How difficult would it be to create a spherical mold about 18-24" in diamater? I need two half spheres for casting an acrylic mold (i know this is for metal casting but i figured the technique is some what the same). I have an acrylic sphere that is the exact same diamater for what I need, but it is two brital when cut in half.

Is this something that I could do myself? If not, should I pay to have a mold made? How much do you think it may cost if I did have it made? I know this is hard to determine, but can anyone give me a general idea like $100-$200. I have a very low budget for my project.

Oh btw, the sphere needs to be hollow.

does the mold need to be metal?
If not, use fiberglass. You can use your acrylic sphere as a pattern, coat it with a release agent, and make a mold off of it.
Any glass shop could do this easily or I can give more information on how you would do it if you want to do it yourself.

Matt

Forgot to mention that I want it to be casted w/ an acrylic mold. I haven't done any calculations yet, but the walls will need to be 3/4-1" thick around the sides. I would also like the inside to have molded brackets. I do not know the technical term for this. I will be fastening aluminum inside the case.

I would prefer to do it myself, is this feasible? Any suggestions? I have never casted anything before so if you know of any helpful sites please link'em. Thank you.

This sounds like a perfect application for rotomolding. You can have a mold cast using aluminum and then finish machine the detail for your shere. This is probably going to cost you between $12k-$30K. I hope you are wanting to make more than one.

How difficult would it be to create a spherical mold about 18-24" in diamater? I need two half spheres for casting an acrylic mold (i know this is for metal casting but i figured the technique is some what the same). I have an acrylic sphere that is the exact same diamater for what I need, but it is two brital when cut in half.

Is this something that I could do myself? If not, should I pay to have a mold made? How much do you think it may cost if I did have it made? I know this is hard to determine, but can anyone give me a general idea like $100-$200. I have a very low budget for my project.

Oh btw, the sphere needs to be hollow.

Just a Soild CAD Model or the Actual Sphere.

I'll do a CAD Model for you for $50.00 US. The Actual Part will cost a lot more than that.:)

i'm not sure....would 3d printing work???

This sounds like a perfect application for rotomolding. You can have a mold cast using aluminum and then finish machine the detail for your shere. This is probably going to cost you between $12k-$30K. I hope you are wanting to make more than one.

...yeah I do not have that sort of budget

Do you need a solid sphere or 2 domes? If you need domes use a vac press like they have on mythbusters and do one half at a time.

Do you need a solid sphere or 2 domes? If you need domes use a vac press like they have on mythbusters and do one half at a time.

I need two domes that when placed together, create a perfect sphere. I love mythbusters, but I can't remember the vac press. Will I be able to make a perfect sphere?

what tolerance are we talking here ?

Tolerance?

diameter: 18-24"
thickness: approx. 1"

Tolerance?

diameter: 18-24"
thickness: approx. 1"

what tolerance on roundness

also do you have any pics or drawings of what you want to mold
or is this what you want to mold

also what suffice finish do you need

I am sorry, but what do you mean when you say "tolerance"? Do you mean how perfect do i want the overall shape to be?

Heres a very simple image of what i am trying to do:

http://i21.photobucket.com/albums/b295/ChronicCodez/8-Ballcopy.jpg

The green area is what will be inside the shell

I am sorry, but what do you mean when you say "tolerance"? Do you mean how perfect do i want the overall shape to be?

Heres a very simple image of what i am trying to do:

http://i21.photobucket.com/albums/b295/ChronicCodez/8-Ballcopy.jpg

The green area is what will be inside the shell
yes that's what i mean

so you just need the shell

can this part be made in four pieces

also what material can it be made from

I would prefer that it be done in two pieces. The top half of the shell needs to be one piece, it will look much better that way. Would it be easier to make four pieces? And if so, why?

I would prefer to cast an acrylic resin so that it is at least some what translucent.

it all depends on how this sphere is made if its mill the tool would have to reach down 12 inches

what are you casting this sphere

or using this sphere to cast

Let me describe what I am trying to do.

Imagine a spherical shadow-box. There will be something inside the sphere, approx. 20-25 lbs. I would like it to be some what translucent. Preferably a tinted black look, like tinted windows on a car. The top portion of the shell needs to have these features, the bottom half can be a solid color, and does not need to be translucent.

I do not want to go into too much detail at the moment.

Do you know anyone with a potter's wheel?

You could turn this on a wheel using some clay and a template of a quarter circle to create a hemisphere. The template will need some sort of jig to hold it steady. This might either hinge, or move in a linear motin relative to the rotating wheel. Or it could just be a surface you rest the template against. You can then cast a negative plaster mold directly off the clay positive. I assume you can then cast your plastic directly off of plaster...

I've done this before and it works. Just requires patience (like everything else!).

Carlo


BTW, this is called jiggering in ceramic manufacturing

http://www.pottery-books.com/axner/equipment/powerarm-main.php

The image gives a good idea of how this works...

Let me describe what I am trying to do.

Imagine a spherical shadow-box. There will be something inside the sphere, approx. 20-25 lbs. I would like it to be some what translucent. Preferably a tinted black look, like tinted windows on a car. The top portion of the shell needs to have these features, the bottom half can be a solid color, and does not need to be translucent.

I do not want to go into too much detail at the moment.

do you need the mold or the sphere?

Let me see if I understand. You want to cast a hollow sphere about 20 inches in diameter (exterior), with a 1 inch thick wall. This sphere can be cast as two hemispheres, to be joined later. One of these halves needs to have provision for a support structure inside. You have a sphere very much like the one you want, but it's too brittle.

If this is correct, then here's how you do it.

Take your existing sphere, and saw it in half. Take one of those halves, and attach it to a sheet of plywood, or some other base material. This will be your master from which you will create your mold. Now, coat the whole thing in a release agent. What's that you say? Well, I suspect that the "search" box will have your answer. Now, take your coated master, and layer on some fiberglass cloth. Coat the fiberglass cloth in epoxy. Do another layer of cloth, and another layer of epoxy. Repeat untill you have a reasonably solid mold. Two or three layers will work, but you may want more, depending on how durable you want the mold to be. Let the whole thing cure. This may take a long time (days). Once it's cured, pry it off of the plywood. You now have a mold that will create a sphere with an outside diameter equal to that of your original.

Now, to create the inside mold. Take your newly created mold, and coat its inside with release agent. Now, pack it with a temporary filler until you have a hollow sphere that meets your requirements (1 inch thick wall). I would suggest using clay as your filler, as its easy to come by. Now, repeat the whole mold-making process from above, but on the inside of your clay bowl-thing. Once it's dry, pry it apart and discard the clay.

You should now have two moulds, one for an outside and one for an inside. To make your final sphere, mix up your acrylic (tinted to taste), coat your molds in yet more release agent, and pour the acrylic into the outside mold. It will pool in the bottom. Now, clamp your inside mold on, and it will force the acrylic up and out to form your hemisphere. Let the whole thing cure (again, days), and pry apart. You should now have a hemisphereical acrylic dome.

Building your support structure into the inside during casting would make things much more difficult, so I would suggest making it seperately and just gluing it in.

Note that I have never actually done this. I've done similar things, but never something quite like this, so there may be flaws in the plan. It's free internet advice, and you get what you pay for.

Good luck.

Yes! Thats perfect Qwindelzorf.

This project has brought me nothing but frustration. I went through five globes before I found this site.

One thing though, the sphere looses strenght when I cut it in half. It becomes flemsy. How do you think I could reinforce it before I start hacking at it? I would to insure that I create a perfect sphere.

I had some thoughts on your dilema.

I do have my doubts what you end up with will ever be a perfect sphere. An approximation using 2 hemispheres, is about all you can hope for. Getting it crystal clear and seamless probably won't happen either.

To get something functional. I would purchase 2 globes 2" different in diameter. Cutting both in half and using half of each one will give you an inside and outside mold surface with 1" air space in between. With each half properly supported in a frame structure and keyed/aligned together should work well spaced apart and bolted together. Heck, if the 2 globes were cut with care you might just get 2 molds.

Complex plastics (http://www.complast.com/balls/?OVRAW=poly*%20sphere&OVKEY=plastic%20sphere&OVMTC=advanced)

Problems you may encounter or prepare for are:

Verify the globe material is compatible with the molding liquid you plan to use.

Pouring slightly above the split line to have something to trim to later. Expect some shrinkage from where you fill it when in liquid form too. This is rather hard to do when the molds were cut on their center line. It might prove worse to cut the mold globes above the centerline, when removing the 1" thick hemisphere could become locked in place.

Exothermic heat cure may distort the mold surfaces. A slow cure is better than a fast hot cure.

It looks like a challenge, and not a cheap one at that!

DC

forget this project buy the ball you can climb in side of and have some fun
http://www.complast.com/balls/?OVRAW=poly*%20sphere&OVKEY=plastic%20sphere&OVMTC=advanced

Thanks for the advice One of Many. I think I will definantly use all the advice everyone here has given me.

Another question of mine is how would I determine the total volume of acrylic I would use for a globe. I am writing all my notes in a composition book for record purposes and I would like to have a formula. Lets say I want a 24" sphere with a thickness of 1". How would I determine this?

give me the two radius and i can model it for you

Using the inside dimension of the outer sphere and the outside dimensions of the inner sphere. Subtract the 2 volumes and divide by 2 for one half the sphere.

Sphere volume calculator (http://grapevine.abe.msstate.edu/~fto/tools/vol/sphere.html)

DC

awesome ty

Your biggest problem is the master or the cavity shape. Since it hast to be hollow roto molding would do it, but I am not sure poly carb can be rotomolded. We do injection and roto molding. Oh we have our own tool shop and designer....Hi. If I could ask a few questions. 1st why so thick? How many do you need? There are several other rapid prototype solutions to do what you want cheaper than sla, or sls. If you want to machine a part for a pattern it will take a machine with a lot of z travel just to cut 1 hemishpear. email me direct gsilberberg@progressiv-plastics.net

Hello Brothers...

I am a new comer.

I want to make aluminum candle holder, with the shape like a little cup, maybe only 5 cm (dia). Can my brothers show me, what kind of metal to make this mould ?. Cast iron, or stell, or ... I dont know...

For information, I've little cnc from china, Y-3, with brand name 'king cut' that maybe can make that mould...

Thanks alot for your information...

Bye

Triono, Jogja, Indonesia