Fabricate and CNC Machine Cost: A 7-Step Estimate

• 1
  Key takeaways
• 2
  What actually drives fabricate and CNC machine cost
• 3
  Material grade and stock form
• 4
  Geometry and tolerance: the two biggest multipliers
• 5
  Quantity, setup, and the break-even point
• 6
  Step by step: from drawing to a cost estimate
• 7
  Cost multiplier by material and tolerance
• 8
  Tolerance and finish add-on

Every quote we send breaks into five buckets: material, setup, cycle time, finishing, and inspection. Material is billed by the kilogram plus a cut-off allowance. Setup covers programming, fixturing, and the first-article check. Cycle time is machine hours multiplied by the shop rate. Finishing and inspection are quoted as separate line items because they leave the spindle.

Engineers often ask for a price per part before the geometry is frozen. That number will move. A pocket that is 40 mm deep and 6 mm wide needs a long-reach end mill that deflects, so the cutter runs at reduced feed. Widen the pocket to 12 mm and the same feature machines twice as fast with a standard tool. Design decisions like this matter more than the material price per kilogram.

Quantity changes the picture too. Setup is a fixed cost. If setup is 4 hours and cycle time is 20 minutes per part, the first part costs five times the tenth part. Break-even between a soft-tooled prototype and a production run usually lands somewhere between 500 and 2,000 pieces, depending on geometry. Below that, machining wins. Above it, casting or stamping can pull ahead.

The cheapest quote is rarely the one with the lowest hourly rate. It is the one where the process plan matches the geometry. A part designed for three-axis work that gets pushed onto a five-axis machine pays for capability it does not use. A part with undercuts that gets forced onto three axes pays for extra fixtures and hand work.

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  Material gradeDrives both stock price and cutting speed.
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  Feature aspect ratioDeep, narrow pockets need long-reach tools and slower feeds.
• 3
  Tolerance classTighter than ±0.05 mm adds inspection time and scrapped parts.
• 4
  QuantitySetup cost per part falls as volume rises.

Aluminium 6061-T6 is the default for prototypes and brackets. It cuts at high surface speed, holds a good finish, and welds or anodizes without drama. 7075 is stronger but costs more and machines slower. 2024 has better fatigue properties and worse corrosion resistance, so it usually needs a coating.

Stainless 303 is the free-machining grade and the right pick for shafts and fittings that do not see chlorides. 304 and 316 resist corrosion better but work-harden quickly. Feed too light and the tool rubs, which hardens the surface and dulls the cutter. 17-4PH sits between stainless and tool steel; it machines at 40% of the speed of 6061 and needs a heat-treat step for full hardness.

Titanium Ti-6Al-4V and Inconel 718 are the expensive end. Both have low thermal conductivity, so heat stays in the cutting zone. Tools wear fast, feeds and speeds drop, and cycle time can run 5 to 10 times that of aluminium on the same part. Use them only where the temperature or strength requirement is real.

Stock form matters as much as grade. Plate is cheaper per kilogram than bar but wastes more material on a round part. Near-net forgings cut cycle time but add tooling cost and lead time. For a 50-piece run, buying plate and machining from solid is usually the lowest total cost.

A simple bracket with through-holes and flat faces machines in one or two setups on a three-axis mill. An organic housing with deep cavities, thin walls, and blended surfaces needs five-axis work and longer cycle times. Our five-axis centers handle this in fewer setups, which cuts fixture cost and reduces the chance of stacked tolerance error.

Wall thickness is a quiet cost driver. Below 1 mm in aluminium, chatter becomes likely. Below 0.5 mm, the part may deflect during clamping and spring back after unclamping. If the design allows 1.5 mm to 2 mm walls, the cutter can take a heavier pass and the quote drops.

Tolerance is where cost climbs fastest. A general tolerance of ±0.1 mm is standard shop practice. At ±0.05 mm you add in-process checks. At ±0.005 mm, we may need temperature control, a finishing pass with a fresh tool, and a coordinate measuring machine report. Each step adds time, and rejected parts carry the cost of the good ones.

Surface finish runs on a similar curve. As-machined at Ra 1.6–3.2 μm comes off the machine. Ra 0.8–1.6 μm needs a finishing pass. Ra 0.2–0.8 μm needs polishing or grinding as a second operation. Specify the finish your sealing surface actually needs, not the whole part.

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  Fewer setupsFive-axis work can cut three setups down to one.
• 2
  Wall thicknessKeep aluminium walls above 1 mm to avoid chatter.
• 3
  Tolerance zonesCall out tight tolerance only on mating features.
• 4
  Finish scopePolish sealing faces, leave the rest as-machined.

Setup is the fixed part of every quote. It includes CAD review, CAM programming, fixture design, tool selection, and the first-article inspection. For a simple part this is 2 to 3 hours. For a complex housing with a custom fixture it can be a full day.

Cycle time is the variable part. If setup is 3 hours and cycle time is 15 minutes, the setup adds 12 times the cycle cost to a single part. At 100 parts, setup adds 12% of one cycle. This is why a prototype quote looks high and a production quote for the same part looks reasonable.

Fixture design is often the hidden cost. A part with a flat face and two holes can be held in a standard vise. A part with no parallel faces needs a custom soft jaw or a dedicated plate. If you can add a clamping boss or a flat datum that gets machined off later, do it. That one change can remove an entire fixture from the quote.

Below about 500 pieces, CNC machining is usually the lowest total cost. Between 500 and 2,000 pieces, compare against vacuum casting or die casting. Above 2,000, die casting or stamping normally wins if the material and tolerance allow. The crossover moves with geometry, so ask for both quotes before committing.