Houston CNC parts: precise machining explained
This page explains how Houston CNC parts are held to precise tolerances on 5-axis and mill-turn equipment, and where the limits sit. It is written for design engineers and buyers who must judge whether a drawing can be cut as drawn.
What precise machining actually controls in Houston CNC parts
Precision in CNC is not one number. A drawing carries several independent claims: size, position, form, and surface. A Houston CNC parts program that holds Ø50 ±0.005 mm on a bore may still fail if the bore sits 0.03 mm off the datum. Engineers who treat tolerance as a single value usually spend the most time in first-article review.
Size tolerance tells you how wide a feature may be. Position tolerance tells you where it may sit relative to a datum. Form tolerance covers roundness, straightness, and flatness. Surface finish covers roughness at a scale of micrometres. Each one is produced by a different part of the process, so each one fails for a different reason.
The practical consequence: a shop that quotes one flat tolerance for every feature is either oversimplifying or planning to inspect less than you asked. A precise Houston CNC parts quote should separate features by function. A bearing seat needs a tight size and roundness; a clearance hole needs position, not size.
We hold ±0.005 mm (±0.0002 in) on critical features, and we say so on the drawing rather than in a brochure. Everything outside those features can be cut to a looser band, which lowers cycle time without touching the parts that matter.
Heat, growth, and why your Houston CNC parts move
Aluminium expands about 23 µm per metre per °C. A 300 mm 6061 part that warms 5 °C from cutting grows roughly 0.035 mm. That is seven times the size tolerance on a critical bore. The metal is not wrong; the temperature is.
This is why a machine shop that measures parts hot and cold gets two different answers. On tight work we let the part stabilise on the granite before final inspection. For long runs we monitor coolant temperature and the shop floor, not just the spindle.
Thin walls make it worse. A 1.5 mm wall in 7075 will bend from clamping force before it bends from cutting force. Rough the part, release the clamps, let it rest, then finish. Two setups cost more than one, but they hold form.
If your design has a 0.5 mm wall next to a 20 mm boss, expect to pay for that transition. We can cut it. We will also tell you where the risk sits before the first chip.
How 5-axis setup reduces error stacking
Every refixture adds a new datum error. A part cut in three setups stacks three positional errors, even if each setup is perfect. Five-axis machining cuts that stack by reaching five faces in one clamping, which is the main reason the process exists.
Simultaneous 5-axis is not always faster. It is more accurate on parts with angled faces, deep pockets on multiple sides, and contoured surfaces. We run 16 simultaneous 5-axis machining centers alongside 27 three-axis machines, and we route work to whichever holds the tolerance with fewer setups.
Tool access decides more than axis count. A deep pocket with a 4:1 depth-to-diameter ratio is fine with a long end mill at reduced feed. Past 8:1, tool deflection starts to dominate and no machine can compensate. Change the geometry or accept a larger radius.
We check this before quoting. If a feature cannot be reached without a tool that will chatter, the DFM note comes back with the fix, usually within 12 hours.
Material behaviour that changes Houston CNC parts
Aluminium 6061 cuts clean and holds ±0.005 mm on most features. 7075 is stronger but more prone to stress relief movement after roughing. On a 7075 bracket, leave 0.3 mm for the finish pass and let the part cool between operations.
Stainless 316 work-hardens. A dull tool rubs instead of cutting, and the surface hardens under the cut. Keep the feed per tooth up and never dwell. 17-4PH in the H900 condition cuts well but will move if you remove 3 mm of stock in one pass.
Titanium Ti-6Al-4V (TC4) needs low surface speed and flood coolant. Heat goes into the tool, not the chip. Expect shorter tool life and a higher piece price. If the part does not need titanium, aluminium or 17-4PH usually does the job at a lower cost.
Plastics behave in the opposite way. POM and PEEK expand with heat and can melt at the cut. Sharp tools, high speed, air blast. A ±0.005 mm call on a PEEK part is realistic only when the geometry is stiff and the wall is thick.
Which process fits your Houston CNC parts
Match the feature, not the marketing
| Part feature | Best process | Typical tolerance | When it does not fit |
|---|---|---|---|
| Angled faces on 3+ sides | Simultaneous 5-axis | ±0.005 mm | Flat plate, one face only |
| Round turned features | Mill-turn center | ±0.005 mm | Prismatic block with no turning |
| Deep pocket, 4:1 ratio | 3-axis with long tool | ±0.01 mm | Past 8:1 depth-to-diameter |
| Thin wall under 1.5 mm | Two-stage 3-axis | ±0.01 mm | Wall under 0.5 mm in 7075 |
| Large frame, 2 m long | Gantry, 4,000 mm travel | ±0.01 mm | Feature smaller than 5 mm |
| Prototype, one piece | 3-axis or 5-axis | ±0.01 mm | Casting already tooled |
| 10,000+ identical parts | Mill-turn with bar feed | ±0.005 mm | Low volume under 50 pieces |
The trade-off in one line
If your part has angled features on several faces, choose simultaneous 5-axis and pay for fewer setups. If it is a flat plate with simple holes, choose 3-axis and pay less. Do not buy 5-axis for a part that never leaves one plane.
Houston CNC parts: common questions
Can you hold ±0.005 mm on a 300 mm aluminium part?
Yes, on defined features and with the part at thermal equilibrium. Size tolerance and position tolerance are separate claims, and we need to know which features carry the tight call.
A blanket ±0.005 mm across a 300 mm aluminium frame is not realistic because thermal growth alone can exceed it. Mark the critical features and we will quote to those.
How many setups will my part need?
Prismatic parts with features on three faces usually need one 5-axis setup or two 3-axis setups. Turned parts with cross-holes run on a mill-turn center in one setup.
We decide the routing before quoting, and the DFM note states the setup count so you can compare it against other offers.
What surface finish can you produce as machined?
As-machined finish sits around Ra 1.6–3.2 μm. A fine finish pass reaches Ra 0.8–1.6 μm, and lapping or polishing can reach Ra 0.2–0.8 μm on flat and cylindrical faces.
Deeper pockets and internal corners will be rougher than the outside of the same part. Finish calls on internal geometry need a specific Ra value on a specific face.
Do you inspect every part?
Yes. We run a raw material check, in-process monitoring, and a final inspection before shipment. Inspection reports are available on request.
First-article inspection is standard on a new program. For high-volume runs we use in-process probing so drift is caught during the run, not after.
What is the smallest order you accept?
There is no minimum order quantity. One prototype and a 10,000-piece run both go through the same quoting process.
For a single prototype we often recommend 3-axis or 5-axis milling rather than tooling, because setup cost dominates at that volume.
How do you handle confidential drawings?
Uploads are secure and confidential. We can sign an NDA before you send files, and we do not display customer parts in marketing material.
If the project needs it, we restrict file access to the engineers and machinists assigned to the job.
Get your Houston CNC parts quoted
Send the drawing and we return a quotation with a free DFM analysis within 12 hours. Production can start within 24 hours of approval.
12-hour quote100% inspectionNDA on request
More from GreatLight
We publish setup notes, tooling trials and inspection data from the factory floor.
