Introduction: Flag Display Base: 7-Flag Adjustable Angle Bouquet

By JML Structural Engineering
About: I consider myself a jack of many trades; master of some. My mother taught me to sew and my father taught me to work on cars and to think deductively. I have a Bachelor's Degree in Architectural Engineering, sp…

In September, 2010, I volunteered to build a float for a Halloween parade. The theme of the float was American history, incorporating historical flags and a replica of the Liberty Bell. The float concept featured two seven-flag “bouquets” flanking the Liberty Bell replica. Because of time constraints, the flag bases that I made were crude: thrown together quickly just to get the job done on time.

Over the subsequent months, I used the displays for some campaign events and quickly became dissatisfied with their limitations. The flags were not firmly mounted; the display angle of the flag poles was fixed; and they included no weights to stabilize them. The new design corrects these deficiencies.

I had three goals with my flag base design.

1. Secure support of the flags to maintain them in whatever position I chose to place them.
2. Adjustable display angle of the flag group(s) with reliable simultaneous control between vertical and whatever lower limit I established.
3. Inclusion of counterweights internally and/or externally.

The new design accomplishes all of these, allowing the flag groups to be displayed at any angle between 90 degrees (vertical) and about 63 degrees. The angle is adjustable using a ¾” socket. I included internal weights and built additional external weights that can be easily carried like a briefcase and quickly attached to the rear of each base unit.

Step 1: Tools and Materials

A. Tools
1. Drill
2. Saber saw
3. Slide miter saw
4. Belt sander
5. Drill press with vice
6. ½” Forstner bit
7. 1½” hole saw
8. 4” hole saw
9. Grinder
10. Welder

B. Materials
1. Wood glue
2. Rubber cement
3. Card stock
4. Poster board or equivalent (I used the discarded backs from tablets and legal pads)
5. ½” plywood
6. ¾” plywood
7. ¼” plywood
8. 1 x 4 clear pine
9. 1½” pine (2x scraps)
10. ½” diameter wood dowel rod
11. 1¼” PVC pipe
12. ¾” PVC pipe
13. 4” PVC pipe
14. Steel bar ⅛” x ¾”
15. Steel bar 1½” x ⅛”
16. Steel angle 1½” x 1½” x ⅛”
17. ¼” x ¾” bolts with nuts
18. #8 x 1⅝ in countersinking-head deck screws
19. Size 114 screw eyes (¼” inside eye diameter, 0.080” wire diameter, 15/16” overall length)
20. ½” steel rod
21. ½” threaded rod
22. ½” nuts
23. 3/16” x ¾” role pins

Step 2: Design Concept and Nomenclature

After some development, I settled on a design that uses seven pivoting “pockets” all linked to a central disc. When this disc is raised or lowered, it changes the angle of the pockets. As the design evolved, I found it useful to add an angle indicator that is visible on the top of each base. This provides a means for the user to match the display angle set on each of the two bases.

Step 3: Upper Pivot Assembly for Flag Support Pocket

The upper pivot assembly provides a stable pivot point at the top of the 1¼” PVC pipe that forms the flag support pocket. It consists mainly of a ¾” clear pine core sandwiched between two layers of ¼” plywood. 7 assemblies are required for each completed base.

After gluing a layer of ¼” plywood to each side of a length of clear pine and allowing the glue to dry, the plywood/pine pivot assemblies are sawn apart and a 1½” diameter hole sawn in each one. The sawn holes are then sanded smooth.

The completed holes in the plywood/pine assemblies will be slightly larger than the outside diameter of the 1¼” PVC. To make them fit snuggly, I shimmed the annular space using card stock and/or cardboard strips. The typical space required two layers of cardboard. I carefully cut the two lengths such that the rings fit snuggly having neither a large gap nor overlapping ends that would lead to buckling of the ring when assembled. I test fitted the layers and then glued the layers together with the seams offset. I then glued the lap, coated the outer surface with glue, inserted the ring into the sawn and sanded hole, an inserted the PVC to hold it in place while the glue dried. I did not glue the PVC to the cardboard.

After I had several pivot assemblies completed to the point of the cardboard shimming glued in place, I sanded the faces smooth to remove any cardboard extending beyond the plane of the ¼” plywood. I then placed a group of them on a PVC pipe, clamped them together, and sanded all edge surfaces smooth to try to make them all the same profile.

Later in the construction process, I realized the need to round the inner corners of the pivot assemblies. This was to allow more material remain in the upper cover and reduce stress at the reentrant corners of the notches. I did not document this rounding process photographically. I printed a pattern on card stock, mounted the pattern on cardboard, cut it out with a knife, and traced the curve on each assembly. I then used a belt sander to round over the corners.

Step 4: Lower Guide Pin Assembly for Flag Support “Pockets”

The lower guide pins restrict the side-to-side movement of the bottom of each flag support pocket so the pocket can rotate smoothly in a single plane. Each is comprised of a ½” dowel rod mounted in a wood plug that is fastened inside the bottom of the 1¼” PVC pipe that forms the pocket. 7 assemblies are required for each completed base.

I made the guide pin assemblies from wood plugs sawn from 2-by scrap using a 1⅜” hole saw to produce plugs approximately 1¼” in diameter. I sanded the outer surface of these plugs by mounting them in my drill press via a ¼” bolt, steel washers, and a coupling nut.

To drill the ½” diameter hole in the center of the plug, I made a drill jig from 2-by scrap following most of the same steps as plywood/pine pivot assemblies. The main difference is that I omitted the ¼” plywood outer layers. I shimmed a short piece of 1¼” PVC tightly inside the hole and added a drywall screw to use as a set screw. This allowed me to place the plug inside the PVC, secure it with the drywall screw, and drill the ½” hole using a Forstner bit. Use caution in tightening the drywall screw so that it does not extend far enough into the wood plug to be hit by the Forstner bit, dulling the bit.

Step 5: Steel Lifting Links

The steel lifting links connect the bottom of each flag support pocket to the central lifting disk. Each link is comprised of two ⅛” x ¾” x 6¼” steel bars with a ¼” hole drilled at each end to allow bolting to the flag support pocket at one end an the central lifting disk at the other. 14 (7 pairs) are required for each base.

I marked the ⅛” x ¾” bar stock for cutting using pencil lines on masking tape and cut the lengths using a small angle grinder with a cutting disk. After cutting all of the segments, I compared their lengths. In spite of my best efforts to make all of the segments exactly the same, there was some variation. I located the shortest piece, marked it for drilling, and drilled the two 17/64” holes spaced 5½” on center. I used this first piece as a template for all of the others.

My drill press vice has the capacity to clamp 7 stacked segments for simultaneous drilling. I placed the drilled template on top of  6 undrilled segments and aligned the bit so I could drill through the template hole and into the others. After the first hole was complete, I inserted a ¼” bolt to align these seven segments and adjusted the vice to allow me drill the holes at the other end. I repeated this process until I had all 28 segments drilled.

To round over the ends of the links, I bolted groups of 7 segments together at both ends and clamped them in my bench vice for grinding. I then buffed the ground surfaces using my belt sander. Note that I only rounded over one corner at each end of the links, since rounding over the other corner is superfluous.

Step 6: Assembling Flag Support Pockets and Lifting Links

I used hex head sheet metal screws as the pivot axles. To install them, I drilled pilot holes in each side of each upper pivot assembly. I cut the 1¼” PVC to length and inserted the sections into the shimmed pivot assemblies. I shortened/blunted the screws by the grinding off the points. The purpose was to allow these screws to push against the cardboard shim material with out penetrating it – clamping the PVC in the holes – with the heads extending far enough to serve as the pivot points. (I considered placing short sections of steel brake line on the screws to act as bearings but I have not yet decided that this is necessary.)

I wrapped the plugs of the lower guide pins with card stock to shim them snugly inside the PVC and installed them. I marked the PVC and drilled pilot holes for the screw eyes. I did my best to start the screw eyes in the same position so that, when in place, the center of the eye would be close to the same distance from the pipe on all of the assemblies. I reamed out the eyes with a 17/64” drill bit to allow the bolts to slip through more easily.

With the screw eyes in place and reamed, I placed a lifting link segment on each side and fastened them with a ¼” bolt and a lock nut. Snug the nuts just enough so that the link can swivel freely without rattling.

Step 7: Faceted Sides and Pivot Supports

The faceted sides are made of ½” plywood, notched to permit clearance for the rotation of the pipe support pockets. The upper pivot supports are attached to the sides and provide an additional connection between abutting sides.

I started by ripping material slightly wider than the finished, beveled-edge facets and then cutting them to length. I laid out the notches with an additional 1/32” clearance on each side and deep enough to allow the upper pivot assembly to rotate without binding. I drilled out the corners, cut the notch using a saber saw, and sanded the notch edges smooth.

I made the pivot supports from 2-by scrap that I planed smooth, ripped to the rough width, and cut into substantially knot-free pieces. I glued a piece on each side of the notches in the plywood. For the typical facets, i.e., the 5 that don’t abut the rear cover, I glued all of the blocks in place, allowed them to dry, and then carefully made a 15-degree bevel cut on each edge. In an effort to get a tight, gap-free fit, I cut each one to fit the edges of the plywood base as closely as possible, since these edges were not perfectly identical.

To complete the pivot supports, I routered the ¼” grooves in which the pivot axles sit.

For the two facets that abut the back of the unit, I glued in place the pivot support associated with the beveled edge and completed the bevel cut as described above. The opposing pivot supports extend all the way down to the ¾” plywood bottom since they also serve as the mounting surface for the rear panel. I delayed sizing these extended supports until I was ready to fasten those sides to the bottom panel. These supports were then planed to the proper thickness to allow a snug, gap-free fit of the rear panel.

Step 8: Flag Support Guide Tracks

The flag support guide tracks are pairs of ½” plywood arcs with ½” spacers between them.

I printed a pattern on card stock, mounted the pattern on cardboard, and cut it out with a knife. Using the pattern, I traced the shape on a piece of ½” plywood that I had already ripped to the width of the track sections. I laid out the pieces so the curved cuts faced each other to minimize waste. Using a saber saw, I made pairs of curved cuts, followed by a straight cut on a slide miter saw, alternating until all pieces were cut. I then clamped them all together and used the end of a belt sander to shape and smooth all of the curves simultaneously to make them effectively identical.

I cut the spacers from wood that I planed down to ½” thickness but ½” plywood could also be used for this purpose. The photos only show the triangular spacer at the inner end of the track. There is also a small spacer at the outer end, which sets the outer limit of the lower guide pin when the flag support pocket is in the vertical position.

Step 9: Central Lifting Disk and Base Disk

The central lifting disc is comprised of quadrants of pine sandwiched between layers of plywood to tie them together, tightly fitted inside a ring of 4” PVC, and fastened together with the screw eyes that connect it to the lifting links.

I used quadrants of pine rather than one single piece to avoid having the screw eyes penetrate end grain. I cut the quadrants from scrap 2-by material, making sure that the edge grain was parallel to the hypotenuse of the triangles, and glued them to a piece of plywood having the center already marked with a hole drilled to match the pilot of the 4” hole saw. After clamping and allowing to dry, I drilled the pilot hole through the pine to mark the center of the remaining layer of plywood. After this layer was glued in place, I cut the disc using a 4” hole saw in the drill press.

Using a ¼” bolt, fender washers, and a coupling nut, I mounted the cut disc in the drill press and sanded the circumference smooth. As with the lower guide pin plugs, I wrapped the disc with cardboard and paper to shim it tightly inside a ring of 4” PVC. I secured the wood disc inside the PVC using a drywall screw. As with the flag support pockets, I marked the PVC and drilled pilot holes for the screw eyes; threaded in the screw eyes, starting them in the same relative position; and reamed out the eyes with a 17/64” drill bit.

I drilled (3) ½” holes in the disc: 1 for the lifting screw and 2 for the guide rods. Using a 1” Forstner bit, I drilled a recess in the bottom of the wood filler for the ½” lifting nut. This nut, which engages the threaded rod for the lifting screw, is attached via a mounting plate. From ¼” x 1½” steel stock, I cut a piece that would fit across the inside diameter of the 4” PVC. I drilled a ½” hole for the threaded rod and a 13/64” hole to be tapped for a ¼-20 thread. A ¼” machine bolt with a countersink head secures the mounting plate to the bottom of the disc assembly.

To actuate the lift angle indicator tape, I attached on the rear of the disc a tab cut from a strip of sheet metal. It is attached to the disc via two wood screws and has a hole near the far end for the sheet metal screw that secures the indicator tape to the actuating tab.

The construction of the base disc is similar to the central lifting disc, minus the screw eyes, lifting nut, and indicator tab. There was no need to assemble the pine disc from quadrants, since no screw eyes are present around the circumference.

Step 10: Lifting Mechanism Upper Bracket

The lifting mechanism upper bracket provides a bearing for the lifting screw and lateral support for the guide rods. Since it is fastened to both the top and back covers, either one of these covers can be removed individually without compromising support of the lifting mechanism. If I had used wider materials, this step would have required less welding, but I used materials that I had lying around the shop.

I extended the horizontal leg of the 1½” angle by groove-welding flat stock and grinding it smooth. Then I printed a template of the hole layout, adhered it to the bracket, and drilled the holes: (3) ½” holes for the lifting screw and guide rods and (1) ¼” hole for a screw to attach the bracket to the top cover. I also drilled (2) ¼” holes in the vertical leg to attach the bracket to the back cover. I welded ¼” hex nuts to the underside/inside surface at the screw locations.

After establishing the length of the threaded rod for the lifting screw, I determined the location of the 3 nuts. One nut at the bottom serves as the vertical support for the threaded rod. The two at the top secure the rod to the upper bracket. With the nuts located on the rod, I drilled a 3/16” hole through each one to allow installation of roll pins to lock them in place.

After assembling the threaded rod, lifting disc, and upper bracket, and secured the nuts with roll pins.

Step 11: Assembling Bottom and Sides

After cutting the simple rectangular shape of the bottom panel from ¾” plywood, I marked the layout of the oblique edges and used a slide miter saw to trim them. I ripped another piece of ¾” piece to the rough height of the triangular alignment/spacer blocks and cut them to size also with the slide miter saw. After marking the layout of the pieces on the base panel, I used the assembled flag support guide tracks to help locate the spacer blocks on the plywood bottom panel before gluing and screwing them in place.

I then glued and screw completed base disc and flag support guide tracks to the plywood bottom.

After trimming the facet panels to fit the edges of the bottom panel, I glued them in place, secured them with a ratchet strap clamp, and clamped the tops together using spring clamps. I worked with only two or three facets at a time. When I was satisfied with their alignment, I screwed them in place using deck screws into the edge of the plywood bottom to help maintain alignment while the glue dried.

Step 12: Top Cover and Painting

I forgot to photograph the process of cutting the notches in the top cover. Similar to the base panel I cut a simple rectangular shape from ½” plywood and cut the faceted edges using a slide miter saw.

I fastened the top cover to the assembled sides using deck screws and marked the notch locations using a combination square to transfer the locations from the plywood edge to the top surface. Using a printed pattern stiffened with cardboard, I traced the notches on the top, removed the top from the sides, cut the notches using a saber saw, and sanded the edges smooth using a drum sander on the drill press. I drilled the holes for all fasteners, the lifting rod nut, and the indicator viewer. I beveled the indicator viewer with a 45-degree router bit.

I then painted all of the pieces with semi-gloss black.

Step 13: Internal Counterweights

The internal counterweights consist of 2” PVC pipe with square end caps and filled with concrete. They include a threaded insert inside the bottom cap that allows them to be fastened to the bottom panel of the display base.

To make the threaded inserts, I bevel-groove-welded coupling nuts to fender washers. Using a bench grinder, I beveled all six sides at one end of the coupling nuts; bolted the nuts and washers to a perforated steel angle for support; and welded the perimeters. It is very important to unbolt the nut-washer assemblies immediately after the welding is complete. If the nuts are allowed cool, the resulting shrinkage may cause them to grip the bolts tightly enough to make removal extremely difficult.

I drilled ¼” holes in PVC bottom caps. I then temporarily bolted the cooled nut-washer assemblies to the caps, drilled small holes for the mounting screws, and reamed the holes to countersink the machine screw heads that fastens the threaded insert flanges to the PVC caps. After cementing PVC caps with threaded inserts onto the pipes, I plugged the threaded inserts with the ¼” mounting bolts, and supported the inverted pipes on wood blocking.

I estimated the amount of concrete fill needed by calculating the volume of the pipe to be filled. Based on a concrete density of 145 pounds per cubic foot, I calculated the weight of this volume. Ignoring the weight of the mixing water, I measured the dry materials needed, placing them in a plastic bucket for mixing. As an engineer, I must emphasize the importance of minimizing how much water is used. It is very tempting to add water in order to make mixing easier, but this weakens the concrete. Use as little water as possible in order to produce a stiff cement paste within the aggregate (stone) matrix.

Using a small trowel or similar implement, fill the pipes with concrete, allow them to cure until firm, and then remove the ¼” bolt that is plugging threaded insert. If you wait too long to remove these bolts, you risk their becoming bonded to the curing concrete and difficult, if not impossible, to remove.

Drill a small vent hole in each of the PVC top caps before cementing them in place, to allow the air trapped inside the caps to escape. Without this vent hole, the caps will be virtually impossible to press on very far.

Step 14: Display Angle Indicator

I did not take step-by-step photos of the construction of the indicator assembly so I have provided 3-D renderings to depict its construction.

The display angle indicator consists of a roller-supported paper tape loop printed with a scale graduated in 1-degree increments. The loop is connected to a tab that extends from, and is actuated by, the central lifting disc. The paper tape is kept taut via a spring that pushes against the sliding support of the bottom roller. There are two rollers at the top of the assembly so this area of the graduated tape is displayed flat. The rollers are nylon bushings with bearings made from short segments of steel brake line. Fender washers keep the tape in place, and drywall screws fasten all of these components to the wooden support structure.

The most challenging aspect of this part of the project is generating the scale to be printed on the tape. The nature of the lifting device results in a non-linear relationship between the vertical movement of the central lifting disc and the angle of the flag support pockets. In order to establish the mathematical relationship, I diagrammed the geometry; labeled the constants and variables; worked out the trigonometric relationships; and developed the associated equations. I entered these equations in a Microsoft® Excel spreadsheet that I created to generate the lift distance required to rotate the flag support pockets to each angle as measured from horizontal. This distance ranges from 0.0000” (no lift) for 90 degrees (vertical) to 6.4531” for 50 degrees.

In AutoCAD, I offset the distances generated in the spreadsheet to create the non-linear scale. The image I posted of the graduated strip shows how some of those distances relate to the scale. Since the loop is longer than a single letter-size sheet, a second strip of paper has to be spliced to the graduated strip.

Step 15: Final Assembly

Using a wooden drill jig to locate mounting holes for internal counterweights, I drilled the holes in the bottom panel and through the spacer blocks. I then reamed the holes to countersink the machine bolt heads and installed the internal counterweights.

Next, I inserted the steel guide rods into base disc; installed the assembled lifting mechanism; installed all flag supports, connecting the inner ends of the lifting linkages to the central lifting disc; and bolted in the counterweights.

Step 16: External Counterweight

The external counterweights were not part of the original design concept, which is part of the reason I forgot to photograph the process of making them. I decided to add these components after the first field test of the base units.

The weights within the external counterweight units consist of concrete-filled 2” PVC pipe with square end caps. Each external counterweight assembly contains 3 weights, which are held in place within wooden cradles. The units connect to the rear of the bases via vertical rails and a half dovetail. The half dovetail ledge pulls the counterweight tight to the base to align locking pins.

I made the cradles by cutting each half to the correct cross section; clamping them together; marking the centers of the half-circle notches at the joint; cutting the notches with a hole saw; and sanding the holes with a drum sander in a drill press. Similar to the flag support pocket upper pivot assemblies, I used layers of card stock and cardboard to create shims to allow the assembled cradles to firmly grip the concrete-filled pipes. I wrapped scrap pipe sections with shim material and tested the fit in the sawn holes. After the shims were dry, I split them into halves and glued them into the cradle with which they were test-fit. I put the scrap pipe sections in place, assembled the two halves of the cradle, and clamped them together while the glue dried. I then cut the assembled cradles to the correct length.

I cut the enclosure panels to size, glued the bottom panel to the front panel of each counterweight assembly; glued and screwed one half of the cradle pairs to this bottom-front assembly; and glued and screwed installed the handle backer block between the cradles. I cut a rectangular hole with rounded corners in each top, sanded these holes smooth, and rounded over the exposed edges. These holes serve as recesses for the carrying handles. I then glued and screwed the top in place.

I glued and screwed the remaining pairs of weight support cradles to the rear cover. The rear cover assembly fastens in place using 3½” deck screws, firmly clamping the 3 pipe weights in place.

I incorporated two options for locking the exterior counterweights to the rear of the flag base units – ¼” bolts and ¼” cotterless detent pins – because I didn’t know which one I would prefer. The locking fasteners pass through holes in locking rails on the rear covers of the flag bases and into holes in locking rails on the front covers of the external counterweights. These holes are reinforced with steel washer plates made from ⅛”-thick steel flat stock that is fastened to the wood structure using deck screws. To hold the ¼” bolts in place when not in use, each inner washer plate of the flag base locking rails include a nut welded in place to serve as a threaded insert. This allows the bolts to be threaded out to the “unlocked” position and stored there until needed.

The locking rails and half dovetails are glued and screwed to the rear and front panels of the flag bases and exterior counterweights, respectively.