Start with the part shape
A 3D model gives the shop the shape it needs to plan and program the job. STEP (or STP) is the most common format because almost any CAD system can open it.
A model alone often leaves things out. Critical dimensions, tolerances, threads, surface finish and inspection notes usually belong on a drawing.
Say what the part is made of and how it is finished
Name the material and grade you want. If a substitute is fine, say so, so the shop does not have to guess.
List finishes, coatings, heat treatment and markings up front. They change sourcing, handling, lead time and inspection.
- Material and grade, plus any acceptable substitutes
- Finish or coating
- Heat treatment or hardness
- Cosmetic or handling requirements
Give the quantity, and what comes next
One prototype and a repeat production run can be made very differently. Include the quantity you want quoted and, if you know it, how many you expect to need over a year.
If you want prices at a few different quantities, ask for them by name.
Make sure every file shows the same revision
The model, the drawing and the request should all point to the same revision. Mixed revisions are one of the easiest ways to get a correct quote for the wrong part.
If you are moving a part from another supplier, write down the requirements that decide whether a part is accepted. Don't count on the new shop knowing what the old one learned over time.
Share the date you need, and how firm it is
A target date helps the shop judge whether it has room and what a rush would cost. Say whether the date is a hard deadline or a goal.
A complete request lets you compare suppliers on the same job instead of on different guesses.