Creating a sheet metal bathtub is a great way to have some fun, strengthen your layout skills and create something you can use or pass on as a gift. These galvanized bathtubs, mostly used by children, were once common in America.
They were made in many different sizes, some with plain designs and some with intricate stampings on the side. Today, you'll find these old tubs in antique stores with a hefty price tag attached. Many of them are used as planters, fountains and magazine holders.
In this article, only a few measurements are given to provide a basic idea of dimensions and proportions. The steps can easily be adapted to make a bathtub of any size.
To begin developing the pattern for the bathtub, draw both the top view and elevation as shown in Figure 1. There are three separate sections plus the base that need to be developed for the bathtub. These sections are: the foot end, the middle section and the head end of the bathtub.
The top view illustrates that even though there are three different areas of this pattern to develop, we still have two symmetrical halves. That means that the patternmaker only needs to develop one half of the foot and head of the tub, as shown in Line 1-2, the tub's center.
The bathtub ends and midsection contain equal and unequal tapers. The foot of the tub is an equal taper. In the diagram, this is shown the one radius center, marked "A," for the top and base of the tub. The equal taper follows through the midsection of the tub; this is shown in the shaded area of Figure 1.
The head endThe head end of the tub has two centers, marked "B," for the base and "C" for the upper head end of the tub. These two centers, offset from one another, create an unequal taper, which needs to be developed using triangulation. The foot end of the tub can be developed using triangulation, or because of its equal taper, it may be made using the radial-line method.
As shown in the elevation view of Figure 1, the foot end has a very slight pitch, making it more difficult to use the radial-line method. Both ends of this bathtub will be developed using triangulation.
Begin the layout by drawing a straight line as shown from Point 1 to Point 2 (See top view, Figure 1). Near one end, mark an "A" on the line for reference. It will be used to make an arc for the top and the base on the foot end of the tub. The radius for the foot can be of any radius you choose. In the example, the width at the foot of the tub will be around 15 inches, so our radius would be 7 1/2 inches.
Now using Point A as center, draw an arc as shown from Point 3 to Point 4. Keeping one end on Point A, center and extending the length of the trammel points by 1 inch and make another arc from Point 3' to Point 4', as shown.
Now you have established both the base and the top of the foot end of the tub. You will use this in obtaining the necessary information needed to create a true-length triangle for the foot end of the tub. On Line 1-2, measure over from Point A about 20 inches and mark it Point B. This becomes the radius center for the base at the head end of the tub. The width at the base (head end) for this particular pattern is about 17 inches, for a radius of 8 1/2 inches.
The upper flareThen using Point B as center, make an arc from Point 5 to Point 6 as shown in Figure 1. On Line 1-2, measure over 1 3/4 inches to establish Point C. You should have created a 10-inch arc, using Point C as center from Point 5' to Point 6', to develop the upper flare for the head end of the tub. Note that you may choose any pitch that you desire. There is no reason for the dimensions used here other then the final look chosen for this exercise.
Connect points 4 and 6, and points 3 and 5 with a straight line. Draw lines parallel to lines 4-5, 3-6, as shown, from points 4' to 5' and points 3' to 6'. From the top view in Figure 1, you can see the true length of the base and the top rim of the bathtub.
In the diagram, the project lines drawn to establish the height of both ends of the tub in the elevation drawing are shown in red. The two inside red lines establish the base, shown by Line 7-9. Line 8-10 is the height of the foot and head end of the tub.
The example uses 14 inches as the height at the head end of the tub and 9 inches for the foot end of the tub. Once again, these can be of any height that works for your design. Connect Point 7 to Point 8, Point 9 to Point 10 and draw a line from Point 8 to Point 10.
Establishing the true lengthsAs stated earlier, you only need to make the true lengths for one half of the foot end and the head end of the tub (see shaded area in top view of Figure 2). These true lengths will work for the other half of each end.
The first step is to divide the arcs drawn from Point B and Point C into equal spaces, as shown. (Five equal spaces were used on the head end.) Label as shown, starting with No. 1, which represents the beginning of the arc drawn from Point B. The base should have odd numbers, 1 through 11. The top (rim) of the tub at the head end is divided into the same amount of spaces and labeled with even numbers, starting with 2 through 12. No. 2 is the beginning of the upper arc. Connect Point 1 to 2, Point 2 to 3 and 3 to 4, etc., as shown by the dotted line in the top views shaded area, until you connect Point 11 to Point 12, as shown.
SeamsConnect the beginning of both arcs drawn from points B and C (see Figure 2) by drawing a line from Point 1 to Point 2. Typically, this would be an edge or seam for the sidepiece. To develop a seam that would run perpendicular to the base, Point A, shown as line A'A" in the elevation view, has been added.
These dotted lines drawn in the shaded area in the top view of Figure 2 all represent the base length of a particular triangle. All even numbers, 2 through 12, shown in the top view of Figure 2, represent the height of each triangle. Because the upper rim of the bathtub is slightly pitched from the head to the foot of the tub (Figure 2, Line DE), the heights of points 2, 4, 6, 8, 10 and 12 are not equal.
To determine the height of each line, drop lines from points A, 2, 4, 6, 8, 10 and 12 in the top view, perpendicular to Line FG, the base of the tub, in the elevation view. This will establish points A', 2', 4', 6', 8', 10', 12' on the base and A", 2", 4", 6", 8", 10", and 12" on the top rim. The length of each of these lines, A' to A", 2' to 2", 4' to 4", etc., through 12' to 12" will be transferred to a diagram of triangles as shown in figures 3 and 4. A diagram of triangles is one easy method used to determine a line's true length.
To begin developing the triangles diagram, draw a horizontal line of random length, as shown in Figure 3 from Point A to Point 12'. Starting with Point A, take the distance from Point A to Point 1 from the top view in Figure 3 and establish this distance using Point A as center and making a reference mark at Point 1 along the line in Figure 3.
‘Diagram of triangles'Reset the dividers to the length of Line 1-2 from the top view in Figure 2. Then using Point 1 as center, create a reference mark to establish Point 2' on the line, as shown. Repeat this with points 2' to 3, 3 to 4', 4' to 5, etc., until all points through 12' are referenced on this line.
Draw lines perpendicular to the line established from Point A to Point 12' at all the even numbers. Using your dividers, transfer all the heights from the elevation view shown in Figure 2 as lines 2' to 2" and 3' to 3" to the proper line.
This establishes your "diagram of triangles" as shown in Figure 3. Notice that you will see that all odd numbers are referenced only on the line, with no perpendicular line representing any height. This is because in the Figure 2 top view, the odd numbers are established on the base of the tub, so therefore have no height. The objective of developing the diagram of triangles is to establish the true length of lines (see Figure 2, top view) 1 and 3 to 2, 3 and 5 to 4, 5 and 7 to 6, 7 and 9 to 8, etc.
Now look at Figure 4. Draw a line that connects the odd numbers to the even numbers: 1 to 2", 3 to 2", 3 to 4", 5 to 4", etc. These red lines are the true-length lines needed to develop the pattern of the tub's head. The true-length lines for the foot are established in the same manner.
True-length linesDevelop the pattern for the head of the bathtub (Figure 5) by using the established true-length lines shown in red in Figure 4. Set your dividers or trammel points to the distance from Point 11 to Point 12 in Figure 4 and transfer this to Line 11-12 in Figure 5. This is the center of the head end of the bathtub; the layout on the right side is the same layout for the left side.
The distance from Point 12 to Point 10, 10 to 8, etc., and Point 11 to Point 9, 9 to 7, etc., is the length you have divided the arcs drawn from points B and C in Figure 2. It would save time in the layout to have separate dividers set for these two repetitious arcs.
Once you have drawn the line Point 12 to Point 11, make an arc from Point 12 to Point 10, using 12 as center. Set the trammel points using the distance of 11 to 10" from Figure 4. Now using Point 11 in Figure 5 as the center, draw an arc that intersects with the arc made from Point 12. This intersection becomes Point 10. Do this on the right and left side of Point 12 at the same time to not have to reset the trammel again repeatedly for the second half.
ArcsWith the dividers set for the distance from Point 11 to Point 9 in Figure 2, and using 11 as center, draw an arc near Point 9, as shown in Figure 5. Take the distance from 10" to 9 in Figure 4 and using Point 10 as center (see Figure 5), make an arc that intersects with the arc drawn from Point 11.
Repeat these steps similar through to Line 1-2. To locate Point A in Figure 5, set your dividers to the distance Point 2 to Point A in the Figure 2 top view. The arc from Point 1 to Point A is taken from the triangles diagram in Figure 4. The intersection of these two arcs becomes Point A.
Foot endCreate the foot end of the bathtub (Figure 6) in the same manner as described for the head. This bathtub pattern may be completed in as many pieces as you want.
To develop the pattern for the sides of the tub, it should be noted that the distance from Point 1 to Point A is also the distance of the side near the head of the tub. The distance from Point 21 to Point 22 is the height of the side near the tub's foot. These measurements will be used to develop the two side patterns shown in Figure 7. The length of Point 1 to Point 21 is shown in the Figure 2 top view. The bottom can be developed from the top view in Figure 1.
No allowances were made or given for any seams. The bottom of the tub can be attached by the use of a double seam. The sides can be attached using the grooved-seam method or perhaps a pocket seam would work. The top should have a wired edge for strength.