MARS Recumbent bicycle projects

Zotefoam Manual - Trimming and Cutting
A project by John Tetz - April 2005

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

It’s a challenge to trim the edges of each section accurately so they can be glued together to make a beautiful fine line. Here’s the system I developed:
This shows the addition of a second piece of tape parallel to the color separation line. The center is the actual color separation line.
Here is a small area of Zotefoam heat-formed over the mold, ready to be trimmed. This represents the yellow top section.
This is a detailed section view of the above. The aim is to rough cut enough of the excess Zotefoam so that the lower tape becomes visible. About half of the tape should be visible after cutting. I use 1” wide tape.

This shows a system of marking the outside surface of the Zotefoam so that a razor can be guided accurately along this line. Make a marking guide about 1.5” long from a piece of wood the thickness of the Zotefoam. Screw a thin piece of metal to the wood, with a hole in the metal to allow a pen to mark the color separation line. Visually align the guide along the bottom edge of the lower tape and slide it along with the pen, marking the Zotefoam. The bottom tape edge is for trimming the top. When making the cuts for a side, the upper tape is the reference line.

This shows the blade at an angle; it is pushed rather than drawn through. I find this is more accurate because it is easier to see that the razor is following the line – not covered by the hand. The angle of the razor shown gives a long length so that the razor has less tendency to waver. The razor has to be super sharp. I use a wet stone to keep the blades sharp.
Warning: after trimming but before removing the part, make registration marks so the part can be repositioned accurately for assembly. Make an edge mark at the front wheel section line, for example. All four sections of Zotefoam can be cut and then later assembled on the mold. This system turns out to be accurate enough to give fine separation lines.

This shows a close up of the nose area with the fine color separation line. For production, a fiberglass template would be made and placed over the formed Zotefoam so a line can be drawn for cutting.

Next: Glueing

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