MARS Recumbent bicycle projects

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

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

Before describing the mold, here is a photo of the Velotrike I built with a foamshell made using the technique to be described. The shell is 94” long and 26.8” wide; it weighs about 7 lbs. Total vehicle weight is 41 lbs.
This drawing shows the basic top and side view of the layout. The 13” horizontal line from the tip of the nose to the tail is the main reference line at the maximum width of the shell. Other reference lines will be described later. For the vertical sectional views I used the bottom bracket, front wheel, shoulder, and rear wheel as reference points. An additional 10” section is useful because of the fast-changing nose curves. The vertical dashed line represents the tail junction. The tail is removable for fixing a flat and for removing the trike from the shell for maintenance or to be used as an unfaired vehicle. The removable tail also reduces the size of a container needed for shipping or transporting in a car. Make a print of this very important drawing for reference while you read through this manual.
The basic mold construction material is common 2” thick home insulation, which usually comes in 24 x 96” sheets. The maximum width of this Velo Trike is 26.8”. If a 2” vertical center section is used and the sides are made in separate halves, then the maximum width for one side is 12.4”.

This shows the layout in a sectional view at the front wheel, which is at the maximum width of the shell. When laying out the various stacks of mold foam for cutting, both a wide stack section and one of the less wide upper stacks can be cut from one sheet of rigid foam. The center section is a side view of the shell; it acts as a convenient reference point for these dimensions when carving the mold foam.

Note that the stack starts on the 13” line. The entire stack above and below this is at a known reference dimension. These 2” section lines make wonderful references on the actual mold. They also help when generating the initial drawings of the side, top, and sectional views.

I use the front wheel section as the major reference. The position of the trike has to be known accurately to fit the wheel cutout on the shell, plus accounting for toe and heel clearances, so all the stacks have this important reference drawn in on the back edge, even on the front edge. This helps with alignment when gluing the stacks together.

This shows the vertical reference lines. Another important reference is the 22” height line, the bottom of the entry door, which is about the highest you can comfortably get your foot up and over the shell edge when climbing in and out. The 27.5” line is where the canopy hinges on the right side and opens on the left side. It is also the separation line for the Turtle Deck and the color separation line from the front wheels through to the tail. The line deviates from this dimension as it goes down toward the nose.

The main shell is divided into a separate top, two sides, and a bottom. One reason is the sheet size of the Zotefoam, around 40” wide (and 80" long, another reason for a removable tail). The location of the joint of the top and sides is carefully chosen to minimize the amount of compound curving needed using a flat sheet of Zotefoam. This is also a convenient place for the color change, which helps hide the separation line. I made cardboard sectional templates as guides when carving the mold.
The mold with template.
Here is the almost finished mold. Note that it is bolted together on the front and rear wheel section lines. Later I added another bolt at the 10” section. It is difficult to clamp the rigid foam securely enough to hold it in position because the foam collapses. I even tried 1” dowels through the center section, but they, too, allowed movement. Possibly a 3-4” diameter plastic pipe would act as a better locater. I could have glued the sides to the center, but I wanted to be able to separate them to reduce bulk and weight when transporting or storing the mold.

Note also that the mold can be rotated. This is very important when carving, but more importantly the mold has to be properly orientated when heating and forming the Zotefoam (see Forming).
This shows the center section with a wooden block through which a pipe can be inserted so the mold can be rotated. A similar one is on the tail. Make sure there is enough height above the table so that the mold can be rotated to the positions required for heating the Zotefoam. The tail block is located much higher than the nose.
Finally, make a fiberglass nose piece. The nose piece is a high compound curved area. To aid in forming it, the Zotefoam is glued to the fiberglass, making a strong and stable nose area, strong enough for a nose support off the vehicle. First lay some shrink wrap Mylar over the mold foam to act as a mold release, then apply one layer of Crowfoot weave fiberglass, which is enough.

This shows the fiberglass on the nose just before epoxy resin is applied. Below it you can see the Mylar, which will be thrown away. Remove the fiberglass to trim the edges, then replace it on the mold and hold it on with a couple of small pieces of masking tape. To remove the main shell from the mold after it is fully formed, that masking tape has to release on its own because you can't get to it.

Next: Lay out the color separation lines.

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