Thursday, April 26, 2012

Wooden Globe, fiberglass edition

So I decided to build a globe.  After figuring out the maps, the next step was working out the structure of the globe itself.  My general plan is to glue wood veneer onto the surface of a sphere, so obviously the first thing I need is a reasonably sized sphere.  I wanted my globe to be relatively large, on the order of 16 to 18 inches in diameter.

My first thought was a sphere made of wood.  It turns out that making a wooden sphere of this size is an art in itself.  While you may be able to buy a wooden sphere, a large one wouldn't be cheap.  I considered plastic,  but was worried about how glue would work on that kind of surface.

I eventually decided to make a sphere myself using fiberglass.  So I went down to the toy store, bought a 16" diameter red rubber ball, and covered it in fiberglass cloth and epoxy resin with a structural filler.

The ball had Spider-man on it.

To support the globe, I bought bearings and a 3/8" brass rod.  I cut the globe in half and removed the remnants of the rubber ball.  Then I mounted the bearings in blocks of wood at the north and south poles. 

Spider-man left his mark.
North pole is at the bottom of the photo.

The bearing at the north pole is entirely internal to the globe.  The bearing at the south pole where the supporting rod enters will be the only opening in the globe.  Gluing the halves back together with some more epoxy and filler leaves us with a sphere free to rotate on its axis.

Tuesday, April 17, 2012

The start of making a wooden globe

I always liked globes. A few years ago I got the idea to make one out of wood and I actually started this as a project. Now I'm making a belated attempt at documenting some of this process.

Making a globe has to start with a map.  The best source I had for this was Google Maps, so I painstakingly took screenshots and merged them together to create a map of the world.

Google Maps uses a Mercator projection.  Before it can be useful as a template for making a globe, it needs to be massaged into a shape that we can trace onto a sphere.

A gore is a segment of a three-dimensional shape fabricated from a two-dimensional material.  We need to transform this Google map to look something more like this:

The gores of Waldseemüller's 1509 globe of the world

First, transform to a equirectangular projection.  I did this using a photoshop plugin called Flexify 2 which I was able to get to run under GIMP.

I found a page which has a satellite image of earth with 12 gores (as well as images for other planets), but I want political boundaries for my globe so this doesn't help.  However, that page also has a link to a perl script which can transform an image into gores.  I used this perl script to generate a map with  36 gores.

With some careful scaling, this can then be printed and traced onto the surface of a sphere using carbon paper.