Free CNC Machining Manual

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  What a free CNC machining manual actually explains
• 2
  3-axis, 4-axis and 5-axis: which setup fits the part
• 3
  Tolerance and surface finish: where the numbers come from
• 4
  Features that cut cleanly and features that fight the tool
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  From file to first article: how the manual is applied
• 6
  Matching the setup to the part

A free CNC machining manual is not a list of machine brands. It is a way to reason about material removal: a rotating cutter is pushed into stock, and every parameter you choose changes heat, force and surface. Once you see the cut as a mechanical event, drawings become readable.

The chain is short. CAD geometry becomes a toolpath, the toolpath becomes G-code, and the controller drives axes to that path. Errors enter at each link: a loose model, a tool that cannot reach a corner, a fixture that lets the part move. Most scrap comes from the third link, not the first.

GreatLight runs 127 high-precision CNC machines across three wholly-owned plants, with 16 simultaneous 5-axis machining centers. That mix matters because the right answer is rarely the biggest machine. It is the one whose travel, spindle and workholding match the part in front of you.

Read the rest of this manual as a set of boundaries. Each section states what a process can do, what it cannot, and the signal that tells you to switch.

A 3-axis mill cuts on three linear axes. The tool always points down. Use it for prismatic parts with features reachable from one direction: plates, housings, brackets, pockets with open tops. It is the cheapest minute on the floor and the easiest to inspect. Do not force a 3-axis setup on a part with undercuts or holes on five faces; you will pay for extra fixtures instead.

A 4-axis mill adds rotation about one axis, usually A. The part turns while the tool stays put. This suits cylindrical work with cross features: shafts, connectors, cam profiles, parts needing indexing around a bore. A Ø400 mm rotary table covers most of that work. The limit is reach; a deep radial slot on a long shaft may still need a second setup.

A simultaneous 5-axis center moves tool and part together. It reaches compound angles and sculpted surfaces in one setup, which protects datum relationships. It is the correct call for impellers, turbine housings, medical instruments and automotive engine parts. It is the wrong call for a flat plate, where the extra axis buys nothing and costs programming time.

Practical rule: count the faces that carry toleranced features. One or two faces: 3-axis. Features wrapped around a single axis: 4-axis. Features on non-orthogonal faces, or a datum you cannot afford to lose: 5-axis.

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  3-axisPrismatic parts, one dominant direction, simple fixtures.
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  4-axisShafts and round parts with indexed cross holes or slots.
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  5-axisCompound angles and contoured surfaces in a single setup.

Tolerance is not a single factory number. It is the result of machine geometry, tool stiffness, thermal drift and how the part is held. GreatLight holds ±0.005 mm (±0.0002 in) on features that are accessible, rigidly fixtured and not dramatically long. That last condition is where most drawings fail review.

Consider a 300 mm aluminium arm with a ±0.02 mm bore spacing. The bore itself is easy. The spacing fights thermal expansion and tool deflection over a long reach. A ±0.005 mm callout on that spacing would need a temperature-controlled cut and a different strategy. The honest answer is to loosen spacing and tighten the bore.

Surface finish follows the same logic. Ra 1.6–3.2 μm is a normal as-machined result. Ra 0.8–1.6 μm comes from finer stepovers and sharper tooling. Ra 0.2–0.8 μm usually means a finishing pass with a small nose radius, and sometimes a secondary operation. Do not specify a finish you cannot measure; buy the number you can verify with the equipment on your bench.

Material changes all of it. 6061 aluminium cuts fast and holds tight tolerance. 316L stainless work-hardens and pushes tools. Ti-6Al-4V (TC4) runs hot and needs lower surface speed. Inconel punishes any rigidity mistake. A tolerance that is routine in aluminium can be a two-pass problem in titanium.

Every cutter has a radius, so every internal corner has a radius too. A 6 mm end mill leaves roughly a 3 mm corner. If your drawing calls for a sharp internal corner, someone has to EDM it or hand-file it, and both add cost. Design the corner radius to match the largest tool that can enter the pocket.

Pocket depth is the next constraint. A rule that holds in practice: keep depth at or below 4× the tool diameter for aluminium and 3× for stainless. Beyond that, the tool chatters and finish degrades. If a pocket must be deeper, expect a smaller stepover and longer cycle time.

Wall thickness matters as much as depth. Thin unsupported walls deflect under cutting force. Below about 1 mm in aluminium, the wall may sing or spring back after the vise releases. Adding a rib or leaving stock for a finishing pass usually costs less than a scrapped batch.

Threads, holes and text are easy wins. Standard metric and imperial threads cut reliably. Laser marking handles character heights down to 1.5 mm, so serial numbers and logos can go on the part without a second vendor.

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  Corner radiusMatch it to the tool that will rough the pocket.
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  Depth-to-diameterStay near 4× in aluminium, 3× in stainless.
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  Wall thicknessKeep above 1 mm unless the geometry supports it.

The workflow is predictable. You send a 3D model and a 2D drawing with critical dimensions marked. We return a quotation and a free DFM analysis within 12 hours. The DFM report flags features that will not cut as drawn, tolerances that conflict with geometry, and setups that add cost without adding function.

Production can start within 24 hours of approval, and parts ship in 3–5 days for most work. Those windows assume the drawing is frozen. A revision after tooling starts resets the schedule. If a dimension is still under discussion, mark it as reference and machine to the model.

No minimum order quantity applies. One prototype and a 10,000+ part run use the same process sheet, which matters when you are proving a design. Every part is inspected before shipment: raw material check, in-process monitoring, final inspection, with reports on request.

Confidentiality is often the first question from engineering teams. Uploads are treated as secure and confidential, and a non-disclosure agreement is available on request before files move. Send the model when the NDA is signed, not after.