A 3D print is only ever as good as the file it starts from. A model that looks correct in CAD can produce dimensional drift, support nightmares or outright print failures when it has not been prepared properly for manufacture. The good news is that almost every common issue can be caught with a short checklist before the file leaves your workstation.
This guide walks through the prep steps we use internally before any production print, written for engineers and designers sending work to a service bureau. Following them removes most of the back and forth that delays a quote and keeps your project on schedule.
The preparation workflow
Export in the right format. STL is universally understood for FDM but approximates curves with triangles, so push the export tessellation tighter for any organic geometry. STEP preserves parametric geometry and is the better choice for tight tolerance engineering parts. We also accept OBJ, 3MF and several native CAD formats.
Check for non manifold geometry. Open meshes, inverted normals and edges shared by more than two faces all cause slicer failures. Repair them at source rather than relying on auto repair tools downstream. Fusion 360 has a Mesh Repair workspace, Blender ships with the 3D Print Toolbox add on, and most slicers flag problems on import.
Set the model to millimetres and confirm the units. Imperial units imported into a metric slicer is one of the most common causes of a part arriving at 4 percent of its intended size, and it is one of the easiest issues to avoid.
Check wall thickness against the process. For FDM with a 0.4 mm nozzle, design walls to at least 0.8 mm, with 1.2 mm preferred for handled or functional parts. For SLA printing you can drop to roughly 0.5 mm, but thin resin walls warp easily during washing and curing.
Plan orientation for minimal supports. Overhangs above about 45 degrees from vertical need support. Chamfering, filleting and splitting a model into bonded sub assemblies can remove a significant proportion of support material and reduce both lead time and cost.
Apply fits and clearances for any mating parts. FDM typically holds about plus or minus 0.2 to 0.3 mm. Use 0.3 to 0.4 mm clearance for a sliding fit, 0.1 to 0.2 mm for a press fit and 0.5 mm or more for a relaxed assembly. Prototype before committing to a full run.
Quick first pass test
If you are unsure about the file, slice it in a free tool such as Bambu Studio or PrusaSlicer first. Layer view will reveal missing roofs, ghost geometry and accidental internal voids in under a minute, well before the file reaches a quoting team.
Final upload checklist
Run through this short list before sending the file to a service bureau or uploading through our quoting portal. It captures the most common issues that send a file back to design and adds only a couple of minutes to the workflow.
Model is a single watertight solid with no open faces
All dimensions are in millimetres and the units are saved with the file
Walls are at least 0.8 mm for FDM and 0.5 mm for SLA
Mating parts have realistic clearances built into the geometry
STL exported with maximum deviation under 0.01 mm
Model sits flat on the chosen build plane with no overlapping bodies
Once the file passes the checklist, send it through our quote form and we will come back with material options, lead time and price in writing.
References