Redesigning to Grid Columns

If you can’t go out, go up

The spacing between LEDs on the strand are really the limiting dimension in this project. We needed to go wider on the grid to we could hide the frame elements. Since they are 0.75” wide, you need at least that or double if the grid sections are framed stand alone and set side by side. But, since the LEDs can only be 3” apart it can’t be done. The idea of framing around the edges of the grid is out.

Looking at the blueprints where the pixel wall is to be installed, the width is used up accommodating 48 pixels. The height is not. At 25 pixels tall, we have roughly 21 inches of clearance. So we need a way to support the grid elements so they can keep their minimal spacing and create a seamless LED pattern. Starting with flipping the ribs from horizontal to vertical was the first step.

Sketch with Paper 53

Once you have two vertical planes capped by a footer box to hold electronics and a header box to provide a rigid frame it all comes together. The front plane is the thin ribs that hold the bottles in place. The back plane is a more solid sheet of plywood with holes to place the bottle necks but mainly forms the backbone of the c-shape frame. This setup also means we can pre-assemble and pre-wire each grid section and limit the amount of work in the field.

Straighten up those lines up

Now that a direction has been found, it is time to convert rough sketches to machinable drawings. The grid spacing is the most important so we started there. The bottles are placed 3 inches on center which drives all other dimensions. For a panel to hold 400 pixels, we need 8 columns of 25 pixels. For stability we added some solid sections at the top and bottom of each rib. To seamlessly match panels together, two of the ribs, headers need flat edges on one side that are half the spacing between a pixel. Once laying them out on our material, we added extra parts to reduce waste and to have extra parts around in case of breakage.

Aspire Drawing of Ribs and Headers

The back plane needs planned out accurately so the neck of the bottle will fit and be level. The boxes that form the footer and header are broken down into their six box-jointed panels. Box joints will hold the parts together for easier test fitting. For actual assembly, screws or liquid nails will make it more permanent. The panels were created from scratch in Aspire. We start with the outer dimensions of all sides. A copy of each panel, an interior panel, is then reduced by the thickness of the material on each side. So an outer panel of 9in x 12in has a centered inner panel of 7.5in x 10.5in Each tab/slot is a fixed size of 3in x 0.75in and centered on the side of the outer panel. Tabs are welded to inner panel. Slots are subtracted from the outer panel. Then each panels need to be checked for proper tab/slot alignment. For the footer, we started design with the top panel so we could make sure that is was supported more by the top edges of panels below it than by just tabs.

Aspire Drawing of Back Plane, Header and Footer boxes

You want me to cut what?

Aspire is a CAM System - Computer Aided Machining. With our drawings, we then create toolpaths so the ShopBot knows what tool is cutting where. Our first step is adding fillets to our design. Since the bit we cut with has a diameter, we can’t cut perfect 90-degree interior angles. The fix is to cut “dog bones”, which are small pockets in every interior corner - a signature of machine cutting. Next we add hold down markings. Since we don’t have a vacuum system, we attach material to the work surface with polymer nails. Once the material is loaded, the ShopBot moves around drilling small holes so we know where to nail it down.

We lay out our cutting files in steps. Sheet 1 is marked for hold down, then slots are cut, and finally the parts are cut out. Each step is a separate cutting file which allows natural break points in the machining. You can pause a file and re-start it from a specific line number, but we did not have a good experience the only time we tried it.

Preview of Sheet 1: Back Plane and Boxes

Preview of Sheet 2: Ribs

Next up: cutting the parts.