What a drawing needs to contain for an accurate quote

The eight-point checklist

None of these is difficult to supply. All of them change the quote.

#	What to include	Why it changes the price
1	Overall dimensions and a scale	Sheet nesting. A part 5 mm too wide for a standard sheet line doubles the material cost.
2	Material grade and thickness	Cast versus extruded is 20% of material cost; optical grade is 3×. Thickness drives both material and machining time.
3	Critical dimensions, marked	Three critical dimensions and twelve critical dimensions are different jobs. Marking them lets us price the actual requirement.
4	Tolerance per dimension, not globally	A blanket ±0.1 mm across a whole drawing can triple the price for no functional gain.
5	Edge finish	As-machined, flame polished and diamond polished differ by up to 40% in finishing time.
6	Surface treatment	UV print, screen print, frosting, painting — each adds a separate operation and a separate setup.
7	Quantity, and whether it repeats	Setup is amortised across the run. A repeat order changes how we fixture the job.
8	What it assembles into	A part that mates with something else needs its fit faces toleranced and its reference edges defined.

File formats

In rough order of usefulness:

• STEP (.stp) — best for machined 3D parts. Contains full geometry and can be checked for interference.
• DXF — best for flat cut parts. One layer per operation if you have it (cut, engrave, drill).
• DWG — acceptable, but check that the drawing is 1:1 and that dimensions are actual, not overridden text.
• PDF, dimensioned — workable for simple parts. We will re-model it and send the model back for confirmation.
• STL — acceptable for a cover that has to match a 3D print, because it reflects what was actually printed rather than the nominal design.
• A photo with a ruler — enough for a rough price, not enough to manufacture.

Five things that cause a wrong quote

1. Dimensions that do not add up. A drawing where the overall length is 300 mm but the segment dimensions sum to 302 mm. We will notice and ask, which adds a day — better than machining to the wrong figure.

2. A tolerance that is physically impossible. ±0.05 mm on a 500 mm acrylic part is beyond what thermal expansion allows. We will say so and propose a realistic value.

3. Missing material callout. "Clear plastic" is not a specification. It could be acrylic, polycarbonate, PETG or PS, and the price difference is 3×.

4. Features that cannot be machined. Internal undercuts, closed cavities, zero-radius internal corners. These need a design change or a different process, and it is cheaper to find out before quoting.

5. No indication of quantity break. A quote for 10 pieces and a quote for 1,000 pieces are different exercises. Send the range and we will quote each step.

What the DFM note contains

Every quotation comes with a short design-for-manufacturing note. It covers:

• Features we recommend changing, and what it saves
• Dimensions where the specified tolerance is tighter than the function needs
• Wall thickness or span concerns, with the load assumption we used
• Hole placement relative to edges, where chipping is likely
• Proposed joint positions for bonded assemblies, with the reason
• Anything we cannot make as drawn, and the alternatives

This is not a sales document. It is the list of things we would want to know if we were the buyer, and it is the reason most of our repeat customers send drawings without a specification sheet.

If this is your first order from China

Three practical suggestions:

Order a sample first. It costs more per unit than production and it answers the questions that a quotation cannot. If the sample is wrong, you have lost a week; if the production run is wrong, you have lost a month and a container.

Agree the inspection standard before production. "Good quality" is not a standard. Agree what will be measured, with what instrument, and what the acceptance threshold is. Put it on the sample approval.

Name the Incoterm in the enquiry. A price without a term is not comparable to another price without a term. FOB and DDP quotes for the same goods can differ by 40%.

Check whether you are talking to a factory or a trader. An acrylic manufacturer quotes from its own machine hours and can move a tolerance without asking a third party for permission; a trader cannot. Ask for the plant address and the list of processes run in-house — both are quick to verify and hard to fake.