tooth and nail puzzle

[peter]

Did anyone ever find the correct answer to this puzzle?

just came across this puzzle at work.

Thanks,

Peter

[Phil-in-MI]

Sorry, I wondered into this NG from rec.woodworking NG.

This is an old-tyme puzzle, that is normally phrased How-did-the-nail-get-there-in-the-first-place. Lots, and lots of posting on this puzzle, and the solution along with it's companion, the wood pencil in the wood block on Wood Working forums, NGs and so forth.

(the solution was on the Public TV show, The Woodwright's Shop with Roy Underhill a few seasons ago.)

Soak the wood in boiling water for several minutes. (actually, a whole lot longer than several minutes!) Compress one end (section) of wood in a wood vice, and squeeze to compress. (Takes a lot of effort, vice must be bolted to workbench. A "put-your-back-into-it" type of effort.) Wood will remain compressed until re-immersed in boiling water. Normally, will return to original size.

Some tips: Type of wood does mater, softwood (Pine, Redwood, etc.) is better than hardwoods (hickory, maple, white oak, etc.) Can be done with Red Oak, but scrap 2x4 Pine is so much cheaper. Wood with larger distance between growth rings is better than close dense wood growth rings. Wood should start off as kiln dried, less than 10% moisture. (Walls of the cells and all that...) Wood grain direction makes a difference (flat straight grain, and NO KNOTS.) Vice with hardwood jaws will leave fewer scars to give away the solution. The end sections are normally twice the length of the middle sections. (I don't know why; IMHO, for looks only.)

Phil

[Phil-in-MI]

Sorry, I thought this was the rec.puzzles NG I didn't notice this was the rec.woodworking NG.

[peter]

Thanks for your reply and sorry if I posted in the wrong newsgroup. The puzzle was posed to us as "how do you get the nail out of the block?" I wonder if boilng and a vise would work for that too?

[Phil-in-MI]

Peter:

Yes, it will.

BTW, what I meant to say in my last post: I apologize for the tone of my reply, which was aimed at non-woodworkers. In this NG my reply to your original post should have been: Boiling water --> squeeze in vice --> boiling water.

Everyone who follows this NG would have already known everything else I wrote. I suspect many who read this NG were insulted by the tone of my choice of words.

Phil

[RicodJour]

Why wouldn't the nail rust and stain the wood? That would certainly point towards water being involved in your...errr...solution. I suppose the nail could be stainless steel, but I've never seen a 16d common stainless nail.

R

[Eigenvector]

I was kind of wondering why the wood wouldn't swell around the nail, making it all but impossible to extract.

[Doug Miller]

Because the wood swelling will make the holes *larger*, not smaller.

[RicodJour]

Why wouldn't the wood swell in all directions?

R

[George]

It will, and take a bit of compression set before it contracts.

[Doug Miller]

It does -- but it does not swell *uniformly* in all directions, because wood does not have a uniform structure. Its fibers are long and narrow, with the long axis parallel to the trunk of the tree. The extent of tangential dimensional change (parallel to the growth rings) in response to changing moisture content is, as a general rule, approximately double the extent of radial dimensional change (perpendicular to the growth rings), and either one is several orders of magnitude greater than the axial dimensional change (parallel to the trunk of the tree).

To put it in somewhat simpler terms: when a piece of wood absorbs moisture, it gets wider. It also gets thicker, but proportionately by only about half as much as it increases in width. The length hardly changes at all.

[Kate]

It does -- but it does not swell *uniformly* in all directions, because wood does not have a uniform structure. Its fibers are long and narrow, with the long axis parallel to the trunk of the tree. The extent of tangential dimensional change (parallel to the growth rings) in response to changing moisture content is, as a general rule, approximately double the extent of radial dimensional change (perpendicular to the growth rings), and either one is several orders of magnitude greater than the axial dimensional change (parallel to the trunk of the tree).

****OUCH! My head hurts!

To put it in somewhat simpler terms: when a piece of wood absorbs moisture, it gets wider. It also gets thicker, but proportionately by only about half as much as it increases in width. The length hardly changes at all.

****Thanks... from the old blonde broad.

[RicodJour]

There's no need to put it more simply - I'm more than passably familiar with wood properties. It sounds like what you're saying - correct me if I'm wrong - is that the wood fibers around the nail are somehow different than the wood fibers not next to the nail. The wood fibers run in the same direction, and the hole is drilled in the same direction as well. How can the wood fibers react differently?

R

[Mark Jerde]

It does. Any two points get further apart -- whether it is wood or air between them.

Does heating a nut make it clamp tighter to the bolt? No, the threaded hole gets larger, making it easier to crack loose a stubborn nut. That's what they said in mekanical injineering kollege.

-- Mark

[Eigenvector]

That's not really a fair comparison to what is being discussed. We aren't heating or cooling the wood. Thermal contraction and expansion is not the mechanism employed here.

[Eigenvector]

I don't understand what you mean. Could you explain?

[Doug Miller]

Quite the contrary. I'm saying that they're all the same.

They don't.

Suppose for the sake of illustration that the width of the board increases by ten percent when it's saturated with water; suppose further that we have a

1/4" diameter hole drilled in the middle of a board that's 2.25" wide (1" on each side of the hole).

The board swells to a total width of 2.25 + 10% = 2.475". The wood to the left of the hole started out 1" wide, and swells 10% to 1.1". So does the wood to the right of the hole. Total 2.2" left and right. Leaves

0.275" for the hole, no?

It's *exactly* the same principle as heating a piece of metal to enlarge a hole for making a friction fit: metal expands when heated, and wood expands when it gets wet. Holes in metal get larger when heated, and holes in wood get larger when wet. The only difference is that since wood does not expand at the same rate in the x and y axes, due to its non-uniform structure, circular holes in wood become elliptical when they expand, instead of remaining circular as do holes in metal.

[Doug Miller]

The question is the behavior of the holes when the medium expands. The mechanism of expansion is irrelevant.

[RicodJour]

RicodJour

I'll argue my point with a very simple test that you can do for yourself. Drill a hole the exact size of a nail in a piece of wood, drilling along the grain. Soak the wood overnight. You don't have to boil it. Try to insert the nail the next morning. The wood will have expanded, and the hole will have gotten smaller, not larger. The hole may not be perfectly round, but the net area of the hole will be smaller. I've done this. Try it, you'll see.

Simple practical tests outweigh theoretical ruminations. Ask Richard Feynman...well, he's dead, but he'd agree with me.

R

[Doug Miller]

Nonsense.

Pardon me for being very skeptical of your claim to have actually done that. I'll perform my own test and report the results.