Teaching Compass Ruler with Magnetic Pivot and Suction Cup Center

The problem

When teachers draw geometric diagrams on a vertical blackboard, standard compasses rely on a sharp metal point to anchor the center. On smooth slate or painted whiteboards, that point often slides downward under the weight of the drawing arm as it sweeps, distorting the circle. According to the patent, existing teaching compasses are difficult to keep firm on the blackboard, the center easily shifts during drawing, and errors frequently appear in the final shape.

The solution

1. The compass uses two wooden rulers (first ruler 1 and second ruler 2) joined by a hinge with arc-shaped ends. Both surfaces carry measurement scales.
2. The drawing end features a circular first connecting block 4 with three clamping rods 5 arranged in a circle. A fixing ring 6 slides over the rods to squeeze them inward, gripping a piece of chalk.
3. The pivot end has a circular second connecting block 7 holding a rounded positioning end 8. Embedded exactly in its center is a spherical first magnetic bead 9.
4. The separate circle center positioning mechanism 3 starts with a rubber suction cup 301 made of transparent rubber, topped by a circle center positioning block 302 with a central positioning hole 303.
5. Inside the hole, a first telescopic tube 304 and a second telescopic tube 305 slide against each other, buffered by a first spring 306 and guided by limit grooves and sliders. A telescopic positioning rod 307 with a second spring 308 extends further down, ending in an arc-shaped rubber pad 309 that meets the board.
6. A docking end 3013 sits at the top of the first tube. Its upper face has an arc-shaped groove holding a second magnetic bead 3014, which attracts the first magnetic bead. Its lower face carries a ball that slides against the positioning block.
7. Airflow is controlled by a first vent hole 3011 on the first tube and a second vent hole 3012 on the block and sealing gasket 3010. Twisting the docking end aligns or blocks these holes to set or release the suction.

Who it is for

• Educational equipment distributors supplying public and private schools with durable geometry tools.
• Whiteboard and chalkboard manufacturers looking to bundle a specialized drawing accessory designed for smooth vertical surfaces.
• Teacher training programs and universities where education majors need demonstration tools for math pedagogy classes.
• Office supply brands expanding their drafting and presentation lines with a magnetically anchored drawing instrument.

How it works

The main parts

Using the compass

1. Load the chalk - slide the fixing ring (6) down toward the connecting block (4) to spread the three clamping rods (5). Insert a piece of chalk between them and push the ring back up to lock it.
2. Mark the center - use the chalk to draw a small dot on the blackboard where the circle’s center should be.
3. Set the suction base - twist the docking end (3013) so the first vent hole (3011) separates from the second vent hole (3012), closing the air path. Place the transparent rubber suction cup (301) over the dot; the arc-shaped rubber pad (309) on the telescopic rod (307) rests directly on the mark. Press the positioning block (302) down to expel air and stick the cup to the board.
4. Attach the compass arm - bring the positioning end (8) of the ruler close to the docking end. The first magnetic bead (9) and second magnetic bead (3014) have opposite polarities, so they snap together. The ball on the bottom of the docking end slides against the positioning block.
5. Draw the circle - adjust the hinge angle to set the radius using the scales on the rulers. Swing the first ruler (1) and second ruler (2) around the magnetic pivot while the chalk traces the circle. The suction base helps reduce downward slipping.
6. Release the base - after drawing, pull the compass arm away from the magnets. Twist the docking end to align the vent holes again. Outside air flows through the second vent hole (3012) and first vent hole (3011) into the suction cup, breaking the vacuum so the mechanism can be lifted off the board.

Applications

Middle school geometry lessons

Teachers demonstrating properties of circles, tangents, and inscribed angles need round shapes to avoid confusing students. The transparent suction cup lets them place the center precisely over a pre-drawn point on the chalkboard, while the magnetic pivot keeps the wooden arm stable throughout the sweep.

High school physics diagrams

Physics instructors frequently draw circular motion paths, magnetic field lines, and orbital trajectories on large whiteboards. Because the telescopic positioning rod uses springs to maintain pressure against the board, the compass accommodates slight surface irregularities. The wooden rulers provide enough rigidity to span radii required for large-scale diagrams visible from the back row.

Teacher training colleges

Education majors learning instructional methods practice board work extensively before entering real classrooms. Providing trainees with a tool that removes the frustration of slipping centers helps them focus on lesson delivery rather than struggling with basic drafting. The twist-to-lock vent mechanism requires no complex setup.

Architectural and design sketching on presentation boards

Professionals presenting concepts on large foam-core or matte-painted boards sometimes need to scribe precise arcs during live demonstrations. The rubber pad protects delicate presentation surfaces from puncture marks left by traditional needle points. The magnetic connection allows the drawing arm to be detached and reattached if the presenter needs to switch between multiple center points.

Adult education and community workshops

Instructors in community centers often work with older adults who may have reduced hand strength or dexterity. Pressing a large transparent suction cup is easier than forcing a sharp metal spike into a hard board. The sliding fixing ring for the chalk requires minimal finger pressure compared to screw-type chucks.

Where it is less suitable

• Paper drafting - the suction cup requires a smooth, non-porous vertical surface like glass, slate, or coated whiteboards; it will not adhere to paper or rough walls.
• Very small circles - the physical size of the suction base and the wooden hinge limits how tight the radius can be set.
• Outdoor use - dusty or wet environments compromise the vacuum seal of the rubber suction cup, and wind can shift the lightweight wooden arms during drawing.