Topographic model in foam – first steps

This has nothing really to do with my own model railway but it’s a model-making project I’m working on and I thought I’d share it here.

If you’ve never seen one before a topography model is something we’d build to study the shape of either existing terrain or a proposed plan for a building site. Normally I would use layers of matt board or something similar to build up each layer of the model. For this project I can see needing a bunch of identical forms so we can cut them apart and modify them to plan new approaches. My usual method, I worry, might just be too slow to be worthwhile for this.

Over the long weekend I thought a lot about the project and have settled on using foam for the model. Today I took some time to catch up with friends and familiar places and visited Great Hobbies to see if they might have thin sheets of extruded foam that normally might be used for building lightweight model airplanes. They had one sheet of a product I think called Depron(?). It is 3mm thick and looks to me like the same foam you’d normally see as a meat tray at the supermarket. A 24×48″ sheet costs about $6 so it could quickly become expensive. In the meantime I’ve been thinking about trying to use my router to cut a block of foam into the desired finished shape. Tonight I gave it a try.

The foam I used was an old scrap of 1″ bead board foam. My local Home Depot sells a full 48×96″ sheet of this stuff for under twenty dollars so it will certainly be affordable enough for this application. I planned on shaping the foam using my router. I chucked a 3/4″ straight bit into my router. I figured it might make the most sense to start with the deepest and work up to the shallowest area – thereby leaving me a place at a consistent height to always place the router’s base on while working. On went my respirator and goggles and I started cutting. Before I started my single biggest concern was tearout as the router went through the foam. I can now say that this is not even a concern any more. The edges are clean and sharp.

The picture above is what I made with a couple of passes. Based on that test I have some ideas for what to do next:

  1. Get a better respirator. I have foam dust in my lungs and it’s lousy.
  2. Cut out some hardboard templates to guide the router
  3. Instead of a straight bit use something with a bearing that can “trace” a shape
  4. Plug in the vacuum to try and control the dust – this process creates an incredible amount
  5. Cut shallower. I planned the steps in my test model at 3mm per but observe a 1mm kerf from the router bit so perhaps 2mm per step will work better

In short the idea works and I will persue it further on a more formal piece before the end of the week. Tomorrow I’ll cut out the hardboard templates and try using them.

Stay tuned!


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