Platers Drawing Tutorial

Cone-to-Dome Offset Intersection
by Alan Martin

I decided to put together a platers drawing tutorial using QCad. If you are a boilermaker and want to use a CAD package to create your developments then I recommend QCad because it is professional, quite easy to learn and also has a free version. Throughout this course I will assume that you already know how to create a simple drawing in QCad, if not then you should visit www.qcad.org to find out more.

QCad Interface

The image above shows the full interface of qcad in dark mode, it is possible to change it to light mode if you wish, but I will leave it in dark mode through-out this tutorial. Notice the toolbar on the left side for drawing lines and circles etc and the layer list on the right side. Layers are very useful because you can make each line a different colour if you wish so that is easy to distinguish projection lines from intersection lines for example. In the next slide, I will show you how I developed the line of intersection between the cone and the dome using QCad.

Lets Start

Once you have created all of the layers that you need for each line in the drawing go ahead and draw full size, the front and half top views of the cone and the dome showing the element lines for the cone which are shown in a dark grey colour. The element lines on the cone are needed for projecting the cut-out pattern of the cone if it is required. Take note that the center lines for both the cone and the dome are shown because they will be needed later.

Horizontal Lines
Next, you need to draw at least FOUR equi-distant horizontal lines across both the cone and the dome in-between their end points as shown in yellow. This is necessary in order to drop vertical lines from their respective points of intersection down to the half-plan view.

Drop Vertical Lines
Notice the magenta vertical lines that are drawn from the points of intersection on the dome onto the center of the half-plan view.

Drop Vertical Lines

Also, notice the magenta lines that are drawn from the points of intersection on the cone onto the center of the half-plan view.

Radial Arcs

Next, locate the center point of the cone on the half-plan view and scribe semi-circles using the distance of each vertical line from the center point of the cone.

Radial Arcs

Next, locate the centre point of the dome on the half-plan view and scribe semi-circles using the distance of each vertical line from the centre point of the dome.

Intersection Points

Carefully mark off each of the points where the two arcs intersect as a guide to finding the actual shape of the cone.

Shape of the Cone

Now join these points together to obtain the true shape of the cone as seen in the half-plan view.

Curve of intersection

Ok, now that we have the shape of the cone in the top view, we can easily find the curve of intersection in the front view. Start off by projecting vertical lines upwards (green lines) from each point on the shape of the cone towards the front view.

Curve of intersection

Then where the green lines intersect the yellow lines mark off each point so that you can obtain the actual shape of the curve where the cone and dome intersect each other.

Curve of intersection

And finally, by joining these points together you will have found the curve of intersection - good job!

Thanks.😀

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