I am in the processes of research, reading, note taking etc to build a portable Newt probably 14" to 16". Its going to be a long term project as it will take at least 8 months to save the money for the glass.
Began with the two books "The Dobsonian Telescope" Kriege and Berry and "Portable Newtonian Telescopes" Highe.
Three months later I have a spreadsheet with dimensions, calculations and scale drawings on graph paper.
Interesting to note the difference between the two books. Kriege (old school) Strong, well built and Large.
The more recent approach to design appears to be based on how you establish and implement the balance or M point, as this shapes the rest of the design. Kriege uses the middle top of the mirror box as the point of balance.
Highe uses a spreadsheet to calculate the precise point of balance. In my case, based on best estimates, my distance is 17 1/4 inches. This will be used to define the Radius of the Altitude bearings. Thus enabling a low mirror box and rocker.
Look forward to following your progress Neil. I thought first of going with a compact design but might make that my second foray into the ATM world.
My current build will be along the SDM/Obsession lines as portability is not really a concern.
I'll watch this with interest, ready to pinch any good ideas you come up with!
My 8" Dob is solid tubed and can be a handful to transport. I've seen some of the nested box designs people have made and think that's a good way to do it.
When I get around to this - and it won't be until the end of the year at least - I intend to make an octagonal secondary cage which nests inside the mirror box, which nests inside the rocker box. I'm not planning to make it as tiny as some of the air transportable ones people make, the plan is to make it fold down into a solid wood chest small enough to fit upright in the back of my Yaris hatchback with a small footprint.
Sourced Aluminium C channel, T-Nuts, Collimation Screws, (have to exchange them for longer ones with a smaller head, to recess into the top of mirror cell).
Will have to remember to not cut out the triangle mirror cell middle section until it has been positioned over the exact middle of the mirror box base plate and marked with a Center hole and collimation screw holes.
All first time stuff. Rocker bar shaped, center hole sorted
Wow, after reading the thread from Matt building his state of the art Newt I feel like a total amateur. Very inspiring though, and informative.
My prototype continues using free construction grade ply
(was used as cement form work). Rocker bar shaped, center hole sorted. Mirror cell holes for collimation bolts aligned on mirror box bottom board. (that bit has to be accurate).
Thanks Neil, I am just copying what others have designed and adding little bits along the way.
Nothing wrong with using formply Neil, I spent 12 years cutting that stuff and supervising others doing the same. I am watching your design with great interest. Keep the pictures coming!
Progress for the day:
Cut out the mirror box sides.
Found clevis pin the correct length for aluminium rockers
Found one spring and ordered more (8 required) 1/2 inch diameter and 1/2 compressed.
Testing a longer collimation screw to fit two widths of 19mm ply, and counter sunk springs, plus room for wing nut with some travel. Hard to estimate exact length.
Resting sides together for photo. Will use 1/2 inch ply not 3/4 inch in final version.
Back on task after some days away. Glued bottom and sides of mirror box and a fair bit of sanding on edges to make up for (degree of error!!!)
I too cut lids and bases oversize and then get the belt sander out to bring them back to size after the glue has set, that way you don't have to worry about splintering edges.
Marking out Alt bearings and rocker. Attempting to use same method as Highe by using the same board for both left and right versions of bearings plus one side of the rocker. Could get interesting when it comes to routing !!!!
Had a hack at sawing the corner off the mirror box (leading corner about 2 and 3 inches) last night using a hand saw through the lot in one go. Don't think I will try that one again with the final project.
Time for routing both Alt Bearings on the same ply sheet. Router jig is anchored with a nail at 17 1/4 inches. Requires extension board off the central sheet for the second bearing.
Using the cut off to create the correct arc for one side of the rocker. Expect to duplicate this using the router duplicate bit method.
Now to position both bearings on the mirror box in the exact same position with the exact same anchor positions.
Completed second side of rocker using the duplicate router bit and nailed two end boards to test if it all works. Its all about margin or error, how square each board or routed edge is.
Tested how much can be trimmed and shaped off the Alt beams to provide Azimuth to Horizon movement.
Have to test exact anchor points for each beam so the the curvature is the same both sides.
Rocker end boards and base board pinned. Its time to get some accuracy so that the mirror box moves freely but with not to much slop, about 1/8 of an inch. Used narrow pinning nails to test. Used the base board to get things square before gluing and screwing.
