Custom RTV Mold Costs Versus a Steel Part-Tool Quote

If you're quoting a custom RTV silicone mold, soft tooling is not a discounted steel mold. It is a different bill of materials: master, mold box, platinum or tin skin, registration, and a support jacket.

A steel production tool is a longer-life stack for vulcanized silicone parts: plates, cold-runner, heaters, polish, tryout. You amortize it across shots. You don't dump pectin into it.

If you compare “the mold price” as two numbers, you will pick the wrong one. Compare the stack, and name which object ships: a flexible cavity you pour into, or a molded article.

The stack, not the sticker

Every custom RTV mold quote is five buckets.

1. Master (pattern). CNC, SLA/DLP, machined metal, or a finished sample. Surface and size start here. Full UV post-cure, wash, and barrier coat are part of the price, not a courtesy.

2. Mold box / flask. Walls that set pour height and keep the jacket square. A warped plywood flask prints as a tapered block.

3. RTV cavity. Platinum or tin, mix 1:1 or 10:1, vacuum degas, Shore 10A–20A skin typical for undercut food tools.

4. Keys, cores, jacket. How the halves find themselves, how a hollow extracts, and the mother mold so the sheet does not sag 0.5–1.5 mm.

5. Expected life, expressed as dumps you trust, plus recast. Not a warranty. A construction intent. A recast of the RTV skin against the same master is how you restore life; it is not a new steel tool.

Piece price of the *dump* sits outside this stack. Mixing an RTV jacket quote with an LSR piece price is how a cheap glove “wins” and then loses on sag and recasts.

Common mix-up: two quotes, both say “mold”

A brand wants a 12-cavity bear, 18 mm tall, food-contact, about 2,000 dumps a month.

RTV route: CNC or SLA master, keyed two-piece platinum RTV, rigid jacket, maybe a second recast in the price. Change a logo by recasting the face.

Production-part route: heated steel or aluminum, and for LSR a cold-runner. That quote will not dump pectin.

Both PDFs can say mold cost. Ask which object ships.

What moves an RTV number

• Master complexity. CNC vs print vs a physical sample. Undercuts, two-sided logos, cores.
• Split vs open-back. A one-piece glove is cheaper until it tears.
• Jacket. Optional on a tiny shallow tray. Not optional on a large wet dump.
• Cavitation. 1–2 to freeze peel, then duplicate. An 8-cavity aluminum LSR tool is a false comparison.
• Food-contact path. 21 CFR 177.2600 / LFGB on the finished *cavity*, not a logo that says “FDA approved.”
• Recast included or extra. Paying a tooling charge does not, by itself, give you unrestricted transfer rights or free recasts.

Printed polymer *LSR cavities* and CNC aluminum *part* tools are the parts conversation. They run hot. They are not this product.

Steel production molds, as contrast only

Steel is a class plus LSR-specific hardware: cold-runner, cavity heat, vacuum, clamp. SPI 101–105 are cycle-life intents for *part* tools. Don't stamp Class 103 on a platinum glove. If you actually need that stack, open a parts OEM RFQ.

What people get wrong: buying steel “because we will go to production” while the mascot still has three competing lips. Another: staying on a sagging glove for a year, then discovering fill-weight was never mapped.

The comparison that actually changes the buy

Use dumps *and* change-risk, not volume alone.

| If this is true | RTV custom mold | Steel part tool | | --- | --- | --- | | Geometry still moving | Correct. Iterate the master. | Wrong. You will pay for steel twice. | | Lifetime is hundreds of dumps | One skin, maybe no jacket if tiny | Overbuilt | | Lifetime is thousands of dumps, design frozen | Jacket + recast plan | Only if you need molded *parts* | | You dump food, wax, resin | The job | Wrong machine | | You need vulcanized LSR/HCR articles | Wrong asset | The job |

What to ask when you're buying

• Master type, and who keeps it?
• Skin Shore, platinum vs tin, jacket yes/no?
• Recast of the RTV skin included after wear or a logo change?
• Cavity count vs monthly dumps, after freeze?
• Is this quote a cavity you pour into, or a part tool?

Worked example: 12-cavity bear, two stacks

Same 12-cavity 18 mm bear, ~2,000 dumps a month. RTV: master + box + 10A–20A platinum skin (mix 1:1, vacuum degas) + jacket + one recast priced. Fill-weight map on FA. Steel LSR 12-cavity for a silicone toy of the same outline is a different factory physics. We would not blend them into one number.

ISO 3302-1 might class a rubber article. It does not price a jacket.

When this article is the wrong quote

If you already know you need thousands of molded silicone *parts*, don't use this RTV stack as fake steel. Quote HCR or LSR on a parts OEM. A tiny artisan tray can skip the jacket. Geometry can override quantity: one deep core can cost more than a small compression tool.

Related reading: custom RTV molds, hidden costs, TCO, gummy trays.

How to read two quotes without fake unit prices

Ask both vendors to split:

• Construction (master / box / skin / jacket / recast — or steel class if they insist on a part tool)
• Expected life in dumps or shots, as an intent
• Tryout and first-article packet included
• Dump or piece-price drivers at two volumes

Then do the only arithmetic that matters: tool + (dump × volume) + expected scrap + one planned recast or modification. RTV wins when that last term is likely and the object is a cavity. Steel wins when the object is a part and the volume is high enough to bury the steel.

Put this on the RFQ: “Quote RTV master+skin+jacket as one stack. Don't blend a Class 103 LSR tool into the same number. Name recast.”

Send master photos or the STL, finished dimensions, and the material you will cast. We will review the split, jacket, and whether a recast belongs in the price.

We would not recommend blending RTV and steel into one sticker

We would not recommend an 8-cavity aluminum LSR bridge as a “cheap RTV.” We would not skip the jacket to win the mold price and then pay it back in 0.5–1.5 mm sag. We would not cut steel “so we can scale later” while you still dump pectin. Raising Shore A first is the wrong fix for a floppy cavity.

RUUIPON Mold Structure Decision: quote the cavity stack. Flat back? open-back. Deep undercuts that will not peel? two-part / core. Soft 10A–20A or wet dump? mother mold in the price, not as a change order.

flowchart TD
  A[What ships?] --> B{Flexible cavity you pour into?}
  B -->|yes| C[Master + box + skin + jacket]
  C --> D{Geometry frozen?}
  D -->|no| E[Cheap master; delay extra cavities]
  D -->|yes| F[Jacket + recast in the price]
  B -->|vulcanized silicone part| G[Stop: steel/aluminum part RFQ]

Typical shop values

Caption these as typical shop values, not a named lot.

| Item | Typical shop value | | --- | --- | | Cavity Shore | 10A–20A platinum RTV, jacket behind it | | Mix | Platinum 1:1 or 10:1; vacuum degas | | Linear shrink | ~0.1–0.3% (platinum) | | Loaded-tray edge sag | About 0.5–1.5 mm without a jacket | | 12-cavity 18 mm bear | ~2,000 dumps/month is a common first band | | Life | Count dumps + recast against the unsanded master |

FAQ

Is an RTV mold just a discounted steel mold? No. It is master, box, skin, keys, and jacket, built so you can pour a dump and recast the skin. Steel is a longer-life stack for molded *parts*: class, heat, cold-runner, tryout. Compare those buckets, not two stickers.

Why can't I compare an RTV jacket quote to a steel LSR quote? Cycle life is dumps, not shots, and the machine is a person or a depositor. The object that ships is different. Treat them as different POs.

When does a 1-cavity RTV beat a Class 103 steel tool? When you need a cavity to dump into, geometry is still moving, or lifetime is hundreds to low thousands of dumps. Steel while three lips compete is paying twice — and still will not dump pectin.

Should I 8-cavity an RTV tray to save dump price before freeze? Usually not. Extra pockets are extra recast area. Freeze peel and fill-weight on 1–2 cavities, then duplicate.

What two stacks belong on one RFQ so quotes are comparable? RTV master+skin+jacket with recast named, and — only if you also need parts — a separate LSR/HCR line. Same dump, same flash at the split, split as construction, intended dumps, tryout packet. Then add tool plus dump times volume plus one planned recast.