
The other day I was asked by a SketchUp user how to place slats on the back of an Adirondack Chair he was drawing. The chair is similar to Tom Begnal's chair in FWW192. The fellow had already drawn the parts of the chair and had most of it assembled but the slats were giving him a bit of trouble. Here's what he sent me and following that, what I came up with for him.

The slat components as he had placed them were close but not quite right. I copied the two back supports and the center slat away from his model so I could work on them.

I strared with the back supports and added a guideline between the midpoint of the top arc on the upper rail and the midpoint of the arc on the bottom arc on the bottom rail. This guideline is where the centerline on the back of the center slat will fall. I suppose technically it could be argued that it isn't unless the slat itself is curved to match the curve of the support. It would probably be easier to cut lands on the back supports.

For illustration, I drew a vertical plane on which to work. This is an option when you're doing this but I used it to make it easier to see what's going on during the rotation of the center slat.

I selected the center slat and then the Move tool. I grabbed the slat by the midpoint of the back bottom edge and moved that to the intersection of the guideline and the bottom arc on the lower support.

Next I hid the lower rail and orbited so I could get at midpoint of the bottom edge of the slat and see the guideline. I got the Rotate tool and rotated the slat so the back face is aligned on the guideline.

At this point the center slat is in place. the vertical face is no longer need nor are guidelines. The next step is to figure out how to place the rest of slats. We could manhandle the rest of the slat components into place but that's a lot of work. Instead we'll create a point on which to use the Rotate tool and make a radial array.

I opened each of the back support components for editing. On the upper support I selected the top arc and right clicked. I chose Point at Center from the context menu. This places a guidepoint at the center of the arc. I repeated this for the lower arc on the bottom support rail. Then I closed the components and connected the two guidepoinyts with a guideline. This line looks to be vertical but it isn't.

Thie above image shows a guideline marked "Horizontal" (although it is hard to read in this msall image) and shows a guideline placed at 90° to the nearly vertical one. This was done by orbiting into positoin so I could place the green protractor tool on the upper guidepoint and then place the new guideline perpendicular to that line. The horizontal guideline, the pink sector and the 90° tag are only for show here. You wouldn't need to draw them.

I drew a vertical face with edges on the perpendicular guidelines. The size and actual shape of this face are not important. It'll be deleted later.

Push/Pull on the face gives us the top face with is the important one. I pulled it in both directions to make it easier to see but it really doesn't need to bbe that large. The actuall Push/Pull distance is unimportant as long as you end up with the face.

With the center slat selected, I got the Rotate tool. Ctrl invokes the copy mode. I placed the Center of Rotation on the upper guidepoint so that the protractor was laying on the face I created in the last step. Notice it is black rather than the blue it would be if the rotation axis was parallel to the blue axis.
I grabbed the center slat component at the point where it intersects the arc on the upper support. Niotice that as with the Move tool, it is possible to grab the component anywhere. Since the important thing for the initial rotation is to have the edge of the slat align with the left end of the arc, I grabbed the component there.

So the first copy of the slat component is placed to align with the end of the arc at the top of the support. I hit Enter...

...followed by /3, Enter to make a total of three copies of the original slat.

The fellow who drew this named the slat components "Slat 1" through "Slat 4" working from the center outward. With the Components browser opened to In Model, I selected the component in Slat 2's position and then right clicked on the real Slat 2 in the components browser. I chose Replace Selected from the context menu.

This process was repeated for each of the other slats which left me with the next stage.

That's half way or so. To make the opposite side, I could have gone through the same process but I chose a slightly faster way.

I selected all four of the slat components and copied them over toward the right side. I used the Scale tool to mirror the slats.


Then I moved the mirrored slats back to the chair. The center slat is symmetrical so I grabbed it by the top left corner and pulled the four selected components over so that corner corresponded with the top left corner of the original center slat. Obviously this results in two instances of the center slat component in the same space but it puts the other slats in their proper places.

I got the Select tool and while holding Shift, I deselected the three slats leaving the one center slat selected. A tap on the Delete key eliminated that extra center slat component.

It's difficult to see in these small images but the slats as drawn overlapped each other. I fixed that by editing them and increasing their tapers a bit. The outer two slats only got some additional taper on the inside edges. I left the outside edges alone.

All that is left is to finish placing the seat slats (which I've covered in a
previous post but didn't do here) fix a tall cool drink and have a seat in the shade.

Dave