SLS build-share pricing, explained

Ask ten shops how they price an SLS part and most will say “per cubic centimetre, plus a bit”. It is the wrong unit, and it is wrong in a way that hurts twice: you overcharge single small parts so badly that you lose them, and you undercharge full builds so badly that you wish you had.

The right unit is a share of a build.

What a build costs

A powder-bed build is an event. It takes a machine for a number of hours - layers to lay down and expose, plus cooling, which on a natural-cooled nylon build can be as long as the print. It consumes powder, both the powder that becomes parts and the powder that does not. It takes labour to set up, to break out and to clean. That total is the cost of the build, and it is very nearly the same whether the cake is full or contains one bracket.

So the question is never “what does this part cost”. It is: what fraction of a build is this part responsible for?

The cell

A part in a cake occupies a box: its oriented bounding box, grown by the gap you keep between parts. That is its cell. Your machine has an effective envelope - the usable build volume, which is smaller than the brochure number. And your nester achieves some packing efficiency: the fraction of that envelope it fills with cells rather than air.

The part’s build share is then:

share = cell volume ÷ (nesting efficiency × envelope volume)

Two consequences follow immediately, and both are uncomfortable the first time you see them.

A single part carries the whole build. If a customer orders one 40 × 40 × 40 mm bracket, its cell is about 0.1 % of your envelope - but you are not going to run a build for one bracket, and if you do, it costs you a build. This is why powder shops either wait to fill a cake (and quote a longer lead time) or quote the single part at what it really costs and let the buyer decide.

Ten of the same part cost far less than ten times one. They share the build. This is the largest quantity break in manufacturing and it is not a discount - it is the cost structure being passed on honestly.

The powder that never becomes a part

Here is the line most spreadsheets miss entirely. Powder that is in the cake but not sintered has been through a thermal cycle. You can reuse some of it, but every build needs a proportion of virgin powder - your refresh ratio, typically 30–50 % for SLS PA12 and lower for MJF.

So: unsintered powder × refresh ratio is waste, and it is a real cost of the build, charged by build share like everything else. A shop that prices only the sintered volume is giving away a meaningful fraction of its powder budget on every job.

Orientation matters more than you would think

Because the cell is an oriented bounding box, how the part sits changes its cell volume - sometimes by a lot. A long thin part laid flat has a very different cell from one standing up. And height drives the number of recoat-and-expose cycles, which is the machine time.

Which means that for powder, orientation is a pricing decision as well as a quality one, and it is worth letting the system pick the cheapest orientation that still meets your quality rules.

The two numbers to get right

Everything above is arithmetic once you know two things:

1. Nesting efficiency. What fraction of the envelope your nester really fills. Shops guess 70 %; the honest number for mixed single parts is often nearer 50–60 %.
2. Build time per millimetre of height. Recoat plus expose per layer, expressed per mm. Typically 5–8 min/mm for SLS and 3–4 for MJF - but it is your machine.

Both are calibratable in Quotometry, which means you do not have to guess: hand it builds you have actually run with their real times, and it fits them.

Why this is worth the trouble

A shop pricing powder per cubic centimetre is running a cross-subsidy it cannot see: dense compact parts subsidise sprawling ones, and full builds subsidise near-empty ones. Build-share pricing makes each job carry its own cost, which is both fairer to your customers and considerably more informative to you.

How Quotometry prices SLS, in detail →