Kennewell CNC machining expertise, explained for engineers

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  What Kennewell CNC machining expertise means on the floor
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  3-axis, 4-axis, 5-axis, and mill-turn: which one fits
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  How tolerance and surface finish are actually held
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  Material behavior that changes the process plan
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  What raises the price of a CNC part
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  Matching the part to the process

Kennewell CNC machining expertise is not a badge or a slogan. On the floor it comes down to three decisions made before any chip is cut: how many setups the part needs, how the tool reaches each feature, and how much the material will move after the clamps come off. Get those three right and the part is repeatable. Get them wrong and you chase dimensions for a week.

A setup is any time the part is unclamped, rotated, and re-zeroed. Every setup adds a new datum handoff, and each handoff contributes error. A part with features on five faces can need three or four setups on a 3-axis mill. The same part on a 5-axis center with a Ø400 mm rotary table may need one. That difference shows up directly in tolerance stack and in lead time.

Tool access is the second gate. Deep pockets, undercuts, and cross-drilled holes set the minimum tool diameter and the minimum tool length. A 3 mm end mill needs a length-to-diameter ratio under roughly 5:1 to stay rigid. Push past that and the tool deflects, the wall tapers, and surface finish drops from Ra 0.8–1.6 μm to something you can feel with a fingernail.

Material behavior is the third gate. Aluminum 6061 moves little and cuts fast. Stainless 316 work-hardens if the feed is too light. Titanium Ti-6Al-4V (TC4) conducts heat poorly, so the cutting edge absorbs it. Inconel is worse. The same geometry that runs clean in aluminum can scrap a batch in Inconel unless speeds, feeds, and coolant strategy change with the material.

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  Fewer setups, tighter stackEach re-clamp adds a datum handoff and its own error.
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  Tool L:D under 5:1Longer reach means deflection, taper, and rougher walls.
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  Material sets the recipeAluminum, stainless, titanium, and Inconel need different speeds and feeds.

A 3-axis machine moves the tool in X, Y, and Z while the part stays fixed. It is the fastest and cheapest option when all machined features are reachable from one direction, or from a small number of simple rotations. Prismatic plates, brackets, housings with one open face, and most fixture plates belong here. If a part fits a 3-axis envelope of 500 × 500 × 450 mm, keep it there.

A 4-axis mill adds rotation around one axis, usually A or B. This suits parts with features on four sides of a cylinder or a rectangular block, such as shafts with flats, manifolds with ports around a bore, and cam profiles. The part is indexed to each face without a full re-clamp, so angular position stays consistent. It is a middle step, not a replacement for 5-axis.

A 5-axis center moves the tool and the part at the same time. The payoff is not speed, it is access. Contoured surfaces, deep cavities with drafted walls, impellers, and parts with features on five faces cut in one setup. That removes the datum handoff error and shortens the queue. The trade-off is programming time and a tighter fixturing requirement, because the part must be held rigidly while it rotates.

A mill-turn center combines turning and milling on one spindle. Parts with a turned body plus cross-drilled holes, milled flats, or slots finish in one setup instead of two machines. This is common in hydraulic fittings, motor shafts, and sensor housings. If a part is mostly round with a few off-axis features, mill-turn usually beats a separate lathe and mill sequence.

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  3-axisOne-direction features, prismatic parts, lowest cost per part.
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  4-axisIndexed features around one axis, shafts and ported blocks.
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  5-axisFive-face access in one setup, contoured and deep-cavity parts.
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  Mill-turnRound bodies with off-axis features, one setup instead of two.

Tolerance is a stack, not a single number. The drawing may call ±0.005 mm on one bore, but the achievable result depends on the machine, the fixture, the tool, and the thermal state of the part. On a rigid setup in aluminum, ±0.005 mm is routine. On a thin-walled part held in a vise, the clamping force alone can distort the bore by more than the tolerance before the tool touches it.

Surface finish follows the same logic. Ra 1.6–3.2 μm is normal as-machined output. Ra 0.8–1.6 μm needs a controlled finishing pass with a sharp tool and steady feed. Ra 0.2–0.8 μm usually means a separate finishing operation or a secondary process such as lapping or fine turning. Asking for Ra 0.2 μm on a deep pocket with a 6 mm tool is a cost conversation, not a specification.

The right way to set tolerance is by function. A bearing seat needs a tight bore and a tight roundness callout. A clearance hole for an M6 bolt does not. Over-tolerancing the second feature adds inspection time and slows the whole job without improving the assembly. We mark those features during DFM review and ask whether the tight callout is functional or inherited from an older drawing.

Inspection closes the loop. GreatLight checks raw material on receipt, monitors dimensions in process, and inspects 100% of parts before shipment, with reports on request. For a first article, the report is where you confirm that the drawing, the setup, and the measured part agree. If they do not, the fix belongs in the setup, not in a rework bench.

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  Tolerance is a stackMachine, fixture, tool, and thermal state all contribute.
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  Finish is a separate passRa 0.8–1.6 μm needs its own controlled finishing cut.
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  Tolerate by functionBearing seats tight, clearance holes loose.

Aluminum is the default for prototypes and many production parts. 6061 and 6061-T6 cut fast, hold tolerance well, and take anodizing cleanly. 7075 is stronger but less weldable and more prone to stress relief movement after heavy material removal. 2024 behaves similarly. If a part has thin walls and a lot of removed stock, expect to rough, let it rest, and finish in a second pass.

Stainless 303 is the free-machining grade and the easiest of the stainless family. 304 and 316 are tougher and work-harden if the feed is too light, so the tool must stay engaged and cut, not rub. 17-4PH (SUS630) machines well in the solution-treated state and gains strength after aging, which is useful for shafts and valve parts. 440C holds a hard edge after heat treatment and is common in wear components.

Titanium Ti-6Al-4V (TC4) and Inconel are where process planning matters most. Both hold heat at the cutting edge, so tool life drops fast without high-pressure coolant and conservative speeds. Titanium also springs back, which means a finishing pass may need a spring pass to hit the final dimension. Inconel work-hardens aggressively. Light cuts and dwell are the fastest way to scrap a part.

Plastics and composites have their own rules. POM and PEEK hold tolerance but move with temperature. Carbon fibre eats tool edges and needs dust extraction. PMMA chips and can crack at a sharp corner. The fixture often matters more than the cutter here, because soft materials deform under clamping pressure and then spring back after the cut.

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  Aluminum6061-T6 for general work, 7075 where strength is needed.
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  Stainless303 free-machining, 316 for corrosion, 17-4PH for aging.
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  Titanium and InconelHeat at the edge, springback, work-hardening risk.
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  PlasticsFixture and clamping pressure often decide the result.

Setup count is the largest single cost driver on low-volume work. One extra setup adds fixturing, a datum handoff, and queue time. On a run of 20 parts, a second setup can add more to the price than the material. This is why a 5-axis quote sometimes comes in lower than a 3-axis quote for the same geometry: fewer setups can outweigh the higher machine rate.

Feature geometry is the second driver. A pocket with a 6 mm corner radius needs a 6 mm tool, which limits depth and forces multiple passes. Tighten that corner to 3 mm and the tool gets smaller, the passes multiply, and the risk of tool breakage rises. Sharp internal corners cannot be milled at all; they need EDM or a relief. Designers who keep internal radii at least one-third of the pocket depth usually get a cleaner quote.

Tolerance and finish come next. Moving a callout from ±0.05 mm to ±0.005 mm may require a finishing pass, a temperature-stable setup, and a CMM check. The same applies to surface finish. Each step adds time and inspection. On a production run of 10,000 parts, the same decisions still matter, but tooling amortization and cycle time take over as the main levers.

Post-processing is the last line item. Anodizing, plating, powder coating, bead blasting, and laser marking all add handling and lead time. Laser marking has a minimum character height of 1.5 mm, so fine text on a small part may not be legible. Planning the finish before the geometry is final avoids a second round of handling.

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  Setup countThe biggest cost lever on low-volume work.
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  Internal radiiKeep radius at least one-third of pocket depth.
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  Tolerance stepsTighter callouts add passes and inspection.
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  FinishesEach process adds handling and lead time.