The Top 5 Mistakes I Made Ordering Custom Parts (And How Fictiv Helped Me Fix Them)

Five Questions About Custom Manufacturing That I Learned the Hard Way

I'm a mechanical engineer who's been handling custom manufacturing orders for about 7 years. I've personally approved over 200 orders, and I've made enough mistakes to fund a small vacation. This article answers the five questions I wish I'd asked before my first order. If you're new to this, start here.

1. What's the single most common mistake engineers make when ordering CNC parts?

Underspecifying the material. Most buyers focus on the part geometry and completely miss the material callout. I once ordered 500 aluminum brackets with just "6061-T6" in the notes. The shop used 6061-O (annealed). It was machinable, but the parts bent under load. $3,200 wasted.

Everything I'd read said "just pick a standard grade." In practice, I found that specifying the temper—the -T6, -O, or -T651—is as critical as the alloy. My rule now: always check the full ASTM spec.

According to common industry standards (ISO 2768), unspecified tolerances default to ±0.1mm for basic dimensions. If your design relies on a specific fit, call it out explicitly.

2. Why does Fictiv's instant quoting sometimes look higher than a local shop?

Because Fictiv shows you the final price, not a starting bid. I learned this the hard way with a local shop. They quoted $800 for a 50-piece injection mold. The final invoice? $1,250 after "setup fees," "material surcharge," and "revision costs."

Fictiv's platform includes those costs upfront. The vendor who lists all fees upfront—even if the total looks higher—usually costs less in the end. I've learned to ask 'what's NOT included' before 'what's the price.'

Oh, and I should add: that local shop's "cheap" quote ended up costing 30% more than Fictiv's transparent one. A lesson I won't forget.

3. How do I choose between CNC machining and 3D printing for a prototype?

Short answer: stress matters.

If your prototype will bear a load—even just holding a bracket in place—go CNC. If it's purely a visual or fit check, 3D printing (specifically SLS or MJF) is faster and cheaper.

I once 3D-printed a structural part for a test fixture. It looked fine on my screen. The result? Cracked under 50% of the expected load. $450 wasted, plus a 3-day delay. That's when I learned: 3D printing is for form, CNC is for function.

For Fictiv, you can upload the same CAD file and get quotes for both processes. That's what I do now—compare both side-by-side before committing.

4. What about surface finish—is that really a big deal?

It's the difference between a part that works and a part that looks like it works.

On my third order, I specified "as-machined" for 200 aluminum parts. The vendor delivered them with visible tool marks. The parts fit perfectly, but my client rejected them on appearance. $890 in rework plus a 1-week delay.

Now I always specify a surface finish. For CNC parts, a 63 Ra (micro-inch) finish is standard. For 3D printing, vapor smoothing or bead blasting can make a huge difference. Fictiv's quoting system lets me select the finish upfront—saves that argument.

The conventional wisdom is that surface finish is optional. My experience with 200+ orders suggests that specifying it from the start prevents costly rework and saves relationships.

5. What's one thing you'd tell your younger self about ordering parts?

Don't approve a quote without a DFM (Design for Manufacturing) check.

I used to upload a CAD file, get a price, and approve it within an hour. Then I'd get a call from the shop saying "this feature is unmachinable" or "this corner radius is too tight." Revision costs added up fast.

Fictiv's platform automatically runs a DFM check before you submit. It flags undercuts, tight radii, and unsupported features. It even suggests alternative tolerances. That feature alone has saved me thousands.

I only believed in DFM checks after ignoring one and getting 50 unusable parts. Now I treat it as a non-negotiable step.

One more thing—my experience is based on about 200 mid-range orders with domestic suppliers. If you're working with luxury or ultra-budget segments, your experience might differ significantly. But for standard custom manufacturing, these principles hold up.