Say what you are making, and what changes between parts
A prototype supplier who is told "machine these parts" will quote a job. A supplier who is told the part family, the volumes and what changes between them can quote a route. Write down the material, the tolerance that actually matters on each feature, the surface finish you need and why, and how many pieces you need now and in three months. Say explicitly which drawings are provisional and which are frozen; a supplier who knows which drawings will change can plan around them instead of quietly assuming the first issue is final.
Give the function of the part, not only its geometry
The information that most often changes a prototype outcome is what the part has to do. A housing that has to hold two bearings in alignment, a cover that has to keep oil in, a bracket that has to survive vibration: each of those statements lets the supplier pick the datum, hold the right tolerance, and refuse to save cost somewhere you cannot afford it. Without function, the supplier holds every tolerance to the drawing and still produces a part that does not assemble.
State the inspection you will use to accept the parts
Tell the supplier how you will check the work: which features you will measure, with what, and what you will reject. If you need a dimensional report with each batch, ask for it in the enquiry rather than after delivery, and specify which dimensions it covers. If the parts feed an assembly test rather than a measurement, say so — a supplier who knows the part has to fit something checks fit, not just size.
Give the schedule as a set of gates
A single requested date invites a late delivery. Give three dates instead: the date you need the first articles, the date you will have inspected them and closed the issues, and the date you need the balance. Then state what your own turnaround will be on inspection, because a supplier planning a schedule needs to know how long you will take to respond. Prototype programmes fail on the gaps between gates, not on the machining.
Ask about process, fixtures and the things that drive cost
Ask how the supplier intends to hold and machine the part, whether any fixture or tooling is needed and who pays for it, and which features are driving the price. Then ask what they would change to make the part cheaper without breaking its function. Suppliers answer this well when the enquiry is honest about function and volumes; the answer is also a fair test of whether the supplier is engineering or quoting.
Agree the change and quality route before the first cut
Write down how a drawing change is issued and priced, what happens to parts already made against an earlier issue, and how a non-conformance is handled — rework, replace, or accept as-is with a concession. Also fix what documentation comes with the parts: material certificates where the material matters, measurement records where they were requested, and the revision number marked on the parts or their packaging. Prototype work goes wrong when nobody can tell which issue of a drawing a physical part came from.
Use the supplier's engineering time deliberately
The most valuable thing a good supplier gives at prototype stage is a critical review before machining starts. Ask for it in writing: send the drawings and the functional requirement and ask for the list of features that are difficult, unnecessary, or expensive for no benefit. Where the work also involves test rigs, fixtures or small automation, a supplier with an engineering side can take that scope as well; PowerDe's engineering services cover product development and manufacturing automation alongside its equipment lines, and its product development work can be given the assembly context rather than a part in isolation.
Send one document, and ask for one answer
Put the part family, the function, the tolerances that matter, the inspection you will apply, the three gate dates and the change route in a single enquiry, and require every supplier to answer the same headings. Send it to PowerDe through the contact page and ask for the critical review and the cost drivers, not only a price. Comparing the reviews tells you more than comparing the prices.
