Price an SLS part as a share of a build. Cost the whole build first: machine hours including cool-down, the powder that has to be refreshed, inert gas and the labour to set up and break out. Then charge each part the fraction of the build’s usable volume that its cell occupies, plus its own sintered powder and handling. The share depends on how well your nester fills the build, which is why quantity, orientation and part shape move SLS prices far more than part weight does.
Key points
- An SLS build costs nearly the same whether it is full or holds one part.
- A part’s build share is its cell volume divided by the build volume your nester can really fill.
- Nesting efficiency and packing density are different numbers; both matter.
- Refreshed powder, the unsintered powder replaced with virgin, is often a larger cost than the powder in the parts.
- Cool-down can last about as long as the print and occupies equipment.
- Orientation changes the cell and the build height, so it is a pricing decision.
What does an SLS build cost?
A powder-bed build is a single event with a mostly fixed cost. Whatever goes in the cake, you pay for:
| Build cost line | What it covers | Scales with |
|---|---|---|
| Warm-up | Bringing the bed and chamber to temperature | Fixed per build |
| Print time | Recoat and laser exposure per layer | Build height, and part area per layer |
| Cool-down | The cake cooling slowly in the machine or a separate unit | Build height and the cooling method |
| Inert gas | Nitrogen or argon while printing | Print hours |
| Powder refresh | Unsintered powder replaced with virgin to keep the mix in specification | Cake volume × refresh ratio |
| Labour | Set-up, unpacking, sieving, cleaning | Fixed per build, plus per part |
The SLS print time is driven mainly by height, because every layer needs a recoat. A tall part forces every layer above the rest of the build, so a tall part should pay for the height it adds.
How is a part’s build share calculated?
Each part sits in a cell: its bounding box in the orientation you will print it, grown on every side by the gap you keep between parts. The machine’s build volume minus border margins is the usable envelope. Your nester never fills all of it with cells; the fraction it does fill is your nesting efficiency.
build share = cell volume ÷ (nesting efficiency × usable envelope)
Multiply the build cost by the share, then add the part’s own powder and per-part labour (de-powdering, blasting, inspection, bagging). Our post on SLS build-share pricing introduces the idea; the rest of this guide covers the numbers that make it work.
Nesting efficiency versus packing density
These two terms are often used interchangeably, and they should not be.
- Nesting efficiency: the share of the usable envelope covered by part cells. It describes how well the boxes fit together. This is what build share uses.
- Packing density: the share of the envelope that is actual part material. It is always lower, because parts are not solid boxes.
Nesting efficiency for a build of mixed single parts is usually well below the figure shops guess: odd shapes, a range of heights and clearance rules all leave air. Identical parts nest more tightly, so nesting efficiency rises with quantity. Good pricing reflects that: a larger order earns a higher efficiency, which lowers the share per part. This is the same logic as any quantity break, but here it comes straight from the physics.
Packing density matters for the powder bill. A build with low packing density has a lot of unsintered powder in the cake, and that powder has been through a heat cycle.
Why does powder refresh cost so much?
Unsintered PA12 in the cake ages with every heat cycle. To keep properties stable, used powder is sieved and mixed with virgin powder at a powder refresh rate, often in the region of 30-50 % for SLS PA12, depending on the powder and the machine maker’s guidance. Over time, that means a portion of the unsintered powder in every build is effectively consumed.
A practical model: unsintered powder in the cake × refresh ratio = powder written off per build. It is part of the build cost, shared like everything else. A quote that prices only the sintered volume leaves this out completely, and on a sparse build it can be larger than the material in the parts.
Why does cool-down belong in the price?
Nylon parts have to cool slowly inside the cake or they warp. On a natural cool this often takes about as long as the print itself. Where the cake cools matters for cost:
- In the machine: the printer is occupied, so cool-down hours are charged at the machine rate.
- In a separate build unit or cooling station: the printer can start the next build, and cool-down is charged at the lower rate of the unit that holds it.
Either way the hours set your lead time. A fast-cool option can shorten it, sometimes at a cost to dimensional stability, and it is reasonable to price the two differently.
A worked example: one part at three quantities
Worked example: a 50 × 40 × 30 mm PA12 housing, 25 cm³ of material, in a shared build (example figures)
Build cost: print 16 h × €30.00/h = €480.00; cool-down 12 h × €8.00/h = €96.00; nitrogen 16 h × €2.00/h = €32.00; refresh 9 kg unsintered × 30 % × €55.00/kg = €148.50; labour 2.25 h × €35.00/h = €78.75. Total €835.25. Usable envelope 300 × 300 × 280 mm = 25,200 cm³. Cell with a 5 mm gap: 55 × 45 × 35 mm = 86.625 cm³.
| 1 part | 10 parts | 50 parts | |
|---|---|---|---|
| Nesting efficiency (example) | 40 % | 50 % | 58 % |
| Fillable volume | 10,080 cm³ | 12,600 cm³ | 14,616 cm³ |
| Build share per part | 0.86 % | 0.69 % | 0.59 % |
| Share of €835.25 | €7.18 | €5.74 | €4.95 |
| Own powder: 25 cm³ × 0.95 g/cm³ × €55.00/kg | €1.31 | €1.31 | €1.31 |
| Per-part labour: 5 min × €35.00/h | €2.92 | €2.92 | €2.92 |
| Cost per part | €11.41 | €9.97 | €9.18 |
The single-part price above assumes the part joins a shared build. If it has to run alone, it carries the whole build: €835.25 + €1.31 + €2.92 = €839.48. In practice shops either hold small orders until a build fills, and quote the longer lead time, or offer the dedicated build as an expedited option.
Which policy you choose is a business decision, not a costing one, but it should be explicit. A shop that always assumes a shared build and then runs a near-empty build to meet a promised date has quoted the wrong job. Tie the price to the lead time: a shared-build price with a lead time long enough to fill a build, and a dedicated-build price for a buyer who needs the part sooner. Our guide to lead-time pricing covers how to set that difference.
At 58 % efficiency the build holds about 14,616 ÷ 86.625 = 168 of these cells. With 25 cm³ of material each, that is 4,200 cm³ of parts in 25,200 cm³: a packing density of about 17 %, even in a well-nested build.
How does orientation change the price?
Orientation changes the cell, because the bounding box is measured in the build’s axes, and it changes the height the part adds to the build. A long part standing up has a small footprint but forces every layer above it; the same part lying flat adds little height but takes more area. For pricing, compute the cell in each allowed orientation and choose the cheapest one that meets your quality rules. Warp-prone long flat panels and thick sections are the usual constraints.
What to calibrate
Two numbers decide whether build-share prices are right: your real nesting efficiency for typical jobs, and your real print time per millimetre of build height. Both are easy to measure from builds you have already run. Record the cell volume nested, the build height and the hours from start to unpack, and fit the coefficients from those. MJF vs SLS shows how the same model changes for MJF, and the whole costing method is in how to calculate 3D printing cost.
Quotometry prices SLS by build share only, with nesting efficiency that rises with quantity, refreshed powder, cool-down at its own rate and per-part labour. The SLS process page lists what a shop configures.
Questions people ask
What is build-share pricing for SLS?
Build-share pricing costs a whole SLS build, including machine time, cool-down, refreshed powder and labour, then charges each part the fraction of that build its space takes up. The space is the part's cell: its bounding box in the chosen orientation, grown by the gap kept between parts. The part also pays for its own sintered powder and its own handling.
What is the difference between nesting efficiency and packing density?
Nesting efficiency is the share of the usable build volume filled by part cells, the boxes parts sit in. Packing density is the share filled by the parts' actual material. A build can be well nested yet have a low packing density, because most parts are not solid boxes. Build-share pricing uses nesting efficiency; powder use depends on packing density.
Why do SLS parts get much cheaper in quantity?
Because the build is a fixed event. One part in a build carries a cost close to the whole build unless it can join other work. Ten copies share the build, and a nester can place many identical parts more tightly than mixed single parts, so each one takes a smaller share. The reduction is the cost structure, not a discount.
Does cool-down time belong in the price?
Yes. A nylon build has to cool slowly inside the powder cake to avoid warping, and on a natural cool this can take about as long as the print. If the cake cools in the machine, the machine is occupied. If it cools in a separate unit, that unit is occupied. Either way the hours are real and belong in the build cost.
Quotometry prices every part from your own machines and rates, on your website, in seconds.