Prototype Tooling Versus Production Tooling in One Project: Where the Handover Really Happens
Prototype tooling versus production tooling is usually presented as a choice. In a real silicone weight project it is a sequence, and the two tools are asked to prove different things. The prototype tool answers whether the part can be made and handled; the production tool answers whether the same part can be made ten thousand times without the strap slot drifting, the flash thickening or the Shore hardness wandering between cavities. Treating them as one build is how a project ends up with samples that feel right and a mould that will not run.
What Each Tool Is Actually Asked to Prove
A prototype tool is cut from aluminium or a soft block, usually single cavity, with manual demoulding and no ejector system. It is expected to survive a few hundred cycles, to be re-cut within a week when the design moves, and to deliver parts in eight to fifteen working days. Its job is to confirm wall thickness, the parting line position, whether the insert sits concentric, and whether the strap channel can be demoulded at all.
A production tool is a different object. Hardened steel such as P20 or 718H, four to eight cavities on a balanced runner, temperature control circuits sized for a 165 to 175 C platen, ejector pins and a guided stripper plate. It is built for 50,000 to 100,000 cycles with scheduled cleaning, and it is expected to hold the same dimensions in cavity one and cavity eight. That last sentence is the whole cost of the second build, and it is the sentence a prototype tool cannot test.
The Handover Point: Which Dimensions Carry Over
Almost none transfer automatically, because silicone shrinks. High consistency rubber for a weighted hand piece typically runs a linear shrinkage of 2.5 to 3.5 per cent depending on filler load, wall section and cure temperature, and the prototype cavity is compensated from a first-article measurement that may rest on a single cavity. When the production tool is cut, that compensation has to be recalculated for the real cavity layout, because a four-cavity plate heats less evenly at the edges than a single block in the middle of the platen.
The dimensions that must be carried across explicitly, in the part drawing rather than in conversation, are the wall thickness at the thinnest section, the draft angle on every vertical face (1.5 degrees minimum, 3 degrees on textured surfaces), the radius at the base of the strap slot, the insert pocket depth and its concentricity tolerance, and the parting line height relative to the grip band. Everything else can be re-derived; those five cannot, because they set how the part feels in the hand.
Compression or Injection Changes the Tool, Not the Part
Most silicone studio weights are compression moulded: a pre-weighed charge is placed in the cavity, the platens close, and the material flows to fill the shape under 150 to 200 bar for a cure of five to ten minutes depending on section. A compression tool is simpler, less demanding to maintain and forgiving of a heavy iron insert. An injection tool adds a cold runner, a nozzle shutoff valve and much tighter shutoff faces at the parting line; it shortens the cycle and improves repeatability on thin walls, but it punishes any undercut that a compression tool would simply strip past.
The decision is normally fixed before the prototype is cut, because it decides where the material enters. Moving from compression to injection after the prototype has been approved means a new gate position, a new weld line and, in most projects, a new production tool rather than a modification.
Where Prototype and Production Samples Disagree
Buyers who complain that samples do not match the production feel are usually describing one of four things. Hardness: a prototype run at 45 Shore A from a hand-mixed batch against a production run at 50 Shore A from a masterbatch. Flash: prototype tools are hand-fitted, so flash is trimmed; production flash has to be designed to a 0.10 mm limit at the parting line or it will be trimmed by the operator, inconsistently. Surface: a polished prototype cavity gives a satin part, while a production cavity with a blast finish gives a drier grip. Weight: the iron insert tolerance of plus or minus 2 g is invisible in ten samples and obvious across five thousand.
The practical fix is to specify the production condition in the prototype order: same hardness grade, same surface finish call-out, same insert supplier, and a first-article report that lists cavity number, cure temperature, cure time and measured weight for every part in the sample set.
Sequencing Both Builds on One Calendar
A realistic sequence for a new silicone hand weight runs as follows. Week one to two: DFM review on the 3D model, draft and undercut check, parting line agreed. Week three to four: prototype tool cut, T1 samples in eight to fifteen days. Week five: fit and feel trial with the studio or the buyer, changes marked on the model. Week six: model frozen, production tool released. Week seven to twelve: steel cut, heat treated, spotted in, T1 on the production tool. Week thirteen: T2 with corrected shrinkage, first-article inspection, cavity balance check. Week fourteen to fifteen: pilot run of 300 to 500 pairs, packing trial, final approval.
Two gates protect that calendar. The design freeze gate stops the steel being cut against a model that is still moving, which is the single most common reason a tooling quotation doubles after the fact. The T1 gate stops a pilot run being booked before the parting line is clean. Both gates are inexpensive to run; skipping either is not.
Keeping One Set of Part Data Through the Change
The prototype tool and the production tool should be cut from the same model revision, and the revision number should appear on the drawing, the first-article report and the carton label. Cavity numbering has to start at the prototype, so that a sample from cavity one means the same thing at both stages. Colour is part of the data too: a prototype in a natural or stock shade tells you nothing about pigment dispersion, and a change of shade usually means a change of cure time.
Quadra Fit keeps prototype and production tooling under one part number and one revision log, so a buyer who approves a T1 sample is approving the geometry that the production cavity will be cut to. The moulding and tooling scope is set out under capabilities, finished weight options sit on the product pages, and a tooling review can be booked through the contact page with the 3D model and the target hardness. For a wider view of how prototype tools differ from production tools in rubber moulding, the tolerance and steel guidance published by Apple Rubber covers the same split in a neighbouring material family.
Frequently asked questions
How much does a silicone weight mould cost?
The drivers are cavity count, steel grade, insert pocket complexity and whether the tool needs a cold runner. A single cavity aluminium prototype is a fraction of a hardened four cavity production tool. Ask for the quotation split into prototype, production and spare cavity insert so you can see which line moves when the design changes.
Can I use a 3D printed mould for samples?
For a shape check on a flat, thick part it can work, but not for a weighted piece. The printed resin softens at cure temperature, the surface transfers layer lines into the grip, and the clamp pressure distorts the cavity. Use it for a handle trial, then move to an aluminium prototype tool for anything that will be held in a class.
How many shots before a mould wears out?
A hardened steel production tool for a silicone weight normally runs 50,000 to 100,000 cycles before the parting line needs re-spotting, and the insert pocket is usually the first feature to go. Aluminium prototype tools are good for a few hundred cycles. Plan a spare cavity insert at the production build so a worn pocket does not stop the line.
Why do prototype samples feel different from production parts?
Four usual reasons: hardness grade, surface finish, flash at the parting line and insert weight tolerance. Specify all four in the prototype order and ask for a first-article report with cavity number, cure time, cure temperature and measured weight, then compare like with like.