A 3D model on its own rarely tells a machine shop, molder, or fabricator everything they need to build your part. Engineering drawings and GD&T (geometric dimensioning and tolerancing) are what turn a good-looking CAD file into a manufacturing-ready product design package. At eCadCam, our Glendale studio has spent more than 22 years preparing CAD data for production, and the most common cause of quote delays and rejected parts we see is a missing or unclear drawing. Here is what a complete package includes and why it matters.
Why a 3D Model Alone Is Not Enough
A solid model defines shape, but it does not say which dimensions are critical, how much variation is acceptable, what material and finish are required, or how the part should be inspected. Two shops can read the same model and produce parts that look identical yet fit differently. A drawing removes that guesswork and gives everyone, from the buyer to the inspector, the same reference.
This matters most when a part mates with other components, when you are ordering from more than one supplier, or when you plan to repeat the order months later. Our product design and CAD services routinely include drawings for exactly these reasons.
What Goes Into a Manufacturing-Ready CAD Package
The exact contents depend on the process and the part, but a solid package usually contains the following:
- Native and neutral 3D files: the original SolidWorks, Fusion 360, or similar file, plus STEP for universal compatibility and STL or 3MF if the part will be 3D printed.
- Dimensioned 2D drawings: orthographic views, section views, and detail views that show every feature a supplier needs to make and check.
- Title block information: part number, revision, material, finish, units, general tolerances, and the drawing’s scale.
- Notes and callouts: thread specifications, surface finish requirements, heat treatment, coatings, and deburring or edge-break instructions.
- A bill of materials (BOM): for assemblies, a list of parts, quantities, and any purchased hardware.
GD&T Basics: Controlling What Actually Matters
Plus-or-minus tolerances on every dimension are simple, but they can be both too tight and too loose at the same time. GD&T describes how a feature is allowed to vary in form, orientation, and location relative to defined reference points called datums. A few of the most useful callouts include:
- Flatness and straightness: control the form of a surface, such as a sealing face that must not rock or leak.
- Perpendicularity and parallelism: keep features square or aligned to a datum.
- Position: locates holes, pins, and slots relative to datums so that parts line up during assembly.
- Concentricity and runout: matter for rotating parts like shafts, bushings, and pulleys.
You do not need GD&T on every part. A simple bracket may only need a few well-chosen dimensions and general tolerances. A precision enclosure, fixture, or mechanical assembly benefits far more.
Choosing Tolerances That Match the Process
Tighter is not automatically better. Every step toward a tighter tolerance usually adds machining time, inspection effort, and cost. A good rule is to hold tight tolerances only on the features that mate, seal, or locate, and leave everything else at the general tolerance. It also helps to match the tolerance to the process: a 3D printed part, a CNC machined part, and an injection molded part each have different realistic capabilities, and a drawing that ignores this will either cost more than it should or fail inspection.
If your part will be prototyped first and produced later, we can design the drawing so that critical features are consistent across both stages, which makes the move from prototype to production far smoother.
Common Drawing Mistakes We See
- Missing or conflicting dimensions, so the shop has to guess which one governs.
- No material or finish specified, which forces a call or email before a quote can be issued.
- Tolerances copied from a template rather than chosen for the part.
- Out-of-date revisions circulating between suppliers.
- Datums chosen for modeling convenience instead of how the part actually assembles or gets inspected.
Catching these issues during design is far cheaper than discovering them after parts arrive.
How eCadCam Can Help
We can create drawings from your existing 3D models, update older drawings, or build a complete package from sketches, samples, or reverse-engineered parts. If you only have a physical part, our 3D scanning services can capture it so we can model and document it from scratch.
Ready to move your design toward production? Send us your files or describe your project, and request a quote from eCadCam in Los Angeles. Call us at 213.489.1173 or visit our studio at 4212 San Fernando Rd, Glendale, CA 91204.