Onshape or Fusion Basics

TL;DR

Fully constrain your sketches (especially to the origin and symmetry lines) and drive fit-critical sizes with named parameters like clearanceFit and holeOversize; that’s what keeps hole spacing and mating faces from drifting when you change a dimension.

When to Use Onshape or Fusion (and when not to)

Use parametric CAD for parts that must fit or locate other objects: brackets, enclosures, mounts, spacers, jigs, and anything with hole patterns or mating faces. It shines when requirements change, because you can edit a dimension or parameter and regenerate the whole model consistently. If you’re sculpting an organic shape (figurines, terrain, character models), mesh modeling is usually faster; you can still combine both by importing meshes as references.

Core Workflow (same idea in both apps)

1. Pick a meaningful sketch plane and commit to an origin (Top/Front/Right or a midplane).
2. Sketch the intent using constraints first (coincident, horizontal/vertical, tangent, equal, symmetric).
3. Add only the dimensions that define size; keep location controlled by the origin/axes/symmetry.
4. Confirm the sketch is fully defined before you build features from it.
5. Create the base solid (extrude or revolve).
6. Add functional features as separate steps (holes, pockets, ribs, bosses).
7. Mirror/pattern repeated features instead of re-sketching them.
8. Leave cosmetic fillets/chamfers for late in the timeline so edits don’t break earlier features.
9. Make changes by editing dimensions/parameters, not by dragging faces as a primary workflow.

Starter parameters for FDM mechanical parts

wall

2.0 to 3.0 mm for small parts; increase for load

clearanceFit

0.2 to 0.4 mm per side for sliding fits (FDM typical)

pressFit

0.0 to 0.2 mm interference per side (test first)

holeOversize

+0.2 to +0.6 mm on diameter for bolts/pins

filletMin

0.8 to 1.2 mm for durability and comfort

Feature order that stays editable (timeline hygiene)

• Base shape first, then datums/mating faces, then holes/slots, then ribs/bosses, then fillets/chamfers.
• Prefer a few stable sketches that define interfaces over many “throwaway” sketches.
• Use construction geometry (centerlines, bolt circles) so patterns are driven by logic, not eyeballing.
• Mirror about planes and pattern from a single “master” feature to keep edits consistent.
• Name key sketches/features (Base, MountHoles, CableSlot) so you can find and edit fast.

Modeling with FDM in mind (so the model matches what prints)

Avoid features smaller than your nozzle/line width; tiny ribs, thin tabs, and knife edges either won’t slice correctly or will print weak. Use inside fillets at stress corners (clips, tabs, cantilevers) to reduce crack-start points and improve layer-to-layer load sharing. For holes that must be accurate, model them slightly larger (holeOversize) and plan to drill/ream, or print a small test coupon first; circular holes in FDM often come out undersized due to extrusion width and cooling. Also account for first-layer bulge (“elephant foot”) on parts that must slide or sit flat—adding a small chamfer at the bottom edge is often faster than sanding.

Common CAD-to-print problems