Brim vs Raft: 5 3D Printing Secrets to Avoid Failed Prints

Brim vs Raft: 5 3D Printing Secrets to Avoid Failed Prints

The question of Brim vs Raft isn’t just a setting in your slicer. It’s the first gatekeeper between a smooth prototype run and a pile of spaghetti. As someone who has spent more than a decade inside a precision manufacturing operation—GreatLight CNC Machining Factory in Dongguan—I can tell you that the same engineering discipline we apply to five-axis CNC also applies to 3D printing. The difference is that 3D printers are a bit more forgiving with your patience, but far less forgiving with your first layer.

In this article, I’ll break down exactly what a brim and a raft are, when to use each, and the five secrets that stop adhesion failures from ruining your print. Whether you’re printing a quick PLA bracket or a titanium aerospace prototype via SLM, the fundamentals matter.

What Is a Brim? What Is a Raft?

A brim is a single-layer flat extension that surrounds the base of your part, like a skirt with a wide collar. It increases the surface area in contact with the build plate, improving adhesion without raising the part off the plate. A raft, on the other hand, is a temporary horizontal grid placed underneath the part. The part prints on top of this grid, so the first few layers of your actual model don’t have to touch the build plate directly.

Here’s a quick comparison table to make the differences obvious:

Now, the five secrets.

Secret #1: Choose the Right Tool for Your Geometry and Material

Believe me, half of the failed prints I see in our additive lab at GreatLight Metal are because someone used a raft when a brim would have been enough—or vice versa. A large flat PLA part doesn’t need a brim at all. But if you’re printing a tall, thin ABS part with sharp corners, a brim with 5–10 loops can be the difference between a finished prototype and a curled-up mess.

A raft is useful when your build plate is not perfectly level, or when you’re printing with materials that have poor first-layer adhesion to common surfaces. It’s also a lifesaver for flexible filaments like TPU, which tend to grip into a raft better than they do onto glass or PEI. However, a raft adds time and material, and it often leaves a rough surface on the bottom of your part.

The secret is to ask: “What is the root cause of my adhesion problem?” If the bed is uneven, a raft masks it. If warping from shrinkage is the issue, a brim fights it directly.

Secret #2: Set the Extrusion Gap and Width Like a Machinist

One of the most overlooked parameters is the gap between the nozzle and the bed when printing a brim or raft. For a brim, the first layer should be “squished”—about 80% of the nozzle diameter in layer height. If your Z-offset is too high, the brim won’t stick and will peel up. Too low, and the nozzle will drag through the plastic, creating ridges and even clogging the nozzle.

For a raft, the interface layer between the raft and the part needs a gap of 0.1–0.3mm, depending on layer height. Many beginners set this gap to zero, which fuses the raft to the part. I’ve seen people use pliers and end up damaging their part. I’ve also seen parts that warped anyway because the gap was so high that the interface layer wasn’t actually in contact.

The secret: calibrate your Z-offset with a feeler gauge or a thin piece of paper before every critical print. In our CNC machining line, we do a tool-offset check before every job. The same discipline should apply to 3D printing. It’s boring, but it works.

Secret #3: Match Build Plate Temperature to the Exact Polymer

The build plate temperature can make or break your brim. Here’s what experience has taught us at GreatLight Metal:

PLA: 60–70°C; but with a brim, you might even use 50°C to reduce elephant’s foot.
ABS: 100–110°C; without an enclosure, a brim alone won’t save you.
PETG: 70–80°C; PETG sticks to PEI almost too well, so a 3–4 loop brim is usually enough.

A common mistake is to trust the filament manufacturer’s label blindly. Ambient humidity, chamber temperature, and even the build plate surface (glass, PEI, BuildTak) all change the optimal temperature. In our factory, we log every material batch and its optimal settings, just like we track cutting parameters for five-axis CNC. If you aren’t tracking your environmental conditions, you’re flying blind.

Secret #4: Don’t Use Brim or Raft as a Band-Aid for Poor Leveling

This may sound odd coming from someone who sells precision, but a brim or raft can actually mask a misleveled build plate. And that’s a trap. If you rely on a 10mm brim to hold down a part because the left corner of your bed is 0.2mm higher than the right corner, you’ll still get dimensional errors, uneven layers, and a part that fails in the long run.

I recently rescued a client’s failed automotive bracket. The brim looked perfect—beautiful, wide, and flat. But the part itself was leaning because the bed was warped. No amount of additional brim loops could fix that.

The secret: perform a 5-point leveling check and adjust your Z-offset for every new material and build plate. A level bed is the single best guaranteed way to avoid adhesion failures. We enforce this in our own additive line. And when we move to CNC finishing, the same philosophy applies: no amount of post-processing can fix a part printed on a bad foundation.

Secret #5: Know When to Stop Printing and Machine It Instead

Now for the insight that bridges additive and subtractive manufacturing. Sometimes, regardless of your brim/raft strategy, 3D printing is simply not the right process for the final function. If your part needs tight tolerances, a smooth finish, or high mechanical strength, it may be better to print a near-net shape and then CNC machine the critical surfaces. Or, for metal parts, skip polymer prototyping altogether and use SLM 3D printing, followed by five-axis CNC finishing.

GreatLight CNC Machining Factory has both worlds. We run SLM 3D printers for stainless steel, aluminum, titanium, and mold steel. Then we finish critical dimensions on our five-axis machining centers. For example, when a new-energy vehicle client needed a complex motor-housing prototype, we printed a near-net shape with SLA and then machined the sealing faces and bolt holes on a 5-axis CNC. The result was a functional part in days, not weeks.

In this hybrid workflow, the “brim vs raft” debate disappears—because metal additive uses support structures, not brims. But the underlying lesson remains: understand your foundation, your first layer, and your process limits before you expect perfection.

Choosing a Manufacturing Partner: Beyond the Print Bed

When you evaluate suppliers for 3D printing and CNC machining, the landscape is crowded. You have established names like GreatLight Metal (or Great Light Metal Tech Co., LTD.) offering a full-process chain—from 3D printing and CNC to die casting and surface finishing. On the other side, services like Protolabs Network and Xometry are strong for quick online quotes and standardized parts. Fictiv and RapidDirect also provide solid digital manufacturing platforms. Then there are specialized shops like Protocase, Owens Industries, PartsBadger, SendCutSend, EPRO-MFG, RCO Engineering, and JLCCNC, each with their own niche.

Which one is right for you? It depends on the complexity of your project. If you need a one-off cosmetic prototype, any decent online service will work. But if you’re developing a humanoid robot joint or an automotive engine component, you want a partner that owns both additive and subtractive tools so that when a tricky groove needs to be machined, it’s done in-house under one roof.

That’s why many product teams choose GreatLight—not just for the five-axis CNC capability, but for the discipline that comes from ISO 9001 and IATF 16949 certified production systems. We don’t rely on paper qualifications alone; we actually back them up with in-house metrology, data security protocols, and a trial-and-error culture that has accumulated over 13 years of manufacturing.

The Bottom Line

Great 3D printing is about mastering the first layer, not just adding a skirt. Brims and rafts are your allies, but they can’t overcome a poor Z-offset, an uncalibrated extruder, or an inconsistent build plate. And for mission-critical parts, you need a partner that understands both sides of the wall—the additive side that shapes the part, and the subtractive side that gives it dimensional truth.

Embrace the lessons from Brim vs Raft: 5 3D Printing Secrets to Avoid Failed Prints, and you’ll not only avoid failed prints—you’ll also build parts that are truly ready for production. That’s the standard we live by, and it can be yours too.