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Author : Jeff Branch

Creating a Complex Crest Rail in Sketchup

The crest rail in this model was tricky to create

I have been a woodworker for more than 30 years. One of the fun aspects of this hobby is furniture design. In my early days of woodworking I used graph paper and pencil to draw furniture projects to scale. Now I design almost exclusively in SketchUp. For me, SketchUp gives me the ability to design a project to a very high level. This means I can work out all the needed joinery during design eliminating virtually all guess work during construction.

The design phase is where I am with my current project, a window seat bookcase for my daughter. This bookcase will reside in front of two windows and will serve first as storage space for books and second as a piece of furniture to sit upon.

With this project, I am interested in doing some new things from a design perspective and curves are things which I usually stay away from. As you will see later, the previous design had a seat back with a call this a crest rail which was flat along its upper edge. I had received a suggestion that the design would look less hard with a curved crest rail.

This design change was a challenge for me to create in SketchUp. It meant that I would have to take a rectangular shape and form one flat face along with three curved ones. I am no stranger to using the intersect command in SketchUp, but after repeated attempts, the resulting crest rail containted poorly formed geometry. I got in touch with Dave Richards who writes about SketchUp at Fine and he helped re-orient my thinking to a more simple approach. What you see below is the process he suggested along with the additional steps I took to break the crest rail into three separate components.

The bookcase with the old crest rail removed

Next I create the beginning of the new crest rail: one long, rectangle

Next, I use layout lines to create the upper and lower arcs

Note above, the arcs highlighted in blue. I went ahead and added the mahogany wood texture. The crest rail is not yet a component.

Using the push/pull tool, I remove the area outside the arcs

I make the crest rail a component at this point.

Grabbing the front curve of the legs

Note the curved blue line in the image above. I copy this curved line and use it in the step below.

I hide the leg and crest rail, paste in place the curve, offset the curve 1 inch and using push/pull, extrude the shape shown

I erase the unwanted geometry leaving a “cutter”

With the “cutter” in the same location, I unhide the crest rail, hide the rest of the model and prepare to cut away the unwanted part of the rail

There is a lot going on here. I explode the crest rail – it is no longer a component. This enables me to combine the shapes of the crest rail along with the new curved plane which is used to cut the crest rail into two parts; executed using the intersect command. Then, the unwanted geometry is deleted creating a curved vertical face on the rail.

The crest rail in its final shape, but it is still one long rail, not three individual pieces

Next, I need to intersect the legs with the completed crest rail so I can get three individual parts. To do this, I click once on the crest rail and from the Edit menu, I click Intersect Faces and then click With Model. This imprints the leg locations on the crest rail. I then hide the legs which gives me a better view.

With the legs hidden, you can see their imprint on the rail

In the image above I am beginning the process of deleting everything I don’t want. I want the left side crest rail and the middle.

Here you see the left and middle crest rails converted into components

The completed crest rail; three separate components

The final step was to make a copy of the left side crest rail, flip it and positioned it on the right side. I then added a wood texture.

If that was not enough of a brain workout, I next had to do a similar, but not as complex process of trimming the legs to match the curve of the crest rail. After this was completed, I have a finished design to show my daughter.

The updated window seat bookcase design

Note the flat crest rail in the before illustration and the subtle curve in the after. I think this new design provides a more polished look. Not only did this new design test my SketchUp skills, I think the design will further test me as a woodworker.

Just as in woodworking, with the SketchUp user can often go about a modelling task in a variety of ways. How might you do this differently. Let me know in the comments below.

Jeff Branch is a woodworker, furniture designer and SketchUp user living in Pelham, Alabama, USA. You can find him online at:

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