Chiefwoodworker's Blog

In this installment we will complete the cabriole legs we started in Part 5A. As an example of tables that use the cabriole leg I made a quick and dirty modification to the Office Table. It uses the top we drew in Part 3 of this tutorial series. See the picture at right. The knee in this example extends entirely between the legs. Often it is just a brace that finishes the look of the leg. I am not proposing this design as an example of period furniture; as I said it is a mock up to show what cabriole legs might look like in a finished piece.

You will need to download Tall Cabriole Leg Tutorial Part B, or if you prefer, start with your own model completed in Part A. Both should look like the picture at left.

The basic problem we have to solve today is to transition the square termination of the Upper Leg to the round termination of the Pad; sort of like fitting a square peg into a round hole. There are simple techniques for doing this that look quite nice when viewed from above (looking down at an angle at the leg). But those techniques don’t look good when viewed from the bottom of the Pad looking up. With these simple techniques the foot appears square at the bottom. You can also go to the other extreme and shape each rectangle or triangle, one by one, until you have meticulously carved and shaped the leg. The latter technique is very time consuming and adds little to the quality of the drawing. We are going to take a middle-of-the-road approach, which is relative quick and attractive.

You will soon see why I split this tutorial in two. It is important that you look at, and study, each of the pictures in this part, paying particular attention to rectangles, triangles and lines I have included or erased. As you draw this leg it is easy to get to a place that is overwhelming to repair; when that happens frustration will destroy the learning process. Getting through this tutorial with a successfully completed and attractive leg will prove to you just how doable it is. Later you can make lots of mistakes with the knowledge that the task can indeed be accomplished. So pay careful attention to each drawing.

First we need to position the Pad under the Upper Leg. You will notice from the picture above right that the Pad’s upper defining circle is tangent to the construction line which passes through the Upper Legs right edge. The complementary edge to the right edge is the front edge in this picture. To move the Pad into place we need to move it along the Green axis 1 1/4″ as shown. The remaining two edges are the heel of the slipper. When the Pad is positioned correctly the Pad will extend beyond the edges of the Upper Leg. See picture at left.

Next we need to create the mask that will be used to shape approximately three quarters of the slipper, all but the heel. Select Front and ISO views. Start by drawing a line as shown at right. Notice one end of the line starts at the first vertex of the Pad’s upper defining circle that is clear of the Upper Leg when approaching from the slipper front. It ends to the complementary position on the other side. With X-Ray tool selected you can see its position relative to the center line. This line is temporary and is used only to mark two vertices’.

Turn off X-Ray tool and un-check Upper Leg layer Visible box. There are two construction lines that form part of the mask. In the previous step we placed a temporary line which marked two vertices’. Actually, we are interested in the circle segments just to the right of this line. We need to draw construction lines that coincide with and extend them in each direction to infinity. Use the Protractor tool as shown in the picture at left. These lines are critical, so zoom in to get them right.

You might wonder why these two particular circle segments are used to form these construction lines. The answer is by trial-and-error, but I was looking for a specific result. You will see when we complete this mask, that it rounds the sides and toe as we want, it doesn’t misshape the leg much and it clears the leg at a reasonable point as it extends upward. This will be obvious soon.

Now we need to reconstruct the upper most defining circle of the Pad. Again this needs to be exact, so zoom in close to find the defining points. Using the Circle tool locate the Midpoint of the Diameter line on the top of the Pad and click. Then move to a vertex of the Pad circle and click. This should place a circle and a face exactly on top of the top defining circle of the Pad. Your picture should look as that at right. The 45 degree construction line passing through the intersection of the outer construction lines is used in the next step. Inspect closely to be sure this circle was drawn correctly. Un-check the Pad layer Visible box.

We next add a bounding square to complete the layout of the mask. Add a 45 degree construction line that passes through the intersection of the outer construction lines. It should also pass exactly through a circle vertex; check that it does. This 45 degree line is used with the Rectangle tool to place a bounding square that clears the inner tear drop shape by a reasonable amount (at least an inch for comfort). Delete the unwanted lines and faces. Your picture should look like that at left. You can now delete the construction lines.

With the Push/Pull tool extend the mask downward about an inch. Now, again with the Push/Pull tool extend the top side up another two inches. The resulting mask should be at least three inches tall, extending below the Upper Leg by an inch and extending up the leg about two inches. Check the Upper Leg Visible box. Choose Front and ISO views. You picture should look like that at right.

With the Select tool draw a selection box encompassing the mask, right click and Make Group. Select the Upper Leg, right click and Edit Component. Triple click any surface on the Upper Leg to select all primitives and choose Edit/Intersect/Intersect with Model. Wait patiently for the blue outlines to disappear; there are a lot of calculations your computer needs to make. Click outside the bounding box. Now delete the mask group. Select the Upper Leg and Explode. While the primitives are still selected use the Layers drop down box to place all primitives on Layer0. Zoom in on the toe. Your picture should look as that on the left.

We will start clean-up at the toe, then the sides and then we need to shape the heel. The toe is relatively clean and easy, but because of the added lines on the left of the toe, that side will be trickier. I will clean up my toe first and show you the result so you can refer to it for yours.

My completed toe is at right. Notice the symmetry in the repair after erasing. It required five vertical lines and two sets of horizontal lines. This is because the mask was extended with the Push/Pull tool vertically and the circle vertices’ formed the vertical lines. The horizontal lines are to connect the leg shape that was created by our outlines being extended by the Push/Pull tool in the horizontal direction. Thinking about what forms these lines can often help to know how to repair thing. I leave hiding and softening lines until the end.

Now we will work on the sides of the slipper. See the picture at left for the starting point. It is easy to erase wanted lines so make liberal use of the zoom tool. Also, when you erase a line, and hence a face, you expose a line or face on the other side. To avoid punching through use the Rotate tool often to position your view in such a way that the other side is not exposed. We will complete this side and use it as a template for attacking the other side. They should be very similar, but not necessarily the same. SketchUp after all is not a CAD tool as they say. I’ll go first and show you my results.

My results for the right side of the slipper are at right. The trick is to draw all vertical lines first. There should be a vertical line starting at each vertex of the defining circle of the base, and it will extend all the way to the defining curve of the slipper. Then add horizontal lines to complete the faces. When you are done, experiment by erasing one line at a time. If erasing a line does not eliminate a face then it is not needed. If you lose a face use the Undo tool to add it back and go on to the next line. I haven’t done this for you here, but try it on your own and see what happens. Often you have to add a bunch of lines to coax a face and once the face appears you can go back and erase many of them. You will be very surprised; every line you save works to keep the file size smaller and the display time faster.

All we have left to sculpt is the heel. Take a look at the picture at left. On the part of the heel closest to the toe we need to add material. On the back of the heel we need to remove material. In order to make the transition from the Upper Leg, defined by two line segments, to the Pad, defined by a number of segments in an arc, we will start up a ways on the leg. This next bit of sculpting could be done quite simply with the use of a Ruby script that allows Push/Pull along a vector instead of just a normal. But so far in these tutorials we have opted to use only tools that come with SketchUp. We will continue in that vein and work a little harder, if not smarter.

Look at the picture at right. We are looking directly at the back of the heel. I selected, arbitrarily, a point above where the curve in the slipper side ends to begin sculpting the heel. I have erased all the unwanted lines up to that point. I then counted the number of unused vertices’ on the upper defining circle of the Pad; there are 9. I connected the middle one to the back edge of the heel leaving 4 unused vertices’ on each side. Next I divided the bottom line on each side of the Upper Leg into 4 segments to give me mating connect points between the Pad and the Upper Leg. I make all those connections for a total of 9 lines. Remember that the Pad is a component, and although I am connecting to its vertices’, those circle segments will have to be added because they aren’t shared by the component.

Now it is just a matter of adding the circle segments and completing the triangles. See the picture at left. Note that I also filled in the area near the curvy line that ended the slipper side. On each side I added one vertical line from the circle segment up (followed the Blue axis from the vertex to the top). Then I added lines from that circle vertices’ to all the end points in the curve until the faces filled. Next I began erasing lines one at a time to check for which lines could be eliminated and arrived at a minimum set. Note I was able to get rid of the curvy line.

Now I make the Pad layer visible by checking its Visible box, choose the Pad and Explode. Triple clicking on the Upper Leg selects all but the lowest part of the Pad, so I use Ctrl key plus triple click to add that section to the selection (I still don’t know what is causing this separation and haven’t debugged it). Again I use the Layers drop down box to place all primitives on Layer0. Finally I Make Component and call it Cabriole Leg and place it on a new layer called Cabriole Leg. At this point I can get rid of all layers except Cabriole Leg, Grid, Template and Z-leg. The others have no meaning anymore. All editing now will be done in Edit Component mode. After hiding/softening all lines and edges that we don’t want to show with the Eraser tool and Ctrl key, we have the picture at right.

Just for fun I textured this leg with the cherry texture you have in the model you started with. Go to Window/Materials and Select Tab. Click the little house for In Model materials. In Component Edit mode use the Paint Bucket tool to paint the texture on all surfaces. The picture at left is the result.

My final drawing of these legs can be downloaded by clicking on Tall Cabriole Leg Tutorial Completed Drawing.skp. This ends Part 5 (A & B). For the sixth and final part I have a “carving” planned. I think you will like it. Stay tuned to Chiefwoodworker’s Blog.

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