# GordieGii

1

• Sorry it took me so long to notice your reply.As you can see in the drawing, the center point is not in the center of a tapered board. This is a very tapered board so the error is large. For a much less tapered board the error would be much less, quite possible within an acceptable margin of error, but it is not zero. It does not "always work" regardless of spottd's "analysis" of why.

• It's mostly oxygen, other gasses dissolved in water wouldn't be any worse problem. It would just be nice if there weren't any dissolved gasses at all because then it could be totally maintenance free. If somebody came up with a vacuum pump with no moving parts that would be great.

• With so many questions about strength, I wonder whether adding a layer of thin cloth (like old cotton bed sheets) every few layers would improve the strength.

• Similar product here:http://www.leevalley.com/us/wood/page.aspx?p=32272&cat=1,180,42240

Another possibility (and I have seen people do this dozens of times) is that it is the wrong size Phillips bit. The two most common sizes are #1 and #2 and if you put a #1 in a screw designed for a #2 the point will hit bottom before the flutes are fully engaged. If you put a #2 in a screw designed for a #1 then only the tips of the flutes will engage. In both cases the screw is quite likely to strip, however if you realize your mistake early there is a good chance that switching to the correct size, giving it a bit of a tap to seat it in the screw and applying a lot of pressure while maintaining proper alignment and going slow will allow you to remove the screw. Replace it with one that isn't damaged to avoid problems in the future.

Or in a pinch, some fine sand...

• While a parabola is ideal for an infinitely distant light source, an ellipse is ideal for a light source of a finite distance (such as a fire or lamp) where the two fixed points are the foci. Now if you had a really tall tower (say for a windmill or a water tower) and you could hang a string from it and place your other fixed point closer to the ground then you could draw a section of an ellipse that was pretty darn close to a parabola. Probably just as good as the precision of the Mechanical Mathematician. Of course you would need a tower shielded from the wind... On the other hand you could use this method to draw an ellipse in your camp-site with the fireplace and your chair as the foci and place a bunch of mirrors on the ellipse then you would only need a small fire to keep yourself w…

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While a parabola is ideal for an infinitely distant light source, an ellipse is ideal for a light source of a finite distance (such as a fire or lamp) where the two fixed points are the foci. Now if you had a really tall tower (say for a windmill or a water tower) and you could hang a string from it and place your other fixed point closer to the ground then you could draw a section of an ellipse that was pretty darn close to a parabola. Probably just as good as the precision of the Mechanical Mathematician. Of course you would need a tower shielded from the wind... On the other hand you could use this method to draw an ellipse in your camp-site with the fireplace and your chair as the foci and place a bunch of mirrors on the ellipse then you would only need a small fire to keep yourself warm, or just a couple mirrors on the ellipse behind you to keep your back warm.

Actually I can think of one application that uses on ellipse for light concentration. Ruby lasers (or any optically pumped laser) They use a flash tube (like a camera flash) and a lasing rod or tube with an elliptical reflector around them with the two tubes at the foci. All the light from the flash tube converges simultaneously on the lasing tube. I think this is also the premis behind whispering domes.