In selective laser sintering, the single biggest lever on your cost per part is not the material grade or the surface finish — it is how many parts your geometry lets us pack into one build volume, and how tall the resulting stack is. SLS has no support structures, so the entire chamber is available real estate: every part you nest into the powder bed shares the same warm-up, sinter, and cool-down cycle. Pack the bed to a high density and the fixed cost of the machine cycle spreads across more parts; leave it half empty, or force a build tall on the Z-axis, and each part carries a bigger share of that cost. At Layer X, we price SLS from ₹1,200 per part precisely because packing density and Z-height are the two numbers that move it. This guide explains the build economics behind that figure, and how to design nylon parts that nest well.
Why SLS is priced by the build, not the part
Unlike FDM or SLA, where machines print largely one part at a time and price tracks part volume, SLS is a batch process. A laser fuses PA12 powder layer by layer across a heated bed; the entire volume of loose powder is held just below its sintering temperature for the whole run. That thermal cycle — heating the chamber, sintering every layer, then letting the cake cool slowly enough to avoid warping — is a fixed overhead. It costs almost the same whether the bed holds twenty parts or two hundred.
So the real unit of production in SLS is the build, not the part. Cost per part is, roughly, the cost of the build divided by the number of good parts it yields. Two variables dominate that division:
- Packing density — the proportion of the usable build volume occupied by actual part material. Higher density means more parts sharing the same cycle.
- Z-height — how tall the packed stack is. Machine time in SLS scales almost linearly with the number of layers, and layers scale with Z-height. A build 300 mm tall costs far more machine time than one 150 mm tall, regardless of how much part material sits inside it.
Get both right and the ₹1,200 floor holds even for complex functional geometry. Get them wrong — sparse nesting, a needlessly tall build — and the same part quietly costs more.
Packing density: the number that sets your price
Packing density in SLS is usually expressed as the percentage of the build chamber volume taken up by parts. In practice, achievable density depends far more on part shape than on the nesting software. Blocky, convex parts with few concavities pack tightly. Parts with large hollow interiors, sprawling flat plates, or awkward aspect ratios trap unusable powder around them and drag the density down.
The terminology here follows ISO/ASTM 52900, the standard vocabulary for additive manufacturing, which defines the powder-bed fusion category SLS belongs to. Under that standard, the loose powder is not scrap in the way a machining chip is — a controlled fraction is refreshed and reused build to build — but the powder that ends up locked inside a hollow you designed is powder that could have been part.
Here is how common geometry choices affect how tightly parts nest, and therefore your cost per part:
| Design characteristic | Effect on nesting | Cost-per-part impact |
|---|---|---|
| Compact, near-cubic envelope | Parts interlock; little wasted powder between them | Lowest — best density |
| Large sealed hollow interior | Trapped powder cannot be recovered as part | Higher — wasted volume |
| Long thin flat plate | Forces a wide or tall build to lie flat; poor stacking | Higher — low density |
| Nestable / cupped shape | Parts spoon together like stacked chairs | Lower — density gain |
| Protruding thin spikes or fins | Fragile in the cake; forces spacing for safe de-powdering | Higher — forced gaps |
The single most useful habit is designing an open hollow rather than a sealed one. A drain hole or open face lets us recover the internal powder and, on many parts, lets a smaller part nest partly inside the cavity. On our PA12-CF drone frame case study, opening the internal channels was as much about packing efficiency as it was about weight.
Z-height: the axis that costs you time
If packing density decides how many parts share a build, Z-height decides how long that build takes. The laser has to expose every layer from the bottom of the lowest part to the top of the tallest one — and the recoater has to spread fresh powder for each of those layers whether or not a given part reaches that height. A single tall outlier can add hundreds of layers that most of your parts never use, inflating machine time for the whole batch.
This is why orientation is an economic decision, not just a strength or finish decision. The same part can often be laid flat, stood on end, or angled — and each choice produces a different Z-height for the build:
- Lay the long axis horizontal where possible, so parts contribute width and depth (cheap, plentiful bed area) rather than height (expensive layers).
- Beware the tallest part in the batch. One 280 mm part mixed with a tray of 40 mm parts forces every layer up to 280 mm. Group parts of similar height into the same build.
- Angle for finish, but pay for it in Z. A part tilted to smooth its cosmetic faces gains height. That trade is worth making — but it is a trade, and it belongs in the quote conversation, not a surprise.
There is a real tension here with mechanical performance. Because SLS produces near-isotropic parts — one of the four headline properties of our SLS service, alongside a ±0.2 mm tolerance, no supports, and a 4–6 day lead time — you have more orientation freedom than in FDM, where layer adhesion makes the Z-direction the weak axis. SLS parts are strong in every direction, so you can usually orient for packing efficiency without a strength penalty. When a specific load path or a critical hole does dictate orientation, we honour it; the point is that for most nylon parts, the cheapest orientation and a perfectly strong one are the same orientation.
Designing parts that nest well
Design-for-nesting is a short checklist, and it is worth running before you ever request a quote. It is closely related to the wall-thickness and clearance rules we cover in our SLS design rules for PA12 nylon, but seen through a cost lens rather than a manufacturability one.
- Keep the bounding box compact. The nesting algorithm works with your part's overall envelope first. A part that is mostly air inside a large box wastes that box's worth of bed.
- Hollow out solid masses. Solid PA12 is slow to cool and wastes material; shelling to a consistent wall not only saves powder but reduces the thermal mass that can distort a densely packed cake.
- Add powder-escape holes. Every enclosed cavity needs at least one, ideally two, openings so trapped powder drains during de-powdering — and so the cavity can host a smaller nested part.
- Design families to stack. If you are ordering a batch, a gentle draft or a cupped profile lets identical parts spoon together, lifting density dramatically over parts that can only sit side by side.
- Avoid long fragile protrusions. Thin spikes survive the sinter but are vulnerable during cleaning, so we space them out for safety — spacing that eats packing density. A small fillet or a sacrificial tie can let them nest closer.
Batch size and the density dividend
Packing density compounds with quantity. A one-off part almost never fills a bed, so a prototype carries a larger share of the fixed cycle cost — this is inherent to the process, not a surcharge. Order 10 to 500 identical parts, the sweet spot our SLS line is built for, and those parts fill the chamber together, each one paying a smaller slice of the same build. This is also the reason SLS beats injection moulding below roughly a thousand parts: there is no tool to amortise, so a well-packed SLS build is genuinely cost-competitive for short and medium runs of complex nylon geometry.
When cost and strength pull in different directions
Occasionally the cheapest nesting is not the right answer. A part with a specific fatigue-critical feature, a precise bore that must stay round, or a cosmetic face that must be down-facing may need an orientation that costs a little more in Z-height. The discipline is to make that a deliberate, priced decision rather than an accident. Because our SLS parts are isotropic this happens far less than in FDM — where, as we discuss in our guide to FDM 3D printing and its orientation and layer-adhesion trade-offs, orientation is almost always a strength compromise first. In SLS, orientation is mostly an economics decision, and that is good news for your cost per part.
How Layer X optimises your build
When your CAD arrives, we do not simply drop it into the first free slot in the queue. We assess its bounding box, look for sealed cavities and thin protrusions, and model how it nests against other work in the pipeline. Where a small design change — an added drain hole, a shelled boss, a family designed to stack — would meaningfully lift density or lower Z-height, we flag it in the quote rather than silently charging you for the sparse version. Every SLS order is managed and quality-checked under our ISO 9001 certified system, with the same ±0.2 mm tolerance and isotropic strength whatever orientation the economics settle on.
The takeaway is simple: in SLS, you are not buying a part, you are buying a share of a build. Design compact, open, stackable nylon geometry and keep your batch heights consistent, and that share — and your price — comes down.
Ready to see how your parts nest? Upload your CAD file for a 24-hour quote and we will tell you exactly where the packing density and Z-height are costing you — and how to get them back.