I found this in a 1908 Audel's Millwright's Manual.

If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to.

Okay, "So What?" you say.

Well, note that .7854 means that a circle that just fits into its
enscribed square contains 78.54% of the area of that square. And
that's about 80%. So, an easy way to ESTIMATE the area of a circle in
your head is to simply think "8 tenths of the area of the enscribed
square = the area".

Example: A guy offers you a piece of steel just for coming and getting
it off the place RIGHT NOW!
You need to know the approximate weight of a 5" diameter bar of
steel that is 5 feet long, so you can decide whether you will be able to
lift it into your car trunk by yourself.

So, 5 X 5 = 25. 80% of 25 (in your head) is 20. That's area of the
circle. 20 X 60 (5 feet in inches) is 1200. There's the volume of
the bar! That's all there is to it!

Now for the weight:

A cubic inch of steel weighs 0.283 pounds think 2 Ate 3 (cannibalism
of numbers???). 0.283 is about .3

So the bar weighs 1200 X .3 = (in your head) about 360 pounds.
Sorry, Maybe you can lift it, but I'd have to pass on this one!!!

Well, maybe I could------


Pete Stanaitis

If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to....... Okay, "So
What?" you say.

That's the way I was taught to figure the displacement of an engine in high
school.

Bore squared times .7854 times the stroke. It's really not that different
from the normal way of figuring the area of a circle because .7854 is just
pi/4.

pi/4 * square(diameter) = pi * square(radius). (piRsquare)

In fact it's interesting that you mentioned it now because they were using
the same number on one of the auto TV shows last weekend. I think it was
Two Guys Garage.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"


"Pete & sheri" wrote in message
...
I found this in a 1908 Audel's Millwright's Manual.

If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to.

Okay, "So What?" you say.

Well, note that .7854 means that a circle that just fits into its
enscribed square contains 78.54% of the area of that square. And
that's about 80%. So, an easy way to ESTIMATE the area of a circle in
your head is to simply think "8 tenths of the area of the enscribed
square = the area".

Example: A guy offers you a piece of steel just for coming and getting
it off the place RIGHT NOW!
You need to know the approximate weight of a 5" diameter bar of
steel that is 5 feet long, so you can decide whether you will be able to
lift it into your car trunk by yourself.

So, 5 X 5 = 25. 80% of 25 (in your head) is 20. That's area of the
circle. 20 X 60 (5 feet in inches) is 1200. There's the volume of
the bar! That's all there is to it!

Now for the weight:

A cubic inch of steel weighs 0.283 pounds think 2 Ate 3 (cannibalism
of numbers???). 0.283 is about .3

So the bar weighs 1200 X .3 = (in your head) about 360 pounds.
Sorry, Maybe you can lift it, but I'd have to pass on this one!!!

Well, maybe I could------


Pete Stanaitis

Here's another handy shortcut involving pi: pi = 3.1416... which is very
close to 3 1/7, which is not too far from 3 1/8. An old sheet metal man
showed me this. If you multiply the diameter of a sheet metal pipe by 3
1/8, you get pretty close to the circumference, and it comes out in
fractions that you can read on a ruler. (The little bit extra helps make
the seam. :-)

Pete & sheri wrote:
I found this in a 1908 Audel's Millwright's Manual.

If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to.

Okay, "So What?" you say.

Well, note that .7854 means that a circle that just fits into its
enscribed square contains 78.54% of the area of that square. And
that's about 80%. So, an easy way to ESTIMATE the area of a circle in
your head is to simply think "8 tenths of the area of the enscribed
square = the area".

Example: A guy offers you a piece of steel just for coming and getting
it off the place RIGHT NOW!
You need to know the approximate weight of a 5" diameter bar of steel
that is 5 feet long, so you can decide whether you will be able to lift
it into your car trunk by yourself.

So, 5 X 5 = 25. 80% of 25 (in your head) is 20. That's area of the
circle. 20 X 60 (5 feet in inches) is 1200. There's the volume of
the bar! That's all there is to it!

Now for the weight:

A cubic inch of steel weighs 0.283 pounds think 2 Ate 3 (cannibalism
of numbers???). 0.283 is about .3

So the bar weighs 1200 X .3 = (in your head) about 360 pounds.
Sorry, Maybe you can lift it, but I'd have to pass on this one!!!

Well, maybe I could------


Pete Stanaitis

Nonsense I don't believe this for one second . Let me see if I have it
right . 5 inch hunk of steel 5 feet long and anyone that frequents this
newsgroup would pass on it ? Ha ha , yea more likely they would be
tripping over each other to get there first . If anything we would see
50 posts on how this Rube Goldberg would lift it easier/safer then that
Rube Goldberg . Followed by 100 posts on whether Bush or Kerry in office
would affect how many jobs would be saved from going to China because
you kept this hunk of steel from being shipped to them as scrap . That
and anyone that tried to get between my and that hunk of steel better be
well armed . Opps there goes another 100 posts to determine in gun
packing metal scrongers threaten the world as we know it , :-)
Ken Cutt

I couldn't agree with you more. As soon as I wrote the post, I started
thinking of how I'd do it. I just got out of the hospital yesterday,
being told not to lift more than 20 pounds for 2 weeks, so that makes it
even more interesting.

This sort of thing does happen to me fairly often, though, so it is an
issue to be dealt with. On the other hand, those pieces are often
ALMOST what I need for that next project, but not quite.

Pete Stanaitis
-------------

Ken Cutt wrote:


Nonsense I don't believe this for one second . Let me see if I have it
right . 5 inch hunk of steel 5 feet long and anyone that frequents this
newsgroup would pass on it ? Ha ha , yea more likely they would be
tripping over each other to get there first . If anything we would see
50 posts on how this Rube Goldberg would lift it easier/safer then that
Rube Goldberg . Followed by 100 posts on whether Bush or Kerry in office
would affect how many jobs would be saved from going to China because
you kept this hunk of steel from being shipped to them as scrap . That
and anyone that tried to get between my and that hunk of steel better be
well armed . Opps there goes another 100 posts to determine in gun
packing metal scrongers threaten the world as we know it , :-)
Ken Cutt

Pete & sheri wrote:
I couldn't agree with you more. As soon as I wrote the post, I started
thinking of how I'd do it. I just got out of the hospital yesterday,
being told not to lift more than 20 pounds for 2 weeks, so that makes it
even more interesting.

This sort of thing does happen to me fairly often, though, so it is an
issue to be dealt with. On the other hand, those pieces are often
ALMOST what I need for that next project, but not quite.

Pete Stanaitis
-------------

I hate to admit to this but I seem to work the opposite . If I get a
hunk of metal like this , umm , well does not have to fit an upcoming
project because I start inventing projects to fit it .

Ken Cutt

Leo Lichtman wrote:
Here's another handy shortcut involving pi: pi = 3.1416... which is very
close to 3 1/7, which is not too far from 3 1/8. An old sheet metal man
showed me this. If you multiply the diameter of a sheet metal pipe by 3
1/8, you get pretty close to the circumference, and it comes out in
fractions that you can read on a ruler. (The little bit extra helps make
the seam. :-)


3 1/8 3 1/7. Where does that little bit extra come from?


--
Bill Kaiser


There are three ways to do a job: good, cheap, and quick.
You can have any two.
A good, cheap job won't be quick.
A good, quick job won't be cheap.
A cheap, quick job won't be good.