5 Axis CNC Services: What to Check Before You Send a PO

• 1
  Key takeaways
• 2
  What to compare across 5 axis CNC services suppliers
• 3
  Simultaneous 5 axis CNC services vs 3+2 positioning
• 4
  Part size, tolerance and surface finish you can actually specify
• 5
  Material families and what each one demands
• 6
  Cost drivers, lead time and order quantity
• 7
  When five-axis is the right call, and when it is not
• 8
  How to vet a 5 axis CNC services supplier in 6 steps

A five-axis machining center carries three linear axes and two rotary axes, usually A and B or B and C. The question is whether the control moves all five at the same time while the tool stays in cut. That is simultaneous machining. In 3+2, the rotary axes index to an angle, lock, and the machine cuts as a three-axis job. Then it indexes again for the next face.

The gap shows up on the part, not on the spec sheet. Indexed work leaves a witness line where the toolpath restarts, and the two faces rarely meet cleanly on a contoured surface. Undercut features, deep pockets behind a flange, and impeller blades with variable twist cannot be reached without continuous tool axis change. If a shop quotes five-axis rates for a part that only needs 3+2, you are paying for motion you do not use.

True simultaneous work also cuts fixture count. A part that needs four faces machined can run in one setup on a trunnion table instead of four operations with four datums. Every re-clamp adds a position error and a queue at the machine. For a 200-piece run, one setup instead of four often decides the delivery date.

GreatLight runs 16 simultaneous 5-axis machining centers inside a fleet of 127 high-precision CNC machines, alongside four-axis mills, mill-turn centers, wire EDM and mirror-spark EDM. That mix matters when a part has one contoured face and ten simple prismatic features. We put the contoured face on the five-axis machine and the rest on a three-axis mill, which keeps the price honest.

Size first. Maximum processing size across our five-axis fleet reaches 4,000 mm, with a large-machine envelope of 4,000 × 400 × 150 mm. Medium machines cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact cells run 500 × 500 × 450 mm and 500 × 310 × 200 mm, and a Ø400 mm rotary table handles round parts that need rotation during the cut. Send the bounding box, not the drawing title.

Tolerance is the second filter. We work to ±0.005 mm ( ±0.0002 in ) on defined features, measured on a CMM with the datum scheme agreed up front. That number is not a blanket promise for every dimension. A 900 mm bore and a 12 mm slot do not behave the same way, and thermal drift over a long cycle moves both. Tell us which three or four dimensions carry the function, and we will hold those hardest.

Finish follows the same logic. As-machined surfaces land at Ra 1.6–3.2 μm, a good high-finish pass reaches Ra 0.8–1.6 μm, and fine finishing gets to Ra 0.2–0.8 μm where the geometry allows. Tight finish and tight tolerance on the same face cost time. Often the answer is to machine to Ra 1.6–3.2 μm and let bead blasting or polishing do the rest.

Wall thickness belongs in this conversation too. Thin ribs deflect under cutting force, so a 0.8 mm wall on a 300 mm aluminium housing needs light passes, sharp tooling and a fixture that supports the back side. That is a process decision, not a tolerance note. Flag it in the RFQ and the DFM review will come back with a changed stepover.

Aluminium is the easy half. Grades 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 all machine well at 15,000–30,000 RPM with high helix carbide and air blast or minimal coolant. 7075 and 2024 need more attention on stress relief, because a thin pocket floor can move after the part is off the machine.

Stainless and steel slow the process down. Grades 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH appear regularly, as do 1018, 1045, 4130, 4140, 4340, A36 and tool steel. Lower surface speeds, more heat in the cut, and shorter tool life are normal. 17-4PH in the H900 condition machines differently from the annealed state, so the heat treat step has to be stated on the RFQ.

Titanium and nickel alloys are where five-axis pays for itself. TA1, TA2, TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B or AZ91D all cut hot and work-harden. Keep radial engagement low, use through-spindle coolant where possible, and never dwell. Magnesium adds a chip-handling rule: fine dry chips need a controlled removal plan.

Plastics and composites round out the list. ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre all run on the same machines with different feeds and vacuum or soft-jaw workholding. PEEK and carbon fibre wear tooling fast, so edge quality on a 0.5 mm rib depends as much on the cutter change interval as on the CAM path.

Hourly rate is the least useful number in a five-axis quote. The real drivers are setup count, fixture cost, machining time and inspection time. A part that runs in one setup on a trunnion table often beats a cheaper shop that needs three operations. Ask how many setups your part needs, and compare that answer across suppliers.

Lead time works the same way. We can start production within 24 hours of a released order, and parts ship in 3–5 days for typical work. Our historical late-delivery probability is below 2%. Those numbers assume the material is in stock and the drawing is frozen. A change to a datum or a wall thickness after the first article restarts part of the process.

Order quantity is not a barrier. There is no minimum order quantity, so a single prototype and a 10,000+ part run go through the same quoting process. Prototype pricing carries setup; production pricing amortizes it. That is why a 50-piece quote can look better per part than a 5-piece quote, and why we suggest running the prototype on the production process instead of a shortcut process.

Finishing and inspection are separate line items and should be quoted separately. Anodizing in clear, colour, hardcoat or conductive, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing all change cost and add days. Laser marking needs a minimum character height of 1.5 mm to stay legible.

Five-axis earns its cost when a part has contoured surfaces that meet at compound angles, undercuts that a three-axis approach cannot reach, or enough faces that multiple setups would stack up position error. Aerospace housings, medical instruments with organic contours, engine and EV components with cored passages, and robot joint parts with intersecting bores all fall into this group.

It also wins when the part is large and awkward. A 1,200 mm frame with features on five sides is painful on a three-axis mill and routine on a five-axis machine with the right travels. Same for a part with a deep pocket whose floor is not perpendicular to any face. The tool has to reach it somehow.

Five-axis is the wrong call for flat plates, simple brackets, turned shafts and anything that a three-axis mill or a lathe can finish in one or two setups. It is also wrong for parts where the geometry is simple but the volume is huge and the material is cheap. In those cases, die casting, sheet metal fabrication or vacuum casting will beat machining on unit cost, and we will say so.

A useful test: count the setups. If three-axis needs one or two setups and the tolerances are loose, use three-axis. If it needs four or more, or the tolerances are tight across angled faces, price the five-axis route. The comparison usually decides itself once both numbers are on one page.