Casting Calculator
Estimate casting cavity volume, charge weight, gate and riser feed, sprue allowance, and pattern shrink for metals, resins, plaster, wax, and silicone pours.
Calculation Breakdown
| Material | Density | Linear shrink | Feed note |
|---|---|---|---|
| Aluminum 356 | 2.70 g/mL | 1.3% | Use clean gates and moderate risers for sand molds. |
| Silicon bronze | 8.80 g/mL | 1.8-2.1% | Heavier charge and a robust riser tree are common. |
| Gray cast iron | 7.20 g/mL | 0.9-1.1% | Allow for gating weight and mold loss. |
| Zinc alloy | 6.70 g/mL | 1.1-1.3% | Small risers may be enough for compact shapes. |
| Epoxy resin | 1.12 g/mL | 0.3-0.8% | Gate allowance mostly covers cups and vents. |
| Plaster | 1.55 g/mL | 0.1-0.3% | Use open reservoirs for relief tiles and molds. |
| Casting type | Gate range | Riser range | Planning cue |
|---|---|---|---|
| Small resin or plaster mold | 3-8% | 0-8% | Allow for cup loss, vents, and trimming. |
| Simple aluminum sand casting | 6-10% | 12-25% | Keep feed above the thickest section. |
| Bronze investment tree | 8-14% | 18-35% | Sprues and buttons can weigh more than the parts. |
| Iron bracket or machinery blank | 7-12% | 15-30% | Use conservative feed for isolated heavy bosses. |
| Thin decorative casting | 5-9% | 6-16% | Runners help fill before the section freezes. |
| Project | Typical size | Material | Allowance start |
|---|---|---|---|
| Name plate | 8 x 4 x 0.4 in | Aluminum | 7% gate, 15% riser |
| Bronze pendant tree | 12 small cavities | Bronze | 10% gate, 25% riser |
| Relief tile | 12 x 12 x 0.5 in | Plaster | 5% gate, 3% reservoir |
| Gear blank | 4 in dia x 0.8 in | Zinc | 7% gate, 12% riser |
| Prop shell | Measured volume | Urethane | 6% cup loss, 4% vent |
| Unit | Equals | Best use | Calculator note |
|---|---|---|---|
| 1 cu in | 16.39 mL | Small pattern math | Used internally from inch dimensions. |
| 1 fl oz | 29.57 mL | Resin, plaster, silicone | Shown in imperial volume results. |
| 1 liter | 1000 mL | Metric batch planning | Useful for measured mold volume. |
| 1 lb | 453.59 g | Metal charge weight | Imperial weight output is rounded by material. |
| 1 kg | 1000 g | Metric charge weight | Metric output uses kilograms for larger pours. |
When you are performing a casting, you have to calculate the total amount of material that you are going to need to melt for your process. You might find halfway through the process that you dont have enough material. This can happen if you do not account for the fact that the volumes of the finished part is going to be less than the total amount of material that you poured into the mold.
There are a few different reasons for this. Firstly, you must account for the geometry of the part that you are creating. However, you must also account for the logistics of the process of pouring the material…
How to find out how much material you need for casting
The sprues, the gates, and the risers, that will be used during the casting process. If you did not account for these, you would not have enough material for the casting process to be complete. One of the factors to consider in the casting process is known as linear shrink.
Linear shrinkage occur in metals as the metal liquefies and then subsequently solidifies. Metals like aluminum and bronze experience linear shrinkage. If you create a mold for the desired part, the part will be smaller than you intended when it sets and solidifies.
To combat this, the creator of the molds will create patterns for the mold that are slightly larger to provide for the linear shrinkage of the metal. Another area in which material is consumed during the casting process is the feed system. The feed system includes the sprue, the gates, and the riser.
The sprue is the vertical structure that channels the materials into the mold. Gates are the smaller structure that direct the metal into the mold cavity. The riser is the extra portion of the mold that remains in a liquid state longer than the remainder of the casting process.
This riser is essentially extra material for the feed system that does not end up as part of the final manufacture part. The volume of the sprue, the gates, and the riser must be accounted for in the total amount of material that is required for the casting process. The amount of material that is required for the feed system into the mold will depend upon the material that is used to create the casting process and the mold itself.
For instance, thin pieces will require more smaller gates than heavy metal brackets will require risers. Additionally, the metals of different alloys will require different amounts of material for the feed system. Other materials, such as resin or plaster, will also shrink at different rates than the metal.
In these cases, as well, then, the amount of material for the feed system will need to be adjusted for factors like cup loss and vents when resin or plaster is used in the casting process. For irregularly shaped objects, it is difficult to determine the amount of volume of material that will be required to manufacture the part. The volume of such an object can be determined by using the water displacement method, for instance.
Another way to determine the true volume of the part is to fill the mold with sand, rice, or water. By using these methods, you can find the true volume of the casting process. Once you have determined the true volume of the part, you can calculate the total charge weight for that process.
The total charge weight is the total amount of material that you will pour into the crucible or the mixing bucket. You must account for the fact that some of the material will be lost due to factors like dross and residue. Dross is the layer of metal that oxidizes and forms a layer upon the melted metal.
Residue is the material that adheres to the sides of the resin mixing cup. In these cases, it is better to have some material left over than to have insufficient material to fully complete the mold. By calculating the amount of material necessary for both the part and the feed system and accounting for losses due to dross and residue, you will ensure that you have enough material for the casting process.
