B Tech CNC Machining: What Engineers Should Check Before Ordering

Most parts we quote are 6061-T6 aluminum or 304 stainless. Aluminum machines fast, holds a good finish, and takes anodizing well. 304 is tougher, galls more easily, and needs slower feeds, so the same geometry costs more in stainless. When a part only needs corrosion resistance and light load, 6061-T6 usually wins on both price and lead time.

The drawing matters more than the material. An internal sharp corner is the classic problem. An end mill leaves a radius equal to roughly half its diameter, so a true 90° internal corner cannot be cut from the top. Either add a corner radius, or plan the feature as a cross-drilled hole. Cost also climbs with thin walls, deep cavities, and pockets deeper than four times the cutter diameter.

Features that need a second setup add cost before any metal is cut. A part machined on five sides in one fixture is cheaper than the same part flipped three times, because each flip adds a datum shift and a chance of error. Group features on the accessible faces and leave the rest for a single finishing pass.

Material choice is not only about strength. Thermal expansion, chip behavior, and tool wear all feed back into the tolerance you can hold. Aluminum moves about twice as much as steel for the same temperature change, so a tight-tolerance aluminum part measured on a warm shop floor may read differently in a metrology room.

Our floor runs 127 high-precision machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum part size is 4,000 mm. Rotary tables reach Ø400 mm, which covers most flange and housing work without a second fixture.

Standard milling and turning hold ±0.005 mm (±0.0002 in) on critical dimensions. That is the number to design around. Tighter bands are possible on selected features, but they need climate control, in-process probing, and extra inspection time. Do not put a global tight tolerance in the title block. Apply it to the two or three dimensions that control fit, and leave the rest at general tolerance.

Surface finish follows the same logic. As-machined surfaces land around Ra 1.6–3.2 μm. A good fine pass reaches Ra 0.8–1.6 μm. Optical and sealing surfaces may need Ra 0.2–0.8 μm, which usually means a dedicated finishing pass and a slower cycle.

Small features punish you. A hole below Ø1 mm, a slot narrower than 1 mm, or a thread smaller than M2 needs a small cutter, low feed, and often a second operation. Where the function allows, open the feature up. A Ø1.5 mm hole costs far less than Ø0.8 mm and behaves better in assembly.

Parts ship only after 100% inspection. The sequence is raw material check, in-process monitoring, and final inspection. Reports are available on request. When you need dimensions on paper, say so at quoting time so we can plan the measurement points before the first cut.

For a first article, send the drawing with the critical dimensions marked. A first-article report that lists every dimension is long and rarely read. A report that covers the fit-critical features, the datum scheme, and any callout from ASME Y14.5 is more useful to your quality team.

Process capability matters on volume work. Our historical qualification rate is 99.99%, which reflects stable processes and early detection rather than a promise about any single lot. If a feature is close to the tolerance limit, we flag it during DFM review instead of waiting for the final report.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. That mix covers general industrial, automotive, medical, and information-security requirements. Tell us which framework your audit follows so the documentation package matches it.

Chatter and poor finish usually trace back to setup, not the program. A long tool with a small shank deflects under load. Shorten the gauge length, reduce the axial depth, or add a support. The same part often cleans up with no change to the toolpath.

Dimensional drift across a batch points to heat. A spindle warms through the shift, and the part grows or shrinks as it cools. On tight work we cut a warm-up part, check it, and adjust the offset before the production run. Aluminum parts measured hot can read 0.02 mm off.

Burrs at a cross-hole are a design issue as much as a machining one. A sharp exit edge will burr. A small chamfer or a radius at the exit lets the tool leave cleanly. Where the edge is internal, plan a deburring pass or a tumbling operation instead of hand work.

Thread and bore mismatch in assembly is often a tolerance stack, not a bad part. Check the mating part and the assembly fixture before blaming the machined feature. Two parts inside their own tolerance can still interfere if the stack is not analyzed.

Send a STEP file plus a 2D drawing with the critical dimensions and the datum scheme. We return a quotation and a free DFM analysis within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days. Historical late-delivery probability is below 2%.

There is no minimum order quantity. A single prototype and a 10,000+ part run go through the same review. For low volume we machine from solid. For higher volume we look at die casting or vacuum casting and compare the tooling cost against the machining time.

Uploads are secure and confidential, and an NDA is available on request. If your part is under development, send the model and mark the features that are still open. We can quote two or three variants side by side so you can compare cost against function.

Surface finishing runs in the same plant. Anodizing, plating, powder coating, black oxide, bead blasting, and laser marking are handled after machining, so the part does not leave our control between operations. Laser marking holds a minimum character height of 1.5 mm.