Plate Workflow

Open a past robot CAD and spin it. Point out every flat aluminum piece: gearbox plates holding bearings and motors, the bellypan everything bolts to, little gussets in corners. Tell them ~70% of what they'll model this summer is plates. The skill today repeats on every subsystem.

This is the #1 habit to drill. In Fusion, loose bodies in the root are a mess later — no joints, no clean BOM. Components are Fusion's version of Onshape Part Studios scoped to one part. Activate before sketching so the sketch and body land inside the component. Common mistake: modeling everything in the root, then having to cut/paste bodies into components later.

Demo sketching a rectangle, then add corner fillets with the Fillet tool in the sketch. Push them to fully constrain — drag a line; if it moves, it's underconstrained. Blue lines are the enemy. Pick a sensible origin: put the plate so the origin lands on a meaningful point (a bearing center or a corner) — it makes joints easier later.

Stress: plates are THIN. 1/8 in (0.125) is the bread-and-butter gearbox plate; 0.090 for light gussets; 1/4 in for highly loaded mounts. Switch Fusion units to inches for FRC (Document Settings). Symmetric extrude is handy when you want the plate centered on a reference plane. Common mistake: extruding 1 inch because they didn't read the number — it looks like a brick.

The Hole feature is smarter than cutting circles — it tags holes as holes for the BOM and gives clean counterbores/tapped options. Teach the real numbers: clearance holes are slightly bigger than the bolt so it slides through. 1.125 in bore is the standard for a flanged ball bearing that carries a 1/2 in hex shaft. Set extent to All so it cuts fully through the thin plate.

The 1/2 in grid is the FRC standard — it matches the hole pattern on 2x1 tube, gussets, and most COTS parts so everything bolts together. Demo Rectangular Pattern off a single Hole feature. Pattern the FEATURE (so edits propagate) rather than copying bodies. Common mistake: spacing 0.5 but forgetting to also bump the count, so they get two holes instead of a row.

User Parameters = Onshape Variables. Type the parameter name into a dimension field instead of a number. Then if the team switches from 1/8 to 1/4 stock, you edit one value and every reference updates. Huge for plates that share a thickness. Keep names simple and consistent across the team.

Weight matters — FRC robots have a hard weight limit. Lightening pockets remove material where there's no load. Teach judgment: keep a web of material connecting bolt holes and bearing bores; round the pocket corners (sketch fillets) because sharp inside corners concentrate stress and crack. This is the artful part — show a good example vs. a swiss-cheese over-lightened plate that flexes.