Material is the line on a CNC quote priced before a tool touches the part, and the line buyers check against the metal price online. That comparison looks wrong: the quote is priced on the blank, not the finished part.
For illustration, a 304 stainless bracket finishes at 0.75 kg. At ¥17/kg, the finished metal is worth ¥12.75. A ¥32 material line is not a hidden markup: it prices a 1.65 kg blank and carries a purchasing loss factor on top.
By the end you will know how to rebuild a material line from blank weight, unit price and loss factor, and you can test a substitution before changing the drawing.
The answer up front: material cost = blank weight × material unit price × purchasing loss factor. Blank weight is the part envelope plus a per-side allowance, multiplied by density. The loss factor covers metal that is bought but never becomes a part.
Material Cost Formula and the 11-Grade Reference Table
A material line that cannot be reproduced from the drawing is not an estimate; it is a remembered number.
The table is the default basis in the CNC quote calculator; for the other four quote lines, see the full CNC cost breakdown. Every value can be overwritten, and every price should be.
| Grade | Density (g/cm³) | Reference price (¥/kg) | Difficulty (45# = 1.0) | Usual stock form |
|---|---|---|---|---|
| 45# carbon steel | 7.85 | 5.5 | 1.0 | Bar |
| Q235 structural steel | 7.85 | 4.5 | 0.9 | Plate, bar |
| 40Cr alloy steel | 7.85 | 6.0 | 1.2 | Bar |
| POM (acetal) | 1.41 | 12 | 0.7 | Plate, bar |
| 304 stainless steel | 7.93 | 17 | 1.4 | Bar, plate |
| 316 stainless steel | 7.98 | 25 | 1.4 | Bar, plate |
| 6061 aluminium | 2.70 | 23 | 0.8 | Plate, bar |
| 7075 aluminium | 2.81 | 25 | 0.8 | Plate |
| H62 brass | 8.50 | 45 | 0.9 | Bar |
| T2 copper | 8.96 | 50 | 0.9 | Bar, plate |
| TC4 titanium | 4.43 | 150 | 2.0 | Bar |
Price basis: October 2026 reference prices, estimated for small-lot purchase and not calibrated against settled orders. They move with grade, mill, stock size, quantity and the market; replace them with the week’s purchase price before costing a production order.
Difficulty multiplies cutting time, not material cost. Mixing the two is a common reason a substitution calculation comes out backwards. The other multiplier that changes row time, tolerance grade, is set out in tolerance cost.
Why the Blank Is Priced, Not the Finished Part
A 70 mm diameter cannot be cut from 70 mm bar and cleaned up all round. The stock has to clear the finished surface on every side.
| Blank form | Default allowance per side | What it covers |
|---|---|---|
| Bar | 3 mm | Radial cleanup plus end cleanup |
| Plate | 2.5 mm | Thickness and edge cleanup |
| Forging | 4 mm | Reference only; price the delivered blank |
| Casting | 4 mm | Reference only; price the net casting weight |
Worked example: a 45# disc, ⌀70 × 25 mm finished.
- Blank: ⌀76 × 31 mm (3 mm per side on diameter and on each end).
- Blank volume: π/4 × 7.6² × 3.1 = 140.6 cm³.
- Blank weight: 140.6 × 7.85 ÷ 1000 = 1.104 kg.
- Finished volume: π/4 × 7.0² × 2.5 = 96.2 cm³, or 0.755 kg.
- Buy-to-fly: 1.104 ÷ 0.755 = 1.46.
- Material cost: 1.104 × 5.5 × 1.15 = ¥6.98.
On this part, 32% of the purchased metal does not leave as finished weight: chips, saw kerf and bar end.
Where the 1.15 Loss Factor Comes From
Allowance makes the blank larger. Loss covers what is bought beyond the blank: bar ends, the clamping stub, saw kerf and the last bar length too short to hold.
For a 31 mm blank, a 3 mm saw cut is nearly 10% of the length before any end trim. Add the bar end and the clamping stub and 1.15 is a reasonable first assumption, not a law. The calculator accepts 1.00–1.50.
When full bars are purchased, parts nest well and remnants go to another job, 1.05–1.10 is closer. When material is bought cut to length and remnants stay with the supplier, 1.20–1.30 is more honest. Both are job-costing experience, not a published statistic.
| Loss factor | Material cost on the 1.104 kg blank | Reading |
|---|---|---|
| 1.05 | ¥6.38 | Full bars, good nesting, remnants reused |
| 1.15 | ¥6.98 | Calculator default, mixed purchasing |
| 1.30 | ¥7.89 | Cut-to-length, remnants not returned |
The swing from 1.05 to 1.30 is 24% on the same part. Write the loss factor and the price date in the quotation header. The material line itself is per piece; what moves with batch size is the one-off block around it, as cost per part by quantity works through on the same disc.
Loss applies to bar and plate only. Castings and forgings already carry process loss inside the supplier’s price, so applying 1.15 again double-counts it.
Substitution: Aluminium 6061 vs 304 Stainless
Buyers usually compare price per kilogram: 6061 at ¥23/kg against 304 at ¥17/kg. That points the wrong way. A kilogram of aluminium occupies about 2.9 times the volume of a kilogram of stainless, so the cheaper metal per kilogram can be the dearer metal per part.
Worked example: a plate part, 200 × 150 × 20 mm finished with 35% of the envelope removed, cut from a 205 × 155 × 25 mm blank (794.4 cm³).
| Item | 6061 aluminium | 304 stainless |
|---|---|---|
| Density (g/cm³) | 2.70 | 7.93 |
| Blank weight (kg) | 2.145 | 6.299 |
| Reference price (¥/kg) | 23 | 17 |
| Material cost at loss 1.15 | ¥56.73 | ¥123.16 |
| Difficulty factor | 0.8 | 1.4 |
| Cutting time at 40 min baseline | 32 min | 56 min |
| Cutting cost at ¥80/h | ¥42.67 | ¥74.67 |
| Material + cutting | ¥99.40 | ¥197.83 |
Stainless comes out at about 2.0 times the aluminium subtotal despite the lower price per kilogram. The 40 minutes is template cutting time before the difficulty factor at a three-axis rate; replace it with your own feature rows. Setup, post-processing and overhead are excluded, so the comparison isolates material and cutting.
Substitution usually wins on low-load covers, brackets, housings and fixtures, where stiffness rather than wear resistance sets the section. It usually loses on threads, wear surfaces, food-contact parts, corrosion-critical parts, and anything the drawing calls out by grade for a qualification reason.
Change grade only after the drawing’s mechanical and corrosion requirements pass; purchasing can price a substitution, not approve it.
Castings and Forgings Do Not Use Bar or Plate Prices
The bar and plate formula stops at the stock yard. A casting is bought near-net, with gating, risers and process loss inside the price. A forging is bought at as-delivered blank weight, with scale, flash, bar end and machining allowance inside the price.
No loss factor is applied to either line.
| Grade band | Reference price (¥/kg) | Basis |
|---|---|---|
| HT150 grey iron | 6.5 | Casting net weight |
| HT200 grey iron | 7.5 | Casting net weight |
| QT450-10 ductile iron | 10.0 | Casting net weight |
| ZG270-500 cast steel | 11.0 | Casting net weight |
| ZL104 cast aluminium | 25.0 | Casting net weight |
| 45# forging | 8.0 | Delivered forged weight, loss included |
| 40Cr forging | 10.0 | Delivered forged weight, loss included |
| Stainless or aluminium forging | Quote from supplier | Custom proxy band in the calculator |
Two inputs come from the supplier: casting net weight and as-delivered forging weight. Deriving either from an envelope times density overstates a near-net blank and hides the tooling cost that made it near-net.
Tooling is a separate order-level line; the calculator leaves mould and die cost at ¥0 because it must be quoted.
Buy-to-Fly: Blank Form Decides More Than Unit Price
Buy-to-fly is the ratio of purchased blank weight to finished weight: the single number showing how much paid-for metal ends up in the part.
The 45# disc gives 1.46 from bar. Cut the same disc from a square plate blank, 76 × 76 × 31 mm, and the blank weighs 1.406 kg: buy-to-fly 1.86, material cost ¥8.89 instead of ¥6.98. The unit price did not change. The blank form did.
| Blank for the same disc | Blank weight (kg) | Buy-to-fly | Material cost |
|---|---|---|---|
| Bar, ⌀76 × 31 mm | 1.104 | 1.46 | ¥6.98 |
| Plate, 76 × 76 × 31 mm | 1.406 | 1.86 | ¥8.89 |
Plate costs 27% more because the four corners were purchased as air. Practical rules:
- Choose the nearest standard stock thickness, then check whether a smaller allowance still cleans up.
- Nest small parts in one blank where the drawing allows; the loss factor falls before the unit price does.
- A buy-to-fly above about 3, from project experience, is a design-for-manufacturing conversation, not a purchasing one.
Recalculating the Line in the Calculator
Open the CNC quote calculator and change one input at a time:
- Select the material from the 11-grade list and overwrite the reference price with the week’s purchase price.
- Select the blank form. The allowance default changes with it: bar 3 mm, plate 2.5 mm, forging 4 mm, casting 4 mm.
- Enter the part dimensions, or the supplier-confirmed net weight for a casting and the delivered weight for a forging.
- Set the loss factor between 1.00 and 1.50, then change it alone and watch how far the material line moves.
If the material line moves without the unit price changing, you are looking at blank weight or loss, not at a price increase.
The result is a range, not a point: a check on a supplier’s quote, not a substitute for a written offer. The six-step workflow is set out in the calculator manual.
Frequently Asked Questions
How much does material add to CNC machining cost?
Material cost = blank weight × unit price × loss factor. There is no universal percentage: it depends on buy-to-fly and cutting time. In the disc example the material line is ¥6.98 on a 1.104 kg blank; on the stainless plate example it is ¥123.16.
Is aluminium cheaper than stainless steel for CNC machining?
Usually yes, but not because it is cheaper per kilogram. 6061 is ¥23/kg against 304 at ¥17/kg, yet the same blank costs ¥56.73 in 6061 against ¥123.16 in 304, because the density ratio is about 2.9. Stainless also carries a difficulty factor of 1.4 against 0.8.
Why is my material cost higher than the metal price?
The quote is priced on the blank, not the finished part. Allowance adds metal on every side, and the loss factor adds bar end, clamping stub and saw kerf. A high buy-to-fly part can carry two to three times its finished weight in metal.
Does the loss factor apply to castings and forgings?
No. The casting price already includes gating, risers and process loss, and the forging price is quoted at as-delivered weight. Multiplying either by 1.15 counts the same loss twice.
How do I lower material cost without changing the design?
Start with the blank, not the grade. Use bar for round parts and plate for rectangular parts, choose the nearest stock thickness, nest small parts and buy full bars where volume allows. Check the loss factor against how the material is purchased, and change grade only after density, price and difficulty have been compared together.
Three sentences to take away. First, material is priced on the blank; finished weight is not purchased weight. Second, the loss factor is a purchasing assumption and belongs next to the price, because 1.05 and 1.30 are a 24% swing on the same part. Third, compare materials by density × price × difficulty, never by price per kilogram alone.
Checklist before the quote goes out:
Send the drawing, grade and batch size through the custom parts page and our engineering team will review the blank basis, loss factor and substitution arithmetic against the quote. For a first range, run the calculator; to have the parameters checked line by line, use the quoting page.
References
- GB/T 702-2017 — Hot-rolled steel bars: dimensions, shape, weight and tolerances
- GB/T 702-2017 is replaced by GB/T 702-2026 from 1 November 2026; confirm the edition in force before quoting a long-run order.
- GB/T 708-2019 — Cold-rolled steel sheet and strip: dimensions, shape, weight and tolerances
- GB/T 708-2019 is replaced by GB/T 708-2026 from 1 December 2026.
- Yaxiio CNC quote calculator — default material, allowance and loss parameters, reference basis October 2026
Key Standards
Standards and clauses referenced by this article.
- Hot-rolled steel bars — dimensions, shape, weight and tolerances
Stock bar dimensions and weight tolerances. Replaced by GB/T 702-2026 from 1 November 2026.
- Cold-rolled steel sheet and strip — dimensions, shape, weight and tolerances
Plate stock thickness and weight basis. Replaced by GB/T 708-2026 from 1 December 2026.
References
Sources used for fact checking and background context.
Deep Reading
More systematic selection, procurement, or inspection guides.
- How to Choose a Fastener Supplier: A Sourcing Playbookwhitepaper
A more systematic guide on a related selection or inspection topic.
Related Solutions
Pages for specification checks and procurement discussion.
- CNC Quote Calculator
Rebuild the material line with your own grade, blank form and loss factor.
- Custom Parts from Your Drawing
Drawing, grade and batch size; the engineering team checks the blank basis against the quote.
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