Design. Click. Build.

Create Back Slats

Sat, 08 Nov 2008 23:43:51 GMT

Shaker and Ladder Back Chairs are frequently fitted with curved or bent back slats. A reader asked how to model these compound-shaped components in SketchUp. Below I've shown my method in six steps.

Assume this is the Back Slat design we want to create in SketchUp:

Step 1: Create the flat rectangular plane for laying out the arc shape shown in the above top view. When using the Arc Tool, I prepare a flat plane for layout. I do not try to work the Arc Tool in empty space (always on a surface). My plane is on the Red/Green Axes, so the view below is from the top.

Step 2: Use Push/Pull Tool to pull up the full height of the back slat

Step 3: Now we need to cut a scroll shape in the top edge of the back slat. Create another flat plane in front of the Back Slat (as if a projection of the curved surface). My plane is on the Red/Blue axes. Then create the arc curves on the surface of the plane. I typically draw a straight sloped line to help with the layout of the connected reverse arcs, using the endpoints and midpoint of the sloped line.

Step 4: Push/Pull the arc shape through the back slat. Depress the CTRL Key when using the Push/Pull Tool in this case.

Step 5: Select all, then execute "Intersect Selected", and clean up waste

Step 6: Copy the left half, moving over to the right. Then "Flip along Red Axis", and connect the two halves of the back slat.

In general, when facing components with compound shapes, the "Intersect" feature will probably be required.

Tim
http://killenwood.com

Windsor Stool Exercise - Part 2

Tue, 14 Oct 2008 05:32:12 GMT

Note: Since the inception of this Design. Click. Build Blog in April 2007, I have provided weekly entries on SketchUp - I don't believe I've missed a week. So now I will be taking a break - don't expect to hear from me for the next four weeks. See you in November.

Last week I introduced the first design part for the short Windsor Stool. That exercise mostly covered making the seat. In this second part I show the design steps for the stool undercarriage including legs and stretchers.

Step 1: Create the faces for the turned components, Legs and Stretchers. These are half diameter faces ready for a Follow me to create the turnings.

Step 2: Make a circle path and use Follow me to create the turnings.

Step 3: Now we need to fasten the Legs to the Seat. The Centerline model that we created last week is very useful in positioning the Legs and Stretchers.

Step 4: To rotate the Leg into position, I connect one end of the leg as a fulcrum, make a triangular plane between the Leg and the centerline, then use the Rotate Tool to connect the Leg onto the Centerline.

Step 5: You can use Rotate Copy to position the alternate leg.

Step 6: Finish up copying the remaining legs into position using the Move/Copy Tool , then Flip along Green axis. Once Legs are in position, I do an "Intersect" to create the sockets in the Seat.

Step 7: Accurately place the Stretchers, again using the Centerline model as the reference locations.

Step 8: We need to create the "Sight Lines" on the bottom face of the Seat. These sight lines are very useful for accurate drilling of the leg sockets. With Sight Lines, there is no double angle issue - you set the sliding bevel in line with the sight line and drill to this angle only.

Step 9: Create the full-size Seat Template. Use Top View, parallel projection, and X-ray so you can see both the bottom and top face in the template. You need only to print 1/2 the template, since it can be flipped to mark out the other half of the seat.

Step 10: We also need to know what angles to drill - the seat and leg sockets. I use the Centerline Model to determine these drill angles.

Here is the finished stool along with a taller Windsor Stool. I used fresh cut ash for the turned parts and soaked the tenons in a hot bed of sand to dry and shrink. I used no glue assuming that the joints will tighten as the wood dries. I wedged the Leg tenons into the Seat. Pine was used for the Seat.

Back in November......

Tim
http://killenwood.com

Windsor Stool Exercise - Part 1 (Oct10)

Wed, 08 Oct 2008 04:27:10 GMT

Here is a good SketchUp workout and exercise, which can also lead to a useful shop project. This is a Windsor Stool which would be typical of the early 19th C. It involves an oval seat with bamboo-like turnings. Its overall dimensions are 15 1/2 W x 11 1/2 D x 14 3/8 H.

Even though this seems a small and simple project, the SketchUp design (and indeed the shop construction) is not trivial. Therefore, I will show the complete design in two stages. The Seat is covered in this entry - next week I will cover the design of the turnings and stretchers.

Here is the model of the assembled and final design.

And here is the orthographic dimensioned drawing. I'll attach a pdf version of this drawing for your printing as reference while building the SketchUp model.

Step 1: Begin building the Seat. I start with a circle which is stretched into an oval shape using the Scale Tool.

Note: since publishing this procedure yesterday, I've talked with Dave Richards who provided an easier way of building and sculpturing the seat. I will show his procedure following my original 11 steps.

Step 2: Create a chamfer on lower edge of Seat. This is a drawknife operation for me in the shop, but in SketchUp we need to create the chamfer shape for use with Follow me.

Step 3: Execute Follow me to cut the chamfer

Step 4: Locate socket centers for the Leg tenons. I place a rectangle on the seat bottom surface the corners of which indicate the socket centers.

Step 5: Start the Centerline model of the undercarriage which will provide angles and locations of Legs and Stretchers.

Step 6: Use Push/Pull and Intersect to find the centerline of the Legs

Step 7: Make a Group out of the Centerline model. We will use this later in finding drill angles and locating the Legs and Stretchers.

Step 8: Now we need to "dish-out" the top surface of the Seat. I use a travisher in the shop, but here we need to make a SketchUp "inshave". In the following few steps I show how to make this SketchUp tool, and apply it to the Seat to create the sculpted shape. In this step, I create a hemisphere which is re-shaped into the "tool".

Step 9: With the Scale Tool, stretch out the hemisphere to make an egg shape.

Step 10: Also using the Scale Tool, squash the deep half-egg into a thin pancake 7/8" deep.

Step 11: Drop the pancake shape into the top of the Seat. Then explode any components and groups and clean-up the waste.

Revision 10/09/08 - as noted above, Dave Richards offered a much easier way of making the sculptured seat. Following are his two steps which are very accurate and efficient.

Step 1: Create a shape for the dished-out seat and a circle path for Follow me.

Step 2: Place some guidelines and use the Scale Tool to create the oval shape.

Next week I will finish the design with the building of the undercarriage Leg and Stretcher turnings.

Tim
http://killenwood.com

Scale, Re-size, Re-use Components

Sat, 04 Oct 2008 04:15:52 GMT

During these few weeks of Windsor chair activity, I've grown to appreciate the Scale Tool. In the past, I've occasionally pulled out this tool (particularly when re-sizing imported photos of furniture). But in Windsors, it becomes almost critical. The Scale Tool is somewhat daunting at first with its multitude of grips (the little green cubes, I think there are 27). And it is possible to do unusual stretching and reshaping depending on which little cubes you grab. But I'm using it in a simple way and mostly just for changing the length of turned components.

So far I've developed four SketchUp models of Windsors shown here together. All but the largest has been used in one of my previous recent blog entries. There are many turned components in these examples which are very much alike. To save modeling time, it is very advantageous to re-use as many turnings as possible, so I'm always keen to find ways to re-shape and re-size something I've already built in SketchUp.

Here is the first example of a component re-used - Stretchers. Three of the chairs above use identical shape and diameters for the stretcher. So once I made the first of these turnings, I quickly resized to fit all the other chairs.
In this case, there are two ways of stretching the length; one is to use the Move/Copy Tool. This requires an operation on each end of the stretcher by drawing a selection box around the end tenon (be sure to include the inside shoulder of the tenon in the selection). Then using the Move Tool to stretch out each end an equivalent length.

The second way to change the length is to use the Scale Tool. Here are the steps to this process:
1. Select the component and select "Edit Component"
2. With the Select Tool, draw a box to select all component faces and edges.
3. Click on the Scale Tool. You will immediately see that the component is surrounded by SketchUp's Scale Box. You'll see all the small green cubes which are the grips.
4. On one end of the Stretcher component, move the cursor over the center-most green grip which will now change to red. Then hold down the mouse button while dragging the mouse in the direction of the length change.
5. Most of the time, I want the stretching to happen about the mid point of the component. So I hold down the Ctrl Key before I begin dragging the grip.

The Arm Posts are also identically shaped in two of the Philadelphia chairs, so I again used the Scale Tool to change the length only.

In most of these chairs, the Front and Back Legs are different in length. I use the Scale Tool to build the second from the first leg.

The same is true for the Bulbous legs which are identical except for length on two of the chairs. Also the Front and Rear Legs are different in length. The Scale Tool is particularly useful for these complex turnings.

The Medial Stretchers are identically shaped on three of the chairs. In this case you can use the Move/Copy Tool to change length. Therefore the length changes would be made on the ends only, not affecting the center bulb and its surrounding decoration.

I also re-used the spindle components which are very similarly sized on these chairs except for length.

Tim
http://killenwood.com

Flatten a Curved Component

Sat, 27 Sep 2008 05:13:15 GMT

One major complexity of Fan Back and Comb Back Windsor chairs is the bent Top Rail. I described how to make this component in an earlier blog entry on September 6. But that is not the "end of the story" for the Top Rail. Another issue remains - how to make the template for this rail for creating the blank piece of lumber which will be steamed and bent. I puzzled over the method to create this template and discussed with my blog partner Dave Richards. He alerted me to a plug-in that solved this problem. In the following, I will describe how I used this plug-in.

Here is the Top Rail as it is installed in the Fan Back Windsor.

Step 1: I work with a half-rail to simplify the work. My first step is to create a separate component of the curved front face only.

Step 2: Download the Unfold Plug-in from http://sketchuptips.blogspot.com/2007/08/plugin-unfoldrb.html
I tried using this plug-in several different ways. One was to simply select the entire face after selecting the Plug-in. It worked but there was cleanup required. So I tried other alternatives. The following steps worked best for me.
1. Turn on Hidden Geometry under the View Tab
2. Click on the Plug-in, then click on each of the individual faces in sequence from left-to-right.
3. Rotate the resulting flattened face to line up with the Red axis

With this process you can see the bent shape incrementally flatten out.

Step 3: Make the full-size template by setting the camera to Parallel Projection and Front View. I added the carved volute outline to the template.

Here's the resulting finished Top Rail.

Tim
http://killenwood.com