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Old 04-06-2020, 12:13 AM
Bjim (Jim Brydon)
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Fixed post grinding/polishing machine.

Hi all! I started making a grinding/ polishing machine last year( 2019). It is mainly made from odd junk I had around with a few bought pieces. I bought some pulleys, bearings and belts from Bearing Services Taree, shafts from Manning River Steel and skate board style wheels from Bunnings. The motor is from an early exercise machine that I found at a road side council cleanup. It has a spring loaded pulley where if the motor assembly moves toward the other pulley via a crank handle, the motor pulley gets bigger giving me variable drive at the turntable. The belt attaches to the pulley of a bbq spit worm drive 30:1 reduction ratio I got from a garage sale for $10 - it just needed a clean, new grease and now works really smoothly. From the worm drive a stepped pulley on it I got for nothing (off an old drill press) and belt to another step pulley on the turntable drive shaft drives the first turntable and provides more variable speed. The first drive shaft can be connected to another drive shaft via belt and equal pulleys so that I can grind/ polish two mirrors at once. The two mirrors at once are necessary as I want to make at least one binocular telescope which needs identical (or very close to within a couple of mm) focal length mirrors. Pic attached more if interested.
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Old 04-06-2020, 09:20 PM
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Sunfish (Ray)
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That is remarkable. I have just been been reading about grinding machines and the complexity of the movement required is fascinating. A three body problem .

I have been given some partially complete newt mirror blanks and it will be a long term project to complete them . Seems no one does this anymore. Problem being also that no one will coat them anymore either.
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Old 05-06-2020, 06:15 PM
Bjim (Jim Brydon)
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Thanks Ray! The fixed post is the simplest machine I've found. Gordon Waite is the expert as far as I could see and once I found his utube videos I knew I had to make one. Gordon has a lot of utube videos his company makes "Renegade" dobsonian scopes and very openly discusses everything about telescope making. He's got a very good drum sander design to. There is a mirror coater in Tuncurry NSW (Saintech is his company name)but I don't think he will be going on for much longer as he has apperently sold his business and now winding up. If he is no longer doing it when my mirrors are done I will probably try one of those spray on Angel coatings or just follow the formulas in the Atm book 1. Sorry about last night. I tried to attach some photos but only one would attach and it appeared no one had looked at it so I deleted the whole thing. I'm a bit dense and am trying to navigate the site but I can't get some things to work properly. It may be my very old overloaded iPad. Here is one extra photo of my machine.
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Old 06-06-2020, 06:01 PM
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Sunfish (Ray)
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Thanks Jim I checked out those links to machine grinding and there are a lot of other very detailed videos on hand work from a fairly professional mirror maker so that was good.

I have seen the Angel products silver solutions on other sites and some NZ CN people have coated some big mirrors in similar ways. A worker at one observatory I read on CN spent years doing temporary silver coating for testing of their mirrors using a standard proprietory solution procedure and double head spray gun, like automotive finishers. . Expensive solutions if you do not like the result. But enough is supplied to redo many times.

Some of the big mirrors are protective silver coated I see on various sites with layers of nickel and other metals under various gas mixtures which seems even more complex than the aluminium vacuum sputtering vessels. All seems a bit complex and shame if we cant get mirrors coated here. Big mirrors would be worth the cost.
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Old 06-06-2020, 08:26 PM
Bjim (Jim Brydon)
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Ray, my two mirrors are 7.5 inch. I am going to figure them to a sphere as they will be a long focal length (3000mm). The sagitta is only 0.7521mm according to my calcs (could be wrong) so not much glass to remove. I don't know how I'll go getting a good sphere as I've read that higher numbers are harder to interpret shadow wise but a ronchi may be the way to go. I think from my studies of the sphere it is a lot easier to get a smooth surface as introducing a parabolic figure can lead to zones and dog biscuit roughness. I want to keep this first Bino as simple as I can. Long focus telescopes are easier on eyepieces and eye relief for my old eyes and glasses.
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