Bizarre request - how would you do it?

[TrailRat]

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

[PDQ]

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" wrote in message = news: [e-mail]... | 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 |

[Tom H]

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]

You mean sealing in the sensor equipment as I go? Sounds like a lot less hardwork too.

[Wood Butcher]

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

[John Grossbohlin]

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

[DonkeyHody]

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

[TrailRat]

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

[Wood Butcher]

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

[Wood Butcher]

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]

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.

[hylourgos]

...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

[Brooks Moses]

"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

[TrailRat]

The assumption is toughest to destroy, they ain't been told a lot i've seen the paper work given to the pupils.

[TrailRat]

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:

[alexy]

Wow, they really are different. Nothing in the current one about the box needing to be lighter than air!

[TrailRat]

I did that on purpose honestly. The award for spot the typo goes to Alexy.

I meant descent honestly.

[Juergen Hannappel]

[...]

You could also try to time the ascent during the rebound, if the box (and ground) should proove to be sufficently elastic.

>

[Morris Dovey]

| 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

[Morris Dovey]

| 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