RTV Volume Calculator: Envelope, Mother, Waste

A silicone volume calculator is only useful if you feed it the right volumes: the pour envelope after CAD lock, the displaced volume of the living resin production mother (and cores), and the waste you will never recover - cup heel, vacuum foam, sprue, and the extra you mix so you do not short the last corner. Convert cm3 to grams with the grade density, then add a waste factor. Skipping waste is how a 1:1 platinum mix dies mid-pour and leaves a foam face you cannot sand back on a food logo. We quote rubber by that stack, not by outer tray size.

On this site the path is photos, sketch, or CAD, then a 3D-printed pattern, often a temporary silicone flip, a resin production mother, then batch RTV. The mother is not the pattern. Free DFM. HTV/HCR compression mold tooling is also quoted on RUUIPON.

The object on this page

Pour envelope: length x width x pour height to the planned shut, in centimetres, after any dam. Do not use the plywood outside. A 300 x 200 x 40 mm interior is 2,400 cm3 before anything sits in it. Mother displacement: the living resin production mother occupies volume the rubber will not. CAD is the honest number. A water-displacement check on a sealed mother is the shop backup when the STL is hollow. Cores that stay in during the pour subtract too. A hollow print that floods internally adds rubber unless you seal the print first - and that print is a pattern, not the mother.

Waste: typical shop practice is a 10-20% extra on small pours and 5-10% on large block pours, plus a cup heel so the vacuum chamber does not run dry. Foam that climbs the bucket during degas is rubber you already mixed. Density converts volume to grams. Platinum RTV is often around 1.1 g/cm3; use the TDS for the named grade. Mix 1:1 or 10:1 by weight, never by the volume marks on a cup.

An open-back glove uses less rubber than a block pour of the same part - that is a structure decision, not a calculator trick. Vacuum degas makes the mix look taller before the foam collapses. If you fill the cup to the brim to match the calc, you will overflow the chamber and starve the pour. Loaded-tray sag of about 0.5-1.5 mm is a support-shell problem, not a pour more silicone problem. Extra wall thickness is usually the expensive way to fake stiffness. If your email still says "master, box, keys, jacket" as the buy, you are listing shop furniture, not the object.

Common mix-up

Buyers send 800 ml of silicone from a kitchen jug. A/B is weighed. A 10:1 grade grabbed off volume marks is how you get a sticky face and a hard back. Another mix-up: quoting one rubber weight for twenty production skins from a prototype that used a smaller envelope. MOQ 20 is twenty of the locked design, each needing its own grams plus a shared living mother. Recast grams can be lower if the support shell already exists and you only pour the skin. Catalog copy that says cut a resin master skips the pattern-vs-mother split. We will not quote that sentence.

Typical shop values

Reference values only. Confirm material-specific limits against the supplier’s technical data and agree project acceptance criteria before production.

Worked example

A resin figurine, block mold. Pour envelope 180 x 120 x 70 mm - 1,512 cm3. Living-mother displacement from STEP 420 cm3. Net 1,092 cm3. Density 1.10 - about 1,201 g net. Waste 15% because it is a first vacuum pour - about 1,380 g to weigh, split 1:1. Support shell was plaster, quoted as a separate line. CAD was USD 50 because we only had photos; lock, then 3-7 business days for the prototype skin. Production was MOQ 20 of that keyed block, not 20 kg of leftover rubber. Food was never on this PO - jewelry-adjacent resin is not a 177.2600 article.

Stay on this page / skip this page

Stay when you need RTV grams for a pour cavity: envelope minus living mother plus waste.

Skip compression HCR preform weight - that is a mill ticket; finished parts are an HTV product or mold RFQ here, or a different LSR-tool RFQ - ask us. Skip a purchased stock tray with unknown wall. Skip guessing box height from a lifestyle photo of the finished soap.

We will not mix to the exact net grams with no heel. We will not thicken the RTV wall to replace a support shell on a wet dump. We will not volume-mark a 10:1 platinum on a food cavity. We will not cut a resin master as the written shop path.

Related: how molds are made, contact.

What to send

• Part envelope L x W x H and cavity count
• Photos, sketch, or CAD; structure: open-back / block / split / plug
• Support shell: yes/no and material (separate from RTV grams)
• Pour: food / resin / wax / plaster / concrete (concrete and jewelry are not food)
• Mix: platinum 1:1 or 10:1

Send the envelope to [email protected] or contact. WhatsApp +86 135 3006 2969.

FAQ

Can I use an online silicone calculator and just send you the grams? Send pour envelope, living-mother volume, and structure. Calculators that skip waste and open-back vs block will short a pour. We re-run the stack.

Is 1 ml of RTV equal to 1 gram? Usually not. Use the named-grade density, often around 1.1 g/cm3, and weigh A/B. Volume marks on a cup are how 10:1 mixes go wrong.

Does platinum shrink change how much I mix? Typical platinum shrink is about 0.1-0.3% linear. You still mix the grams to fill the envelope. Compensation lives on the pattern and the living mother, not in a smaller cup.

If I order MOQ 20, is that 20 times the prototype grams? Twenty skins of the locked design, each needing its pour, unless we are recasting into an existing support shell with a defined skin volume.

Do I pay USD 50 to get a volume number? The USD 50 is for simple 3D when that CAD scope applies. Volume is a quote input we can run from a STEP. Photos-only still needs a model before the grams are honest.