Swiss bow made easy

Swiss bow made easy

The Swiss arch, also called a link arch, is used for larger roof projections as a connection between gutter and downpipe. With an almost right-angled tube knee and the cylindrical design, the conditions are not exactly ideal. For example, there is a risk of blockage and the drainage behavior could also be better. Nevertheless, Swiss arches, along with gutter pots, are considered the jewels of any roof drainage system. Since time immemorial, they have adorned many buildings and channel rainwater from the gutter into the pipe with timeless beauty and elegance. For us tinsmiths, Swiss bends also offer the opportunity to show what we can do. Unfortunately, in reality it often looks different: Take measurements, call the wholesaler and shortly thereafter assemble the industrially manufactured water deflector. Industrially manufactured elbows are usually in two parts and consist of a pipe angle and a pipe elbow, which is drawn in (folded) on one side by a special process. The expanded elbow and the elbow are simply plugged together. To be noted:

  • The plug-in connection at the 87° angle must be made watertight.
  • The poorer drainage behavior must be taken into account in the channel calculation.

Is manual work still up to date?

Are we assemblers or craftsmen? Of course, the purchased link arc is perfectly manufactured and more economical, but the decisive factor is that old knowledge is increasingly lost. In addition, the industry is at its wit’s end at the latest with the tapered design. A plumber who masters his craft must know certain activities and working techniques. This also includes designing and fabricating a Swiss bow. In order to impart these skills and expertise, there are the inter-company apprentice training courses, known as ulus for short. There, skills are taught that are not sufficiently taught in the specialized companies. It is mostly old techniques that young plumbers repeatedly fail to understand. Those who master these working techniques are much less likely to have problems on the construction site. In addition, the ulus also teach new techniques and materials such as foil roofs and liquid plastics.

Situation on the construction site

And here we go: To achieve a visually pleasing result, the number of segments should be chosen so that the individual pipe sections do not become too long. As a rule of thumb for the average segment length, three quarters to one whole pipe diameter can be assumed. First, the dimension from the center of the gutter to the center of the rain pipe and the pipe diameter are determined according to the gutter calculation. In our example, it is a six-piece channel with a conical inlet and an 80 mm rainwater pipe. The projection is 240mm.

Construction in nine steps

1. Make a quarter circle with the determined projection.

2. Remove a half or a full pipe diameter at the upper end (half diameter visually nicer, diameter more slope).

3. Draw a line from the resulting intersection to the piercing point of the quarter circle, the circle distance to the right side gives the length of the arc to be divided up. To the left side, at the right angle to the constructed line, the arc is extended. This is the center line from the pipe bend in the slope.

4. Dividing the length of the bow into equal parts.

The formula is: number of intermediate parts x 2 + 2. In our example, three intermediate sections x 2 + 2 = 8. The first and the last division are located on the pipe. With this number of intermediate sections, the division can be made by angle bisector. If this is not possible, the angle must be measured, then divided by the calculated value and the result deducted.

5. Make two more quarter circles with the pipe diameter.

6. We draw perpendicularly the lines of the pipe to the first divider, from this point of intersection we go via the tangent to the next divider.

7. Once we reach the top, the lines are extended until they intersect with the pipe from above. If you connect the intersections, you get the miter of the contra-angle handpiece.

8. To ensure the seam overlap at the spigot and rainwater pipe, the minimum dimensions ≥30mm must be observed. For optical reasons the middle length has to be adapted to the middle segment length.

9. Tightening of the body edges – finished.

Parts I, II, III and IV are processed in the classic way using the twelve divisions and the removal of the respective heights.

For practice

1. Tear out the Swiss elbow on a scale of 1:1.

2. Unwind segments I, II, III and IV. Segment III is needed three times and can be traced (don’t forget fold allowances).

3. Cut out rebate cutouts about 2mm deeper (because of rework).

4. Edge the folds. Caution: Seam right -open.

6. Pipe fold with self-bent folding chisel (sheet 2 x 10mm folded over results in three sheet thicknesses).

Close the fold (the lower edge of the sheet is visually separated – blue line on the picture to make this clear).

Stop the sheet metal chisel at the blue line and push it through, always tap the center of the chisel with the wooden or plastic hammer so that the ends of the chisel do not settle in the workpiece.

7. Scribe inaccuracies on a straightening plate and rework them (1 to 2mm may be added with a clear conscience, since each fold adds to the assembly process). It is best to adjust small unevennesses with the file. When reworking, make sure that the bevel is not changed. The segment should then lie as flat as possible.

8. Mark the fold allowances again and make them slightly with the flat-nose pliers or the beading machine.

9. Lift the curved individual segments on top of each other, secure them with a collet and mark them out. Check the inside and outside for a perfect fit – if there are any deviations, center them out.

10. For beading, the edge can again be made with the flat nose pliers or the beading machine. Here, too, several passes give the material the appropriate time for compression.

11. Once the board is set up at 90°, the top is filed down – the seam becomes more uniform.

12. Now the inside of the angle is immediately closed to about 170°, since it will be more difficult to close later with the hammer. Apply this process to the semicircle. Towards the center make a transition to the 90° board.

13. The individual sheet metal pieces can now be inserted.

14. Then close the seam slowly and evenly.

15. On the inside of the angle, the fold can be pressed shut with the piccolo or flat-nose pliers. Closing with a hammer is almost impossible (especially on the contra-angle).

16. Fold part by part. Pay attention to the fold line.

17. And finally check on the 1:1 drawing. This step can also be done during the whole manufacturing process.

The downloads for these instructions can be found here.


With practice, you can quickly create beautifully shaped and individually manufactured Swiss bows. For me as an instructor, the moment when the trainees proudly hold their component in their hands is particularly valuable. Finally, tinsmiths are among the few trades that understand how to make three-dimensional workpieces from two-dimensional material.

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