CNC Processing Order Guide

• 1
  What an order actually is
• 2
  Step 1 to 3: quote, DFM, and material lock
• 3
  Step 4 to 6: process route, setups, and tooling
• 4
  Step 7 to 9: first article, production, and inspection
• 5
  Where the order breaks down
• 6
  Which machining route fits which part

A CNC order is not a file transfer. It is a set of decisions made in a fixed order, and each decision constrains the next one. Material sets the cutting speed. Cutting speed sets the tool. The tool sets the smallest internal radius you can get. Tolerances set how many setups are needed, and setups set the price. If you reverse that chain and pick a price first, you will usually rework the drawing later.

The order starts long before the machine runs. A shop needs three things from you: a 3D model (STEP or Parasolid), a 2D drawing with critical dimensions and tolerances, and a quantity with a target date. Missing any one of those turns into an email thread, and email threads are where most of the calendar time goes.

This page follows the sequence GreatLight uses from first upload to shipment. It covers what we check, what we ask back, and the points where a part is better made another way. Nothing here replaces a DFM review on your actual geometry, but it tells you what that review will look at.

• 1
  ModelSTEP AP214 or Parasolid, one solid body per part, no suppressed features.
• 2
  DrawingCritical dimensions, GD&T datums, thread callouts, and finish notes.
• 3
  QuantityPrototype count and expected annual volume, even if the second number is rough.

Quotation and free DFM analysis come back within 12 hours for most jobs. The DFM report is the useful part. It flags wall thickness under 0.8 mm, deep pockets with a depth-to-width ratio above 4:1, sharp internal corners, and tolerances tighter than the process can hold on that geometry. Each flag comes with a suggested change and the cost difference.

Tolerance is the first place engineers over-specify. GreatLight holds ±0.005 mm (±0.0002 in) on critical features, but applying that to every dimension multiplies inspection time and setup count. A practical drawing marks 5 to 15 dimensions as critical and leaves the rest at general tolerance. Everything else follows the title block.

Material choice happens here, not later. Aluminum 6061-T6 and 7075 cover most brackets and housings. Stainless 303 machines cleanly for shafts, while 316L is the pick when corrosion or a medical environment matters. Titanium Ti-6Al-4V and Inconel cut slowly and wear tools, so they need a real reason. Plastics like POM and PEEK behave differently again: POM holds tight tolerances, PEEK resists heat but moves after machining.

• 1
  Aluminum6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, ADC12.
• 2
  Stainless and steel303, 304, 316, 316L, 17-4PH; 1018, 1045, 4130, 4140, 4340.
• 3
  SpecialTi-6Al-4V, Inconel, magnesium AZ31B, beryllium copper.

Process planning matches the part to a machine. A 5-axis machining center machines five faces in one setup, which matters when hole positions must stay true to each other. GreatLight runs 16 simultaneous 5-axis centers and 16 mill-turn centers, both of which cut setup count. A 3-axis machine is still the right answer for a flat plate with holes on one face; moving that job to 5-axis only adds cost.

Setup count is the strongest cost driver after material. Every new orientation needs a fixture, a zero point, and a re-check of datums. A part that needs four setups on a 3-axis machine may need one on a 5-axis machine, and the second route is often cheaper despite the higher hourly rate.

Tooling follows from geometry. Internal corners cannot be sharper than the cutter radius, so a pocket drawn with a 0.5 mm corner needs a 0.5 mm cutter, which is slow and breaks easily. Opening the corner to 2 mm or 3 mm lets a larger, stiffer tool run at higher feed. Deep holes need a longer drill with more deflection, so a hole 10 × diameter deep may need peck drilling and a pilot hole.

The largest envelope is 4,000 mm, with a 4,000 × 400 × 150 mm travel on the long machines. Medium frames run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact cells cover 500 × 500 × 450 mm and 500 × 310 × 200 mm, with a Ø400 mm rotary table for round parts. If your part sits near a travel limit, say so early; workholding eats into the envelope.

Production can start within 24 hours of an approved quote and frozen drawing. The first article is the checkpoint. It is measured against every critical dimension, not sampled, and the report goes to you before the rest of the batch runs. If a dimension is drifting, it is far cheaper to correct at article one than at part 200.

In-process monitoring runs through the batch. Operators check critical features at defined intervals, and cutting tools are changed on a count rather than after a failure. This is what keeps a run consistent when a single tool cuts 300 parts.

Inspection is 100% before shipment. That means raw material certification on arrival, in-process checks, and a final dimensional and visual inspection on every part. Reports are available on request, including material certificates and dimensional results. The historical qualification rate is 99.99%.

Surface finish is chosen with function in mind, not appearance alone. As-machined surfaces run Ra 1.6–3.2 μm, which suits brackets and internal faces. Ra 0.8–1.6 μm covers most mating and sealing surfaces. Ra 0.2–0.8 μm is for bearing seats and sliding fits, and it usually needs a separate finishing operation. Anodizing, plating, bead blasting, and laser marking are added after machining; laser marking needs characters at least 1.5 mm tall to stay legible.

• 1
  As-machinedRa 1.6–3.2 μm for non-critical faces.
• 2
  FineRa 0.8–1.6 μm for seals and mating faces.
• 3
  PrecisionRa 0.2–0.8 μm for bearing and sliding fits.

Most order problems are not machining problems. They are drawing problems that surface after the quote. The usual one is an incomplete drawing: a model with no tolerances, or a drawing that contradicts the model. When the two disagree, the shop has to ask, and the clock stops.

The second is tolerance stacking. Five dimensions each at ±0.05 mm can add up to ±0.25 mm across a stack, and if the assembly needs ±0.1 mm, no single feature can fix it. Adding a datum and a positional tolerance on the pattern is usually cheaper than tightening every dimension.

The third is finish specified as a look rather than a number. "Smooth" is not measurable. Give a Ra value and a reference surface. If a part needs a cosmetic anodized finish, note which faces are visible; masking and hand work add cost that is hard to estimate after the fact.

Quantities under about 50 parts rarely justify a casting or a dedicated fixture. Above a few hundred, a soft fixture or a casting pays back quickly. Above 10,000 parts, the route decision deserves a separate review, because the cheapest process at 100 parts is often not the cheapest at 10,000.