My Outback Travelscope
Me, my new scope, and a bloody big rock. (Courtesy George Brandie)
My new airline-portable telescope is featured in the March 2013 issue of Sky&Telescope, but given the publication's finite page space, it wasn't possible to include a great number of photos. So, presented here are a series of detail images along with some construction tips and tricks. Keep in mind that this isn’t intended to be a full description of the scope and how it's built — it’s merely a supplement to the S&T article, so be sure to give that a read first.
A router with a compass jig is the best tool for cutting the various circles my scope's design requires. Remember to always secure your work piece to some scrap wood and to cut the outer circumference first. Here I’m finishing up one of the scope’s side bearings.
Shown above are the front secondary ring and the rear plate of the primary mirror cell. One of the keys to this scope’s design is that all circular parts have the same outside diameter. Naturally, it’s best to cut all these before resetting the router’s circle-cutting jig for other work.
One way to get nice, accurate cuts in aluminum is with a table saw. I have taped the scopes trusses together so that they can be cut to the same length on a single pass through the saw.
I wanted to be able to assemble the scope by running screws through the front and rear plywood pieces into the aluminum struts. To do that, I needed to install threads in the ends of the struts. I did this by making some cubes of ¾-inch plywood, into which I inserted ¼-20 T-nuts. I used J-B Weld to glue these assemblies in place inside the struts. It works like a charm. As you can see from the photo above, I made a couple of extra blocks just in case I messed up.
Here is the optical tube fully assembled. Now I can easily figure out where the scope's centre of balance lies, which is crucial for figuring out the placement of the side bearings and determining the dimensions of the rocker box. I simple rested the scope on a pole and moved it laterally back and forth until I found the balance point, which I then marked with a pencil on one of the struts. Remember to put your favourite eyepiece in the focuser though for accurate balance.
Back to the router. The best way to ensure that the curves in the rocker box sides come out identically is by routing a complete circle from a single piece of wood. Then, all you have to do is cut the piece in half, trim away the excess, and you have nicely matched rocker sides. Just be sure to draw all your cut lines first!
Here are all the rocker-box pieces. Pencil marks indicate where to cut wood away to reduce weight.
I used a jig saw for the rocker-box cut outs. Note the holes I drilled beforehand so that I could insert the jigsaw blade at the start of the cuts.
Here are the rocker-box parts before assembly. By trimming away the excess wood, I was able to cut its weight in half without significantly reducing rigidity.
The fully assembled rocker box, all ready for painting.
You can use any outdoor paint or stain for telescopes, but I like odour-free and easy-to-clean Verathane Diamond Wood Finish.
I used Ebony Star textured laminated for the side bearings and the undersside of the rocker box. Cutting the strips for the side bearings is pretty easy. You can get neat results with the score-and-snap method by using a sharp utility knife guided by a yardstick.
Contact cement is the best way to glue Formica to plywood.
The completed scope ready for first light I'm pleased to say that the scope turned out better than I'd hoped. It's not only more rigid than its previous incarnation, it is also 10 pounds lighter.