Why We Sometimes Say No to a Print (and What Happens Next)
We won't take your money for a print that will fail. What makes us flag a file, from thin walls to the wrong material, and what happens next.
Every now and then we reply to an order with "we don't think this will work as it is." It can feel like a strange thing for a print service to say. We're turning down money, after all.
The reason is simple. We won't take your money for a print that will fail. A part that snaps, sags in the heat or won't fit costs you the price, the wait and often a second order somewhere else. Telling you before printing is cheaper for everyone, and it's the reason every model is checked by hand before it goes on a printer.
What "no" usually means
Most of the time it isn't a flat no. It's a "not like this." In practice there are three outcomes:
- We flag a risk and you decide. The part will print, but something might cause trouble. We tell you what and why, and you choose whether to change it.
- We suggest a fix. A thicker wall, a different orientation, a better material, or a small clearance on a fit.
- We tell you FDM is the wrong process. Some jobs need a different kind of printing altogether. We say which one, and what to ask a provider for.
A real decline, where we won't print it at all, is rare. It's for parts we're confident will fail at their job, or deadlines we can't meet.
What triggers a flag
These are the problems we see most often, roughly in order.
Walls that are too thin
Walls under 0.8 mm print but are fragile, and anything thinner than 0.4 mm won't come out at all. We recommend 1.2 mm for most parts and 1.6 to 2.0 mm for functional parts. A clip or tab that looks fine on screen can snap the first time you use it.
Overhangs with nothing underneath
FDM builds layer by layer, so each layer needs something below it. As a general rule, overhangs steeper than about 45 degrees need supports. Supports add material and leave marks where they touch. Sometimes a different orientation removes most of them. Sometimes a small chamfer in the design does the same job.
The wrong material for the heat or load
This is the one people least expect. Material choice decides whether a part survives where it's going to live.
| Where the part lives | Common choice | Why it fails | What we'd suggest |
|---|---|---|---|
| Inside a parked car | PLA | Softens around 55 to 60 °C | PETG (~80 °C) or ASA (~100 °C) |
| Outdoors in the sun | PLA | Absorbs moisture and can warp in direct sun | ASA, or PETG for sheltered spots |
| Gear, hinge or snap-fit used again and again | PLA | Rigid and can snap under sharp impact | Nylon or PETG |
| Snap-fit or clip | PPS-CF | Stiff but brittle, cracks under impact | Nylon or PETG |
| Near an engine or hot tooling | PETG or ASA | Beyond their heat range | PA-CF (~150 °C), PAHT-CF (~180 °C) or PPA-CF (past 200 °C) |
Our post on outdoor materials goes into the sun and rain question in more detail.
Fits with no clearance
Typical FDM tolerances are ±0.2 to 0.5 mm, and holes usually come out 0.1 to 0.2 mm smaller than designed. A peg modelled to exactly the size of its hole won't go in. If parts need to fit together, we'll point out where a small clearance is needed.
Small printed threads
Printed threads work best at M6 and larger. Below that we'll usually suggest heat-set brass inserts or a pilot hole for a self-tapping screw.
Detail FDM can't hit
FDM lays down a line of plastic a fraction of a millimetre wide. Very fine features, like tiny text, small miniature faces or hair-thin details, can blur or vanish. If the detail is the whole point of the part, FDM isn't the right process.
A date we can't meet
If we can't hit your deadline, we'll say so before you pay anything. A tight date we might miss is worse for you than a straight answer today.
When FDM is the wrong process
We only do FDM. When a job needs something else, we tell you which process fits and what to ask for, so you can go to a provider with the right questions.
| Your part needs | Process that usually fits | What to ask a provider |
|---|---|---|
| Very fine detail and a smooth surface (miniatures, jewellery masters, small figures) | Resin printing (SLA or MSLA) | Which resin, what layer height, and where support marks will land |
| Complex internal shapes, no support marks, tough nylon parts | SLS or MJF (powder bed nylon) | Which nylon grade, whether the surface is dyed or raw, and the typical tolerance |
| Metal strength, or temperatures beyond plastics | Metal printing or CNC machining | Which alloy, whether post-machining is included, and the inspection they do |
| Long-term or commercial food contact, or thousands of identical parts | Injection moulding | Certified materials, tooling cost and lead time, and minimum order quantity |
For a side-by-side of FDM and resin, see FDM vs resin 3D printing.
What happens after we flag something
Here's the soft landing. Nothing is lost, and nothing is charged before you agree.
- We tell you what we found. Plainly: what the risk is and why it matters for your use.
- We suggest the fix. A wall thickness, a clearance, an orientation or a material. We don't redraw your model, but we tell you exactly what to change.
- You decide. Change the file and re-upload it on the quote page for a fresh price in seconds, switch materials, or go ahead as it is if you accept the risk.
- If it's not for us, you walk away free. An order can be cancelled at no cost while it's still awaiting payment.
One thing worth knowing: our free reprint covers prints that are wrong or defective. It doesn't cover a part that printed exactly as modelled from your design but doesn't fit. That's exactly why we flag design risks before printing rather than after.
A quick self-check before you upload
- Are all walls at least 1.2 mm, or 1.6 mm for anything that takes load?
- Do mating parts have a clearance, and are holes sized for printing slightly small?
- Will the part see heat, sun, chemicals or repeated flexing?
- Are any threads smaller than M6?
- Does it fit within about 325 × 320 × 325 mm, or does it need splitting?
- Is the finest detail bigger than a line of plastic can draw?
Our guide to preparing STL files covers the export side.
Quick FAQ
Will I be charged if you flag a problem?
No. Flags happen before printing, and you can cancel at no cost while an order is awaiting payment.
Can I print it anyway?
Usually, yes. Most flags are risks, not dead ends. If you understand the risk, it's your call. We only decline outright when we're confident the part will fail at its job.
Will you fix my model for me?
We're print-only, so we don't do CAD work. We'll tell you exactly what to change, and you re-upload the revised file.
Do you recommend specific companies for other processes?
No. We tell you which process fits and what to ask for, so you can compare providers yourself.
Not sure your part will survive its job? Get an instant quote and we'll check it before anything prints.
