Page 5 of 5 FirstFirst 12345
Results 61 to 74 of 74

Thread: George's Telescope - Consolidated Threads

  1. #61

    Declination Shaft Installed

    Here is the mount so far. The declination shaft is installed in it's housing. I ended up cutting the housing down by about eight inches in length after realizing that it did not need to be nearly as long as I had made it.
    dec_shaft_installed.jpg
    Next up is the pedestal and the scope mounting platform and rings.

    PS Sorry about the terrible image. I have exceeded the capacity of my "photo booth"!
    David DeCristoforo

  2. #62
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    6,210
    Quote Originally Posted by David DeCristoforo View Post
    Here is the mount so far. The declination shaft is installed in it's housing. I ended up cutting the housing down by about eight inches in length after realizing that it did not need to be nearly as long as I had made it.

    Next up is the pedestal and the scope mounting platform and rings.

    PS Sorry about the terrible image. I have exceeded the capacity of my "photo booth"!
    David, your work really deserves a new photo booth! I used some PVC pipe, some thin white cloth, and a piece of curved mat board to make a booth for turnings. But for the whole telescope you might need a really big booth!

    photo_cube.jpg

    I'd love to read the book you publish on making this - sketches, shop shots, finished scope out under the stars!

    JKJ

  3. #63
    I made a photo booth like that years ago. But this thing is too big for it. So I either have to make a bigger version or fake it. As it progresses from here, it’s only going to get bigger!

  4. #64

    Scope Rings

    Scope rings done and mounted. I left a bit of “wiggle room” on the I.D. to allow for still to be applied leather liners. Next up is the pedestal.

    scope_rings_2.jpg

    scope_rings_1.jpg
    David DeCristoforo

  5. #65

    Close Call...

    For almost two years now, I have devoted every spare minute and every cent I could get my hands on to my telescope project. All other ideas about things I might want to make have been pushed to the back burner. When I started out, my intent was to build a Dobsonian style mount which is a fairly simple rocker box design, mostly simple “flatwork” using plywood. But once I discovered the GEM mount I could not shake loose the idea of building one. The decision probably cost me a year and required much more expensive material, time and fussy detail work than I ever intended to invest in this. Getting it (mostly) done was a great relief and my focus could shift back to the scope itself.


    I have documented every step of this project and I needed a pic of the mount in it’s completed state. Having no really good setup for this, I set the mount on top of a stool with a fabric backdrop. That worked out OK and I goy my pics. Then I had to get to work so I thought I would move the mount back into the house the next morning. You might well imagine my discouragement when I entered my shop to see the mount lying on the floor amidst a tangle of lathe tools, extension cords, pieces of wood and other stuff. Apparently, since there is, at this point, no counterweight to offset the weight of the scope rings, the upper (declination) shaft had rotated, throwing the whole thing out of balance and causing it to topple over.


    My first action was to simply turn around and go back into the house. It took me almost an hour to calm myself enough to go back out to asses the damage. After detangling the cords and tools and wood enough to pick up the mount, I got it back up on the bench. The whole time I was looking for the inevitable broken parts and ruined components. I could not imagine this happening without major damage and I feared that I might not have the heart to do it over even if I could salvage many of the pieces.


    But to my utter amazement, there was almost no damage. A few chips in the paint, easily touched up and one slightly more significant chip on the upper edge of one of the rings that required a bit of bondo to repair. But, outside of that, the mount was completely intact and undamaged! My sense gratitude is of galactic proportions. I might take a break from this for a few days….


    FWIW, The mount is now safely back in the house, no worse for the wear and all is well...
    David DeCristoforo

  6. #66
    I was fearful ,though safe enough, as I read. Thankful all is well, thanks for keeping informed.

  7. #67
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    6,210
    Yikes, I probably would have fainted!

  8. #68

    Counterweight

    After the near death experience with the mount toppling over, I decided that I’d better come up with a counterweight right away. I will have to add weight to this once the scope is mounted but until that point I cannot determine exactly how much weight will be needed. The intention is to drill into the ends of the counterweight, fill the holes with lead shot and then plug them. That will be easy enough to do when the time comes but for now, this is sufficient to offset the weight of the mounting platform and rings.

    counterweight_1.jpg
    David DeCristoforo

  9. #69
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    6,210
    Quote Originally Posted by David DeCristoforo View Post
    ...The intention is to drill into the ends of the counterweight, fill the holes with lead shot and then plug them.
    I've also used lead shot for balancing in wood. After determining the exact weight needed I mixed the shot with a little epoxy to keep it in place. My use was to balance dressage whips for equestrian use. For this use it kept the loose shot from moving.

    After the close encounter with splintering I think I might also do something else temporarily, such as tying a rope to a screw eye in the ceiling!

  10. #70
    Quote Originally Posted by John K Jordan View Post
    I've also used lead shot for balancing in wood. After determining the exact weight needed I mixed the shot with a little epoxy to keep it in place. My use was to balance dressage whips for equestrian use. For this use it kept the loose shot from moving.

    After the close encounter with splintering I think I might also do something else temporarily, such as tying a rope to a screw eye in the ceiling!
    We used to bed the shot in silicone to weight chess pieces. That or epoxy will be used here. I actually thought about considered the whole tie down thing but sitting on a solid table with the counter weight, it’s actually quite stable.

  11. #71

    Inclinometer

    In order for a GEM mount to function properly, several adjustments need to be made. Probably the most important is that the polar shaft angle needs to be set to the lattitude at which the scope is located. Some form of indicator is needed. I decided to mount a simple pendulum type inclinometer on the polar shaft. There are many available but all suffer from the same drawback in that they are made of plastic. Not good so I decided to try making one out of wood. This is not, I am sure, up to NASA specs but it gets the job done well enough. The pointer was turned using a split paper joint. The lower bulb is drilled out on the back and a 1/4” steel ball was glued into the hole to add some weight at the bottom.

    inclinometer_1.jpg

    Here is is mounted on the polar shaft...

    inclinometer_2.jpg
    David DeCristoforo

  12. #72

    Mount Completed...

    So it's finally standing on it's own two... or three, yes, three... feet...er... wheels... I mean wheels. Whatever... the mount is done. Well, it's as done as it can be at this point. I may change out the casters for something a bit more elegant before I'm finished with this and I'm still contemplating adding setting circles. But for now, it's finished and I can move on to completing the scope itself.

    mount_done.jpg
    mount_detail.jpg

    The upper part of the mount rides on a heavy duty (350 lb load rating) turntable bearing and rotates a full 360 degrees. It is pretty free spinning, maybe more than one might want. I had anticipated this and built in a tensioning nut. You can see it under the mount tubes. There have been many "design opportunities" in the building of this thing and one of them was making the opening for the tensioning nut too small to get your hand in to grip it. So I drilled six holes around the rim of the nut and made a spanner to tighten it.


    All in all, this has been a major diversion from my original plan which was to build a Dobsonian type scope which uses a much simpler rocker box mount. I'm glad now that I went with building the GEM mount but I also glad it's done and I can move on now..
    David DeCristoforo

  13. #73
    Join Date
    Mar 2015
    Location
    East Tennessee
    Posts
    833
    All I can say is WOW!!!!!!!
    What an awesome piece. I'm sure it will be a family heirloom.

  14. #74
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    2,691
    Sorry I missed this from the beginning. I'm just now seeing it.

    My best friend, and I, started building telescopes when we were 14 and 15, in 1964. Getting 60mm refractors for Christmas one year, and being disapointed in them, we decided to start building larger ones. Complete telescopes then cost about the same amount of dollars as they do now, so that made them REALLY expensive back then.

    Edmund Scientific sold telescope making kits, and books. That's where we started, and bought the Amateur Telescope Making series of books. The kits were glass blanks, and tool, for grinding mirrors of different sizes.

    We built a number of them, with the largest being a 12-1/2" f/6. For the 12-1/2", we built a 12x12 observatory with a roof that rolled off, when we were Junior, and Senior in High School, by truck headlights at night, in the middle of one of the cow pastures where I lived. Back then, we were fortunate to have very dark skies where we lived-different than that now.

    Ours, of course, looked nothing like yours. Ours were simply for being used.

    Long story shortened, my friend now has one of the offices on the end of a hall in the Science building at NASA. He's won all sorts of awards. He wasn't in on the building of the Hubble, but when they needed to fix it, he took our 12-1/2" mirror in to be checked, and it was something like a factor of 3 better than anything they had there. He was put on the team to come up with a fix for the Hubble. We had used a micrometer, for the Focault test, made from a 1/4-20 screw, and the mirror was ground in my bedroom.

    I have very much enjoyed the building of your telescope.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •