Drawing and Developing Rake Crown Profiles
A little over a year ago we published an article about Eave Returns. While the focus of that article was about creating a “Poor Man’s Return,” we continue to receive comments and emails asking about how to develop the required molding profiles for a “Classical” eave return and pediment.
In order to cover this subject thoroughly, we have enlisted the help of frequent TiC contributing authors Keith Mathewson and Jed Dixon. This three-part series will cover not only traditional and modern methods for developing the required profiles, but also a few different methods for producing and cutting the moldings. Let’s get started…
Classical pediments come in a variety of forms. One thing that does remain constant, though, is that their eaves follow the specific order of a classical entablature. As the moldings break around the corner, the cornice splits at the crown molding’s fillet to create a separate raking cornice and horizontal cornice. While the proportions of the parts may differ based on the specific order being used, the crown molding on the eave always remains in its designed position so that its fillets remain plumb.
Moldings are designed to be placed in a specific position so that they reflect light and cast shadows in a particular way. Some crafty carpenters have found a solution to rake transitions by using a single profile. However, in order to make the required rake transition with only one stock crown molding profile, the crown on the eave must be “rolled” or tipped out of position so that it mates with the crown on the rake like a normal outside corner. If the rake is steep, the eave crown can become almost horizontal.
In order to replicate this classical detail correctly, an additional custom profile is needed for the raking cornice.
Another difference between classical broken pediments—and one that is much harder to distinguish—is the design of the top return. In many broken pediments—I could cite both contemporary and historic examples—the top return is cut square, which simplifies the required molding profiles. But there are also examples of top returns that are cut plumb: the crown, the corona, and even the bed molding are returned with a plumb cut, which requires an additional molding profile, one that is far more elaborate and almost flamboyantly ornate.
|The main parlor mantelpiece in Drayton Hall was patterned from William Kent’s “The Designs of Inigo Jones,” published in 1727. Several changes were made, but ironically, this broken pediment includes a plumb cut on the returns. (photo by G.Katz)|
|Plumb cut returns are more complicated and therefore more rare. This broken pediment decorates a Palladian window in the stairwell of the Nightingale–Brown House, in Providence, RI. (photo by G.Katz)|
Nowhere could I find documentation that supported the exclusive use or ‘correctness’ of plumb-cut upper returns over square-cut upper returns. In fact, the choice seems to be one of style: on many simple homes, especially those built for and by tradesman in the late 18th century, square-cut returns were common and more fitting. Whereas, on homes built in the high-Georgian style, plumb-cut returns were occasionally used.
Keep in mind, the return is a small detail—literally, the pieces are extremely short and barely visible. However, the eave return is not a minor detail, and the pieces are easily distinguished and must follow the rules of classical design.
Step 1: Trace the eave crown molding’s profile in its designed position using a small off-cut of the molding to be used.
|Step 2: Draw a horizontal line above the traced profile to act as a storyboard of the molding’s projection.|
|Step 5: Record the information from the eave profile’s storyboard by marking the points onto a storyboard template. Then, reposition the template to the rake profile storyboard line and transfer the points.|
|Step 6: Extend perpendicular lines from each point on the rake storyboard line until they intersect with their corresponding rake guide.|
|Step 7: Use a straight edge and a flexible curve to connect all the new intersection points and plot out the shape of the required rake profile.|
This new custom rake profile is the only molding needed for most jobs. However, for more ornate broken pediments—those with a plumb-cut corona, a second custom profile must be developed for the upper return at the top.
|Step 8: Draw a horizontal line above the rake guides for the return profiles storyboard.|
|Step 9: Reposition the storyboard template to the rake storyboard line with its projection in the opposite direction and transfer the points.|
|Step 10: Extend vertical lines from each point on the return storyboard line until they intersect with their corresponding rake guides.|
|Step 11: Use a straight edge and a flexible curve to connect all the new intersection points and plot out the shape of the required return profile.|
A Computer Modeling Alternative
If you’re an avid TiC reader, you already know that we are huge fans of SketchUp. It’s a terrific program for working out designs in 3D and a tool that every carpenter should include in his/her tool belt—especially since SketchUp Make is available for FREE!
Creating 3D models of your projects can not only help you refine a design and work out construction details in advance, it can also help solve geometric problems that were once done only on the drafting board with complex drawings.
Creating an Accurate Profile in SketchUp
Having accurate molding profiles in your drawing is useful for creating a realistic representation of the final product. For basic renderings and shop drawings, their exact size and shape isn’t that important. But, if you plan to use a specific profile to develop another profile, accuracy is VERY important (garbage in-garbage out).
You can find a lot of CAD files online for molding profiles that are helpful, especially if you are using SketchUp Pro. Some progressive molding manufacturers, like WindsorONE, are also now including their profiles in the SketchUp 3D warehouse. While these downloadable files are great resources to have, you can’t always count on having the profile you need available, or that the profile you download is accurate enough. Sometimes you might need to re-create a custom profile for a specific job, too.
In the following videos, I’ll go through my method for creating an accurate copy of a given molding profile in SketchUp, and then share some advanced techniques that can be used to develop the rake and return profiles.
Once the required profiles are developed and the molding is produced, you’ll still need to know how to cut them to fit. Here are the basic cuts at a glance.
If you’re cutting ‘in position,’ the horizontal crown is cut exactly the same way as any other outside corner—nested upside-down in the saw, the base of the saw represents the ceiling or the top of the crown. Simply swing the miter to 45 degrees, so that the miter cuts through the edge of the crown.
The rake crown is a little more confusing because it must be cut right-side-up, so that the miter is cut through the face of the crown. The thing to keep your eye on is what part of your saw represents what. Also, when cutting the rake crown, the miter setting must be swung to the pitch or rake of the roof (in this example that’s 30 degrees), while the bevel is rotated to 45 degrees to create the mating miter with the eave crown.
Nipping the fillet off the bottom of the rake crown will probably require an acute angle jig—even if the rake is more than 30 degrees, you can only miter to 60 degrees on the right side of most miter saws (Note: some molding profiles may require that this cut is done carefully with hand tools, so that the cyma portion of the profile is not disturbed). But you won’t need an acute angle jig for the ridge miters—simply position the crown so the fence represents the roof or ceiling, and set the miter to the pitch angle.
While this level of detail normally isn’t within the scope or budget of most contemporary projects (no doubt the reason for the aptly-named “Poor Man’s Eave Return!”), it’s a classical detail that was once very common. Even if you never go through the process yourself, I hope you will now be able to recognize it when you see it and appreciate the work that is involved. I know I’ve walked right past this detail many times in the past, without ever realizing its complexity.