Layout method used to develop fittings
A recent article described how to develop a fitting using a layout method known as “parallel line development.”
It was a simple method and demonstrated how to develop the intersection of two round pipes to form a tee.
Hopefully you have a better understanding of how to project all points on the profile to establish the intersection on the elevation view because you’ll need that with this fitting here as well.
This article is going to continue with developing a pattern using a parallel line with the round pipe intersecting a cone shown in Figure 1. Not as simple as the pipe-to-pipe work, but not too complicated as many of the steps are repetitious, making it only a little more time consuming.
The focus will be the pattern for the round pipe that intersects the cone, shown in the red shaded area of Figure 1. As already mentioned, there are many repeating steps in this particular pattern. As the pipe intersects the cone, there are several different planes to establish. It’s more important to focus on establishing one of the many points in detail and have you repeat these steps as you make your way through laying out the pattern.
The first thing to do will be to draw the fitting to scale to include an elevation - both end and side views - and include a plan view of the cone and the intersecting pipe, as shown in Figure 2.
It’s important here to have an exact location of the intersection/miter. If you were to move this miter up or down the cone, the circumference of where the pipe intersects the cone will be of a different diameter.
The second step is to divide Profile 1a and Profile 1b into equal parts - also shown in Figure 2.
To determine the intersection of the two pipes as shown in Figure 1, you will need to project a series of lines from Profile 1a and Profile 1b.
You should understand that each one of the perpendicular lines projected down from points a, b, c, d, e, f and g of Profile 1b will also represent a different plane surface on the cone as if you were slicing it into pieces.
You’ll need to transfer these locations to Profile 2. Project a line from Point b to Point b’ as shown in Figure 3 profile 1b. Set your dividers on this line from the center line of the cone (1a) to the edge of the plane XX’ of the cone referenced as 1b. Transfer the distance of Line 1a-1b to profile 2-1, to 2b and make an arc or circle as shown from 1 to 2b in profile 2. This dashed circle in profile 2 establishes the plane surface you need to extend or drop a line down to from B1.
Draw a line from B1 perpendicular to Line P1-P2 and extend this line slightly past the arc drawn from 1 to 2b. Where the line drawn from B1 intersects with the arc drawn from 1 to 2b, draw a horizontal line to B3. B3 establishes point b of the intersection/miter. These steps must be repeated for all the points, a through g, of both profiles. Figure 4 illustrates the similar steps taken for a through d.
Developing the pattern
Once you have established all the points - a through g - in the side view as shown in Figure 5A, extend Line 1-2 to Point 3 to the right as shown. Along this top line, shown as g through g, mark off equally the number of spaces you divided the circumference into back in Figure 2 and reference these as shown in Figure 5B.
Mark off the true-length line perpendicular to each of those points, g through g, by setting your dividers to the similar point in drawing A and transferring this set distance to drawing B. We illustrate this by example C to C1 in Figure 5A and 5B.
Using a steel rule, you can connect each true-length line to finish this pattern.
It is typically easier and often faster to develop a shorter pattern of the miter as in Figure 6. Just because the pipe with the miter is long, that doesn’t mean you have to develop the pattern on this longer piece. It would be good use of shop scrap and lesson the risk of error to develop the pattern of only the miter and then transfer this to the piece to be used for the fitting.
The cone and developing the pattern of the opening on the cone using a different method will be discussed in a future article.
Stop by the forums at Wisconsin contractor Bud Goodman’s www.TheSheetMetalShop.com for any questions and more printable practice drawings on sheet metal layout.