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jnapier

Multi-Piece Slip Cast Mold Help

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Hi guys,

 

I am looking to make a multiple piece mould (imagine I'm casting coke can's and want to make a mould that casts 6 of those coke cans at once). It would be a one piece mold, as in one piece of plaster like a brick with 6 holes in it and a 'plate' piece underneath it.

 

Would this cause an issue to cast 6 masters assembled like a grid, in terms of how the water absorbs into the plaster?

 

ie. With two placed next to each other, would the water absorb through and clash with the water being absorbed from its neighbour?

 

Any help would be great!

Cheers.

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I'm trying to imagine what you are attempting to create, but I think you will have some trouble pulling that shape from a mold.

It would be easier to cast each one seperatly then assemble them with slip.

 

If the plaster is too thin in between, it will cause casting problems.

1" of thickness in the plaster would work. It may be possible to go less than 1" if the plaster mold was really dry. 

 

A sketch or a picture of a sculpture would help

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If a single can mold has 1 1/2 inch sides, then putting in multiples would require having that same distance for each can on the adjoining sides, or 3 inches.  Really simpler to do six one-can molds -- in making the molds, weight, storage, etc.  In that way, if one of the cylinders gets damaged, you only need to replace a single can mold rather than a 6 pack mold. 

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If a single can mold has 1 1/2 inch sides, then putting in multiples would require having that same distance for each can on the adjoining sides, or 3 inches.  Really simpler to do six one-can molds -- in making the molds, weight, storage, etc.  In that way, if one of the cylinders gets damaged, you only need to replace a single can mold rather than a 6 pack mold. 

 

I was thinking the same and if they are round items, you can make round moulds, thus using less plaster.

 

Also if they take a lot of slip to fill each one, by the time you have poured the last one, several minutes will have elapsed.  Then when they are "cast" and you're ready to pour the slip out, you will have to pour them all at the same time, and each one could end up slightly thinner from first to last.  If they are individual, you can time the pour in/pour out better to get a matching set.  A friend has many, many moulds, and only the smallest items are in multi-item moulds - handles, sprigs etc.

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I think two cans would be the limit as your going to fill and dump them so thats an issue with more-also the wall thickness will need to be thick.

Whats your plan on a two piece mold the domed bottom is on the bottom piece of said two piece mold?The top of can will be the fill holes???

This would work better as a 3 piece mold.

Mark

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If the items in question are small, them a multiple mold works just fine. We do sake cups this way, and tiny vases. For anything bigger than a teacup, double molds may work, but more single molds work better than gang molds. When there is enough plaster to pull the right amount of moisture, they get heavy quickly. Add the weight of the slip, and dumping them is a two person job. Also, the slip you dump tends to go everywhere, sometimes into other molds in the gang....

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make them individually.  use very large cups from 7-11 giant drinks to hold the plaster if the shape and size are really like a coke can.  sink the model into the cup so it stays where the plaster will be thick, not all the way to the narrow bottom.  try a few to get it right.

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Thanks guys, to clarify theyre similar in size to a coke can but have no underhangs etc, very simple cylinder object to slip out.

 

I think I'm commited to do multi piece moulds- but I may try a 3 piece instead of a 6 piece so I don't have to pour as long and plaster isnt as heavy.

Many single moulds just take up too much space and is a lot of handwork.

 

Thanks for the advice!

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We made many thousands of aroma therapy lamps in  a 3 piece single molds-the object was about 5 inches tall when bisque fired.That was middle 90's. It had a curved top like the bottom of a coke can.I still suggest single molds for this size object. How many of these finished pieces do you need? Are you making a master and then working molds or is this more a one off deal?

Mark

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I have a whole bunch of masters, as I already have been casting them indidivually for a while but now want to bulk cast many of them. Having 6 individual molds is just to big and unwieldy I've found.

The vase has a thinner top so it needs to be a two piece mold (a flat plate of plaster and a 'toilet roll' shape top to lift off and slip the piece out.

 

I think if I have 3 in a row it wont be a big deal, as long as it absorbs properly.

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If, as you have written:  " Having 6 individual molds is just to big and unwieldy I've found." is true, you will really learn what unwieldy is when you handle a mold for three vases.  If you intend to reuse the mold multiple times, as quickly as possible, you need to make the plaster between the vases at least as thick as the outside walls of the mold or there will be moisture problems.  Interior walls will take longer to dry, and that means any casting will take longer to set up because the plaster will be absorbing moisture from both sides.  

 

Most working molds need walls at least 1 1/2" thick (refer back to comments made by bciskepottery) and double that to 3" between what you cast .  Add up the depth of plaster needed, plus the size of vase (I've allowed 2.5") and you come up with a length of 16 1/2 " , width of 5 1/2", height of 5"; plus the base plaster which also needs to be at least 1 1/2" thick.  Actually, if the base is to be 16 1/2" long, I'd make it reinforced with burlap, or mesh of some sort and another 1 1/2" of plaster.  Hope you are strong, in good shape, and have a friend to help. Because when you fill the mold and have to dump the excess slip, I'm not sure the word unwieldy will any longer suffice.

 

Shirley

oldlady and Mug like this

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If production is your ultimate goal, you may wish to consider a different process all together.
A hydraulic clay press can occasionaly be found reasonably priced at auction.
This could handle multiple simple shapes efficiently.

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