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  1. #61
    astrogirl's Avatar
    astrogirl is offline Main Sequence
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    Hey Plateglass, how is it all going?

    You only get one life - make the most of it!

    Location: Longitude 0° 0' 0" Latitude 51° 28' 38"N
    Equipment: Nextstar 4se
    Software: Stellarium
    Knowledge: Always open to and happy to be learning!
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  2. #62
    Art Bianconi's Avatar
    Art Bianconi is offline Banned
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    Default Converting a chop saw to a sphere generator

    Hi Plateglass!

    In recent years I've been fortunate to see a number of enterprising people design and build machines for pre-curving mirror blanks. They all shared one thing in common: they swung like pendulums from adjustable anchors overhead onto a table similar to a lazy Susan but with a mechanical brake.

    The rotating fixture was built onto the table of an old drill press that allows the material to be raised incrementally.

    I've used a number of diamond tools purchased from THK DIAMOND TOOLS. I found them on e-Bay. Remarkably good tools of high quality and very affordable!

    Prior to that I had to make my own, a process that started when I built my Schiefspiegler telescope and had to treppan the convex secondary from it's parent disk.

    Bi Metal hole saws work best for treppaning if the teeth are left in place. The kerf makes a slightly wider cut that allows the body of the hole saw to spin without grabbing the glass. It also helps some to squeeze the hole saw slightly to make it slightly out of round a few thousandths. That widens thr cut too which allows more clearance in the cut which helps promote coolant flow.

    I have used ordinary hole saws for this process in concert with a coolant and 40 grit abrasive. The process was so easy and predictable, I built a 10 inch diameter "hole saw" which worked great. Only problem with that tool is that it's so big and heavy, I can only use it to treppan glass with a vertical milling machine.

    The diamond hole saws work great but the diameter was limited to 5 inches max. That may have changed.

    Please remember to wear a mask and use a coolant to keep glass dust down. Nasty stuff!

    You are in for a lot of fun! Keep us posted please!

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    Last edited by Art Bianconi; 05-29-2011 at 01:13 PM.

  3. #63
    plateglass's Avatar
    plateglass is offline Main Sequence
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    Default I got lost

    Hi everyone sorry its been a while i seem to have got lost in that thing called life !!
    Not much happening but i did finish the 9 1/2 mirror and it works fine,heres a video of it being polished
    [ame=]Polishing a 9 inch mirror on a machine i made - YouTube[/ame]
    im now working on a 12 inch f5 down to 25 micron at the moment

    oh yes i brought a televue 17mm type 4 nagler eyepiece im not convinced it was worth the 225 pounds i paid but once i finish the 12 inch and get the mirror silvered then ill be able to test it out on the stars, I have just used it on my 9 1/2 inch un silvered mirror on the moon and planets, its slightly sharper than my binocular eyepiece i have.
    what else ...oh yea stay tuned for my video on cutting a mirror blank with a tile cutter table saw, I have decided to make a not so perfectly round mirror as it takes too long to cut circles out of 19mm glass, the tile cutter saw does it in about 20 minutes instead of 3 hours !!
    Hi to Keith and astrogirl too !!


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