20.5.18

10" f/8 another look + saw sled.

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The recent failure and dismantling of yet another washing machine provided a second 12" diameter drive pulley. It seemed like a good basis for a new mirror cell which would allow plenty of fresh air around the glass.

The previous, full sheet cell lies in the background and weighs quite a lot. A central hole was for a cooling fan. A full, 3/4" plywood disk had closed the tube. Again with a central hole for the fan.

The two pulleys look made for the job if I add mirror support pads and collimation screws. Their rims are a both a nice 'rattle fit' in my steel, 12" ventilation tube.

Monday: While I ponder the cladding of the dome I am pottering around the octagon looking for earlier oversights. I replaced one larch plank where the original had ugly cutouts for an earlier trapdoor's hinges. The plan now is to hinge the trapdoor beyond the top of the ladder/stairs. Which meant I could close off the obs. floor sides close to the sides of the ladder. More larch sawdust and splinters later and I found I had to add two more floor joists to pick up the added planks nearest the pier legs. My timber is round shouldered. So I was able to slide the joists in on their sides and then bring them upright with a long Bessey F-clamp. Not without some effort I should add! Then the joists just needed a hefty tap with a lump hammer to set them to full depth. Now I just need to screw the flooring down onto them to finish the job.

Tuesday: Another warm and sunny day with hours of H-alpha staring at a rather indistinct sunspot. I am still waiting for the arrival of a low profile T2-T2, helical focuser. Plus a 2.6x GPC to tame the focus shortening of the binoviewer.

I started building a sled for the table saw. This involved making two strips of plywood as runners for the slots and a 2' square x 3/8" sheet of ply for the top. After the runners were made exactly to size I propped them up above the table surface and applied wood glue for the top to rest on. The plywood top was then heavily loaded to ensure close contact. The weights were carefully placed directly over the runners to avoid bowing of the top plate.

Apart from a little glue escaping sideways this went well by the time I had to put the saw away overnight. I need a sled to make repeatable miter cuts on the sides of the trapezium covering panels. Since the angles are all very similar, though right and left handed, there will be a need for small variations in the cut angle.

I shall have to arrange an adjustable push bar and a fence for the sled to make repeatable, angular cuts without waste. The panels are all under 60cm wide but will have to be laid [mostly] to one side of the saw blade for cutting. I'm hoping the 2'x2' sled top will be enough to support the panels without getting in the way.  

Click on any image for an enlargement.
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