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Free investment flask calculator

Work out how much investment powder and water to mix for a flask. Pick a standard size or enter your own, subtract your model if you know it, and set the water ratio.

Runs in your browser. Nothing you enter is uploaded.

Your design

Choose a flask and a ratio under Options. The amounts update as you go.

Your choices update the result automatically.

Options

Flask size
Model displacement
To use mm³, divide by 1,000.
Wax is about 1.0 and castable resin about 1.1. Check your resin’s data sheet.
Investment mix
Calibrated to the Ransom & Randolph flask chart at a 40/100 ratio. Use your investment maker’s value.
A little extra covers what stays on the mixer and in the bucket.

Result

Choose a flask and a water ratio to see how much to mix.

How it works

  1. 1

    Pick the flask

    Choose a standard size, or enter a custom diameter and height in inches or millimeters.

  2. 2

    Add your model

    If you know the model’s volume, or the weight of its wax or resin pattern, the page subtracts it. Leave it off for a bare flask.

  3. 3

    Mix

    Set the water ratio, read the grams of powder and water, and follow your investment maker’s mixing instructions.

The flask formula
Flask volume is π × radius² × height. The model’s volume comes out, 10% extra goes in, and the slurry weighs about 1.75 g per cm³. Powder is the slurry weight divided by one plus the water ratio.
Mixing
Use deionized water at 72–75 °F (22–24 °C), and add the powder to the water. Mix and vacuum for the times on your investment’s instruction sheet.
Estimates
Casting numbers are estimates. Check the amounts against the chart that comes with your investment, and use the maker’s ratio.

Questions

How much investment do I need for a 3 × 4 inch flask?

About 640 g of powder with 10% extra and no model, and less once a model is subtracted. The page works it out for any size.

What ratio should I use?

Most makers give 38 to 40 parts water per 100 parts powder, with less water for large castings and more for fine detail. Use the ratio on your investment’s instruction sheet.

How do I add a model?

Enter its volume in cm³, sprue included, or the weight of its wax or resin pattern. Wax is about 1.0 g/cm³ and castable resin about 1.1.

Can I find the model’s volume?

Yes. The lost-PLA sprue builder works out the volume of a model with its sprue, and the casting weight calculator reads the volume of any STL.

Is my file uploaded anywhere?

No. The conversion runs in your browser with the JavaScript on this page. Your data never leaves your computer, and nothing is kept after you close the tab.

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Source code and license

You can inspect the code and the licenses here. Models are parsed and measured on your device.