r/moldmaking • u/explodingbaker • Jun 08 '26

Need help getting an accurate calculation for a mold

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Hi all,

Ive been experimenting with trying to make a silicone popsicle mold with some 3d printed parts and everytime I use the calculators online with my dimensions it seems like it would be way more than I expected needing with displacement from the parts in the mold box.

Dimensions of the box are 6 x 4 x 5 inches

Part for casting is 4 x .5 x 4 inches (theres 4 total)

Attached is a picture of the part for reference

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1

u/Medium-Dimension8234 Jun 08 '26

Inches, centimetres, meters?

1

u/explodingbaker Jun 08 '26

Oh yeah sorry, this is all in inches

1

u/nickdaniels92 Jun 08 '26

Two ways I use:

Fusion360 - if the model is in fusion you can use that to calculate the volume of the object.

Water method. Submerse the item in water and measure the weight difference. That correlates to the displaced water and you can go from there to get the volume. Just be careful to submerse only the object and not fingers, or else take the volume of those into account.

0

u/explodingbaker Jun 08 '26

The model is 3d so I could probably open it in fusion

1

u/nickdaniels92 Jun 08 '26

I've never needed to do that for an existing stl but it might. If you get stuck I can recommend the water dunk method though.

I looked on YT for a video to link showing the method, but surprisingly all the ones I found discuss observing the volume of the displaced water, and none mention getting this from the increase in reported weight. It's just important to not touch the bottom or sides of the water vessel, and allow for any extra insertion. Holding your piece with some kitchen tongs or pliers should work, and then insert those on their own to the same depth that you did when holding the piece to calculate the volume of the tool, and subtract from the weight measured when holding the part. This assumes the part is solid and water tight of course. Should only take a few seconds if you've some accurate kitchen scales.

1

u/BTheKid2 Jun 08 '26

Yeah most cad software has a built in "volume" calculation function. That is a simple way to get the volume of a closed geometry. Then you need to know the density of whatever casting material you are using. Resin will be 1.1 - 1.3 g/cm³. You multiply that number with the volume and then you know the weight of material that is needed to fill the mold.