What Are Raft Layers in 3D Printing? A Cost Controller’s Guide to Custom Fabrication Quotes

I’m a procurement manager at a 140-person industrial equipment company. I’ve managed our custom fabrication budget ($1.2M annually) for 7 years, negotiated with 45+ vendors, and documented every order in our cost tracking system. I still get surprised by quotes—but rarely by the part. Usually it’s the assumption behind the part.

If you searched for what are raft layers in 3d printing, you probably saw a slicer setting. A raft is a sacrificial lattice printed under the model. It helps adhesion and warping. It also adds material, machine time, and removal labor. That little detail explains a lot about why a $14 prototype quote becomes a $19 invoice.

The same pattern shows up in laser welding, CNC machining, and even niche parts like VMC boxer jig heads. The quote looks clean. The assumptions are not. This is not a vendor problem, at least not only. It’s a buying problem.

The surface problem: the quote looked simple

When I visited Shop Star Micronics the first time (this was back in 2023), I assumed the hard part was finding a supplier with enough processes. Star-Micronics lists CNC machining, fiber and CO2 laser cutting, 3D printing, press brake, and injection molding. The Star Micronics official site made the capability list look broad. Broad is useful. Broad also means more places for assumptions to hide.

Take 3D printing. A shop can print a part with or without a raft. Both can be correct. If the model has a large flat face, a raft can reduce the risk of corner lift. If the part has a smooth bottom surface, a raft can leave marks that require sanding. If the RFQ says only 3D printed prototype, the vendor chooses. You may get a cheaper quote because they skipped the raft—and then pay for a failed build or a rough finish.

Laser welding has the same shape. A welding machine laser welder is not just a box. If you outsource, the quote depends on fixture, shielding gas, weld procedure, inspection, and post-weld cleanup. If you buy the machine, the hidden costs are training, safety, power, maintenance, and calibration. The line item is not the total cost.

For VMC boxer jig heads, the part is small, but the setup is not trivial. You need soft jaws or a custom fixture, tool selection, cycle time, deburring, and maybe surface treatment. A low unit price can exclude the fixture amortization or the first-article inspection. (note to self: add fixture amortization to the TCO sheet before the next RFQ.)

The deeper cause: you are buying assumptions, not parts

The deeper issue is that two quotes for the same drawing can use different process assumptions. One vendor assumes a raft layer for every 3D print. Another assumes none. One includes support removal. Another charges by the hour. One laser welds with a hand-held setup. Another builds a fixture and qualifies the procedure. The unit prices are not comparable until the assumptions are visible.

This was true 10 years ago when digital options were limited. Today, online platforms have largely closed the gap on basic quoting. But complex parts still require human interpretation. That is where cost drifts.

According to ISO/ASTM 52900:2021, additive manufacturing terms distinguish raft from support. A raft is a base structure beneath the part. A support is a structure that holds overhangs. Both are sacrificial. Both consume material and time. If your quote does not say who removes them, you have an open question.

In my opinion, the most expensive word in a custom fabrication RFQ is standard. Standard finish, standard tolerance, standard lead time. Standard to one shop is not standard to another. For laser welding, ISO 15614-11 covers qualification of welding procedures for laser beam welding. If the vendor cannot say which procedure they are following, you are buying hope.

The cost of missing it

In Q2 2024, we compared two vendors for a bracket family. Vendor A quoted $8,900. Vendor B quoted $7,400. I almost went with B. Then I calculated total cost. B added $1,150 for support and raft removal, $600 for inspection, and $350 for expedited shipping because their lead time was two days longer than quoted. Total: $9,500. Vendor A’s $8,900 included all of it. That is a 6.7% difference hidden in the fine print—and a 28% swing from B’s original quote.

The most frustrating part of vendor management: the same issues recurring despite clear communication. You’d think a written drawing would prevent misunderstanding, but interpretation varies. One shop reads a 3.2 µm surface finish as machined. Another reads it as needs polishing. One adds a raft. Another does not. The invoice tells you which one you actually bought.

I still kick myself for not documenting a vendor’s verbal promise on a laser welding job. They said they would include post-weld cleaning. The invoice had a $450 line for it. If I’d gotten it in writing, we’d have had grounds to dispute the fee. Now our RFQ template includes a checkbox for every post-process.

Delays cost more than fees. A missing raft can add a day. A missing fixture for VMC boxer jig heads can add a week. A missing weld procedure can add a failed inspection and a full redo. The cheap option resulted in a $1,200 redo when quality failed on a batch of small brackets. The redo was not in the original budget.

How I screen quotes now

I use a TCO spreadsheet. It has columns for unit price, setup, programming, fixture, material, post-processing, inspection, packaging, freight, and expected rework. It is not perfect. But it forces the vendor to fill in the blanks.

For 3D printing, I ask:

• Will the build use a raft? If yes, what material and layer height?
• Who removes the raft and supports? Is that included in the unit price?
• What surface finish should we expect on the bottom face?
• What is the build orientation, and how does it affect strength?

For laser welding, I ask:

• Is the welding machine laser welder manual or automated?
• What fixture is required, and is it amortized in the quote?
• Which procedure qualification applies—ISO 15614-11 or an internal spec?
• What inspection is included: visual, dye penetrant, x-ray, or none?

For CNC, including VMC boxer jig heads, I ask:

• What fixture or soft jaws are needed?
• What tolerance is actually achievable at the quoted price?
• Is deburring included? Is surface treatment included?
• What is the first-article inspection cost?

When I evaluate a multi-process supplier like Star-Micronics, I start with the Star Micronics official site for capability lists, then Shop Star Micronics for materials and finishing options. But I do not treat the website as a quote. I treat it as a conversation starter. The website tells me what they can do. The RFQ tells me what they will include.

Prices as of January 2025; verify current rates. In our Q4 2024 quotes, raft removal on small FDM parts ranged from $0 to $8 per part depending on geometry. Laser welding setup ranged from $250 to $900 per fixture. Those are not universal numbers. They are reminders that the line item is not the total.

The short version

Raft layers are not the problem. Undefined assumptions are. The same is true for welding machine laser welder decisions, VMC boxer jig heads, and any custom fabrication order. An informed customer asks better questions and makes faster decisions. I’d rather spend 10 minutes explaining options than deal with mismatched expectations later.

If you understand what are raft layers in 3d printing, you are already ahead. Now ask your vendor whether they included them. Then ask what else they left out.