Send the right file.

Most jewelry projects start with a file, and the file decides how much of the quote is guesswork. A supplier with a solid model, units and a drawing can quote in a day; a supplier with a photograph has to design the part first.

The formats, and what each is for

Two of these cause most of the problems: STL and the photograph.

What STL loses, and why it matters

STL stores a surface as a mesh of triangles. It has no concept of a cylinder, a radius or a dimension — only facets. STEP is a different proposition: the format is written to ISO 10303, which is why it carries exact surfaces and a unit system. Three consequences follow from the mesh.

No units. An STL is a set of numbers with no scale. A 20 mm pendant and a 20 m gate can be the identical file. The factory has to guess, and a guess that is wrong is discovered after the model is printed.

No tolerance. A curved surface in an STL is a series of flat triangles. How close they approximate the true curve depends on how the file was exported, and nothing in the file says which.

No feature information. Holes, threads and fits are approximations of triangles. A machining supplier cannot set up from a mesh.

STL is useful for one thing: printing a model to hold before committing to tooling. Send it as an extra, not as the file.

Units and scale: the mistake that repeats

Every model must state millimetres. Two people can export the same design in different units and neither file announces which.

Three habits that prevent it:

• Draw in millimetres from the start. Converting at export introduces rounding.
• Put the overall dimensions on the drawing, not only in the model. 32.0 mm overall length is verifiable; a model is not, until someone measures it.
• Put one known dimension in the file name or the email: "pendant, 32 mm tall, STEP". It costs a sentence and removes a whole category of error.

Ring sizes follow the same rule: the model should carry the inner diameter, and the drawing should state the size system — US, UK, EU or millimetre diameter. "Size 7" means three different things depending on who reads it.

What the drawing adds

A model plus a drawing is a manufacturable package. The drawing carries what geometry cannot:

The dimensions that must be held. A small number, toleranced individually. Everything else falls under a general tolerance block.

Wall thickness and minimum section. A cast part needs a minimum wall to fill; a drawn or stamped part needs a minimum to form without cracking. The model may show a 0.5 mm section that cannot be produced in the chosen process.

The alloy. 304, 316L, 430 or a specific grade. It changes the cost, the corrosion behaviour and, for anything worn against skin, the compliance position. Sheet stock is usually specified to ASTM A240, and nickel release on the finished piece is settled by EN 1811 testing at a lab rather than by a statement on the drawing.

The finish, and where it stops. Polished faces and brushed sides on the same part is a normal request and an extra operation. Say which is which on the drawing, not in an email. The FTC's Jewelry Guides at 16 CFR Part 23 also require a coated part to be described as coated, so the finish line on the drawing is a labelling decision as well as a production one.

The assembly relationship. If the part meets another part, the interface dimension and the tolerance belong on the drawing. This is the dimension that decides whether the product works.

What a factory needs in the email

Five items make a quote possible without a design round:

1. The file — STEP or 3DM, plus DXF if there is a flat component
2. The drawing — PDF, with units, tolerances, alloy and finish
3. The quantity for this run
4. The process preference, if there is one — cast, stamped, machined, laser-cut
5. Any reference piece or photograph that shows the intended feel, clearly marked as reference

With those five, a quotation reflects the actual part. Without item 2 it reflects an assumption, usually the cheaper process — which is how a project is re-quoted after the tooling is cut.

If you only have a sketch

That is workable and common. A dimensioned sketch with three views, the overall size in millimetres, the alloy and the finish is enough to start, but not enough to quote precisely: the missing detail has to be designed first.

Expect a two-step reply in that case: a design or modelling cost, then a production quote once the model is approved. That is a normal sequence, not an obstacle — and it is cheaper than discovering the assumption after the mould exists.

Where the part is a pendant or a charm, one critical dimension usually covers it; a ring needs the inner diameter, band width and size system. The tolerance language for that drawing is set out in dimensional tolerance, and the document it sits inside is covered in what a tech pack contains. Send file, drawing and quantity through the RFQ page.