How to get a 3D print file approved by your customer before printing

A failed print is easy to spot. A print that's perfect but not what the customer meant is worse: the material and machine time are gone, and you're arguing about who said what. The fix is a 3D print file approval before anything goes on the printer: the customer sees the exact file, confirms the details that matter, and says yes on the record.

This guide is for 3D printing services, print farms and makers who print customers' files or design parts for them. The advice works with any slicer and any way of sending files.

#How does a 3D print approval work?

1. 1

   Get the file and the brief together

   Ask for the file, the quantity, the material and colour, and what the part is for. "A bracket for a shelf" and "a bracket that holds a 5 kg monitor arm" print differently.

2. 2

   Check the file yourself first

   Size, wall thickness, holes, overhangs and whether it fits your build volume. Fix or flag anything that won't print as it is.

3. 3

   Decide how you'll print it

   Orientation, supports, layer height and infill. These change strength, surface finish and price, so the customer should know your choices.

4. 4

   Send a proof

   Send the file as you'll print it, with the key measurements, the orientation and a short list of things to confirm.

5. 5

   Get a clear yes to one version

   "Approved: v2, PETG black, 3 off" is an approval. "Looks fine" on the phone is not.

6. 6

   Print the approved version only

   If anything changes after approval, it's a new version, and it needs a new yes.

#What should the customer confirm before printing?

Use this as a checklist in your proof email or order form:

• Size. The overall dimensions, and any that have to fit something: "Overall 84 × 40 × 22 mm. The two holes are 4.2 mm for M4 bolts, 60 mm apart." Ask the customer to check these against the real part it fits.
• Units. Say the unit every time. "40" can be millimetres or inches, and the file itself may not say (see below).
• Tolerances and fit. If parts snap, slide or press together, say what clearance you've allowed. As an example, you might write "0.2 mm clearance each side on the lid"; the right figure depends on your printer and material, so use your own.
• Material and colour. Name the material and the exact colour. Screen colours differ, so offer a sample photo or a physical swatch for colour-critical jobs.
• Orientation. Show which way up it prints. Layer lines run across the part, so orientation affects strength along each direction and which faces look smooth.
• Support marks. Say where supports will touch and that those surfaces will show marks. If a face must be clean, the customer has to tell you now.
• Visible faces and finish. Which side faces the user? Is sanding, priming or painting included?
• Quantity and deadline. How many, and when they need them, not when they'd like them.
• Scaling. If you scaled the model, say so and by how much.

#Why STL files cause size mistakes

STL is the most common print format, and it doesn't store units. An STL holds a list of triangles with bare numbers. A part designed as 40 mm is saved as "40", and the software opening it decides what 40 means. Most slicers assume millimetres, which is why it usually works. A viewer or 3D app that assumes metres or inches shows the same file at a very different size.

What that means in practice:

• Measure, don't trust the preview. Check two or three known dimensions before you quote or print.
• Watch for round factors. A part that measures 25.4 times too big or small was probably modelled in inches. A factor of 10 or 1000 is millimetres against centimetres or metres.
• Prefer formats with units when you can. 3MF records its units, and STEP from a CAD program carries real size. See STEP vs STL vs IGES.
• Write units in every message. "84 × 40 × 22 mm", never "84 × 40 × 22".

STL also carries no colour or material, so a proof made from an STL will look grey. Say what colour it will be in words.

#How should you word the proof?

A proof email that's easy to say yes to:

Hi Tom,

Here's your bracket ready to print. Please check:

- Size: 84 x 40 x 22 mm overall. Holes 4.2 mm, 60 mm apart.
- Material: PETG, black. Quantity: 3.
- Printed flat side down. The underside will be smooth;
  the curved top shows fine layer lines.
- Supports touch the inside of the hook only.

If all of that is right, reply "approved" and I'll print
tomorrow morning. Any change after that is a new quote.

Keep the list short and specific. Customers read the first few lines carefully and skim the rest.

#Getting the approval on record in MeshMarkup

If you send proofs as files by email, the customer needs software to open them and you can't see what they checked. With MeshMarkup, you upload the file and send a review link that opens in any browser, with no account or install for the customer.

• Measure. The customer can click More tools, then Measure, and two points to check a distance. Measurements assume the file is in metres, so a millimetre STL reads 40 mm as 40 m. Tell the customer to read metres as millimetres, or upload a 3MF or STEP, which come in at real size. See measuring and wrong size or scale.
• Notes. On a Leave feedback link, the customer clicks the spot they mean and adds a note, such as "this face must be clean". You reply on the same note and set its status.
• Section cut. For wall thickness or internal features, a section cut you set on the model page is saved, so the customer opens the model already cut. See section cut and exploded view.
• Sign-off. When everything is answered, send a Sign it off link (Solo plan and up). The customer clicks Approve v2, which only works once no notes are OPEN or IN PROGRESS. The model shows Approved, with the name they typed and the date.

Put your print settings (material, orientation, supports) in the email or a note, since the 3D view shows the shape, not how you'll print it. A sign-off isn't a contract or an e-signature, so keep it alongside your normal order terms.

#Questions

#What if the customer approves and the part doesn't fit?

Check the proof. If the dimensions they approved match the print, the fit problem is in the design, and a reprint is a new job. That's why the proof should list the dimensions that matter, in words.

#Do I need an approval for every reprint?

Not if the file and settings haven't changed. Name the approved version in the order, and print that one.

#Should I send a photo of the slicer preview?

It helps, especially to show orientation and where supports touch. A screenshot with the supports visible answers most "why is this face rough?" questions before the print.

#How do I handle files I can't print as they are?

Say so before quoting, with the reason and an option: "The walls are 0.6 mm, too thin for this material. I can thicken them to 1.2 mm, or print in resin."