This blog is mainly about Telescope making, and some things about my politics. At last we finally have a President that can say "Fool me once; shame on you. Fool me twice; shame on me." instead of mixing up with an old Who song.

Saturday, January 31, 2009

Reflective Break

Ok, so it kind of got cold this past fall and then Christmas and New Years and then all the other stuff, politics-wise. And I ran out of polish anyway (got some more now though). And a huge bill on my truck has pretty much left me in the design phase again.

So I've promised myself and several friends, that I would be starting out with a Steam Punk telescope. Cherry, brass, inlay, carving, maybe some leather and gold leaf (! right). I saw some nice minimalist designs that I liked, Jan vanGestal's 30cm in the Netherlands has a really simple 6pt mirror cell, I am designing a similar 4pt one. Another guy named Tim Nott in Australia, has a 16" tri-dob that he did a great job on, and I was seriously considering it too. It's a truss type OTA, but also liked the Pletestone cantelevered design. no links to that anymore :(. And before all that I saw a really nice design "Captain Nemo" by Anthropologist Ross Sackett. Featuring beautiful wood, brass, inlay, metalwork, and even gears and chains, its a marvel to look at and an inspiration, and I said "someday".

I went about scratching around other designs, like this partially completed one:
(click to enlarge them) It has a very open structure. In fact, the mirror is just laying there on its four points beneath it, and two on the side (against which it rests when you tip the whole thing away). It would work fine, but its kind of unsafe for several reasons. Most importantly, its a magnifying mirror. That means if I leave it out in the sun during the day it could blind someone passing by or start a fire very easily - even without a reflective coating. Also, it could get damaged by a stick falling from a nearby tree, or sand kicked up. Being so open like that has the nice feature of being very light weight though. But it has lots of very odd angles to it, and frankly, I am not up to the task of getting those very well, so early in my wood working experience.

But it gave me some good ideas. First, its a tri-dob. I like that. It mans that the mirror and the telescope above it sit in the middle of a triangle which is very stable and low to the ground. Also the two cresents are smaller than a traditional Dobsonian, and there is a center one of bigger diameter under the mirror. If I ever wanted to motorize it, then all I would have to drive would be that center rocker, and not two outer ones. The secondary mirror holder would have been a wire spider like Jan vanGestal uses.

This led to another one that is more enclosed version of the same thing. here is what the mirror box part of it would have looked like:

I threw some nice cad formatting in there to see what it would look like. Basically its 1/4" plywood bottom, top and sides. The three crescents are the same though. This design would be really easy to put a flip up cover so that the mirror would be protected when not in use. Popping the mirror out would be simply a matter of lifting it out with a little cradle tool so that I could store it in its storage box. I really liked this design. But again, its beyond my ability. All that curved wood is made by laminating and building up my own thick plywood from thinner plywood. I could do it after a few prototypes, but I have no experience with that, and it would look like crap with all kinds of compromises and rationalizations on my part before I got done. The other thing with this is the trusses. While they make the assembly very stiff (just like my mirror grinding stand in previous posts here), they are hard to put together right. This wouldn't be the case if I could simply put it together and leave it, but I want this thing to be portable, so they have to be easily disassembled each night. Making the hardware that will let you do that, and still be strong enough would be a difficult undertaking. Six truss poles is better than eight of them, but not by much. I made that design with TurboCad drawing software if you are curious. Fun stuff.

So, I went back to the drawing board - virtually - and decided that I needed to re-learn a lot of things that I haven't had to use since I was a college kid at GT. Things like stress, strain, elasticity, tension, compression, beams, moments of inertia, moments of insanity. What I really wanted was something that was strong enough, and stiff enough not to act like an archers bow every time I touched it. What it looked like afterwards could be 'art' if it looked wierd, or 'design' if I could make form follow function. Basically, a statement of excentricity - my favorite thing!

Then I looked on my Barack Obama calendar and there for January 30 is a quote by Nelson Mandela. - "There is no passion to be found in playing small - in settling for a life that is less than the one you are capable of living". Ok, so that clinched it. Back to the Steam Punk telescope, just do it.

Looking for inspiration I checked back at Ross' website and saw that he had updated it to include other designs I was unaware of. He also had some engineering pages that confirmed a lot of what I was discovering, and I became convinced that his "Moonsilver" series of scopes were simple enough and customizable enough that they fit right into what I was thinking.

So, my aim is to make a telescope that looks something like these images. I made them with Google Sketchup. Its a free program that really helps in visualizing what you want to make, and it allows you to make sure that all the moving parts won't knock into each other. Here is my interpretation. Or you can actually download the sketchup files and use them yourself. (they are copyrighted by me, so ask before taking. I'm into open source, so they are copyrighted so as to maintain that. contact me for details). Anyway, here is a link to the .skp file.
A view from the rear-side. This is what it would look like as you walk up to it. the eyepiece is in the brown thing at top left. That is connected to the base by a bent aluminum pole. Its bent so you back won't be.

Viewed from the other side - front side. the black circle is a light baffle that leaves the optical train unencumbered. It is mounted on its own smaller tube and is easily removable if its not needed for the night - like up in the north Georgia woods. Here in Atlanta, though, its needed, as there are too many street lights near my house.

Looking at it from the front. The diagonal mirror is held by a single curved piece of 1/8" aluminum. I might make that brass, and carve it :) What I don't show here is the lid for the mirror box.... details, details.

From the left. Here you can see the single crescent
(instead of three with the other design), and the attachment arm between the pivot point and the mirror box. This arm has attached to it the large 2.5" bent aluminum strut tube. The smaller bent 1/2" tube for the light baffle is attached to the end of the crescent. This is probably not a great idea, and I amy change that. The holes in the cresent do two things. they make it lighter with no loss in strength, and they make it look cool. Probably need some inlay here.

A view from the back. The septgonal mirror box
will have mirror columnation and safety screws in the bottom of it to adjust the mirror with.
One thing to note here is the two platforms at the bottom. The top of them has a 16 gauge steel plate attached to it for smoothness. It rides on the bottom one with roller bearings. I haven't decided how exactly yet. But it has plenty of room if I want to motorize it.

A view frm the right. Here, the vertical arm with the pivot point in it (a 3/8" bolt) rests on the base. At the end of the pivot arm is a carving like on a fiddle head or old time battering ram!

A view from the top. As you can see the base
rings are just that, rings. I may change that, because I probably need a vertical pivot point. But maybe not.

Again, you can see some holes, this time in the mirror box. Same reason.

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