How-to: Prepare a Technical Brief for Outsourcing Resin AM Parts

Why the Technical Brief Matters

A technical brief is the contract between your engineering team and a service bureau. When you outsource 3D printing, the bureau must understand exactly what you need before they can price the job. A vague request leads to generic quotes, missed tolerances, and expensive rework.

The brief serves three purposes. It sets the engineering intent, defines the quality expectations, and clarifies the commercial scope. Without it, the bureau fills in the gaps with assumptions that rarely match your needs.

This guide walks through the structure of a solid brief. It covers the prerequisites, the core sections, and the final verification steps that turn a rough request into a actionable production plan.

Prerequisites: What You Need Before Writing

Before drafting the brief, gather the core assets. You need the final CAD file, not a work-in-progress. Service bureaus work from stable geometry. If your file changes after the quote, the pricing and build plan change too.

You also need a clear material selection. Do not leave this to the provider unless you have a specific reason. Resin AM offers many options. Each has different mechanical properties, surface finishes, and post-processing needs. Choosing the material yourself limits the bureau’s freedom to suggest cheaper alternatives that may not meet your performance targets.

Finally, decide on the quantity. A single prototype and a batch of fifty parts follow different build logic. The quantity affects build orientation, support structure, and post-processing time.

Step 1: Define the Part and Quantity

Start the brief with the part identity. List the part number, description, and revision. Include the material and color. State the quantity per build and the total required.

The reason for this step is clarity. If you need ten brackets for testing and then fifty for assembly, the bureau needs to know the split. Mixing these in one request creates confusion about which build parameters apply to which part.

Specify if the parts are functional or decorative. A decorative part may tolerate loose tolerances. A functional part requires tighter control. This distinction helps the bureau allocate resources correctly.

Step 2: Specify the Material

List the resin type, color, and any required certifications. If you have a specific resin in mind, name it. If you are open to alternatives, state the properties you need.

Common properties to list include tensile strength, flexural modulus, heat resistance, and chemical resistance. Do not just say “strong resin.” Define the strength values and the test conditions.

The reason for this step is to prevent substitution. If you request a standard ABS-like resin and the bureau substitutes a flexible TPU-like material without approval, the part may fail. Explicit material selection locks in the mechanical behavior.

If you require a specific certification, such as biocompatibility or food contact compliance, state it clearly. Not all resins meet these standards, and the bureau needs to know before they start quoting.

Step 3: State Tolerances and Critical Dimensions

List the general tolerance for the part. Most resin AM parts hold within a few hundredths of an inch, but your tolerance may be tighter. State the tolerance class you require.

Identify critical dimensions. These are the features that must be within tolerance for the part to function. Examples include hole diameters, flatness of mating surfaces, and clearance fits.

The reason for this step is to prioritize inspection. A bureau cannot inspect every dimension on every part to the same depth. By highlighting critical features, you direct their attention to the areas that matter.

If you require a specific tolerance on a specific feature, state the value. For example, “hole diameter of 5.00 mm plus or minus 0.05 mm.” Avoid vague terms like “close to nominal.”

Step 4: Define Surface Finish Requirements

Surface finish is a common source of dispute. Resin AM parts often come with a visible texture from the build layer. Post-processing can smooth this out, but it adds cost and time.

State the required surface finish. If you need a smooth finish for aesthetics or for a fit, specify the method. Sanding, vapor smoothing, or painting are common options.

The reason for this step is to manage expectations. If you request a mirror finish without stating it, the bureau may deliver a standard textured surface. That surface may be acceptable for a prototype but not for a final production part.

Also specify any areas that do not need finishing. If only the visible faces need to be smooth, say so. This reduces post-processing time and cost.

Step 5: Include Post-Processing and Assembly Needs

List any post-processing steps required. This includes support removal, washing, curing, and any mechanical operations. If you need drilling, tapping, or deburring, state it.

The reason for this step is to avoid surprise costs. Post-processing is a major part of the total cost. If you leave it out, the bureau may assume standard removal and curing only.

Specify if you need the parts assembled. If you require sub-assemblies, describe the assembly process. If you need threaded inserts, state the insert type and size.

If you require a specific coating or paint, name the material. Do not just say “black.” State the paint type and finish.

Step 6: Define Inspection and Quality Requirements

State how the parts will be inspected. Do you need a dimensional report? A CMM report? A visual inspection certificate?

The reason for this step is to define acceptance. Without a defined inspection method, “good” is subjective. A CMM report provides objective data. A visual inspection relies on human judgment.

Specify the acceptance criteria. State the maximum deviation allowed for critical dimensions. If you require a specific quality standard, name it.

If you need first article inspection, state it. First article inspection is a detailed check of the first part against the drawing. It is more expensive than standard inspection but provides higher confidence.

Step 7: Provide the CAD and Drawing Files

Attach the final CAD file. Ensure the file is in a neutral format like STEP or IGES. Do not send native CAD files unless requested.

Include the 2D drawing with all dimensions, tolerances, and notes. The drawing is the legal reference. The CAD file is the geometry.

The reason for this step is to avoid interpretation errors. A CAD file may have ambiguous features. A 2D drawing clarifies intent. If the CAD and drawing conflict, the drawing wins.

State the file version and date. If you have multiple revisions, indicate which one is current. This prevents the bureau from working from an old file.

Common Mistakes to Avoid

The most common mistake is leaving the material open. You say “please use the best resin.” The bureau chooses the cheapest one. The part may not meet your mechanical requirements.

Another mistake is omitting post-processing. You assume the part will come out smooth. It does not. You then request sanding, which adds cost and delay.

A third mistake is vague tolerance language. You say “tight tolerance.” The bureau uses a standard tolerance. The part does not fit.

Finally, do not send incomplete files. A missing hole or a broken wall is a problem. Send the final, clean geometry.

Step 8: Verify the Quote and Build Plan

Once the bureau returns the quote, verify the details. Check the part count, material, and post-processing included.

The reason for this step is to catch errors. Bureaus make mistakes. Quotes may miss a part or include an extra service.

Ask for the build plan. How many parts are in the build? What is the build orientation? This information helps you assess risk.

If the quote is off, ask why. Do not assume the bureau made a mistake. They may have seen a requirement you missed.

Final Verification Checklist

Before sending the brief, run through this checklist.

1. Is the CAD file final and in a neutral format?
2. Is the material specified?
3. Are critical dimensions identified?
4. Is the quantity clear?
5. Are post-processing steps listed?
6. Are inspection requirements defined?
7. Is the drawing attached?

If you can answer yes to all of these, your brief is ready.

How to Handle Ambiguity

If you are unsure about a requirement, state it as a question. For example, “Can you provide a rough finish on the internal surfaces?”

This gives the bureau room to suggest a solution. It also shows you are thinking about the part, not just the price.

Avoid questions that can be answered with a yes or no. Instead, ask for options. “What are the options for achieving a smooth finish on the top face?”

This approach leads to better dialogue and a more tailored solution.

When to Use a Service Bureau

A service bureau is the right choice when you need speed, expertise, or volume. If you have the equipment and staff, in-house printing may be cheaper.

If you are prototyping a new part, a service bureau can provide feedback on the design. They see many parts and can point out issues.

If you are in production, a service bureau can provide overflow capacity. This keeps your line running.

Choose the bureau based on fit. A metal AM bureau may not be the right choice for a polymer part. A local bureau may be better than a remote one for iteration.

Use a service bureau when you need to outsource 3D printing to focus on your core business.