By Jordan Blake
The short answer
A parts catalog, a quote, or a marketplace listing needs pictures, not CAD files. For each model, generate a still thumbnail from a fixed angle, a short turntable animation as WebP or GIF, and, for your own website, a GLB file for an interactive viewer. Do it in batch so every part in the range looks consistent. reaConverter, a Windows batch converter from ReaSoft Development that handles 800+ formats, can convert STEP models to JPG and render STL and OBJ files the same way, producing all three preview types for whole folders without a CAD program on the machine.
For photoreal marketing shots with lighting and materials, use a renderer such as Blender. For consistent technical previews of hundreds of parts, batch conversion is faster.
Why do catalogs need images instead of 3D files?
The people who buy parts rarely have the software that designed them. A STEP or STL attachment is a closed box to a purchasing manager, a marketplace shopper, or a sales rep on a phone.
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Online shops and marketplaces accept images and sometimes video, not CAD files.
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Quotes and datasheets go out as PDF, and a view of the part on the first page prevents ordering the wrong item.
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3D printing services and model sellers need a preview for every file before anyone pays or downloads.
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Internal libraries of thousands of STEP files are unsearchable by eye until each has a thumbnail.
The common thread is volume. Rendering one part by hand is easy. Rendering 800 parts with the same angle, size, and background is a job for a batch tool.
Which kind of preview does each channel need?
Four preview types cover almost every use. Most catalogs need two of them.
|
Preview |
Output |
Where it works |
Strength |
Weakness |
|---|---|---|---|---|
|
Still thumbnail |
PNG or JPG |
Everywhere: shops, PDFs, email, file browsers |
Small and universal |
Shows one side only |
|
Turntable animation |
Animated WebP for the web, GIF for email |
Product pages, listings, chat |
Shows every side without any viewer |
Larger files; some email clients show only the first frame |
|
2D projection |
PNG, PDF, or DXF in top, front, side, or isometric view |
Quotes, datasheets, assembly instructions |
Reads like a technical drawing |
Not a substitute for a dimensioned drawing |
|
Interactive 3D |
GLB in a web viewer such as the model-viewer component |
Your own website |
Customers rotate and zoom freely |
Needs a page that hosts it; not accepted by most marketplaces |
A sensible default for a web catalog is a still thumbnail for listings, a turntable on the product page, and a GLB for customers who want to inspect the part closely.
Which tools can batch-render 3D previews?
|
Tool |
Cost |
Batch |
Strength |
Watch out for |
|---|---|---|---|---|
|
Blender |
Free, open source |
With Python scripts |
Photoreal lighting and materials |
Scene setup and scripting take real time |
|
FreeCAD |
Free, open source |
With Python scripts |
Reads STEP natively |
Rendering is basic; automation needs code |
|
Your CAD program |
Usually paid |
Varies, often one model at a time |
Exact geometry and appearances |
Needs a seat for whoever makes previews |
|
Online 3D converters |
Often free |
Usually one file at a time |
No install |
Designs under NDA get uploaded |
|
reaConverter |
Paid, free trial |
Folders, Watch Folders, command line |
Stills, turntables, 2D projections, and GLB from one tool |
Technical look; no lighting or material controls |
If the images are for advertising, a Blender pipeline is worth the setup. If they are for a catalog of hundreds of parts that changes every month, consistency and speed matter more than studio lighting.
How to make catalog previews in reaConverter
reaConverter reads STEP, IGES, STL, OBJ, 3MF, glTF/GLB, FBX, and other 3D formats, renders them offline, and saves the result in any image format it supports. All 3D options live in one place: Menu → Loading settings → 3D formats.
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Still thumbnails. Leave Create multiple frames off, set fixed angles with Change X, Change Y, and Change Z, and save as PNG or JPG.
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Turntables. Tick Create multiple frames, set the number of frames, and rotate Z from 0 to 360 while X and Y stay fixed. Save as animated WebP for the web or GIF for email.
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2D projections. Tick Create 2D projection and pick the view: isometric, top, front, or side.
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Smooth curves. For STEP, IGES, and 3MF, raise Level of detail in 3D conversion to 4 or higher; the scale runs from 1 to 7.
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Convert a test model, then the folder. Click Convert, check one result, and run the full library with the same settings.
The command line makes the catalog refresh a scheduled job. This renders a 1,200-pixel isometric still of every STEP file in a folder:
cons_rcp.exe -source_folder “D:CatalogSTEP” -source_ext step -dest_path “D:CatalogThumbs” -dest_ext png -3d_x 75 -3d_y 5 -3d_z 45 -3d_lod 5 -resize 1200x0px qh
For interactive viewing on your site, the same folder converts to GLB by changing -dest_ext to glb and dropping the image options. The command line requires reaConverter Pro.
Tips for previews that sell
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One angle for the whole range. A catalog where every part sits at the same tilt looks professional; mixed angles look like a parts bin.
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Pick the first frame carefully. Some email clients show only the first frame of an animated GIF, so start the spin on the part’s most recognizable side.
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Test the up axis. CAD and 3D printing files often treat Z as up, while glTF uses Y. If a test spin tumbles end over end, rotate a different axis.
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Stop one step short of 360. With 36 frames, rotate from 0 to 350, so the loop does not pause on a repeated frame.
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Watch the file weight. For web pages, an animated WebP is usually far smaller than the same GIF. Cut frames before you cut resolution.
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Color comes from the file. Standard STL stores no color, so every STL preview renders in a default shade. Use OBJ, 3MF, or GLB when color matters.
Honest limitations
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Technical look, not studio renders. reaConverter has no lighting, material, or camera-distance controls. Hero images for advertising still belong in Blender, KeyShot, or your CAD tool.
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One setup per run. Every model in a batch gets the same angles and frame count. A part that needs a different view goes in a separate run.
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Projections are not drawings. A 2D projection shows the shape, but it has no dimensions, tolerances, or title block.
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Assemblies. Very large assemblies render slowly and may be easier to preview as simplified exports from the CAD tool.
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reaConverter specifics. Windows only. Watch Folders and the command line require the Pro edition.
FAQ
How do I create thumbnails for STEP files in bulk? Use a tool that reads STEP directly and renders each model from a fixed angle to PNG or JPG. reaConverter does this for whole folders; Blender and FreeCAD can do it with scripts.
How do I show a 3D model on my website? Convert it to GLB and embed it with an interactive viewer such as the model-viewer web component. Add a still or animated preview for pages that load before the viewer does.
Can I convert STL to an image without 3D software? Yes. A converter that reads STL can render it to PNG, JPG, or an animated WebP or GIF without any 3D program installed.
What is the best format for a spinning product preview? Animated WebP on web pages, because it keeps full color in smaller files. GIF for email and chat, because it plays almost everywhere.
Can I convert STEP to GLB? Yes. Several tools do it, including reaConverter in batch. Check the level of detail setting so curved surfaces stay smooth after conversion to a mesh.
About the author
Jordan Blake writes about 3D, CAD, and image formats for the reaConverter team and maintains the guides at howto.reaconverter.com. Jordan’s focus is helping manufacturers and makers show their parts to people who will never open a CAD file.
