Equal-Slope Rectangular Funnel Panel Layout

Define the openings and reference lengths

The upper opening is 600 by 400 mm and the lower opening is 400 by 200 mm. Center both rectangles on a common vertical axis and separate their planes by 300 mm. The model assembles four open-ended faces between those rectangles.

The length difference is 200 mm and the width difference is also 200 mm. Dividing each difference between its two sides gives a 100 mm setback in both horizontal directions. Equal setbacks with the same vertical height produce equal face slopes. Equal slope describes the inclination of the four faces.

The two pairs of panels have different end widths. The long pair connects 600 to 400 mm and the short pair connects 400 to 200 mm. Keep these pairs identified while measuring and cutting. The editable example checks the equal-slope condition as dimensions change.

Calculate the true developed dimensions

Each face slant height is S = √(300² + 100²) = 316.23 mm. This line lies in a face, perpendicular to its parallel end edges. The vertical height is measured between opening planes. Locate both references before transferring the face layout to a flat sheet.

The corner joins move 100 mm in each horizontal direction while rising 300 mm. Their true length is E = √(300² + 100² + 100²) = 331.66 mm. Use this length to check the oblique edges where adjacent faces meet. The trapezoid slant height and corner length each follow their own line.

Each long panel has area (600 + 400)S / 2 = 158113.88 mm². Each short panel has area (400 + 200)S / 2 = 94868.33 mm². Add two of each to obtain 505964.43 mm² of ideal surface area. Use unrounded S in the area calculation.

Worked example dimensions

Mark the panels and inspect assembly

Draw each panel with parallel upper and lower edges separated by the 316.23 mm face height. Center the shorter edge within the longer edge, giving 100 mm at each end. Join matching corners and verify the 331.66 mm oblique edge. Repeat for the other panel pair using its own end widths.

Original and Mark show the flat panel outlines. Cut separates all four trapezoids. Form raises them into the rectangular transition while preserving every edge length. Rotate the model to inspect both openings and all four corner seams.

This example develops four separate ideal panels with centered openings. Changing only one opening difference can make the face slopes unequal. Use the general rectangular funnel tool for dimensions outside the equal-slope condition. Review seam construction, thickness and joining allowances before preparing workshop blanks.

Review the fabrication detail

Review actual thickness, seams, kerf, rolled edges and fabrication allowances before cutting. The model gives ideal geometric panel surfaces.