Figure 1

Making a one-piece transition pattern allows you to easily duplicate some of your most used pieces.

There are many timesaving transitions you can have ready to duplicate, seam, bend and ship out. Many of your typical transitions can be duplicated and put in stock.

Figure 2

A lot of folks still lay out transitions in four pieces: the top, bottom and two sides. Usually it’s because they were taught this way or perhaps it was because people could see what was actually going on. Maybe it seemed easier? Whatever the reason, it’s definitely more time consuming.

Begin by developing a pattern of a typical transition that is flat on top and done in one piece. Many of you will find that you can save time - or money - doing it this way.

In Figure 1, two separate views are shown. One is the top view, and then by projecting lines down you create an elevation view. The top view in Figure 1 is shown in true-length from Point C to B, or 12 inches in length. You know this because this particular pattern is flat on top and so it would be in its “true-length form.”

Figure 3


To see patterns or pieces of patterns in true-length form, you can look at the pattern from a second view. It must be perpendicular to its plane surface. And the elevation drawing in Figure 1, Line DE shows the top view perpendicular to its plane and therefore its true length.

The side view (elevation view) in Figure 1 is not shown in true length; however, the elevation view shows that the two heights, 10 inches and 8 inches, are in true length and it shows the true length of the bottom edge from points F to G.

From the top view - Line CA, which represents the true length of the sides, also shows that the elevation views of the sides are not in true length. To make the patterns for the sides of the transition, you must use the distance from Point C to Point A in the top view. You have to then add the necessary allowance to each piece for the seams to run them through whatever machine you use to make your seams.

Why all this talk on true length? You really need to have an understanding of this for most sheet metal layout work. This transition is a relatively simple one and you still need to know how to obtain your true-length lines to do the layout.

Figure 4


You can avoid many of these steps and lessen your chance of error if you create auxiliary views of the sides, as shown in figures 2 and 3. Keep them as part of a one-piece pattern.

Using your steel square aligned from points 1 to 2 (Figure 2), draw lines as shown from Point 1 to Point 1a, striking a reference mark at the height of this particular side, in this case 10”. Flip your steel square and do similar with the distance from Point 2 to Point 2a, and draw a reference mark. Strike a line from Point 1a to Point 2a and repeat with side two as shown. Now those sides are done.

The last section that needs to be added to the layout is the pattern for the slant bottom. You can layout this pattern on either end. The first step is to duplicate the offset from Figure 1, A to B. Mark the reference points C and as shown in Figure 3, transfer the offset made from A to B from Figure 1 to the pattern in Figure 3.

Using A as center, draw an arc as shown. Rest the square on the line from Point C, tangent to the arc, and slide it over until the other leg of the square becomes aligned with Point A. This establishes Point B on the arc.

Figure 5

Now strike a line from Point A to Point B and by flipping your square, continue this line to Point A1, which is the length from Point 2 to Point 2b from Figure 2.

To establish the distance from Point C to Point C1, see Figure 4. Again using the square, place the square from Point C tangent to the arc established in a previous step. Using the other leg of the square, strike off the distance of Point 1 to Point 1b from the top view (Figure 2).

Now a line from C1 to A1 and the four sides for this one-piece transition is finished. The only steps that need to be completed are the allowances for the seams and cleats (S-drives) as shown in the completed pattern, Figure 5.

For more information on manual sheet metal layout, visit