6th floor, time the ascent.
>> Wow, they really are different. Nothing in the current one about the
>> box needing to be lighter than air! <G,D,&R>
>
>
> I did that on purpose honestly. The award for spot the typo goes to
> Alexy.
>
> I meant descent honestly.
You could also try to time the ascent during the rebound, if the box
(and ground) should proove to be sufficently elastic.
>
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto:[email protected] Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23