Tutorials PartCraft help Getting started
The exact kernel and the mesh kernel
PartCraft builds solids with two geometry kernels: a small mesh kernel that is ready at once, and the exact OpenCascade kernel that loads in the background. What each one can do, how to tell which is working, and what changes offline.
Written for PartCraft 0.3. The same help is inside the app: press F1.
A geometry kernel is the engine that turns your history into a solid. PartCraft has two, and both run on your computer as WebAssembly programs:
| Mesh kernel | Exact kernel | |
|---|---|---|
| Engine | manifold-3d | OpenCascade (OCCT) |
| Ready | At once, a few seconds after opening | Loads in the background after the app opens: a larger download, about 7 MB |
| Round shapes | Flat facets (see Curves) | True circles, cylinders, cones, spheres and tori |
| Volumes and areas | Of the faceted solid, a little low | Exact |
| Sketches, extrude, cut, revolve, holes, patterns, mirror | Yes | Yes |
| Fillets, chamfers, shell | No | Yes |
| Open (import) STEP | No | Yes |
| STEP export | Faceted only | Exact AP242 or AP214, and faceted |
| Drawing views | From the facets; no section views | Exact hidden-line views, section views |
| Picking edges and faces for features | No | Yes, whole edges and faces |
You do not choose: PartCraft builds with the mesh kernel until the exact kernel is ready, then switches to it for everything and rebuilds the part.
Which kernel is working
Look at the chip near the right end of the status bar:
| Chip | Meaning |
|---|---|
| "Mesh kernel" | The mesh kernel builds the part (the exact one has not started yet) |
| "Exact kernel loading…" | OpenCascade is downloading and starting; the mesh kernel builds meanwhile |
| "Exact kernel" | OpenCascade builds the part. Hover the chip to see how long it took to load |
| "Mesh kernel only" | OpenCascade could not load. You can keep modeling, without the exact-only features |
When it is ready the status bar says, for example, "The exact kernel (OpenCascade) is ready (loaded in 4.2 s)."
While it is loading, Fillet, Chamfer, Shell and the exact STEP exports are grayed. Their tooltips end with "needs the exact kernel (loading)". Wait for the chip to say "Exact kernel".
If the exact kernel does not load
The status bar says "The exact kernel did not load (…). Building with the mesh kernel: curves are faceted, and fillets, chamfers, shells and STEP need the exact one." Common causes:
- the connection dropped while it was downloading;
- the computer or tablet is short of memory (OpenCascade needs far more than the mesh kernel);
- a browser setting or company policy blocks WebAssembly or Web Workers.
Save your part, reload the page while online, and open the part again. A part that uses fillets, chamfers, a shell or an imported STEP solid still opens with the mesh kernel, but those features show ⚠ not built ("Fillets need the exact kernel (OpenCascade), which is not loaded."), and so do features after them that need them.
Online and offline
Both kernels are downloaded from the site the first time, then run locally. Nothing about your part is sent anywhere.
To work with no connection at all, save PartCraft for offline use while you are online: choose Save for offline in the app bar and wait while it counts ("Saving 40 of 212") until it says Offline ready. The saved copy includes the 3D library, the mesh kernel and the exact OpenCascade kernel, about 27 MB in all (the exact kernel is most of it), so afterwards fillets, chamfers, shells, STEP import and export, and drawings all work offline. If it says Could not save, click it to try again while online; Offline not available means this browser window cannot keep a copy (private windows and some managed computers). With the copy saved, clicking Offline ready offers Save again (get the newest version) and Remove the offline copy. Details: Working offline.
Online
You are online. If you are about to lose the connection and have not saved for offline use, at least wait until the chip says "Exact kernel": everything then works until you reload the page.
Offline
You are offline. If the chip says "Exact kernel", everything works. If it says "Mesh kernel" or "Exact kernel loading…", the exact kernel cannot finish downloading until you are back online: fillets, chamfers, shells, STEP import and exact STEP wait until then. If the app bar says Offline ready, the exact kernel is in the saved copy and loads offline too: reload and it starts.
Memory and big parts
OpenCascade runs in a background worker so the screen stays responsive while it rebuilds; the status chip says "Rebuilding…" meanwhile. On very long sessions with many rebuilds, PartCraft restarts that worker on its own when its memory grows large. If the browser tab crashes on a big part, save more often and close other heavy tabs.