DIY Rotocasting

Rotational molding, also known as rotomolding, is a molding process for creating many kinds of mostly hollow items. The info is not specific to Classic Cylon Centurions, but SURE can be helpful for them and many, many others projects. Here you'll find various threads with great info from our members for the hobby of costuming.
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Huttman
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Re: DIY Rotocasting

Post by Huttman » Thu Aug 18, 2011 6:12 pm

when i click on the image nothing happends


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Big Al
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Re: DIY Rotocasting

Post by Big Al » Thu Aug 18, 2011 6:17 pm

Huttman wrote:when i click on the image nothing happends

I'm not sure why it won't work for me either
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Re: DIY Rotocasting

Post by Cylon-Knight » Thu Aug 18, 2011 7:58 pm

Looks like it is just a small picture... no larger view to show = no click.
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Big Al
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Re: DIY Rotocasting

Post by Big Al » Thu Aug 18, 2011 8:38 pm

Cylon-Knight wrote:Looks like it is just a small picture... no larger view to show = no click.

Yea it is....that's the only pic they had
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Re: DIY Rotocasting

Post by groupleaderzeta » Tue Aug 23, 2011 4:33 pm

How do you figure out how much resin to use inside a mold for roto-casting?

I want a wall thickness around 1/8 inch (3mm)
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Re: DIY Rotocasting

Post by Big Al » Tue Aug 23, 2011 8:08 pm

groupleaderzeta wrote:How do you figure out how much resin to use inside a mold for roto-casting?

I want a wall thickness around 1/8 inch (3mm)
I personally can't answer that but I'd bet Skullbeast, Jclayman, or Flightldr. could...I searched for the answer on the supply sites but came up empty.

I'm sure it has to do with the size of the mold and the type of resin you are using.

But I'm sure the pro guy's have a calc for it.
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Re: DIY Rotocasting

Post by Huttman » Tue Aug 23, 2011 8:17 pm

groupleaderzeta wrote:How do you figure out how much resin to use inside a mold for roto-casting?

I want a wall thickness around 1/8 inch (3mm)

That, my friend is a tricky feat indeed. It boggled my mind for the longest time. Its too easy to simply give it up ;) Its right there in front of you! ;-)
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Re: DIY Rotocasting

Post by Big Al » Wed Aug 24, 2011 12:47 am

groupleaderzeta wrote:How do you figure out how much resin to use inside a mold for roto-casting?

I want a wall thickness around 1/8 inch (3mm)



Awesome question and I hope this helps. I found this on the Alumilite page although I think this is for a solid part cast in a RTV mold, It may help.

:cylon: Amount of Resin Needed to Cast a Part

Note: There is .554 ounces in 1 cubic inch of Alumilite Resin.

Formula for a Square/Rectangular Piece: Length x Width x Height

Example: If your piece is 3" x 4" x 2" = 24 cubic inches. Take 24 cubic inches x .554 ounces per cubic inch = 13.25 ounces.

Formula for a Round Piece: Pi x Radius (squared) x Height.

Use the same formula as the RTV round mold (section 1) to calculate resin needed. Then multiply that by .554 ounces per cubic inch to determine ounces needed.
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Re: DIY Rotocasting

Post by groupleaderzeta » Wed Aug 24, 2011 9:09 am

I was thinking of something similar, get solid volume. I use the dried rice method. Take that number and divide it by 3. Then use the result as my needed material.

I guess a new experiment is in order. :blush:
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Re: DIY Rotocasting

Post by Big Al » Wed Aug 24, 2011 9:20 am

:cylongold: Calculating Resin amount for Rotocasting


I searched the internet for the calculation of resin used to make a part by Rotocasting and could only find calculations for Mold Making rubber and solid Resin casting.

I searched many suppliers sites and found that alot of hobby guy's are useing "Smooth On" as they make resin specially formulated for rotocasting.

I sent them a request for the calculation and this is what they sent back.

I hope this helps





:cylon: 8-23-2011

How do you calculate the resin amount needed for rotocasting a hollow part? (Costume Helmet such as Stormtrooper, Cylon etc)

we would like to achive a 1/8 inch thickness


I have scoured your site and can only find the calcs. for making molds and casting solid parts.

Please help




:cylon: Date: 2011-08-24 10:52:08
Name: Jason Reese:


Al,
You would need to know the surface area to be coated.
The calculation is similar to determining the amount of rubber needed for a brush-on mold.
For example, using Smooth-Cast 65D as an example resin:
- A one-gallon unit of 65D weighs 16.75 pounds.
- The yield of the resin - per the TB - is 26.4 cubic inches per pound.

1. 16.75 lbs. x 26.4 cubic inches per pound = 442.2 cubic inches of material in a gallon unit
2. Divide 442.2 cu. in. by .175 (1/8") = 2527 square inches
3. Divide 2527 by 144 (no. of square inches in a square foot) = 17.5 square feet
4. A gallon unit of Smooth Cast 65D will cover 17.54 square inches at 1/8" thickness.

Jason Reese
Smooth-On, Inc.

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Big Al
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Re: DIY Rotocasting

Post by Big Al » Wed Aug 24, 2011 10:00 am

:cylongold: Calculation of Rubber needed for a Brush On Mold (Smooth On)


In the previous post, the Smooth On rep said the calc for the resin needed was similar to the calculation of rubber needed for a Brush On Mold.

Here is that Formula



:cylon: Brush-On Mold**

**The volume of clay used to cover the model directly corresponds to the volume of rubber needed to make the mold.

To Estimate the amount of rubber

1.) Form clay into a cube and calculate the volume of the clay.

Volume = Length x Width x Height


Our goal is to make a brush on mold of the cube (used in our example above) by brushing a
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Re: DIY Rotocasting

Post by groupleaderzeta » Wed Aug 24, 2011 11:08 am

I guess its time to dust off the calculus and see if I remember how to use it. :blink:

That's alot of calculations :lol:
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Re: DIY Rotocasting

Post by groupleaderzeta » Sat Aug 27, 2011 6:10 pm

Projects: Design, build, use, modify, recycle, tweak, lather, rinse, repeat

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Re: DIY Rotocasting

Post by Cylon-Knight » Sat Aug 27, 2011 6:20 pm

^ Very nice find, Zeta. Are you going to do some of that?
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Huttman
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Re: DIY Rotocasting

Post by Huttman » Sat Aug 27, 2011 6:29 pm

in regards to that video, i think all those steps are a bit overkill. As far as rubber silicone goes, i think its worth using the stuff that you let sit overnight. You will get more pulls from the mold ;)
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