The quote you get is only as good as the drawings you send
Most buyers start the RFQ process the same way. They take a set of housing drawings, attach them to an email, write "please quote" and wait for a price. Two suppliers reply within a day, a third takes a week, and the three numbers can differ by a wide margin. That gap is rarely a mystery. It is the direct result of the information the supplier had to guess at.
If you are sourcing an enclosure or housing for a milling machine, you are not buying one standard part. You are buying a fabricated assembly whose cost is driven by geometry, tolerances, finishing and volume. The supplier cannot price what they cannot see. This article lists the information a China-based manufacturer needs before it can quote a machine cleaning equipment housing or machine exterior assembly without padding the price for uncertainty, and it explains which missing details turn into change orders later.
1. Drawings in a format the factory can actually open
Send both a 2D drawing and a 3D model. The 2D sheet carries tolerances, datums and notes; the 3D file is what drives tooling, bending and fixture design. Acceptable formats are STEP or IGES for solids, plus PDF or DWG for the drawings. A JPEG of a drawing or a scanned paper sheet is the most common reason a quote comes back vague, because nobody can verify a dimension from a photograph.
Along with the files, state the unit system (mm or inch) and the drawing standard you are working to. If the part came from another supplier and you do not own the original CAD, say so. A factory that recognises an inherited drawing will ask for a sample part before committing to a number.
2. Envelope, interfaces and what the housing has to survive
For a milling-machine exterior, the housing has duties beyond appearance. Spell them out:
- Overall envelope and footprint, including door swing and service access.
- Cooling-air paths, filter positions and the space a filter cartridge needs when it is swapped.
- Cutting-fluid and coolant mist exposure. Coolant mist and chip wash-down are hard on sheet metal and coatings.
- Chip, swarf and wash-down splash zones, so the design can route liquid away from bearings and electrical cabinets.
- Interfaces to the machine base, the enclosure frame, windows, interlocks and the control pendant arm.
If the enclosure must keep coolant mist inside or meet a defined ingress protection rating, say it explicitly. Sealing and drainage drive part count and labour more than any other single requirement.
3. Material, thickness and where appearance matters
State the grade and the gauge, not just "steel". Common choices are cold-rolled mild steel for structural panels, stainless for areas exposed to coolant and wash-down, and aluminium where mass or handling matters. Give the sheet thickness or let the supplier propose it, and mark which surfaces are customer-facing and which are hidden.
This distinction is worth money. A cosmetic panel needs weld grinding, filling and a smooth undercoat before paint; a hidden bracket does not. If you do not separate the two, every panel gets finished to the highest standard and you pay for it in the unit price.
4. Tolerances: overall, cosmetic and functional
Give three tolerance bands instead of one blanket figure. Overall dimensions for fit against the machine frame can be tight. Gap and flush lines on doors and windows are cosmetic and usually need a stated maximum step. Sealing surfaces, hinge bosses and mounting holes for the door interlock carry a functional tolerance that the gasket and the switch depend on.
A blanket tolerance of ±0.1 mm on a two-metre welded frame tells the supplier that fixtures, stress-relief and inspection all have to be upgraded, and the quote rises accordingly. If you only need ±0.1 mm at the gasket line, mark that line and let the rest of the drawing carry a normal fabrication tolerance.
5. Finishing, colour and marking
Send the paint system, not just a colour name. Powder coat or liquid paint, primer plus topcoat or single stage, gloss level, film thickness and the colour reference (a RAL code or a Pantone number) are enough for an accurate finishing cost. Add whether parts are masked after painting, whether graphics and safety markings are silkscreened, laser-etched or supplied as decals by you, and whether you need a salt-spray or cross-cut adhesion check.
If the enclosure is for a steam cleaner machine or another unit that sees hot water and steam in service, mention it. Coating choice and sealing change when a part is regularly exposed to high temperature and moisture.
6. Quantity, release pattern and forecast
Volume is the biggest single lever on unit price for a fabricated assembly. Give the trial quantity, the expected annual quantity and the release pattern you plan to run. Monthly releases with a rolling forecast let a factory reserve laser time and press-brake capacity. Irregular quarterly releases make material buying expensive.
Also state whether you want parts shipped bare, painted, or delivered as a sub-assembly with gaskets, hinges, gas struts, windows and locks already fitted. Sub-assembly moves work to the supplier and changes the quote shape: fewer line items on your side, more value added on theirs.
7. Sample and validation plan
Decide before the quote what "approved" means for this part. A first-article inspection with a dimensional report may be enough for a hidden panel. A customer-facing enclosure may need a signed-off colour board, a gap-and-flush check on a fitted sample and a wash-down or steam test on the sealed version. Tell the supplier who signs off and what evidence they must supply with the sample shipment.
Ask how the factory handles the sample cost. A supplier with a customised cleaning equipment build often reuses fixtures from prototype to production, which brings down the effective tooling charge. Get that arrangement in writing at quotation stage rather than after the sample is delivered.
8. Logistics, packing and the commercial terms
Large fabricated panels damage in transit more often than they fail in service. Specify whether you want steel or timber crating, edge protection on painted edges, and whether parts ship flat-packed for assembly at your plant or fully built. Give the destination, the Incoterms you want quoted, and whether you are comparing FOB and DDP prices.
Add your payment terms, the required lead time for the first release, and the warranty period you expect on coating and welds. A quote that excludes packing, or that prices a lead time you cannot accept, is not comparable with a competitor's number.
9. What to ask the supplier to send back
A useful quote request asks for more than a price. Ask each supplier to return a cost breakdown split into material, cutting, bending, welding, finishing and assembly, plus a separate line for tooling and fixtures, the lead time for sample and for production, and a short DFM note listing anything in the drawing that raised a flag. Suppliers who will not give a breakdown are harder to negotiate with once volumes grow.
A pre-quote checklist
- STEP or IGES 3D model plus 2D drawing in PDF or DWG, with units stated.
- Envelope, service access, cooling-air and drainage requirements.
- Exposure list: coolant mist, wash-down, steam, UV, indoor or outdoor.
- Material grade, gauge, and cosmetic versus hidden surfaces marked.
- Overall, cosmetic and functional tolerances called out separately.
- Paint system, colour reference, gloss, marking method.
- Trial quantity, annual volume, release pattern, forecast horizon.
- Assembly level and packing method required.
- Approval process, inspection evidence, destination and Incoterms.
Send that package and comparable quotes arrive within a couple of days. The suppliers who ask the fewest follow-up questions are usually the ones who will give you the fewest change orders.
Frequently asked questions
Should I give the same drawing pack to every supplier?
Yes. Comparing quotes only works when every bidder worked from the same revision. Number your drawings, state the revision on the request, and note any change made after the first issue.
What if I only have a photo of an existing housing?
Send a physical sample. A factory can measure and re-draw a sample part as a paid service. Photos give you an estimate, not a price you can commit to.
When does tooling cost actually matter?
It matters when the geometry repeats. Bending fixtures, welding jigs and screen-print tooling are one-off charges that amortise over volume, so a low annual quantity makes them a large share of the first year's spend.
Next step
If your housing is part of a machine that needs regular steam or hot-water cleaning in service, tell the manufacturer that duty cycle at quotation stage as well, so coating, sealing and drainage are priced once instead of revised. Send your drawings, the exposure list and your forecast and you will get a number you can act on.
