I got three quotes last month for the same aluminum housing. Same STEP file, same quantity, same lead time request. The quotes came back at $28, $52, and $94 per part. Same drawing, same material, same everything — and the spread was over 3x.

The difference wasn't the shops. It was the RFQ.

Two of those shops were guessing. They saw ambiguity in the drawing and priced the worst case. The third shop had quoted similar parts for us before and knew what we actually needed. But a new supplier doesn't have that context. They see what you send them, and what you don't send them, and they fill in the gaps with assumptions that protect them — not your budget.

Most RFQs I see are missing at least three things the shop needs to give you an accurate number. Here's what those things are, and how to fix them before you hit send.

The six things every CNC RFQ must include

I've quoted thousands of parts, and I can tell you within 30 seconds of opening an RFQ whether the quote will be accurate or whether I'll need to send four emails before I can even start. Here's what separates the two:

1. A 3D model in STEP or IGES format. STEP is the standard. STL files are for 3D printing — they're faceted meshes that lose all the geometric intelligence a CAM system needs. If you send an STL, the shop has to reverse-engineer your part geometry from triangles, and you'll pay for that time. Native CAD files (SolidWorks, Inventor, Fusion 360) are fine if you're comfortable sharing them, but STEP is universal and works in every CAM package.

2. A 2D drawing with tolerances. This is the one people skip most often, and it's the biggest source of quote variance. Your 3D model defines the nominal geometry. Your 2D drawing defines what "good enough" means. Without a drawing, the shop assumes their standard tolerance — which might be ±0.005" at one shop and ±0.010" at another. If your part needs ±0.001" on a bearing bore and ±0.010" everywhere else, the drawing is the only place that gets communicated.

The drawing also carries thread callouts, surface finish symbols, and critical notes — things that aren't in the 3D model. A STEP file doesn't say "break all sharp edges" or "Type II anodize, Class 2, black." The drawing does.

3. Material specification. Not just "aluminum" — which alloy? 6061-T6? 7075-T651? 5083-H321? Not just "stainless" — 303, 304, or 316L? If you write "plastic," the shop will quote the cheapest option and you might get acetal when you needed PEEK.

Also specify whether you're providing material or the shop is sourcing it. Most shops prefer to source because they have supplier relationships and can verify certs. But if you have a specific mill cert requirement or a customer-mandated source, say so upfront.

4. Quantity and delivery schedule. Not just "qty 100." Is that 100 pieces one time, or 100 per month for 12 months? The per-part price at quantity 100 one-time is very different from quantity 1,200 with a blanket order. If it's recurring, say so — the shop might invest in a fixture that cuts cycle time, knowing the volume justifies it.

Also: do you need all 100 at once, or can they ship in batches? Partial deliveries can let the shop fit your job into machine schedule gaps, which can reduce cost.

5. Surface finish and post-processing requirements. As-machined? Bead blasted? Anodized? If anodized, Type II or Type III? What color? Does the anodize need to meet a mil spec? Is there passivation for stainless parts? Powder coating? Silk screening?

Every post-processing step adds cost, lead time, and a supplier handoff. If the shop does anodizing in-house (most don't), it's one throat to choke. If they send it out, there's markup and scheduling coordination. Either way, you need to specify it or the quote won't include it.

6. Target price or budget range. Most buyers won't share this. I understand why — you don't want to anchor the shop to a higher number than necessary. But here's what actually happens when you keep your budget secret:

The shop quotes their standard rate. You get the number and it's 40% over what you can pay. Now you're three days into a week-long quoting process, and you have to go back and ask "what if we changed X?" The shop re-quotes. More time passes.

If you had said "our target is $35-45/part at qty 100, and we're flexible on lead time," the shop might have suggested using 3+2 positioning instead of full 5-axis, or switching from 7075 to 6061 with a hard anodize, or batching with another customer's job to share setup cost. You don't get those suggestions when you keep your wallet closed.

I'm not saying you should name your absolute maximum. But a range gives the shop a design target. Think of it like telling an architect your budget before they draw the plans — it doesn't limit creativity, it channels it toward something you can actually build.

The 2D drawing: what needs to be on it

I mentioned drawings above, but this deserves its own section because it's where most RFQs go wrong. Here's what a usable 2D drawing includes:

Critical dimensions with tolerances. Not every dimension needs a tolerance. If your part has 47 dimensions and 45 of them are just the nominal geometry from the 3D model, only call out the ones that actually matter. A drawing with ±0.001" on every dimension tells the shop "this engineer doesn't know which features are functional, so they flagged everything." That drives cost because the shop has to inspect everything — or worse, they assume you're serious about all of them and quote accordingly.

Thread specifications. UNC, UNF, or metric? Class 2B or 3B? Through hole or blind? Minimum thread depth? These are in the drawing notes, not the 3D model.

Surface finish callouts. The standard machining finish is around 125 Ra microinches. If a surface needs 32 Ra or better, mark it on the drawing with the symbol. If a surface is cosmetic (visible on the final product), say so — the shop might use a different toolpath strategy on that face.

Material and heat treat specs. Alloy, temper, and any required certs. "6061-T6 per ASTM B221" is specific. "Aluminum" is not.

Datum references. If your part has true position callouts or profile tolerances, the drawing needs datums. A drawing with GD&T and no datums is like a map with distances but no starting point.

Notes section. This is where you put the stuff that doesn't fit in a dimension: "Remove all burrs and sharp edges," "Part must be clean and dry — no cutting fluid residue," "Certifications required: material cert + dimensional inspection report," proprietary information notices, finish specifications, quantity, and part name/number.

The most common RFQ mistakes that add cost

Mistake 1: Over-specifying tolerances. The single most expensive thing you can do on an RFQ is put tight tolerances on features that don't need them. A ±0.001" tolerance costs roughly 2-3x what ±0.005" costs on the same feature, because the shop has to slow down the cut to control deflection, might need to rough, semi-finish, and finish instead of just rough and finish, has to inspect it with CMM time, and will price in scrap risk if it's at the edge of the machine's capability.

Before you send the RFQ, go through every tolerance on the drawing and ask: "What happens if this feature is out by 0.002"?" If the answer is "nothing," open up the tolerance.

Mistake 2: Sending an RFQ without checking stock availability. If you spec 3/8" 7075-T651 plate and the shop's suppliers are all out of stock until next month, your lead time just gained three weeks. Before finalizing a material, ask your shop (or check with a metal supplier) whether the material and size you specified is readily available. Exotic grades in non-standard thicknesses can add weeks.

Mistake 3: Not mentioning secondary operations. If your part needs tapped holes that go into a weldment, say so. If the part will be press-fit into an assembly and needs a specific fit, say so. Shops price what's on the drawing, not what's in your head.

Mistake 4: Requesting quotes from too many shops. This sounds counterintuitive, but sending the same RFQ to 15 shops doesn't get you 15 good quotes — it gets you 3 good ones and 12 noise. The best shops are busy. If they see your RFQ has been blasted to every shop in the region, they might not prioritize it. Pick 3-5 shops that match your part's requirements and build relationships with them. The quality of quotes you get from a shop that knows your parts is worth more than the marginal price discovery from shop #12.

Mistake 5: Leaving the lead time blank. "ASAP" is not a lead time. It tells the shop you haven't planned, which means you probably haven't thought through the other requirements either. Give a real date: "Parts needed by July 15" or "First articles by June 30, production delivery by July 30." A real date lets the shop check their schedule and tell you honestly whether they can hit it. If they can't, you'd rather know on day one than day ten.

What a good RFQ looks like: before and after

Here's a real example — identifying details changed, but the structure is from actual quotes I've received.

Bad RFQ:

"Need quote for aluminum bracket, qty 50. STEP attached. Thanks."

This RFQ is missing: the alloy (6061 or 7075?), tolerances (no drawing), surface finish (as-machined? anodized?), lead time, and any quality requirements. I have to reply asking five questions. My quote won't be accurate because I have to assume worst case on everything I don't know. That bracket gets quoted at $62/part because I'm assuming ±0.001" on all features, 7075-T6 material, and a one-week lead time with rush pricing.

Good RFQ:

"RFQ: Aluminum Sensor Bracket, qty 50. Part: Sensor mounting bracket, Bracket-01 Rev B. Material: 6061-T6 aluminum, shop to source (provide material cert). Quantity: 50 pcs, one-time order. Possibility of 100 pcs/year ongoing if quality and pricing work. 3D: STEP file attached. 2D: PDF drawing attached with tolerances (only 3 critical dims at ±0.002", remainder ±0.010" or per model). Finish: Type II anodize, clear (natural), Class 2. No dye. All surfaces. Threads: 4x M4x0.7 6H, through holes, no inserts. Lead time: 3-4 weeks from PO. No rush. Quality: Material cert + dimensional inspection report (3 critical dims only). No full FAI required. Target: $28-38/part. Notes: This replaces an existing cast bracket. Functionally equivalent geometry is fine if DFM changes reduce cost. Call me if you see anything worth discussing."

Same part. But now the shop knows the alloy and who's buying it, what matters dimensionally (3 features) and what doesn't (everything else), the finish and class, the real lead time (no rush premium), the budget (they can suggest cost-saving changes), and that you're open to DFM feedback.

This is the difference between a quote you can trust and a quote that's just a number.

The 60-second RFQ checklist

Before you send your next RFQ, run through this:

The shops that quote you accurately and deliver on time — those are the ones worth keeping. And they'll quote you faster and sharper the fifth time than the first, because they know what you expect and how you spec parts.

Need a quote on CNC machined parts? Send your STEP files and drawings to our engineering team. We'll review each part for DFM, flag anything that will drive unnecessary cost, and return a detailed quote with lead time — typically within 24 hours for straightforward parts. One point of contact, all part numbers managed as a package.