Adjustable Observing Chair

After a few nights as a newbie stooping over to peer in the eyepiece, my back told me to do something about it. I looked for Observer's Chairs available on the market and felt that most were too costly or were not very nice-looking. I came across this design when surfing and felt it was within my limited carpentry skills  and budget ($70) to make. Below is the result. My dear wife made a very very comfortable cushion for it. It may look fragile but it easily holds my 200+ lbs.

(Original design by James Crombie, modified by Dennis Friedman)

Obtain your construction materials (approximately 24ft of 1X2”) clear hardwood (maple or oak) or the equivalent (you may want to consider teak or redwood as well). 

q         1 - 14 x 10 x ½” plywood (Seat base)

q         1 - 3’ length of (5/16-18) threaded rod

q         4 - 5/16 x 2 ½” carriage bolts

q         12 - 5/16 washers

q         10 - 5/16 nuts

q         4 - eyehooks

q         4  - #8 x 2” woodscrews

q         4  - #6 x 3/4 woodscrews

q         1 - 14x l0x 1/4’ plywood

q         1 - 14 x l0 x 2” foam and fabric to suit (a foam cushion will also work)

q         Glue, varnish or paint to finish

q         1 - ¼” cork strip (one sheet)

q         1 – Bungee Cord – approximately 13”  

q         3’ of piano wire or equivalent (strong cord can be substituted)

Cut your lumber to the lengths as per plans 

q       3      - 1” x 2” x 36’            -   main uprights

q       18    - 2” x 2” x 1”             -   fillers between uprights

q       2      - 1” x 2” x 18”           -   leg sides

q       1      - l” x 2” x 16”            -   leg base

q       2      - 1” x 2” x 14”           -   seat sides

q       2      - 1” x 2” x 11 1/16”   -   seat crosspieces

Note:     If you are using lumber thinner than 1” you will have to alter your dimensions to suit. You may add filler blocks to widen the uprights

q      Drill 3/8 holes in the filler blocks and the main uprights, and counter bore a 7/8” hole, ¼” deep to fit the washers & nuts in the top and bottom of the 2 uprights, and at the top of the leg side pieces. Cut 2 pieces of threaded rod 1/8” shorter than the width of the assembled upright. Cut one piece of threaded rod to fit thru the legs and uprights with a washer as a spacer between them.  

q      Spread glue on all mating faces of the uprights and spacers. Assemble and use threaded rod to clamp the unit together. Check that all pieces are aligned and square before final tightening.

q       After the glue has dried measure the distance to die outside of the legs with the spacer washers between the legs and uprights. Mark the leg base accordingly. Round over the top of the legs before assembling. Drill pilot holes for the #10 x 2” screws and glue and assemble the leg. If you have the tools, dowel the leg base first.

q       Measure the outside distance of the upright assemblies and add 1/16” to 1/8” to the measurement between the seat sides. This allows the seat to slide up and down without binding; too much will let the seat get cocked sideways and may drop. Cut the crosspieces to suit and then cut the bevel on one side. Drill the holes and counterbores for the back crosspiece, then attach the seat base and back crosspiece using glue, the bolts and screws. After the glue has dried apply the cork (or rubber) to the bevel of the two crosspieces. The cork provides the friction to keep the seat from slipping when you sit on it.

q       Trial assemble the legs to the main upright and set the length of the cable to get the proper 30-degree angle of the upright. Place the seat on the upright so that it rests on the legs, then set the bottom crosspiece in place so that the seat is level and mark both sides. Remove the seat and clamp the crosspiece in position and drill and counterbore the holes for the bolts Assemble with glue and the bolts but check alignment on the upright before tightening the bolts.

q       If you have a router then use a ¼” rounding bit to radius all edges or use a block plane. Next, sand all surfaces smooth and clean off all dust and apply several coats of exterior varnish. Allow to dry thoroughly and sand between coats (Don’t coat the cork.). After the last coat has dried, install the eyehooks, cable and seat covering.  Place the foam on the ¼” ply, then stretch the fabric over it and staple to the bottom. Place this over the seat board and using the ¾’ woodscrews, attach from the bottom. Insert an eyehook at the bottom of the upright. This puts a little tension to the seat and prevents it from slipping when you get up. And that’s all!

q       You can alter the dimensions to suit your application and available materials I have seen several made of metal tubing. The commercial version is excellent but is rather very pricey.

Suggestions for modification by Dennis Friedman

q       Replace the 24’ of 1”x2” oak with a 4’ x 12” x 2” plank. Rip the 2 lengths of 1 ½” strips from the plank (you make the leg base, leg sides and seat box from these) leaving a board that is ~ 4” x 9” x 2”. You need to cut this remaining piece to a length of 3’. The excess can be used for any other wood needs. The remainder will then form the main structure of the chair.  From this board remove four rectangular sections, which would have formed the empty space between the uprights and the spacers. I think this would require much less overall cutting, fitting, and gluing. In addition I believe the chair might have even greater structural integrity. It also eliminates the need for a top rod.

q       Use a preformed foam pillow with a slipcase cover. It will be more comfortable and durable.  

q       Consider adding a leg base to the front structure to add more stability (its pretty stable as is). If you do so the back legs will not close over this added base. If this is not viable considering adding a slight angle to the front legs to allow more wood to touch the ground.