Technical · File Preparation · UK

File Preparation for 3D Printing

Send us a STEP file. Always, if you have one. STEP holds your part as exact mathematical geometry — true curves, real dimensions, units baked in. STL throws all of that away and hands us a fixed mesh of triangles, frozen at whatever resolution your export settings happened to be. We accept both, and we will print either. But the format you send changes what we can do for your part.

Upload your file → Design guidelines

STEP vs STL 3D printing · 3D print file format · STL export settings · CAD file preparation · 024 7736 0144

The same bracket, both ways. On the left, exact surfaces with true radii. On the right, the same shape approximated by triangles — and once it is triangulated, no software can recover the curve.

STEP / STP

Preferred, every time

Units, always millimetres

1:1

Model at full scale

Free

File review with every quote

The short answer

Send STEP. Not STL.

A STEP file is your actual geometry. An STL is a photograph of it, taken at a resolution you chose without knowing what we needed.

STEP (.step or .stp) is a boundary-representation format. A cylinder is stored as a cylinder — a mathematical surface with an exact radius. STL stores that same cylinder as a few hundred flat triangles pretending to be round. Once it is triangulated, the curve is gone and no software can recover it. Whatever faceting was baked in at export is what we print.

	STEP / STP	STL
Geometry	Exact curves and surfaces	Triangle approximation, fixed at export
Who sets the resolution	We do, to suit the process	You did, before you knew the process
Units	Stored in the file	Not stored — a common source of scale errors
File size	Usually smaller	Grows sharply with resolution
Can we adjust the part?	Yes — add drain holes, split, add machining stock	Only crudely, on a mesh
Multiple bodies	Held separately in one file	Merged into one shell
Repairable if faulty	Rarely needs it	Often does — holes, flipped normals, non-manifold edges
We accept it	Yes — preferred	Yes

Reviewed by the RYSE 3D engineering team · August 2026.

Why it matters here

You can see a low-resolution STL on a finished part

This is not a theoretical concern. Our processes resolve fine enough that the triangles from a coarse STL export show up as visible flats on what should be a smooth curve — particularly on MJF and SLA, where the surface is fine enough to record them. The part is not defective. It was built exactly as the file described. The file just described a faceted approximation.

Send STEP and that cannot happen, because we generate the mesh ourselves at the resolution the process actually needs. Send a coarse STL and we are printing your export settings, not your design.

There is a second, quieter benefit. A STEP file is still editable geometry, so when our design review turns up something — a sealed cavity that needs drain holes, a part that needs splitting for the envelope, a face that needs machining stock adding for a tight fit — we can do it cleanly and send it back for your approval. On an STL, the same job means mesh surgery, and the result is never as good.

A 3D printed bearing housing showing visible flat facets on a curved face caused by a low-resolution STL export, with the triangles highlighted — RYSE 3D file preparation — Flats on a face that should be round. The printer reproduced the file faithfully — the file described a faceted approximation, and the triangles are traced here in red.

What we accept

File formats, in order of preference

We will work with all of these. The order is what it is for the reasons above.

Format	Type	Our view
.step / .stp	Exact CAD geometry	Send this. First choice, every time.
.3mf	Mesh, with units and metadata	A better mesh than STL — it carries units and scale, so scale errors are far less likely. Still a mesh.
.iges / .igs	Exact CAD geometry, legacy	Workable, but older and less robust than STEP. Use STEP if your CAD offers both.
.stl	Triangle mesh	Accepted. Export it properly — see the settings below.
.obj	Triangle mesh	Accepted. As STL, with the same caveats.
Native CAD files	Varies	Ask us. If we cannot open it, we will tell you what to export instead.
2D drawings (PDF / DXF)	Reference	Not printable on their own, but send them alongside the 3D file — critical dimensions and tolerances belong on a drawing.
No file at all	—	Post us the part. We 3D scan and reverse-engineer it. Get in touch first.

Before you upload

Six checks that prevent a delay

None of these take more than a minute, and each one is something that otherwise comes back to you as a query.

Model at 1:1 in millimetres

Full scale, real-world size, metric. Scale errors are the single most common file problem, and they are worst on STL because the format does not store units at all — a part exported in inches arrives 25.4 times too small with nothing in the file to say so.

One part per file

Name each file as the part it contains. If you need six of one part and two of another, tell us the quantities rather than duplicating bodies inside the file. It keeps the quote, the build and the delivery note matching each other.

Solid, watertight geometry

The model needs to be a closed solid, not a collection of surfaces. On a mesh that means no holes, no self-intersections, no non-manifold edges and normals facing outward. On STEP this is rarely an issue, which is rather the point.

Remove what you do not want printed

Delete supports from a previous slicer, reference sketches, construction bodies and any bought-in hardware modelled in place. If a bearing or a fastener is in the file, we cannot always tell whether you meant us to print it.

Flag the critical dimensions

Mark them on a drawing, or just say so in the notes. We inspect to our standard tolerance unless told otherwise, and if a fit is tight we will plan orientation and allow machining stock — but only if we know before the build.

Say what the part has to do

Load direction, service temperature, whether it must be watertight, whether it is a show face. Two sentences here often changes the grade or the orientation we recommend, and it is the difference between a part that fits and a part that works.

If STL is all you have

How to export an STL properly

Plenty of people only have an STL — a downloaded model, a file from a client, a scan. That is fine and we will print it. But if you are exporting one yourself from CAD, the export settings decide the surface quality of the finished part, so it is worth thirty seconds of attention.

Export settings

Higher resolution than you think you need

● Binary, not ASCII — same geometry, a fraction of the file size.
● Chord height / deviation — the maximum gap between the triangle and the true surface. Lower is finer. Around 0.01 mm is a sensible starting point for a functional part.
● Angle tolerance — controls how many triangles go round a curve. Lower is finer; 5° or below is a reasonable default.
● Check the units on export — the dialogue usually asks, and the file will not remember.

Do not overdo it

There is a point of no return

● An absurdly dense mesh produces a huge file that is slow to handle and adds nothing your process can resolve.
● You cannot recover detail by re-exporting more finely from an existing STL — the original curve is already gone. Go back to the CAD.
● If the file is over a few hundred megabytes, something has gone wrong with the settings.
● Still unsure? Send the STEP as well and let us handle it.

A useful sanity check: open your exported STL and look at a curved face. If you can see flats on it on screen, you will see them on the printed part.

Your IP

What happens to your files

●

Cyber Essentials certified

Independently certified security practices covering the handling of customer CAD data and intellectual property. Your files stay inside our own systems.

●

NDAs as standard where needed

A significant amount of our automotive work sits under confidentiality and never appears publicly. If you need an agreement in place before you send anything, say so and we will sort it first.

●

Nothing brokered out

Printing, finishing and inspection all happen in our own facility, so your file is not passed to a third party to fulfil the job.

●

Traceability on every job

Under our ISO 9001 quality system, with part history held on trade accounts so repeat orders do not need re-quoting from scratch.

FAQ

File preparation FAQ

What file format should I send for 3D printing?

A STEP file (.step or .stp), every time, if you have one. STEP stores your part as exact mathematical geometry with units included, so we can generate the mesh at the resolution the process needs rather than printing whatever resolution your STL export happened to use. We accept STL, 3MF, OBJ and IGES as well, and we will print any of them — but STEP gives your part the best result.

What is the difference between a STEP file and an STL file?

A STEP file describes surfaces mathematically — a cylinder is stored as a cylinder, with an exact radius. An STL describes the same shape as thousands of flat triangles approximating it. Once a model is triangulated the true curve is gone and cannot be recovered, so the faceting fixed at export is what gets printed. STEP also stores units, supports multiple bodies separately and remains editable; STL does none of those things.

Will you still print my STL file?

Yes, and a large proportion of the files we receive are STL. It is a perfectly workable format and for many parts the difference is invisible. We are simply telling you the truth about the trade-off: with an STL you have already fixed the surface resolution, and if it was exported coarsely we cannot improve it. If you have the STEP as well, send both.

Why do I sometimes see flat facets on a printed curved surface?

Almost always a low-resolution STL export. The triangles in the file were large enough that the printer reproduced them faithfully as visible flats on a surface that should be smooth. Our processes resolve finely enough to record them, particularly on MJF and SLA. The fix is to send the STEP file, or to re-export the STL from CAD with a finer chord height and angle tolerance.

What units should my file be in?

Millimetres, modelled at 1:1 full scale. This matters most on STL, which does not store units at all — a part exported in inches arrives at 25.4 times the wrong size with nothing in the file to indicate it. STEP and 3MF both carry units, which is one more reason to prefer them. If a part looks wrongly scaled at quote we will query it rather than print it.

Do you accept 3MF files?

Yes. 3MF is a considerably better mesh format than STL because it carries units, scale and metadata inside the file, so the scale errors that plague STL largely disappear. It is still a mesh, so the resolution is still fixed at export and the true CAD geometry is still gone. Preference order: STEP first, then 3MF, then STL.

What if I do not have a CAD file at all?

Post us the part. We 3D scan on site and can reverse-engineer a printable model from a physical component, which is how a lot of obsolete and heritage parts get remade. Get in touch before you send anything so we can advise on what we need and confirm the approach.

Is my CAD data kept confidential?

Yes. We are Cyber Essentials certified, which covers our handling of customer CAD data and intellectual property, and your files stay inside our own systems — nothing is brokered out to a third party. Much of our automotive work runs under confidentiality agreements. If you need an NDA in place before sending files, tell us and we will arrange it first.

Ready when you are

Send the STEP. We will do the rest.

Free file and design review with every quote — we check geometry, wall thickness, drain holes and grade suitability before anything goes on a machine, and tell you what we would change.

Upload your file → Talk to an engineer

Our own ISO 9001 facility in Shipston-on-Stour, Warwickshire. Mon–Thurs 8am–4pm, Fri 8am–2pm. Call 024 7736 0144 or email hello@ryse3d.com.