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Slip casting globes- form?


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#1 Kohaku

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Posted 29 June 2013 - 10:48 AM

I'm interested in slip casting some globes of varying sizes (ranging from maybe 4 inches diameter to possibly as large as 12 inches diameter).

Anyone have any suggestions for where to buy or find a graduated series of rigid spheres, ideally on the inexpensive side of things? I don't want to use my Japanese fishing floats!

I use globes for water features. I find that a perfectly spherical, closed form is pretty hard to throw, however... and deviations from the spherical (even small ones) don't work well for this application....

Posted Image
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#2 OffCenter

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Posted 29 June 2013 - 11:15 AM

How about balls? The inflated kind for children are pretty tough and very cheap. I just used a big one (about 15 inches in diameter) to cast a slump mold from which to make a hump mold. I remember someone using one to make a one-piece (or almost one piece) spherical slip mold by casting the whole thing in one piece with just a hole left in it to deflate the ball and pull it out.

Jim
E pur si muove.

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#3 Kohaku

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Posted 29 June 2013 - 11:55 AM

How about balls? The inflated kind for children are pretty tough and very cheap. I just used a big one (about 15 inches in diameter) to cast a slump mold from which to make a hump mold. I remember someone using one to make a one-piece (or almost one piece) spherical slip mold by casting the whole thing in one piece with just a hole left in it to deflate the ball and pull it out.

Jim


Jim- that was my first thought. I talked with a local potter who does a lot of slip casting, though... and he thought that the plaster would tend to deform anything inflatable. There are things like bocchi balls that are rigid... but it's generally hard to buy these outside of a set.

If anyone's used inflatable balls for this purpose, I'd love to hear about it...
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#4 Biglou13

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Posted 29 June 2013 - 01:43 PM

Google duck pin bowling balls

Of shoot of bowling balls

There a range in size which should cover you..
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#5 Diane Puckett

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Posted 29 June 2013 - 02:56 PM

Maybe an inexpensive globe. If you don't mind dealing with broken glass, it is possible to find cheap garden gazing balls.
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#6 BeckyH

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Posted 29 June 2013 - 05:27 PM

To work with an inflatable, try filling the cottle boards with your plaster and pushing the ball down into it whilst it is still liquid. Draw a line on the equator so you get it to the right place. That will allow you to see if the plaster does deform the ball, and an inflatable ball is only a few bucks. Or visit the local Goodwill store and get a selection of used sports balls. A baseball should be solid enough, and a billiard ball is solid. Maybe you could borrow a bowling ball?

#7 Kohaku

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Posted 29 June 2013 - 06:33 PM

To work with an inflatable, try filling the cottle boards with your plaster and pushing the ball down into it whilst it is still liquid. Draw a line on the equator so you get it to the right place. That will allow you to see if the plaster does deform the ball, and an inflatable ball is only a few bucks. Or visit the local Goodwill store and get a selection of used sports balls. A baseball should be solid enough, and a billiard ball is solid. Maybe you could borrow a bowling ball?


I may have to try this. The options I've looked at online are all pretty pricey (for example- the duckpin bowling balls price out in the 40-100$ range). There are some online venders that sell plastic (polyethylene) balls- but you have to generally order these in lots of 500+
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#8 PeterH

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Posted 30 June 2013 - 08:06 AM

Kohaku,

A search of www.ebay.com for plastic sphere returns;

- a variety of "plastic mould half sphere"s from 4" to 12"
which you might manage to use to create a registered pair of plaster half-moulds.

- a 1 gallon plus plastic fish-bowl (obviously not a full sphere)


Regards, Peter

PS you don't say if you need a full sphere, or how you are going to handle this in
the mould [e.g. removable plug to enable slip pour and partial drain; trim cast
hole and insert plug; invert mound to cast onto plug; remember to make a pin-hole
before firing].

#9 Mart

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Posted 30 June 2013 - 05:23 PM

Do you have access to vertical turning lathe for plaster? You can make make 2 half spheres and build a mold from those semispheres.

If you do not have access to turning lathe, you can use your throwing wheel and quarter of a circle (cut it out from sheet metal, firm plastic, plywood? etc) as your "mold".
First you make a hump out of clay and then you keep adding thick plaster mix (not too runny) on top of it while wheel is spinning slowly. You need to make sure it's soft enough so your mold can scrape it easily to the proper shape. Adjust the plaster/water ratio accordingly and mix small amount of plaster.

huh.. let me draw you a picture Posted Image

#10 Mart

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Posted 30 June 2013 - 05:36 PM

here it is
Attached File  clay_plaster_mod.png   19.06KB   17 downloads

Clay is there to save you some plaster :)

PS! This vertical rod is important because it will help you to keep the "mold" centered.
Mold and rod are connected so that mold spins freely.

#11 Mart

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Posted 30 June 2013 - 05:48 PM

You get the idea if you look at this picture:
Posted Image

This guy is building a part for F1 car model. Mold is turned around and table is fixed.

#12 AtomicAxe

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Posted 30 June 2013 - 07:33 PM

How about balls? The inflated kind for children are pretty tough and very cheap. I just used a big one (about 15 inches in diameter) to cast a slump mold from which to make a hump mold. I remember someone using one to make a one-piece (or almost one piece) spherical slip mold by casting the whole thing in one piece with just a hole left in it to deflate the ball and pull it out.

Jim


This. I've never had an issue with balls deforming unless not properly inflated. I think the largest one I made was about 32" in diameter. Just make sure you put YOUR seam around the balls seam ... oh and fill the plug with clay. But in reality ... I just took a sonotube, cut my section I need for the total height, split it down the side so I could remove it later, and made a mold like I normally would (build up back side with clay around the ball, make key holes and a pour spout, pour plaster on top, flip and remove clay, inspect mold and patch if nessessary, pour second half after using release agent.)

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#13 Kohaku

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Posted 30 June 2013 - 10:23 PM

Do you have access to vertical turning lathe for plaster? You can make make 2 half spheres and build a mold from those semispheres.

If you do not have access to turning lathe, you can use your throwing wheel and quarter of a circle (cut it out from sheet metal, firm plastic, plywood? etc) as your "mold".
First you make a hump out of clay and then you keep adding thick plaster mix (not too runny) on top of it while wheel is spinning slowly. You need to make sure it's soft enough so your mold can scrape it easily to the proper shape. Adjust the plaster/water ratio accordingly and mix small amount of plaster.

huh.. let me draw you a picture Posted Image


Cool idea. Maybe a bit of a naive question... but if you form plaster shapes on a wheelhead or bat, does the plaster come off easily once it's set?
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#14 Mart

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Posted 01 July 2013 - 10:13 AM


How about balls? The inflated kind for children are pretty tough and very cheap. I just used a big one (about 15 inches in diameter) to cast a slump mold from which to make a hump mold. I remember someone using one to make a one-piece (or almost one piece) spherical slip mold by casting the whole thing in one piece with just a hole left in it to deflate the ball and pull it out.

Jim


This. I've never had an issue with balls deforming unless not properly inflated. I think the largest one I made was about 32" in diameter. Just make sure you put YOUR seam around the balls seam ... oh and fill the plug with clay. But in reality ... I just took a sonotube, cut my section I need for the total height, split it down the side so I could remove it later, and made a mold like I normally would (build up back side with clay around the ball, make key holes and a pour spout, pour plaster on top, flip and remove clay, inspect mold and patch if nessessary, pour second half after using release agent.)


Sure, unless the surface is not smooth. It's good idea to put some soap water on all the surfaces, especially if you are pouring the second half of the mold.

#15 AtomicAxe

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Posted 01 July 2013 - 10:58 AM



How about balls? The inflated kind for children are pretty tough and very cheap. I just used a big one (about 15 inches in diameter) to cast a slump mold from which to make a hump mold. I remember someone using one to make a one-piece (or almost one piece) spherical slip mold by casting the whole thing in one piece with just a hole left in it to deflate the ball and pull it out.

Jim


This. I've never had an issue with balls deforming unless not properly inflated. I think the largest one I made was about 32" in diameter. Just make sure you put YOUR seam around the balls seam ... oh and fill the plug with clay. But in reality ... I just took a sonotube, cut my section I need for the total height, split it down the side so I could remove it later, and made a mold like I normally would (build up back side with clay around the ball, make key holes and a pour spout, pour plaster on top, flip and remove clay, inspect mold and patch if nessessary, pour second half after using release agent.)


Sure, unless the surface is not smooth. It's good idea to put some soap water on all the surfaces, especially if you are pouring the second half of the mold.


A release agent should be involved in every step of casting, whether that is thin fine mesh slip, soap, varnish, whatever. It helps. On play balls that are thick rubbery plastic, even when textured will flex and are made to not stick to a whole lot of stuff and have never had an issue with not using a release on the ball itself. Little bit of compressed air will burp it open from initial molding.

#16 Kohaku

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Posted 01 July 2013 - 11:31 AM

A release agent should be involved in every step of casting, whether that is thin fine mesh slip, soap, varnish, whatever. It helps. On play balls that are thick rubbery plastic, even when textured will flex and are made to not stick to a whole lot of stuff and have never had an issue with not using a release on the ball itself. Little bit of compressed air will burp it open from initial molding.


I had an amazingly frustrating morning running around town trying to find balls. Goodwill and Salvation Army are a bust. Wallmart (where I hate to tread) had a few sports balls (basketballs and the like) and a couple hot pink barbie nerf specials. Off to Big Five and the local craft store next.

Really though... it's pretty sad when the biggest retailer in the nation barely carries a ball on its shelves (but 50+ varieties of play guns).

Gad- I sound like my grandpa.
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#17 OffCenter

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Posted 01 July 2013 - 11:40 AM


A release agent should be involved in every step of casting, whether that is thin fine mesh slip, soap, varnish, whatever. It helps. On play balls that are thick rubbery plastic, even when textured will flex and are made to not stick to a whole lot of stuff and have never had an issue with not using a release on the ball itself. Little bit of compressed air will burp it open from initial molding.


I had an amazingly frustrating morning running around town trying to find balls. Goodwill and Salvation Army are a bust. Wallmart (where I hate to tread) had a few sports balls (basketballs and the like) and a couple hot pink barbie nerf specials. Off to Big Five and the local craft store next.

Really though... it's pretty sad when the biggest retailer in the nation barely carries a ball on its shelves (but 50+ varieties of play guns).

Gad- I sound like my grandpa.


I thought they were pretty common. I picked up 5 big balls at a Kroger for about $3 or $4 each and used them for casting then forgot about them in an old falling-down storage shed where they were exposed to the weather and a year later dug them out and used them again. They were strong, very smooth and did not deform when used to cast plaster. The dog even played with one of them and wasn't able to burst it. Try grocery stores, drug stores, Toys R Us, etc.

Jim
E pur si muove.

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#18 Kohaku

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Posted 01 July 2013 - 01:40 PM

I thought they were pretty common. I picked up 5 big balls at a Kroger for about $3 or $4 each and used them for casting then forgot about them in an old falling-down storage shed where they were exposed to the weather and a year later dug them out and used them again. They were strong, very smooth and did not deform when used to cast plaster. The dog even played with one of them and wasn't able to burst it. Try grocery stores, drug stores, Toys R Us, etc.

Jim


Finally found a couple balls in the local drugstore, and a rigid, smooth foam ball at the local craft store. ($9.00 for a five inch chunk of styrofoam!). Three sizes to experiment with- good enough for now.

I live in bumbleputz, Idaho... so my options are limited...
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#19 AtomicAxe

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Posted 02 July 2013 - 07:54 AM

you know, if I was in half an hour driving distance ... I would move to a place if it's named bumbleputz.

#20 Denice

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Posted 02 July 2013 - 08:14 AM

The styrofoam balls work well, I haven't done it but I watched someone make a sphere mold in college sculpture class. I believe it was acetone that he poured in the mold to melt the foam. Denice




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