SPECBUILDR
Custom parts · CNC & sheet metal

Write a build-ready CNC machining spec — and quote it right.

You have a CAD model. SpecBuildr asks a short set of plain-English questions and turns it into a complete machining specification a shop can quote — with tolerances called out where they matter and nowhere they don't.

Start your part spec → Free · no account · ~5 minutes

The problem with speccing a machined part

A shop will machine exactly what your drawing says — including the mistakes. Over-tolerance everything and the quote balloons; under-tolerance the one bore that matters and you get a useless part.

The skill isn't running the mill — it's knowing which dimensions are critical, how to call out finishes and threads, and what tolerances actually cost. SpecBuildr asks those questions in plain language and turns your answers into a clean spec, so the shop quotes what you meant, not what it guessed.

How to specify a CNC part: what the spec needs

A machinable spec comes down to six things. Here's what each means in plain terms — the interview pulls them from the part you already modeled.

01 Part & quantity

What it is and how many you need.

In plain terms: one prototype and a hundred parts get made differently.

02 Material & process

The stock material and whether it's milled, turned, or sheet-metal.

In plain terms: what it's cut from, and how.

03 Size & geometry

The envelope and the features — pockets, bores, threads, bends.

In plain terms: how big, and what's on it.

04 Critical tolerances

Which few dimensions must be tight, and how tight.

In plain terms: where precision costs money — spend it only where it matters.

05 Finish & threads

Surface finish, coatings or anodize, and thread callouts.

In plain terms: how it looks and how it fastens.

06 Assembly & environment

What it mates to and where it operates.

In plain terms: fit, load, and conditions.

How it works

1
Answer a short interview
Describe your application in your own words. The tool asks follow-ups only where they matter and skips what it can safely infer.
2
It fills the gaps
Where you're unsure, it proposes a sensible default and explains the trade-off, so you're never blocked on a number you don't know.
3
Leave with a real spec
Download a clean, build-ready specification — reviewed for major physics and manufacturability violations — ready to send to machine shops for a quote.

Built for the engineer, not the machinist

  • Mechanical engineers and makers ordering machined or sheet-metal parts.
  • Hardware teams sending their first parts out for a quote.
  • Anyone who wants a shop to quote the part they meant — not over-build it.

Questions

How do I specify tolerances for a machined part?

You tell the tool which fits and features actually matter; it applies sensible general tolerances (ISO 2768-style) everywhere else and calls out the critical dimensions tightly — so you're not paying for precision you don't need, or missing the one bore that does.

What do I actually get at the end?

A complete, downloadable machining specification: part and quantity, material and process, geometry, critical tolerances, finish and threads, assembly, and environment — formatted so a shop can quote it directly.

Is the spec trustworthy?

It's generated from your answers and reviewed for major physics and manufacturability violations — it won't ask a shop for something un-machinable. Treat it as a strong, quote-ready starting point, not a substitute for the shop's review.

How much does it cost?

The tool is free to use and needs no account. You keep the spec.

Ready to spec your part?

Five minutes of plain questions. A shop-ready specification at the end.

Start your part spec →