Unit 03 · Lecture 6
Circular pattern, chamfer and thread
The second drawing exercise adds three new tools: the circular pattern, chamfers and modelled threads. It also teaches a dependable way to draw lines tangent to circles.
Video 16:41Reading 8 minUpdated 26 October 2026
What you will build
A 20 mm thick curve part with a curved slot, three M10 × 1.25 threaded holes on a 35 mm pattern radius, 2 mm edge chamfers and 0.5 mm hole chamfers.
You will learn
- Choosing a corner anchor for easy vertical constraints
- Typing equations into dimension fields (37.5*2)
- Tangent lines: draw long and away, then trim
- Building a slot from five circles
- Circular pattern, chamfer and the Thread feature
Before you start
Complete the lever handle first. This exercise uses the same circles-then-trim method.
Step by step
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01
Anchor at a corner
0:48Sketch on XZ (front view). Start at the bottom corner with a 100 mm line from the origin. Draw a Ø100 circle tangent to it, with its centre vertically aligned with the line’s end point.
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02
Let Inventor do the arithmetic
2:18The drawing gives R37.5. In the dimension box, type 37.5*2 and Inventor returns 75. Any simple equation works. Add a Ø50 circle, tangent to the Ø75 circle, 50 mm from the big circle’s centre and vertically aligned with the line’s end.
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03
Draw tangent lines long and away
3:46When a line must be tangent to a circle, draw it longer than needed and slightly away from the circle, then apply Tangent. A short line can technically be tangent but leaves an open profile. A long one trims cleanly.
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04
Build the slot from five circles
5:15Number the slot arcs 1–5 on the drawing. Circle 1 is Ø30, level with the Ø50 circle and 60 mm from it. Circle 2 is Ø90, concentric with the Ø50. Circles 3 and 4 are Ø10 and Ø20, joined by a tangent line.
Circles 1–4 point into the slot and circle 5 points outwards. With the 2 mm wall, add 2 to its radius. Trim, check the tangents, and restore the 15 mm base distance if trimming removed it.
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05
Circular pattern the holes
10:25Draw one Ø10 circle (M10 nominal), 35 mm from the R50 centre and vertically aligned with it. Open Circular Pattern, select the circle as geometry, the R50 centre as the axis, and set the count to 3 over 360°. A smaller angle spreads the copies over just that arc.
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06
Extrude 20 mm
13:18Finish the sketch and extrude the body 20 mm, leaving the slot and holes open.
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07
Chamfer the edges
13:59Apply a 2 mm chamfer to the outer edges on both faces. Shift + middle mouse orbits the part. Then chamfer every hole edge at 0.5 mm, front and back.
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08
Model the threads
14:42Open Thread and pick a hole’s inner face. Keep ANSI Metric M Profile, size 10, change the designation from 1.5 to M10 × 1.25, and keep class 6H. Use Apply to repeat for all three holes.
Thread notation
Reading M10 × 1.25 6H
M10 is a metric thread with a 10 mm nominal diameter. 1.25 is the pitch, the distance between thread crests, so lowering it packs the threads closer together (a fine thread). 6H is the tolerance class for an internal thread. A capital letter means a nut or hole, and a lowercase letter means a bolt.
Total span angle
Circular Pattern divides the count evenly across the angle. Three copies over 360° are 120° apart. Over 180°, they spread across a half-circle.
Common mistakes
- Drawing tangent lines that stop short of the circle. You can’t see whether they’re tangent, and the profile stays open.
- Forgetting the circle that points outwards in the slot, which leaves the wall 4 mm too thin.
- Leaving the default 1.5 pitch when the drawing calls for 1.25.
- Chamfering only the front face.
Practice exercise
Change the circular pattern to 4 holes over 270° and look at the spacing. Then put it back to 3 over 360° to match the drawing.
Check yourself
What do you type to enter R37.5 as a diameter?
37.5*2.
What is the reference for a circular pattern?
An axis, here the centre point of the R50 arc.
In M10 × 1.25, what is 1.25?
The pitch, the distance between thread crests in mm.
Three holes over 360°: what angle separates them?
120°.
Want the graded version? Take the 5-question lesson quiz in the course player after the video.
Written by the CADsmit instructor from the lecture recording and checked in Autodesk Inventor Professional 2027. Last updated 26 October 2026. Spotted an error? Tell us.