BITS U103 · Self-marking practice · Level 2
Rebuild drills — level 2
Four machine parts climbing from a single lug to full tutorial-sheet difficulty. Same deal as level 1 — exact volumes so Fusion marks your work — plus staged checkpoints, because on multi-feature parts the professionals check as they go.
Drills 1–8 taught the commands. These four teach what the tutorial sheets actually examine: decomposing a real part into an ordered feature plan. The method — five questions, the idiom table, blends last — is the From drawing to model lesson; read it first or these will feel like cliffs instead of steps.
Marking is unchanged: Inspect → Physical Properties, match the number, to the hundredth. Every dimension is in millimetres.
The plan is the drill. Before touching the mouse, write the numbered feature list on paper: sketch plane, profile, operation for each feature. Then build, checking the volume at each checkpoint. If a checkpoint mismatches, the error is in the feature you just made — fix it before moving on, exactly as you would in the lab exam.
When your number doesn't match and the checkpoint doesn't tell you why, level 1's symptom table still applies.
Drill 9 — Link plate
The lug, isolated
- A flat link: two R15 rounded ends, centres 60 apart, straight tangent sides (so 90 long, 30 wide overall).
- ⌀12 hole at each end centre. Thickness 8.
Answer key — volume
18 245.31 mm³
19 150.09 means one hole missing; 20 054.87 means both. If you're slightly over and can't see why, check the side lines are tangent to the end arcs — a kink there adds slivers of area.
See the method
- One sketch: centre-to-centre construction line 60, two R15 circles at its ends, two lines tangent to both circles, trim. (Fusion's Slot tool draws this in one go — worth learning, then do it once the long way.)
- Add the two ⌀12 circles concentric with the arcs, same sketch.
- Extrude the stadium (not the holes) 8.
Volume: (30 × 60 + π × 15² − 2 × π × 6²) × 8 = 14 400 + 1 224π.
Drill 10 — Rod support
Base plus upright
- Base plate 90 × 50 × 12, with two ⌀10 holes on the lengthwise centreline, 15 in from each end.
- Upright, centred on the base both ways: 40 wide, 15 thick, rising 38 above the base top to a rounded R20 top (70 overall height), with a ⌀20 bore at the arc's centre.
Answer key — volume & checkpoint
| After base + its holes | 52 115.04 mm³ |
| Finished part | 79 627.43 mm³ |
The upright alone contributes 27 512.39. If the finished number is high by about 4 712, the ⌀20 bore never cut — check the extrude was Cut, extent All, not New Body.
See the method
- Base: rectangle on XY centred at origin, extrude 12; one ⌀10 hole, mirror or pattern for the second. Checkpoint.
- Upright: sketch on the XZ origin plane — two vertical lines 40 apart, closed by a tangent R20 arc at the top, bottom edge on the base top. Add the ⌀20 circle concentric with the arc in the same sketch.
- Extrude the profile symmetric, 15 total, Join — symmetric is what centres it on the base with no arithmetic.
Volume: 90 × 50 × 12 − 2π × 5² × 12 + 15 × (40 × 38 + ½π × 20² − π × 10²) = 76 800 + 900π.
Drill 11 — Clevis fork
One lug, mirrored
- Block 40 × 40 × 30 with a vertical ⌀20 bore through its centre.
- Two fork arms off one face, each 8 thick with a 24 gap between (flush with the block's outer faces): full 30 height, reaching 45 out to an R15 rounded end.
- One ⌀14 hole through both arms at the arc centres.
Answer key — volume & checkpoints
| Block | 48 000.00 mm³ |
| After the ⌀20 bore | 38 575.22 mm³ |
| Finished part | 63 367.08 mm³ |
Each finished arm contributes 12 395.93. High by 1 231.50? One arm's ⌀14 hole is missing — mirror the hole with the lug, or cut once through All so a single hole feature drills both arms.
See the method
- Block centred on the origin, extrude 30 up from XY; ⌀20 bore. Checkpoint.
- One arm: stadium profile (as drill 9) on the XZ origin plane, from the block face out 45 to the R15 arc. Extrude with Start → Offset 12, distance 8, Join — that's the far arm, flush with the face.
- Mirror the arm feature across the XZ origin plane. This is why the block was centred in step 1.
- ⌀14 hole sketched on one arm's outer face, extent All — one cut, both arms.
Volume: 48 000 − π × 10² × 30 + 2 × 8 × (45 × 30 + ½π × 15² − π × 7²) = 69 600 − 1 984π.
Drill 12 — Bearing yoke
The capstone: tutorial-sheet difficulty
- Base: 80 × 50 × 12, two ⌀11 holes on the lengthwise centreline, 15 in from each end.
- Tower, centred both ways: 36 wide, 30 thick, rising 50 above the base top to a rounded R18 top (80 overall height), ⌀20 bore at the arc centre, right through.
- Two ribs bracing tower to base, one each side: right triangles 20 up the tower face × 10 along the base, 8 thick, centred on the tower's width.
- Angled arm off one 30-thick tower face: 24 wide, 12 thick centred on the part's mid-plane, centreline leaving the face 33 above the base top and sloping down at 30°, running 40 to an R12 rounded end with a ⌀12 hole.
Answer key — volume & checkpoints
| Base + its holes | 45 719.20 mm³ |
| + tower with bore | 105 562.57 mm³ |
| + both ribs | 107 162.57 mm³ |
| Finished part | 120 039.73 mm³ |
Each rib is exactly 800. The arm contributes 12 877.17 including its hole. And a modelling reality check: the arm's lug bottom sits at height 13 — just 1 mm above the base top — and its tip overhangs the base's edge in plan. Both are intentional; real parts do this, and your model should match the numbers, not your sense of tidiness.
See the method
- Base centred at origin, holes, checkpoint. Tower profile (two verticals, tangent R18 arc, ⌀20 circle) on the XZ origin plane, symmetric extrude 30, Join. Checkpoint.
- Ribs: triangle on the YZ origin plane, symmetric extrude 8, Join — then Mirror across XZ… check that plane choice yourself: the ribs sit on the tower's 30-thick faces.
- Arm: construction line from the face point (33 above base top) at 30° below horizontal, length 40; stadium 24 wide around it, R12 arc, ⌀12 circle; symmetric extrude 12, Join.
- Nothing to fillet — this part's edges are meant sharp, which is exactly why its volume is exactly checkable.
Volume: (48 000 − 726π) + 30 × (36 × 50 + ½π × 18² − π × 10²) + 2 × ½ × 10 × 20 × 8 + 12 × (24 × 40 + ½π × 12² − π × 6²) = 115 120 + 1 566π.
If you can take drill 12 from blank screen to matching volume in about an hour — plan on paper, staged checkpoints, no un-modelling — you are at the level the tutorial sheets are pitched at. The remaining gap to the sheet itself is only bulk: more lumps, plus a final fillet pass, neither of which is new thinking.