01
Tolerances nobody can hold
A ±0.01 mm callout on a 300 mm aluminum plate forces slow finishing passes and extra fixturing. The part gets made, the price doubles, and the function never needed it. Call out only the surfaces that mate.
Design guides
CNC Machining Design Guides
A working library for engineers who need to release a part file that machines cleanly the first time. Each guide covers one decision: tolerance, thread, material, or DFM detail.
±0.005 mm tolerance16 five-axis centersFrom one part upDFM in 12 hours
15 yearsMachining since 2011
127High-precision CNC machines
±0.005 mmAchievable tolerance
3–5 daysParts ship in
Where drawings break
Four problems that cost you a build cycle
Most rework we see traces back to the drawing, not the machine.
02
Threads that strip or cross-thread
A 1/4-20 UNC thread at 70% engagement in 6061 holds fine. The same thread in a 2 mm wall does not. By the time the assembly torques it, the boss is cracked and the housing is scrap.
03
Undefined datums
When the GD&T frame references a datum that does not exist on the print, the inspector invents one. Two suppliers then measure the same feature from two different origins and both report good parts. The assembly says otherwise.
04
Wall thickness as an afterthought
A 0.8 mm wall on a 150 mm part will deflect under light clamping pressure. By the time it reaches inspection the ovality is real. Thin walls are a fixturing problem before they are a machining problem.
How we work
One guide per decision, checked against your file
We read the drawing the way the machinist will, then tell you what it will cost to hold.
GD&T and datums
Fix the datum scheme before the first cut
Most tolerance disputes are datum disputes. If the print calls out position to A-B-C but the fixture locates on a single face, the inspector and the machinist are measuring two different parts. We walk the feature control frames against the setup plan before quoting, and flag any frame that cannot be checked on the shop floor.
A datum that cannot be fixtured is not a datum. It is a note. On a typical bracket we ask for three things: which face sits on the machine table, which feature sets the second axis, and which hole pattern carries the functional fit. Everything else can float unless the mating part says otherwise.
- 1Datum checkEvery frame mapped to a real setup face
- 2MMC where it helpsBonus tolerance for clearance holes
- 3Inspection planReport format stated before the run
Threads and fits
Thread pitch, engagement, and where threads fail
Threaded features are where a good design goes bad quietly. A 1/4-20 UNC thread needs roughly 1.5 × diameter of engagement to reach full strength in mild steel. In 6061 aluminum that number grows, and in a 2 mm wall there is simply not enough material to reach it. We check minor diameter against wall thickness on every tapped boss.
Pitch diameter drives fit, not the major diameter you see on a chart. A 2A/2B class fit leaves clearance for plating; a 3A/3B fit does not. If the part gets electroless nickel after tapping, the thread grows by the coating thickness on all flanks and the gauge will not enter. Tell us the finish before we cut the thread.
- 1Engagement depthChecked against material and wall
- 2Class of fit2B for plated, 3B for bare
- 3Thread millingFor large diameters and thin walls
Selection
Which detail to fix first
Ranked by how often it changes the quote.
| Drawing detail | Typical effect | What to do |
|---|---|---|
| Tolerance tighter than ±0.02 mm | Extra finishing passes, slower cycle | Keep it on mating features only |
| Wall under 1.5 mm | Special fixturing, risk of chatter | Add ribs or thicken locally |
| Thread class 3B with plating | Gauge may not enter after coating | Use 2B or mask the thread |
| Undefined datum reference | Inspector picks their own origin | Name a face that can be clamped |
Capabilities
What we machine and how
Six routes, one quoting desk. Pick the one your part geometry needs.
01
5-axis machining
16 simultaneous 5-axis centers for contoured faces, impellers, and parts with features on five sides. One setup reduces datum stack-up.
02
4-axis and 3-axis milling
12 four-axis mills and 27 three-axis machines for prismatic work, plates, and housings where one or two setups are enough.
03
CNC turning and mill-turn
16 mill-turn centers handle shafts, fittings, and parts that need turning plus cross-drilling in a single cycle.
04
Rapid prototyping
Machined prototypes and 3D printed parts for form and fit checks before you commit to a production run.
05
Sheet metal and die casting
Brackets, enclosures, and housings when the geometry suits forming or casting better than cutting from billet.
06
Surface finishing
Anodizing, plating, powder coating, blasting, and laser marking, all arranged with the machining order.
Scope
Machine range and stock sizes
Numbers you can design against.
| Item | Range | Notes |
|---|---|---|
| Maximum part size | 4,000 × 400 × 150 mm | Large travel machines |
| Medium envelope | 750 × 1,150 × 550 mm | Also 600 × 600 × 600 mm |
| Compact envelope | 500 × 500 × 450 mm | Also 500 × 310 × 200 mm |
| Rotary table | Ø400 mm | For 4-axis work |
| Materials | Aluminum, stainless, steel, copper, titanium, plastics | Full list on request |
| Minimum order | One prototype upward | No minimum quantity |
Why GreatLight
What the numbers behind the guides mean
Fifteen years of drawing review, condensed.
15Y
Machining since 2011
Three wholly-owned plants in Dongguan and Singapore, 7,600 m² of floor space, and 150 technicians who read drawings daily.
±0.005
Tolerance in millimeters
Held on critical features with in-process monitoring. Fits and finishes are checked before the part leaves the machine.
127
CNC machines
16 five-axis centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers cover most part families.
12 h
Quote and DFM turnaround
Send a STEP file and a print. You get a quotation plus written DFM notes within 12 hours, production can start within 24.
99.99%
Qualification rate
Raw material check, in-process monitoring, and final inspection on every order. Reports on request.
0
Minimum order quantity
One prototype or a 10,000-part run, quoted the same way. Uploads stay confidential and an NDA is available on request.
7,600 m²Manufacturing space
150Technicians
3Wholly-owned plants
<2%Historical late-delivery rate
Requirements and delivery
What each industry asks for, and what we hand over
Aerospace brackets
Thin ribs, tight hole position, full traceability from stock to finished part.
- ±0.005 mm
- 100% inspection
Automotive and EV housings
Sealing faces and bore alignment, produced under IATF 16949:2016 process control.
- IATF 16949
- Ra 1.6 μm
Medical instrument parts
Stainless bodies with defined surface finish and clean handling between operations.
- ISO 13485
- Ra 0.8 μm
Robotics and automation
Repeatable mounting interfaces so the next unit bolts on without shimming.
- Mill-turn
- 3–5 day ship
FAQs
Questions engineers send with the file
Should I tolerance everything to ±0.005 mm?
No. That value is what we can hold on critical features, not a default for the whole print. Every tight callout adds finishing passes, slower feed, and sometimes a second fixture.
Tolerance the fits. Leave cosmetic and non-mating surfaces at general block tolerance and the part gets cheaper without losing function.
How do I decide thread class for a plated part?
Start with the finish. Electroless nickel and anodizing both build on the flanks, so a 3B thread tapped before coating may not accept its gauge afterward.
A 2B class leaves the clearance for coating. If the print demands 3B, mask the thread or cut it after plating and accept the extra handling.
What wall thickness is safe in aluminum?
For 6061, 1.5 mm is comfortable on a part with reasonable support. Below 1 mm the wall starts to move under clamping and cutting forces, and ovality shows up at inspection.
Add a rib, thicken the local area, or switch to a pocketed design. If the thin wall is functional, tell us and we will plan the fixturing around it.
Do you need a 3D model or is a 2D print enough?
A STEP file plus a 2D print for tolerances and notes is the fastest route. The model defines geometry, the print defines what matters.
If you only have a print, we can quote from it, but expect DFM questions on any feature that is ambiguous in two views.
When should I use FEA before machining?
Use it when the part carries load, sees vibration, or has a stiffness target. FEA tells you where material is doing nothing and where a fillet matters.
It does not replace a drawing review. A simulation with an undefined datum still produces a part that will not assemble.
How does surface finish affect the design?
Ra 0.8–1.6 μm covers most mating and sealing surfaces and comes off the machine without extra operations. Ra 0.2–0.8 μm needs polishing steps and adds cost.
Specify finish by function: sealing faces, sliding fits, and appearance surfaces. A general note of Ra 3.2 μm everywhere keeps the cycle short.
Can you sign an NDA before I share the drawing?
Yes. We sign an NDA on request, and uploads through the quote page stay confidential. Design files are not shared outside the quoting and programming team.
For programs with a formal agreement, tell us at first contact and we will route the file accordingly.
What happens if the drawing has a conflict?
We flag it in the DFM notes rather than guessing. A dimension that disagrees with the model, or a tolerance that cannot be measured on the feature it names, goes back to you with a question.
That step is why our quote takes 12 hours instead of 2. It is also why fewer parts come back.
Send a drawing, get DFM notes back
Upload a STEP file and a print. We reply with a quotation and written feedback within 12 hours.
12-hour quote100% inspectionNo minimum order
