I knew from the beginning that the tripod was the most important and - at the same time -the most challenging component. (I had decided to use an internal tripod for time being but there are quite a number of other possibilities which I won't discuss here).
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| my template |
Material: In Germany there are smaller diameter (from memory around 35 mm) hard wood (beech) poles and large diameter (around 67 mm) soft wood (spruce) poles in use. I chose hardwood and a smaller diameter.
Diameter and raw stock: my search for round hardwood timber of suitable diameter did not lead to anything. I found a manufacturer of outdoor umbrellas with hardwood posts but was told that all umbrellas are assembled in China and there was no way I could get the posts by themselves. I eventually ended up going to the local timber yard where the owner cut and planed for me Blackbutt two-by-twos of the right length. The finished cross section was 42 x 42 mm.
Joints: I used sleeves made from Stainless steel pipe Sched 10, 32 NB (OD 42.16 mm, ID 36.62 mm); 400 mm long.
The next challenge was to get the cross section into a suitable shape. I gave up on the idea of a circular cross section and decided on an octagonal shape instead - except for the ends - that needed to fit into the sleeves - which needed to be round. Luck was on my side and Bunnings had a sell off of router bits and I ended up getting a massive 25 mm x 45 degree bit at a greatly reduced price. I then proceeded to use the 1/2 inch router on the router table to fashion 45 degree chamfers on my two-by-twos. As the Blackbutt timber was I pretty tough (after all that is what I wanted) I had to do two passes on each edge. 2 passes on 4 edges times 9 post segments required 72 passes on the router table. Quite a bit of work and quite a bit of mess but in the end I was very happy with the result.
The next problem was the circular cross section. Jan Pennell from the Blue Mountains Wood Turners saved me. After consulting with her colleagues she took on the job. At 1.4 m long the parts did not fit on even the longest lathe. She ended up using two lathes, lined up behind each other! She also had to use several "steadies" to keep the parts rotating smoothly while she worked the 200 mm at the ends. I specifically requested smooth, rounded transitions from the 36.5 mm diameter sections to the octagonal cross section. I also supplied Jan with the pipe sleeves so that she could test their fit during her work.
Each tripod leg consists of two "Type B" sections and one "Type A" section. One of the "Type B" and he "Type A" has the pipe sleeve permanently attached. (Our initial thought that press-fit would be sufficient to hold the pipe did prove wrong - the timber diameter is changing too much with varying moisture conditions and the sleeves became all loose after a while. I ended up securing each sleeve with a countersunk screw). The corresponding ends that fit into the pipe sleeves during assembly were made a loose fit.
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| rounded transition from circular to octagonal cross section |
All in all Jan did the most outstanding job. From the first assembly each tripod leg assembled easily and accurately. I treated them with decking oil and they were almost ready. The only other pieces of hardware that I installed were a cleat one of the lower sections for the rope that lifts the roof and an eye bold at the very top end of a top section in case I want to use is as a flagpole to run a string up to it.
The tripod is most likely over-engineered being of hardwood timber and the stainless steel pipe sleeves but it has proven its durability. It can easily carry my weight whenever I have to climb up on it to untangle any skylight cover shock cords (a task that I try to dodge but sometimes cannot avoid).
