MARS Recumbent bicycle projects

Zotefoam Manual - Gluing
A project by John Tetz - April 2005

Introduction   Mold   Layout   Form   Cut   Glue   Internal Braces   Install the Trike   Tail   Door   Canopy   Turtledeck

I recommend using DAP Weldwood contact cement, one of the few types of cement that sticks to Zotefoam. Buy two or three 3 fl. oz. (88.7 ml) bottles with the application brush inside. Also buy a larger can of it, and when the cement is used up, refill from the can - much cheaper this way. Caution: be aware of fine spider web-like filaments coming off the brush as you take the brush out of the bottle and when applying the glue to the Zotefoam. Generally there is a static charge, which causes the filaments to zap randomly onto the Zotefoam surface. You can wipe the filaments off immediately, but once dried, they will be annoyingly visible.

Start with the yellow top: prepare it by sanding the edges that will be cemented, using 60 grit paper. Try to stay away from the outside surface edge, because the sanding raises tiny tufts that will be noticeable even after gluing. If you do raise tufts, run the hot air gun fairly quickly over the surface to melt the tufts. Experiment on scrap pieces to determine how much sanding is needed and how to remove the tufts by heating.

Lay the top on the mold and position it carefully with the registration marks made after trimming. Use masking tape to attach it to the mold to prevent moving. Then glue the nose area to the fiberglass nose piece in three steps, not all at once. Put down a layer of contact cement across the rear of the fiberglass mold and a corresponding area on the inside of the top. Let it dry at least 7 minutes or more. When dry to the touch, apply another layer of cement, wait about 5 minutes, and carefully bring the Zotefoam into contact with the fiberglass without losing the registration marks. Then repeat the process until the entire top is glued to the fiberglass. This photo shows the yellow top glued to the nose:

The end of the top stops at the horizontal division right at the tip of the nose. This is because the pipe holding the mold does not allow a continuous nose piece. Cut enough of the top away so it can be formed around the pipe. Later this opening can be cleaned up and used for either a headlight or cooling vent.

While you wait for the glue to dry between the top and the fiberglass, prepare a side by sanding the edges. Then rotate the mold so the side can be placed on it without slipping off. Adjust the side to the registration marks that were used during the heat forming and trimming process, then tape in several places.

Because the most critical area in terms of fit tolerance is along the fiberglass nose, gluing should not start here, but rather after the fiberglass nose. First, make sure the side does indeed fit well to the top all along the fiberglass nose area before gluing further back. Glue by sliding the side away from the top far enough to brush on the contact cement. Glue about 8-12”, using two layers of contact cement. When ready, let the two surfaces come in contact together lightly. Do this in very small, carefully controlled steps, about 0.25” increments, for a total of several inches. One way to prevent accidental contact is to use a piece of paper between the two surfaces.

Make sure the levels of the two outside surfaces are visually even before actual contact. Any differences in height will be noticeable. If a section looks good, then push the edges together more firmly. After the first 8-12” are in good contact, push hard with the thumbs down and in towards each other across the division line, hopefully making firm contact all the way to the inside surface which is up against the mold. This will leave thumb indentations on the outside surface. After the glue has thoroughly dried for several hours, go over the indentations with the hot air gun to make the indentations disappear.

Continue this process toward the tail for 12-24”. This will help stabilize the side to the top. Then glue the nose area. Because the Zotefoam is curving inward on a compound curve, it will have to be pulled up away from the fiberglass nose, which will take some effort. Pull it just high enough to get cement inside. That is why the nose should be glued later. Lay about half of the nose with glue, including the edges. One way to prevent accidental contact is to pull the side away from the top just enough to allow contact with the edge of the top in small increments. Try to make contact first with the edge, not with the fiberglass. After a section of edge is in good contact, then allow the Zotefoam to contact the fiberglass. Again, finish by using the thumbs.

Finish gluing the side to the top all the way to the tail cutoff line. This is easier because everything is stable. Again, pull the side away from the top to control accuracy of contact. When finished, use masking tape to attach the bottom of the side to the mold to prevent movement. Rotate the mold to do the second side. Here are the top and right side glued on mold.

I continued the yellow top color below the horizontal division line at the tip of the nose. I formed this section using a hand-held hot air gun and trimming the part to fit into the sides and top. This was a difficult process due to the compound curve and the tight tolerances. This piece has to fit within the already-glued sides. The better way would be to glue this yellow bottom piece in before the sides are glued on using the trimming process.

I did a simple straight cutoff line running across the width of the shell about 12” back from the nose. This turned out to look clunky. It would have been nicer to make a dart shape here.

When both sides are glued and taped, turn the mold upside down to glue the bottom. The bottom has to fit within the two sides, but because of the large dimensions and Zotefoam flexibility, it is not a problem. Start with the joint between the yellow and the leading edge of the bottom. This shows the use of paper to prevent accidental contact of glue:
And the finished bottom view.

After the bottom is glued, lay out the leading edge cutoff line for the canopy. I used the wheel center line as a reference. To locate the approximate center of the axle point that was marked on the mold, cut away a section of Zotefoam in the area of where the axle should be. The area the size of the wheel will be cut away, so you don’t have to be careful here. Using the vertical wheel section line drawn on the mold as a guide, draw in a vertical section line (or use masking tape) to be used as reference to locate the leading edge of the canopy. Use a length of masking tape across the width of the shell to guide the razor blade. The masking tape is an excellent visual guide for a straight line, and it can be adjusted easily.

Next, lightly lay out the lines for the entry door with a removable ink marking pen. I didn’t cut the door out because I didn’t know exactly how far forward the door needed to be to get my feet past it. But I did push a razor through to the inside surface in two spots along the 22” line. These marks provide a convenient reference on the inside surface when gluing in the internal brace. Once the trailing edge of the door is drawn in, the line extends up for the trailing edge of the canopy. The canopy can then be cut off and put aside.

Use a blade of wood or old hacksaw blade to draw a circle representing the wheel radius, then cut out the wheel opening in the Zotefoam. I recommend cutting it about 1” smaller in case you need to move the trike forward or back in the shell for toe/heel clearance, unless your drawings are right on. Final trimming can be done after everything is mounted and checked out. I didn’t cut the wheel turning butterfly area at this time. Mark a wheel section line on the edge of the bottom to be used later as reference point.

The shell can be removed from the mold. The shell will be very floppy and will sag if laid on the floor. Hang it by the nose. Use some heavy coat hanger-like wire inside the nose hole and a rope to a pulley on the ceiling of your shop. This way the shell will take on a very natural aero shape. It will also allow you to work inside when adding the various internal braces.

With the wheel hole cut, an inside line can be drawn on the bottom representing the front wheel section line. This is a reference point for positioning the trike. This is the wheel axle forward/back location.

Next: Bracing

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