For all you engineers/techs out there..... I want to mold a couple of
concrete or quikrete balls about the size of a 8" or 10" cannon ball
depending on the finished weight. If I can get a concrete conversion weight
formula that would be super too.....
Also, is there any relatively cheap molding material that could be used that
-Thanks for any help!
Why don't you get a bocce ball and make a couple of prototypes?
<%= Clinton Gallagher
NET csgallagher AT metromilwaukee.com
URL http://clintongallagher.metromilwaukee.com /
MAP http://wikimapia.org/#yC038073&x=-88043838&z &l=0&m=h
Well, let's see (fires up Excel...)
The formula for the volume of a sphere is 4/3 pi * (radius)^3.
That's about 268 cubic inches for the 8" sphere, and 524 cubic
inches for the 10" sphere.
I have seen weights for conrete listed from 2000lbs per cy
to 4000lbs per cy. I think 2000 is too low; the local
ready-mix plant claims 3000.
Assuming that concrete has a nominal weight of 3000 lbs per
cubic yard, your 8" and 10" cannonballs would weigh about
17 lbs and 34 lbs respectively.
At 4000, your cannonballs would weigh 23 lbs and 45 lbs
I would agree with the 23 & 45 lb answers ........but your other
numbers seem a little low for normal weight concrete
"normal" weight concrete is about 140 to 150 pounds per ft^3 (3800 to
4000 lbs per cy)
Your local mix plant claims 3000 lbs per cy? That's down in the range
of lightweight concretes. Maybe they were talking about compressive
Are you sure you're not quoting compressive strengths (2000 to 4000
PSI) & the numbers just turn out close to density as well? The number
I always use for weight calcs is 150 (lbs/ft^3), that might be a touch
high but it's very close.
In any case the concrete balls will be ~23 & ~45 lbs
to determine weights of other sized balls
as Mark calc'd the volume
4/3 pi * radius ^3. (in^3) * 150 (lbs/ft^3) / 1728 (in^3/ft^3)
units cancel & you're left with lbs
be careful, don't blow yourself up
I KNEW I CAME TO THE RIGHT PLACE!!
Thanks to all you guys for the answers I was looking for...... And for
Ralph...... I am seeing if I can make some inexpensive kettlebells (cast
iron cannonball configurations with a handle) They basically are a
different shaped dumbbell. They are selling for an outrageously stupid price
as far as price to function is concerned. A 35 pounder sells for approx
$50-60 plus another $30-40 for shipping...... Simply ridiculous! I am
thinking that I might be able to mold/cast one out of concrete (inside
plastic ball or something with a handle of some sort).... Of course I have
been known to spend more than what I can buy it for.... :-) Wish I could
find a cheap "more dense material than concrete" so I could make a smaller
form but with the same weight..... ideas?????
-Thanks again for taking time.
Laugh if you want, but this is serious stuff. Kim Jong Il has imported
thousands of square yards of military-grade hardware cloth for his
centrifuges. He will be separating graveltons out of concrete 187
by the end of the year.
Maybe it won't seem so funny to you when Kim is peaing gravel
on Seoul and Tokyo.
Concrete weighs +/- 150 lbs/cubic foot.
This web site
has the weight per cubic foot of other materials, so anything that
weighs more than 150 lbs/cf would be good candidates for your use.
I would point out that gold is over 1200 lbs/ cf but the price
might be out of reach.
Is there a need for your shape to be round? I would think that
you could make up some open wood cubes with broomstick or other
handles. Fill with lead shot from a reloading store, steel
ingots, whatever. You could adjust the quantity in the box or
change the material to increase the weight as needed.
Keep the whole world singing. . . .
Concrete in this area weighs avbout 148 lbs per cubic foot. This is
using aggegates, or stone that has a specific gravity of 2.65. This
means that it weighs over 2.5 times the weight of water for a given
volume. To increase the weight of a gi en volume of concrete, you need
to use a heavier aggregate. Try lead shot to replace some of the sand,
and a trap rock type of aggregate to raplace the larger rocks.
Avoid cement thay is air enytrained, as using this type of cement will
cause the creation of small air bubbles that will equal approx. 6% of
the volume and so reduce the weight of the sample. The use of silica
fume and other pozzolans will increase the weight of the cement sample
Thanks..... All good stuff. I guess I want them round rather than square
cause then I will feel like I have conquered the complete clone. I guess I
can add lead shot or gold but the cost goes up fast pretty fast.....
especially the gold (yuk). I think lead shot is running about $1/lb around
here. I suppose if I could come up with something pretty heavy for the
middle of the mold I could incase it in concrete and end up with a smaller
sphere - maybe something out of steel or lead. Can you buy chunks of lead
or steel, which would be cheaper than lead shot? Anybody got a "round"
-My head hurts!
Round up an assortment of basketballs and the like, sized to suit your
intended weight, that will serve as the form for your set of weights.
Cut a 1.5" hole in the top. Mix up a bag of fiber-reinforced concrete
mix. One bag will get you two weights or more.
For increased weight in the same volume add old nuts, bolts, washers,
etc., the bigger the better, that litter everybody's shop and stir them
into the concrete mix or place them in the ball form as you fill it
with the concrete. Steel is about 3 times denser than concrete so the
weight will add up quickly. I have a few buckets I know I'll never get
around to sorting, much less using, and they're yours if you'll come
get them. Soon. Seriously. I need the space. ;)
What were you planning on using for the handles? A bent piece of rebar
would be nice, you'd need a pretty large bar - beyond your bending
capabilities probably - to keep it comfortable with the larger weights.
Use some Plastidip on the handles for color coding and to keep rust
off of your hands. Or you could use old suitcase handles with bolts
embedded in the concrete.
I don't think I'd be very concerned with small surface voids that
wouldn't affect the strength. They'd probably look better if the
surface was a little rough. So, don't make the mix too wet, and don't
worry about trying to vibrate small bubbles out of the surface.
Cut off the rubber balls after a few days curing and let the weights
set up for a month - the generally accepted period of time for the
concrete to come to its full design strength.
You could paint them, but unless you liked the chipped paint look
that's probably not the way to go. Staining them and waxing or sealing
the surface would be interesting.
Sounds like a fun project, so start working up the sweat now. Enjoy!
Go to a tire store that sells a lot of tires... If you ask nice, they
might give you the lead weights that they take off the old tires prior to
balancing the new tires... Melt them down and make the balls out of
lead... You'll still need some round stock steel for the handles though...
Lead melts easily enough... Just get an old pot that you never want to use
for food again and do it outside... The fumes can be hazardous, so rigging
up a fresh air supply mask will make it safer...
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