Want something to do with those cloudy evenings? Here's a project that will keep your mind on astronomy even when you should be doing other things, like fixing that leaky faucet or spending time with neglected family members.
Ever since I learned the value of sitting while observing, I have wanted a real observing chair. I started out sitting on a simple footstool, but with no height adjustment, it was often quite awkward. I would have loved to pick up a Starbound observing chair (or equivalent), but somehow I just couldn't bring myself to spend $159 or more on a chair, when there are still so many other things to spend money on (like fancy Nagler eyepieces :-) When a guy from my club showed me his home-made chair, I knew I had the answer.
I based my observing chair on the plans available here. However, I made a number of small modifications to these plans as I went along. Some of the modifications were simply a matter of taste, or allowed me to use materials I already had on hand. Others were minor corrections to the assembly instructions and dimensions. When all was said and done, I had only spent about $35 for the whole thing, and I ended up with a very comfortable, durable, and adjustable chair. (The actual cost would probably have been closer to $50 if I hadn't already had some of the materials on hand.)
I used red oak for everything except the seat, which is made of 3/4" plywood. The red oak frame resulted in a strong, lightweight chair which weighs only about eight pounds, but will support at least 200. The seat height is adjustable from 17.5 to 30.5 inches (assuming 50% compression of the foam cushion). Because I often use a refractor, I actually lowered the minimum seat height a little (compared to the original plans) by lowering the location of the middle threaded rod by 1" and shortening the back legs by about 3/4".
If you'd like to build one yourself, here are a few hints & tips based on my experience:
It should be noted that the original drawings call for 1" x 2" lumber, which (at least in the U.S.) really measures 3/4" x 1.5." This meant that a lot of the dimensions in the original drawing were off, if I wanted to use readily available wood. To start with, I simply added two more spacer blocks in each of the three rows, to get approximately the same width as shown in the drawings. Everywhere else, I simply corrected for the reduced thickness and hoped it would be strong enough (which it is).
I made some substitutions in the hardware for the chair as I went along. In some cases, the plans called for screws that were too long for the 3/4" x 1.5" wood that I was using. In others, I simply preferred a different solution. For example, the plan calls for carriage bolts to hold the seat frame together; I opted for wood glue and #10 x 2" wood screws. I used nylock nuts on the threaded rods (the plans never mentioned lock washers); if you do this, you'll need to allow a little extra depth when counter-boring. Also, tightening both ends is a real trick with nylock nuts, because typically one nut will spin all the way, while the other refuses to turn at all, making it hard to center the threaded rod. The solution was to start both nuts & identify the tighter one, then remove the rod and hold it with pliers while turning the tight nut to the appropriate spot on the rod. Finally, re-insert the rod and put the other nut on as usual. (I think you would have this problem with any type of nuts or lockwashers, but at least the nylocks give you a way to deal with it.)
Be sure to use a quality wood glue (not a general-purpose white glue) for the chair, since much of its strength comes from glue rather than fasteners. I prefer Elmer's "Carpenter's Wood Glue," which is available in any hardware store.
Before you start, note that you will need a couple of special tools. One is a Forstner bit for the counter boring operation (a drill bit which creates wide, flat-bottomed holes). It also really helps if you have a small drill press (or even a perpendicular drilling guide), since it is hard to manage such a wide bit with a hand drill. The only other difficult operation is ripping the 30 degree edge on the seat cross-pieces, which I performed with a table saw. The angle must match the slope of the chair back in order to provide maximum friction and support, and the little boards are too narrow to just use a rip fence (cutting guide) on a jigsaw or circular saw.
The bungee cord position is pretty important, as it will limit the adjustment range of the chair if you're not careful. I found that the best cord was a 10" "mini-bungee", which provides light tension and stretches quite a bit when required. Insert the screw eye into the bottom of the seat first, and then test-fit the seat to determine the location for the lower screw eye. You want to find the point that provides the highest possible seat position while still maintaining light tension when the seat is at the bottom.
The chair should be stained & sealed to protect it from moisture. I used a Minwax stain followed by a polyurethane clear-coat, but any good sealant designed for outdoor wood protection should work. I also sprayed the fabric seat cover with Scotch Guard before attaching it to the chair, to keep moisture out of the seat cushion.
If you're worried about the strength of a chair built of 1x2's, there are a couple of modifications I would suggest. The first change, which I would certainly make if I were building a second chair, is to use 1x3's for the seat cross-pieces. When you start with a board that is only 1.5" wide, and then you take off the 30 degree edge, there isn't much wood left to inspire confidence. Another inch of wood would certainly make me feel better (although, as I said, the chair has been tested and holds 200 pounds as-built). The only other weakness seems to be some lateral flexing in the rear legs, mainly at the joints. You could either switch to 2x2's for the legs, or add metal corner braces where the legs meet the rear base plate. If you're really nervous, you could even add a fourth upright instead of just using additional spacer blocks, but I don't think this would ever really be necessary.
All material on this site is Copyright 2003, Neil T. Hobbs.