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I'm posting this from the roof of a building because I can't figure out a safe way down. I've scoured the roof for anything useful, and all I found was a coping saw. I also found a 100 foot ladder, which is firmly connected to the roof (but its length is just hanging from the secured top rung). The building is unfortunately 200 feet tall. How can I use the coping saw to double the length of the ladder?

The wind is really strong, so I will not consider climbing down any arrangement which could possibly be blown apart - that is, if it is possible to separate pieces of the arrangement such that they would not longer function as a 200 foot ladder, I will not climb it. The ladder is unbendable, cannot be cut by anything other than the saw, and cannot be mended once cut. It starts out as one solid piece of material. The saw cannot cut anything other than the ladder and there are no other materials around. I am capable of making precise cuts, if necessary.

In short, how do I use one of these:
$\hskip1.5in$enter image description here
to double the length of one of these:
$\hskip1.5in$enter image description here

(It is necessary, for the intended solution, that the coping saw blade can be released on one side, threaded through an existing cut, and reattached; a keyhole saw would probably also work, but it would be difficult to make the necessary cut. The puzzle is not so much in how one physically makes the cut, but rather what cut is made. I have managed to double the length of the pictured ladder with the pictured tool.)

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    $\begingroup$ For the 'normal' people out there: 100 ft = 30.48m....That's a pretty large wooden ladder. $\endgroup$ – Mark N Jul 15 '15 at 18:42
  • $\begingroup$ @MarkN Indeed... having been on a 40 foot Alumin(i)um ladder I don't think I would trust a wooden ladder that long... $\endgroup$ – Michael Jul 15 '15 at 22:00
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    $\begingroup$ @Michael Aluminum ladders work-harden and must eventually be discarded. Kept in good repair, wooden ladders last forever. The longest ladder in the world is (41.16 m, 135 ft) wooden. Also, the San Fransisco FD takes great pride in theirs. That being said, there is no way to "safely" modify a ladder with a saw except to make it shorter. $\endgroup$ – Mazura Jul 15 '15 at 22:20
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    $\begingroup$ Make sure you report the building for not having any fire escapes after you get down. $\endgroup$ – jpmc26 Jul 16 '15 at 0:19
  • $\begingroup$ I'm often hanging out on Lifehacks SE and thought of this as a real problem first!! Solution as you are on the roof and on the Internet: Send a message to someone to come get you instead of using the saw! :-) $\endgroup$ – holroy Jul 16 '15 at 19:10
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Lay the ladder flat and cut it in half through a plane parallel to the ground, except for...

...the bottom rung, which you need to cut rotating your blade through a multiple of 360 degrees from one end of the rung to the other.

This allows you to separate the two parts by...

...rotating them around the axis of the bottom rung. They remain intertwined, but can rotate in a screw-like manner with each other.

I'm still figuring out how to draw this one.

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    $\begingroup$ This is still not the intended solution (which does not work in 2D and doesn't use the saw as part of end product), but I am immensely impressed with the answer nonetheless and it satisfies all the criteria in my question. (I hope you'll keep the answer around, regardless of whether you think of other answers) $\endgroup$ – Milo Brandt Jul 15 '15 at 3:19
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    $\begingroup$ I'm not sure how to draw it either. But I made that cut, and took pictures of the results. (I think my coping saw's blade will never be the same, though - it did not like twisting on that axis! It took about an hour and a half to do) $\endgroup$ – Milo Brandt Jul 15 '15 at 3:43
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    $\begingroup$ @2012rcampion I think it is a shame that you deleted your original solution. Could you add is as a separate answer? Because it fulfilled all requirements and solved the puzzle in an imaginative way, I think future readers will profit from multiple solutions! $\endgroup$ – Falco Jul 15 '15 at 9:02
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    $\begingroup$ @Meelo Looks like your saw blade couldn't ... cope ... with the strain. $\endgroup$ – talrnu Jul 15 '15 at 13:08
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    $\begingroup$ @talrnu Or maybe that saw blade just didn't make the cut! $\endgroup$ – Mark N Jul 15 '15 at 18:34
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While the answers by 2012rcampion and Chris H are quite creative, I find their solutions to be structurally deficient. In 2012rcampion's solution, the weight of the second half of the ladder rests entirely on the last rung, thereby making it prone to failure under the weight of a human. Meanwhile, in Chris H's solution, the half rungs seem incapable of being able to bear the weight of a human. I have come up with a third solution that is capable of bearing a greater amount of load.

Beginning in the same manner as 2012rcampion, lay the ladder on the ground and split the ladder into two identical half-width ladders by cutting along a plane parallel to the ground. Following that, carve out sliding dovetail joints in the top end of the rails on one half ladder and in the bottom end of the rails on the other half of the ladder. The image below illustrates the cross section of this joint.

enter image description here

This is structurally stronger as the load borne by the second ladder is distributed along the rails. While one may argue that this is weak as well, depending on the thinner width of the rails and rungs, but this would nonetheless reduce the chances of failure by a great extent.

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    $\begingroup$ If we are playing for realism, I would just pull out my phone and call for help; 200 feet is too far for any normal wooden ladder. ;-) $\endgroup$ – Mark N Jul 15 '15 at 18:37
  • $\begingroup$ Rather than slitting the ladder into two equal-thickness parts, it would probably better to slice diagonally so that one part was 3/4 of normal thickness and the other was 1/4 of normal thickness, and assemble them so the 3/4-thickness parts were on the same side. Then make certain that one's weight is concentrated on the thicker side of the ladder. $\endgroup$ – supercat Jul 15 '15 at 22:19
  • $\begingroup$ One could also repeat this pattern as long as they wished, shortening the ladder but strengthening the joint. (Given that we're talking about making a dovetail parallel to the grain of the wood, I would think this would be highly advisable - in the real world, such joints like to fall apart) $\endgroup$ – Milo Brandt Jul 16 '15 at 1:07
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    $\begingroup$ I like this answer a lot, considering the original question includes the word safely. As a structural engineer, I consider all the answers to have significantly weakened the ladder, but this answer by the least! $\endgroup$ – AndyT Jul 16 '15 at 9:44
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1. Cut off all of the rungs, save two. 2. Connect the two side rails with a dovetail joint, forming one 200' rail. 3. Use two rungs to make a lap joint for more strength.

One 200' rail:

-------------------|dovetail|---------------------

And lots of rungs left over:

|||||||||||||||

Any force on the dovetail joint should pull it tighter, and the rungs should keep it from splitting.

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    $\begingroup$ So you turned the ladder into a pole? $\endgroup$ – Luminous Jul 15 '15 at 17:30
  • $\begingroup$ @Luminous: You've not seen a single-post ladder? $\endgroup$ – Joshua Jul 15 '15 at 18:28
  • $\begingroup$ @Joshua Ohh!!!! Okay! I was picturing a pole and that was it. He didn't say what he would do with the left over rungs. $\endgroup$ – Luminous Jul 15 '15 at 19:02
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Original ladder:

----------
|  |  |  |
|  |  |  |
----------

With an assumption:

... Cut all the rungs except the bottom one. Rotate one leg 180° about the uncut rung. Assumption: the rungs are not so tightly fitted that they won't rotate using the leverage of a ladder leg.

Similarly, with perhaps a less strict assumption:

... Cut all rungs except the bottom one. Use the handle of the coping saw to drive the bottom rung out of one leg, rotate this leg and half-rungs 180° and reassemble.

Either way you end up with:

 ----------
 |  |  |  |
          |  |  |  |
          ----------

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    $\begingroup$ I know this isn't the intended solution: mine would work with a tenon saw. $\endgroup$ – Chris H Jul 15 '15 at 12:14
  • $\begingroup$ I thought the same :) $\endgroup$ – Alessandro Jul 15 '15 at 13:29
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    $\begingroup$ So you can't climb down the ladder until you find an open window? Did you bring a parachute suitable for base jumping? $\endgroup$ – Gandolf989 Jul 15 '15 at 15:08
  • $\begingroup$ @Gandolf989, no, you end up with a double length ladder by either method. Whether you'd trust your weight to the rungs is another matter. I've added a sketch, couldn't figure out how to spoiler-mask the ASCII-art but I thought as it's not the answer it wouldn't matter. Also between first looking at the Q and answering the wording was tweaked. $\endgroup$ – Chris H Jul 15 '15 at 15:12
  • $\begingroup$ @ChrisH Dunno how others do it, but I did somehow get it to work... use inline code, plus <br> linebreaks, plus a Unicode EN SPACE at the beginning of each code segment so the whitespace isn't trimmed. $\endgroup$ – Bob Jul 16 '15 at 6:15
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Cut the ladder, with the saw, in half like a sandwich so you end up with two equal parts, half as wide as the original

And then

Use the saw to connect them, by using it like a carabiner, attaching the last step of one to the first step of the other

Not precisely twice as long, but close enough...

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Well here's what I would do in this situation, assuming I was very skilled with a coping saw...

Cut out all rungs. Cut these rungs in half except the last rung. Then cut holes in the side of the poles. You basically have a bunch of dowels and two poles with holes in them. Shove the half-rungs in. Use the full-rung as a joint for the two poles.

Then you end up with something like

|--|--|--|--|--|--|--|. Kind of like a telephone-pole ladder.

To make it more sturdy you can use more full-rungs, depending on how good your ninja landing skills are.

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