Send both. A 3D model in a neutral format such as STEP carries the geometry a foundry needs for feeding and gating studies, but it carries no tolerances, no notes and no revision control. The 2D drawing is what turns geometry into a requirement the supplier can be held to.
What Each File Does
The model answers "what shape is this part". Foundries use it to study wall sections, plan gating and risering, estimate melt weight, and check whether the geometry is castable in the proposed process at all.
The drawing answers "what has to be true about this part". It carries the datum scheme, the dimensions that are functional as opposed to reference, the tolerance grade, surface finish requirements, heat treatment condition, and the revision level that says which version governs.
Why a Model Alone Is Not Quotable
A shop that receives only a model has two options: assume a tolerance scheme, or ask. Assuming means it quotes to the tightest reading it can justify, which inflates your price on features that never needed it. Asking costs days.
There is a second, quieter cost. Without a revision level on the face of the drawing, there is no way to prove later which version was quoted. That ambiguity surfaces at first article inspection, when it is expensive.
What to Put on the Drawing
- The revision level and date, on the face of the drawing.
- The datum scheme, so tolerances have something to reference.
- Clear separation of functional dimensions from reference dimensions.
- The tolerance grade or standard being applied, with individual callouts on the features that need something tighter.
- Surface finish requirement and how it is measured.
- Machining scope, if the drawing covers the finished part rather than the raw casting.
How Buyer24 Helps
Buyer24 keeps drawings, models and revisions attached to the request itself, so every supplier quotes against the same package and no one is working from an old file. Get started →
FAQ
Which 3D format should I send?
A neutral format such as STEP is safest, because it opens in any CAD system a foundry is likely to run. Native files from a single CAD package narrow the pool of shops that can quote without conversion work, and conversion time gets priced in.
Do I need a separate drawing for the machined part?
If features are machined after casting, yes, the machining print governs those features. Many buyers send a casting drawing and a machined drawing together, with the machining scope stated explicitly rather than implied.
What if we only have a model and no drawing?
Say so in the request. A foundry can often quote a budgetary number from a model, clearly labelled as budgetary, and firm it once a drawing exists. Presenting a budgetary number as firm is where disputes start.
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