Savannah CNC Milling Explained

• 1
  Savannah CNC Milling Explained in Plain Terms
• 2
  How the Cutter Removes Metal, and Why Axis Count Matters
• 3
  Why Five-Axis Setups Cut Cost and Error
• 4
  When Standard Three-Axis Milling Is the Better Call
• 5
  Material Behavior and What Tolerance You Can Hold
• 6
  How You Verify the Result Before It Ships
• 7
  Which Milling Setup Fits Your Part

Savannah CNC milling explained in plain terms is simple: there is no separate machining process called Savannah milling. The phrase mixes a place name with a standard subtractive process. The work itself is rotary cutter milling done under computer numerical control, on 3-axis, 4-axis, or simultaneous 5-axis machines.

That matters when you read a quote. A shop that lists Savannah milling may be quoting a 3-axis job with two or three refixturings, or a single 5-axis setup. The machine type drives the price, the lead time, and how much of your tolerance budget gets eaten by repositioning.

GreatLight runs three wholly-owned plants, 127 high-precision CNC machines, and 16 simultaneous 5-axis machining centers across 7,600 m². The work is not tied to one city. It is tied to the setup count on your drawing.

So the useful question is not which city. It is which machine, which fixture, and how many times the part has to come off the table.

A milling cutter is a multi-tooth rotary tool. Each tooth takes a chip as it passes through the workpiece. Feed per tooth, spindle speed, and radial depth of cut set the chip load, and chip load is what decides whether the tool survives or burns.

On a 3-axis machine the tool axis stays vertical. The table moves in X and Y, the spindle moves in Z. Undercuts, side holes, and angled faces need a second or third setup, and each setup adds a datum shift.

A 4-axis mill adds rotation about one linear axis, usually A. The part indexes between faces but does not tilt continuously, so you get more access without full contouring.

Simultaneous 5-axis moves X, Y, Z and two rotary axes at the same time. The tool tip follows a programmed vector, so a Ø10 mm cutter can reach a 15° internal pocket wall in one pass. No repositioning, no second datum.

Every time a part leaves the fixture, two things happen. Datum error enters the stack, and someone spends time re-indicating. On a part with five tight features on four faces, that can be the difference between holding ±0.005 mm and missing it.

Five-axis work holds the part once. The rotary table, typically Ø400 mm on our compact centers, presents each face to the tool. Features that share a datum stay in tolerance because they were cut in the same coordinate frame.

Cycle time does not always drop. Simultaneous motion is slower than a rigid 3-axis cut, and the CAM toolpaths take longer to program. The saving shows up in setup hours, fixture cost, and scrap rate.

A useful rule: if a part needs three or more setups and has a positional tolerance across them, five-axis usually pays. If it is a flat plate with through holes, it does not.

Three-axis milling is not obsolete. It is faster on prismatic parts, cheaper to program, and easier to inspect. A bracket with pockets on one face and holes on the opposite face is a two-setup 3-axis job that runs in minutes.

Five-axis also has reach limits. Deep cavities narrower than the tool plus holder diameter stay unmachined. Long tools deflect, so a slender cutter in a deep pocket will chatter before it reaches the floor.

Size matters too. Our largest travel is 4,000 × 400 × 150 mm, and the medium envelope is 750 × 1,150 × 550 mm. A part that fits those numbers is straightforward. A part that does not needs a different plan.

Hardened material above roughly 45 HRC changes the math as well. Cutting forces rise, tool life drops, and the finish you can promise moves toward Ra 1.6–3.2 μm unless you slow down and accept longer cycle time.

Aluminium is the easy case. 6061-T6, 7075, and 6082 cut clean at high spindle speed and hold ±0.005 mm on a stable setup. Thin walls below 1 mm still move after clamping, so design ribs or accept a two-pass rough and finish.

Stainless 304 and 316 work-harden. If the cutter rubs instead of cutting, the next pass gets harder. 17-4PH in the H900 condition machines closer to steel and needs a different speed and feed window.

Titanium TC4 (Ti-6Al-4V) and Inconel sit at the other end. Low thermal conductivity keeps heat in the cutting zone, so tool life is short and cycle time is long. Expect to pay for that.

Surface finish is a separate decision from tolerance. As-machined parts land around Ra 1.6–3.2 μm. Fine finishing reaches Ra 0.2–0.8 μm. Anodizing, bead blasting, or electroless nickel change the number again, so specify finish and tolerance together.

Tolerance on a drawing is a claim. Measurement is the proof. A CMM report on the critical features is the only way to know whether the ±0.005 mm callout held after the last operation.

GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring, and final inspection. Inspection reports are available on request. The reported qualification rate is 99.99%.

For a first article, ask which features are on the report and which fixture was used to measure them. A dimension checked in a different setup than it was cut can read clean and still be wrong in assembly.

If your part carries a safety or regulatory function, the paperwork chain matters as much as the metal. We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022.