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Thread: George's Telescope - Consolidated Threads

  1. #31
    David, you are quite the craftsman, this piece is amazing already. It'd hard to imagine that your not finished, with the way it already looks. If it was me creating it, I would stop now before buggering it up.
    Len

  2. #32
    Quote Originally Posted by Steve Schlumpf View Post
    David - for most of us, learning how to turn is a lot of fun but extremely challenging when trying to turn two things that look alike. The precision you show in every aspect of your telescope is amazing but I am afraid leaves most of us searching for words. I look forward to each update and really want to see the photos when your grandson actually gets the telescope! Thanks for sharing the journey!!
    +1. And it will be a gift he will cherish his entire lifetime.
    What a beautiful job!

    Fred

  3. #33
    Thanx the forum moderators for putting this all in one place and to John Keeton for suggesting it. I have a couple of other parts done and I'll post those here as well.

  4. #34
    Join Date
    Oct 2006
    Location
    Harvey, Michigan
    Posts
    20,292
    Looking forward to seeing the parts David! Any idea on a projected completion date? Just curious as I realize it may be another month or two before George is ready for the telescope.
    Steve

    “You never know what you got til it's gone!”
    Please don’t let that happen!
    Become a financial Contributor today!

  5. #35
    David, what type of lathe are you using to do this turning with, a metal turning lathe, or a wood turning lathe?
    Len

  6. #36
    My lathe is the one pictured in my avatar, a 50's Rockwell wood turning lathe I inherited from my old man. Stock unit except for the paint job...

  7. #37
    Join Date
    Nov 2012
    Location
    Raleigh, NC
    Posts
    53
    This is fascinating. I look forward to seeing more.

    I'm an occasional stargazer and am wondering if the wood will have any effect on collimation? If you will have to realign more often or maybe less often since wood is not affected by temperature.

  8. #38
    My experience with telescopes is the material the scope is made of is less of a factor in stable collimatoin than the design. I have built or helped build or designed scopes from 25 inches to 1 1/4 inch diameter. The usual suspect in collimatoin issues is the mirror cell. Followed by spider/diagonal flex or slop... The sneakiest issue is focuser tilt. Most focusers don't have adjustments for tilt. Mine do... Occasionally a loose lense in the eyepiece itself appears as a collimation problem. Tube flexture sometimes makes a telescope impossible to collimate reliably.

    some of my telescopes have not needed recollimation for years. Truss tube scopes can need recollimation after each time they are touched. My tensioned truss tube scopes generally stay collimated even after being disassembled and reassembled. Wood is good as a scope material.

    clint

  9. #39

    Additional Components

    These are a couple of additional parts that have been completed.

    This is a "Telrad" finder sight. It projects a target onto the angled glass. I deconstructed one and remade it out of padouk and ebony...

    telrad_1.jpg

    The "stock" plastic version...
    telrad_stock.jpg

    This is the primary mirror cell. The design was generated by a program called "GUI Plop" which plots out the best support points for the mirror. When my grandson heard me talking about this program, he said "Eeew... gooey plop" and went around saying "gooey plop" for the rest of the day.

    cell_1.jpg cell_2.jpg

    The cell will live in the bottom of the main optical tube and, most likely, never see the light of day again once installed.
    Last edited by David DeCristoforo; 09-24-2017 at 12:44 PM.

  10. #40
    David,

    planned a dew shield for that telrad? They tend to dew up and become almost useless in a short time out under a clear night sky. Just my experience...

    Nice looking mirror cell...

    clint

  11. #41
    Quote Originally Posted by Clint Bach View Post
    David,

    planned a dew shield for that tetrad...

    clint
    I have seen several posts on amateur telescope making forums that have to do with adding a dew heater to a Telrad finder. I may get involved with that at some point but first, I want to get the thing built!
    David DeCristoforo

  12. #42

    GEM Mount Polar Adjustment Mechanism Plan

    Here is my plan for the “fine adjustment” mechanism for the mount. Basically, it’s a captured nut and a “gimbal” (dark gray) that pivots in an opening in the center brace. I’m not sure the exact geometry is correct so I will mock this up before making any of the pieces. Any thoughts will be most appreciated. I have already been given a rather brilliant idea in the inclusion of two locations for the locking nut which allows the curved slot to be much shorter that in my original plan while, at the same time allowing a greater range of movement. Needless to say, this will be made of wood with maybe some metal for the pivot pins and possibly bronze bushings for the gimbal pivot.

    mount_4.jpg
    David DeCristoforo

  13. #43
    David,

    that will work. But... Having the elevating screw perpendicular to the lifted axis will be more robust and put less stress on the screw and mount in general. As an example, at very low latitudes, or the equator the elevation screw would not function at all or poorly. That scope may never be set up at or near the equator so it probably is a non issue. Keep in mid that a scope can last hundreds of years and the future is unknown.

    a fine adjustment to align the mount east and west comes in very handy. Imagine the hassle of aligning the elevation and the having to pick up the mount to rotate it east or west... That screws up the elevation. repeat. Repeat. Repeat. Not quick or fun.

    great looking scope!

    clint

  14. #44
    Quote Originally Posted by Clint Bach View Post
    David,

    that will work. But... Having the elevating screw perpendicular to the lifted axis will be more robust and put less stress on the screw and mount in general. As an example, at very low latitudes, or the equator the elevation screw would not function at all or poorly. That scope may never be set up at or near the equator so it probably is a non issue. Keep in mid that a scope can last hundreds of years and the future is unknown.

    a fine adjustment to align the mount east and west comes in very handy. Imagine the hassle of aligning the elevation and the having to pick up the mount to rotate it east or west... That screws up the elevation. repeat. Repeat. Repeat. Not quick or fun.

    great looking scope!

    clint
    The intent here is to have tilt range of 25 to 50 degrees which will make the mount useable anywhere in the continental US. It will initially reside in Davis, CA which is at 38 degrees longitude. The gray rectangle, which represents the carriage that the polar shaft will mount on, is drawn at that angle. I have revised this drawing at least a dozen times. Here is the latest revision.
    mount_5.jpg
    It is taller by four inches (now a total height of 16") to allow for a more perpendicular angle between the carriage and the adjusting screw. The two small circles in the curved slot represent threaded holes for the pin and locking knob (not drawn). Having two locations allows for a greater range of movement without having to make the slot longer.

    Interesting to note: Most of the custom made GEM mounts I have looked at are built to be more or less permanently installed at a specific location (longitude) and therefore have a very limited adjustment range. I wanted this one to be a bit more flexible.

    PS The two pieces of the base are on a bearing (think "lazy susan") so rotation will not be an issue. There will also be an inlaid compass and leveling bubble as well as a locking knob which are not shown in the drawing. This will all sit on a pedestal (design yet to be finalized) which will have adjustable casters. This will facilitate easy movement of the scope as well as leveling once it is in position.
    Last edited by David DeCristoforo; 10-08-2017 at 3:01 PM.
    David DeCristoforo

  15. #45
    David,

    Much better! Your scope will appreciate the extra stability. Some scopes use screw downs to lift the casters off the ground. Even heavy duty casters can be a source of slop while observing. At high powers small flexures add up quickly. The quicker a scope settles down after a move the more enjoyable it can be. I have observed through scopes the "ring". That means they shake after any small movement such as focusing or small adjustments. Your scope seems to be well on its way to being stable and not ringing. Leg to pedestal connections can be a weak point.

    Clint

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