Unit 03 · Lecture 5

Practice exercise: lever handle

This is the first exercise from a real engineering drawing. Instead of drawing arcs one by one, you build the outline from full circles, constrain them to each other, then trim away everything you don’t need.

Video 12:00Reading 7 minUpdated 26 October 2026

Lecture video, 12:00. The written steps below follow the video, with timestamps for each part.

What you will build

A 10 mm thick lever handle: a Ø30 boss, two straight arms of 90 and 130.51 mm, rounded ends with Ø14 holes, and a curved head made from three concentric circles.

You will learn

Picking the right view and anchor point from a drawing
Building curved outlines from circles plus Trim
Working out unlabelled sizes from the dimensions you do have
Why Trim fails on dimensioned circles, and the fix
Sketch fillets

Before you start

You need tangent, horizontal and vertical constraints from Lecture 3.

Step by step

01
Read the drawing and choose the view
0:43
The drawing’s main view carries most of the dimensions, so that is your front view. Start a new Standard (DIN) part and sketch on the XZ plane. Check that the ViewCube is upright.
02
Anchor the Ø30 circle at the origin
1:23
You could start anywhere, as long as everything is dimensioned back to that point. The semicircular boss at the bottom is the most practical choice, so draw a Ø30 circle on the origin.
03
Add the two arms
2:03
Draw lines of 90 and 130.51 mm, tangent to the Ø30 circle. Apply Horizontal between their end points and the origin so they start level with it. Add a Ø14 circle, vertically aligned with the origin and 20.63 mm above the end of the arm.
04
Number the circles
3:25
Count every arc in the outline on the drawing: ten in total (nine arcs and one full hole). Numbering them stops you missing one. Circles 3 and 5 are each a concentric pair of Ø14 and Ø30, aligned with the arm end points and made tangent to the lines.
05
Work out the missing diameter
5:29
Circle 8 is R20 (Ø40) and circle 9 is R34 (Ø68). Circle 10 has no dimension, but it surrounds the others: 15 (boss radius) + 7 (end radius) + 20 = R42, so Ø84.
06
Place the three concentric circles
6:53
Draw Ø84, Ø68 and Ø40 roughly in place and make them tangent to their neighbours. If Inventor warns that a constraint would over-constrain the sketch, cancel it. That relationship already exists. Because the three circles are concentric, a horizontal constraint between their centre and the reference point fixes them.
07
Trim the excess
8:56
Use Trim and zoom into tight corners. If a circle won’t trim (“try removing some constraints”), its diameter dimension is the cause, because trimming turns it into an arc. Delete that dimension, trim, then check the tangent constraints again and restore any that were lost.
08
Fillet and extrude
10:59
Use the sketch Fillet with R7 on the remaining sharp corner. Press E, pick the profile and extrude 10 mm.

Working from a drawing

Circles first, then trim

Arcs are hard to constrain because their end points move. Full circles have only a centre and a size. Constrain the circles to each other, trim, then check the result. That is faster and more reliable for organic outlines.

Missing dimensions aren’t mistakes

Drawings avoid giving the same size twice. If a value isn’t shown, it can be worked out from the others, as with the Ø84 here. Doing that arithmetic is part of reading drawings.

Common mistakes

Starting on the wrong plane, so the handle lies flat instead of standing in the front view.
Using radius values as diameters. The drawing says R20, and the Circle tool wants Ø40.
Trimming before constraining, which leaves you with floating arcs that are hard to fix.
Forgetting to check tangents after trimming.