Simply, how could you cut a sphere perfectly in half?

To put it more in layman terms, if you had a ball of playdoh and a knife, how could you divide it equally?

Without using a million dollars in measuring equipment, so I am talking in my garage. I am going to make a barbeque grill from a propane cylinder and need to cut it in half.

Wrap a tape measure around it. Use a square to draw lines.

[This message has been edited by Zeb (edited 01-07-2014).]

First of all, what tool will you be using to cut it...

Without any measuring device other than a flexible tape measure..........like the one your wife uses for her sewing.
Determine circumference of the sphere by measuring at it's widest area. Do this several times to ensure you have found the widest part of the sphere. Divide by 4.
1/4 of the circumference is exactly 1/2 way down one side of the "ball of playdoh"--the sphere.
Inasmuch as it is assumed to be a perfect sphere, simply attach one end of a string securely to any point on the sphere with a piece of tape. Make that string the same length of the results you got by your division. pull the unattached end of the string down the side, make a mark, then move it along different points on the side of the sphere, marking as you go with a very sharp pencil making sure the other end stays securely in place. You could also just get someone to hold a flexible tape in place at a single point on the sphere and mark it at the required measurement on different points along the horizontal axis. of the sphere.

[This message has been edited by maryjane (edited 01-07-2014).]

lots of ways. what kind of tools you got?
tape measure? wrap it around, find the largest diameter, cut there.
if you need more precision, measure the diameter, divide by four, that's the distance from a "pole" to the "equator". measure those distances from a fixed point all around, cut there.
string? same thing, just fold it twice.
a square will give the same result.
dangit, MJ! "inasmuch"?

[This message has been edited by lurker (edited 01-07-2014).]

quote Originally posted by RotrexFiero: Simply, how could you cut a sphere perfectly in half? a barbeque grill from a propane cylinder and need to cut it in half.

Wait, cylinder or sphere? There is a difference.

Are you just cutting the top off? Not likely, that'd be easy. You're trying to split it in half the long way? What tool do you want to use?

Is it full? If so, use a cutting torch... I really wanna see that!

Simple, put it in a box that touches it on all 6 sides of the box, cut the box in half and enjoy!

Want to find its perfect center? draw a X on the box corner to corner.

[This message has been edited by jetsnvettes2000 (edited 01-07-2014).]

Find a way to spin it around a single pole (mount it to some sort of carousel), or between two opposite points (as on a lathe). At a right angle to the pivot point(s), find the point that sicks out the farthest. Mount a Sharpie at that point and spin the sphere.

If play-doh? Form it into a flat pan. Level it. Cut it in half.

Without play-doh and an actual sphere? Micrometer and math.

Either method needs to account to "saw" width.

If it's a cylinder, go to any welding supply and get a dividing or center finding square. Pretty cheap.
Looks like this:

quote Originally posted by maryjane: kerf

Thanks Don.

I was not familiar with this term. As you know I sell metal. Oddly enough I have to describe this to people regularly. Bitches about to get big leagued with some vernacular!

Wet some surface with colored liquid, water color made with food coloring and roll the sphere across it. You now have a cut line.

[This message has been edited by texasfiero (edited 01-07-2014).]

quote Originally posted by ls3mach: Thanks Don. I was not familiar with this term. As you know I sell metal. Oddly enough I have to describe this to people regularly. Bitches about to get big leagued with some vernacular!

Make sure they understand to measure the teeth, not the bank of the blade. Teeth are set alternately in opposite directions so the blade doesn't bind. Use calipers, engaging 2 or more teeth at a time and do it in several places around the blade--largest measurement --not the average, is the kerf. Same with a bandsaw--do it in several places because teeth set isn't exact all along the length of the bandsaw or round blade.

quote Originally posted by maryjane: Make sure they understand to measure the teeth, not the bank of the blade. Teeth are set alternately in opposite directions so the blade doesn't bind. Use calipers, engaging 2 or more teeth at a time and do it in several places around the blade--largest measurement --not the average, is the kerf. Same with a bandsaw--do it in several places because teeth set isn't exact all along the length of the bandsaw or round blade.

In truth. I only try to explain to take into account 3/16" saw blade. I make my money selling material, I'm not their machine shop. I have a partnership with a FANTASTIC one that I freely give out their information. I try to charge too much so they don't want my labor, just my material, and service. I was just happy for the term describing the "shrink".

To the question at hand. I am curious as to the actual application. None of us have given answers that would be near as accurate as the machinery required. I am thinking this is maybe a proof of theory question?

EDIT. If he is doing something that requires that kind of precious. Invest in some equipment. Otherwise the topic moot to what is the most accurate.

[This message has been edited by ls3mach (edited 01-07-2014).]

Put it in the tub and fill it up to half way then mark the wet line

RotrexFiero, post a picture of the cylinder you want to cut. Why does your cut need to be so precise? Why won't a eyeballed cut be accurate enough?

quote Originally posted by maryjane: ... go to any welding supply and get a ...

Pipe wrap.

quote Originally posted by cliffw: Pipe wrap.

Ayup, but I am more curious of what the exact shape is and object? because if it is like saw a propane cylinder I would really tell you not to do it at all. people get blown up cutting things if they do it wrong. oh sure I have cut and welded gas tanks, oil tanks, propane pigs. but I have done it the correct way, made sure the tanks were purged and made sure they were filled with something that kept the possibility of fire and explosion to a min.

so a little more info would be nice?

re read your post,

NO Don't do it. first of all just how big a tank?

are you absolutely positively sure the tank is completely empty?

Even if you are sure the tank is empty make sure you open the tank valve before doing any kind of cutting, matter of fact take the tank valve off the tank, some of those have valves that do not allow gasses to leak out with the valve open unless there is a hose attached to it. so take the valve off the tank, remove it completely from the tank, I can not express this with any more caution. Even then allow it to sit outside for a couple of days, one day standing up with the valve removed and one day with the tank upside down, then fill it with water and then dump the water out. and then, even then get yourself a tank of CO2 and a hose to fill that tank with while you are cutting it.

please, please, please. PM or email or call me before you do this.

Steve


------------------
Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

[This message has been edited by 84fiero123 (edited 01-08-2014).]

quote Originally posted by Jake_Dragon: Put it in the tub and fill it up to half way then mark the wet line

Exactly what i was going to say! Getho but very effective. I would even put a dye in the water.

But what you would need to do is put the sphere in a container, fill with water, remove the sphere. Measure the water volume that the sphere displaced. refill container to half what the sphere displaced. Mark water line.

quote Originally posted by cliffw: Pipe wrap.

Won't work on a sphere unless you know exactly where center is to begin with. Cylinder yes--sphere--no.
Neither will the water in the tub thing.
Understand displacement guys.
Need OP to return and clarify shape (and size) in question.

[This message has been edited by maryjane (edited 01-08-2014).]

quote Originally posted by maryjane: Won't work on a sphere unless you know exactly where center is to begin with. Neither will the water in the tub thing. Understand displacement guys.

Don re read his post, he want to cut a propane tank in half and make a BBQ grill out of it. read my last post just above you. I have welded, cut, gas, propane, oil tanks and more but you have to be absolutely sure they are empty and not sealed in any way. I hope he reads my post before attempting this or we may just be reading about how he becomes the first man to make it to the moon without a space ship.


Steve

[This message has been edited by 84fiero123 (edited 01-08-2014).]

quote Originally posted by 84fiero123: Don re read his post, he want to cut a propane tank in half and make a BBQ grill out of it. read my last post just above you. I have welded, cut, gas, propane, oil tanks and more but you have to be absolutely sure they are empty and not sealed in any way. I hope he reads my post before attempting this or we may just be reading about how he becomes the first man to make it to the moon without a space ship. Steve

I misread that also. In this case, the solution is simple. Lay it on its side and measure the height. Use one of these to mark the middle.
PIP can't find a server, so here is the link. It is an off-shoot of a dress maker's tool for marking skirt length.

quote Originally posted by texasfiero: I misread that also. In this case, the solution is simple. Lay it on its side and measure the height. Use one of these to mark the middle. PIP can't find a server, so here is the link. It is an off-shoot of a dress maker's tool for marking skirt length.

And again you also misread the question as well, still.
he wants to turn it into a BBQ grill so he may want to use it that way, or the other way.

He may want to use it this way



or this



it all depends on how and what size propane tank he is talking about.

Steve

[This message has been edited by 84fiero123 (edited 01-08-2014).]

He also stated sphere and ball.
I'm guessing you have never seen a ball shaped propane tank. They are are quite popular on small homesteads, take up only a small footprint, and are very stout--a sphere being one of the strongest geometric designs ever made. .

[This message has been edited by maryjane (edited 01-08-2014).]

quote Originally posted by maryjane: He also stated sphere and ball. I'm guessing you have never seen a ball shaped propane tank. They are are quite popular on small homesteads, take up only a small footprint, and are very stout--a sphere being one of the strongest geometric designs ever made. .

You mean like this one?



to be honest I have never seen that kind, but I still stand by my, "Don't do it!" post as to cutting it, unless he is absolutely sure it is empty of all propane.

Steve

------------------
Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

Yes. Usually if you only need a small amount of propane. I don't see them as often as I used to, and they may now be out of production. My sister had one when she first got her country place. I've seen some cut and turned into kettles for cooking off syrup from sugar cane in Louisiana.

quote Originally posted by maryjane: Yes. Usually if you only need a small amount of propane. I don't see them as often as I used to, and they may now be out of production. My sister had one when she first got her country place. I've seen some cut and turned into kettles for cooking off syrup from sugar cane in Louisiana.

Must be a southern thing, up here we have always had those long huge pigs we call them. of course it does get a lot colder up here and we need even larger propane tanks for home heating to we have had the larger ones

Steve

quote Originally posted by 84fiero123: And again you also misread the question as well, still. he wants to turn it into a BBQ grill so he may want to use it that way, or the other way. He may want to use it this way Steve

No, I understand that he wants to use it on its side. I'd just use a tool like the one in the pick and slide it around the tank, marking the cut line.

Personally, I'd just cut it around the cylinder and use it as a smoker. Cut that way, it already has feet attached.

Now, for a Texas bbq cooker!

[This message has been edited by texasfiero (edited 01-08-2014).]

quote Originally posted by texasfiero: No, I understand that he wants to use it on its side. I'd just use a tool like the one in the pick and slide it around the tank, marking the cut line. Personally, I'd just cut it around the cylinder and use it as a smoker. Cut that way, it already has feet attached.

Depends on if it is a pig type propane tank, pigs have feet under them as well, he didn't give us much to go by and hasn't posted since, I wonder if he did it already and is the first man on the moon without a rocket ship?

Steve

quote Originally posted by 84fiero123: Depends on if it is a pig type propane tank, pigs have feet under them as well, . . .

Well, of course they do, or you couldn't pickle them. BTW, don't let your pickled pigs feet drive.

quote . . . I wonder if he did it already and is the first man on the moon without a rocket ship? Steve

Easy enough, since all of the was done on a stage anyway.

I swear, he's just trolling us.

quote Originally posted by Zeb: I swear, he's just trolling us.

It's what it feels like at this point.

Brad

quote Originally posted by Zeb: I swear, he's just trolling us.

quote Originally posted by Fats: It's what it feels like at this point. Brad

Ayup it sure seems like it at this point as he has never posted in the thread since and he does say he is a therapist in his profile, maybe he is just stoking us for some sort of paper he is writing, if he was truly interested in an answer to his question he would be answering at least some of the posts questions we have asked. Ether that or he
"Got Blowed Up Sir!"



Steve

Wow, I didnt think I would get such a response. I was at Lowes and saw the small cooking grills which were basically made from a small tank, some legs, and a burner. A good friend said he had two propane tanks, I believe they are 10 or 15lb standard barbecue grill tanks. Nothing that large. I'm single so I just need something small and I have time so I thought I would would fabricate one.

Sure, I am not going to weld or cut on a propane tank before I am sure it is empty. I'm not crazy.

But, a sure obstacle is making that longitudinal cut, so it closes perfectly. If I screw it up it will look silly, and be nearly impossible to fix. I can use a tape measure but that is only so accurate.

I thought of wrapping it with a piece of long paper and creating a paper cylinder. Then I could fold the paper in half, mark a line on it, and then place it back over the tank. I could then mark the tank. To check I could measure to see that the lines are equally spaced.

quote Originally posted by 84fiero123: . . . maybe he is just stoking us for some sort of paper he is writing, . . .

What Kind of Oddball Questions Will Car Nuts Answer?

quote Originally posted by RotrexFiero: I thought of wrapping it with a piece of long paper and creating a paper cylinder.

Or you could wrap a long piece of paper around it to make a cylinder. Result should be the same.

Put a gallon of propane in it.

Wrap a towel on top dowsed in diesel.

Light the towel and push off into lake.

Shoot it with rifle from considerable distance.

[This message has been edited by pokeyfiero (edited 01-08-2014).]

I have a laser that projects a perfectly straight line but then the problem becomes aligning the laser with the tank. And, then of course doing it again on the other side.

The Egyptians build the pyramids with lesser technology.

The aliens who showed them how to do it had lasers. When the Pyramids were finished the aliens left and took the lasers with them. Lesser technology, indeed.

Put it in a "box" with equal sides and measure the center of a side, cut.



Could make a "jig" for the saw so there are 2 slots that are across from eachother (on two sides of the box) the saw can be guided by.

Like a miter box:

[This message has been edited by 2.5 (edited 01-08-2014).]