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Post by scotttucker on Jun 23, 2022 12:23:46 GMT -7
Tinkering with dome ideas. I am pretty sure I remember reading on a telescope making page (maybe the TROK telescope in Liverpool) that the makers decided to avoid the rough grinding phase of mirror making by bolting an angle grinder to a universal joint and hogging out a sphere that way. Thought I might copy the idea - the basic plan is to hog out some wood to the correct radius and use it as a mould to make some kind of dome covering. Step one was to weld some scrap pipe to a universal joint (originally a steering joint from a Vauxhall Corsa). Then weld on a turnbuckle to allow fine adjustment of the radius and bolt on a bit of steel bar bent and drilled so that you can attach the grinder. Now I need to find a big log or tree trunk or something to grind out.    |
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Post by Ron Walker on Jun 23, 2022 12:57:59 GMT -7
I think you would need a Sequoia to make a dome big enough.
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Post by scotttucker on Jul 8, 2023 23:59:25 GMT -7
After a long pause (nothing unusual there) I am re-starting this experiment. I have attached the universal joint end of the grinder jig to the rafters. I have fixed a wood cutting disc to the angle grinder and used the turnbuckle to adjust the radius of the arm to 2.5m.   |
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Post by scotttucker on Jul 9, 2023 0:02:01 GMT -7
It is going to get very dusty so the Goto is wrapped up and looks a bit like a ghost  |
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Post by scotttucker on Jul 9, 2023 0:16:34 GMT -7
The wood for the pattern is made from 5 sleepers each one measuring 120 x 20 x 10cm. I got them from a very helpful local sawmill. They scooped them off the lorry which was going to take them to be tanalised - I guess it does not matter too much if they are tanalised but given there is going to be a lot of dust I thought it better if they were not full of preservative chemicals. The sleepers are just held into a 1.2 x 1m slab by a couple of batons. The wood has to be thick enough to accommodate the sagitta of the arc. Here is a picture of the completed rig ready to grind.  |
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Post by Ron Walker on Jul 9, 2023 10:28:35 GMT -7
I wonder if a shop vacuum hose could be run along the pendulum so it could suck up most of the sawdust as you are grinding. Will not this type of dome be quite heavy? What is your plan for a frame to place the various sections in?
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Post by scotttucker on Jul 9, 2023 12:34:56 GMT -7
Hi Ron - the wooden section will just form a 'negative' mold - the half baked plan is to seal the surface then pour in dental stone (I have a huge bag left over from telescope making days) or even cement then use the resulting 'positive' mold as a basis for casting in some kind of resin/ composite surface- there are some interesting 'eco' resins becoming available. The reason for needing a positive mold is that I want to form sections with external flanges at the correct angle so they all assemble easily.
I will fill in the detail as I go - the plan is to make a 3v geodesic dome but instead of flat triangles, the triangles will have the right curvature formed by the mold. It is a bit experimental.
I would love to vacuum as I go but don't have a proper shop vacuum and I will get into trouble if I clog up the domestic one.
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Post by Ron Walker on Jul 10, 2023 9:13:25 GMT -7
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Post by scotttucker on Jul 21, 2023 22:54:31 GMT -7
You must be used to my slow posting rate by now. I carved the dome curve into the wood during the week. The turnbuckle turned out to be very useful. The sagitta is about 5cm and the angle grinder handles and guard did not have enough clearance to hog out the curve in one pass - I had to use the turnbuckle to do 3 passes at increasing depths.  |
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Post by scotttucker on Jul 21, 2023 22:58:11 GMT -7
A couple of photos of the completed curve - although it does not show up very well in the photo. Todays job is cleaning up. Then I will fill the cracks and sand it.   |
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Post by Ron Walker on Jul 23, 2023 10:25:10 GMT -7
My understanding is that this is a form upon which a negative will be made and then positives of dome material will be formed against to give the constant curve required for the full dome. These squares (I'm guessing they will be squares, could be triangles) will come from the interior of the circle?
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Post by scotttucker on Jul 23, 2023 13:28:48 GMT -7
Hi Ron. Yes - that is the plan. I am aiming for triangles. I did not even get to tidy up this weekend so as usual progress will be slow.
+ I am really hoping to have some exciting news in the next couple of days which may or may not work out.
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Post by Ron Walker on Jul 24, 2023 8:23:01 GMT -7
A permanent planetarium location perhaps?  ? |
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Post by scotttucker on Jul 24, 2023 13:28:39 GMT -7
Sadly not that. I put a deposit down on it today and am scheduled to pick it up from London in two weeks time - I don't want to count chickens before they are hatched - it begins with the letter Z!
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Post by mrgare5050 on Jul 25, 2023 3:44:32 GMT -7
Sadly not that. I put a deposit down on it today and am scheduled to pick it up from London in two weeks time - I don't want to count chickens before they are hatched - it begins with the letter Z! It COULD be a statue of Zeus, you know I want one! Or are we witnessing the founding of the UK's Planetarium Museum? who know |
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