Choosing the Optics of your scope will be
the single most important part of building your telescope over all other considerations. The quality
of the optics, the optical performance out in the field will be the drive behind all your reserch and
thoughts on weather to purchase a mirror completed or buy a kit and grind your own. Many people will say
that grinding your own mirror is the only way to go although cost is a factor. Mirror kits today can almost rival the
cost of a mirror completed in a factory and if size is a factor to you the larger the mirror the more precise
the grinding and the biger the exspence. There is a ideology that exits between those who grind and figure mirrors
and those who just want to buy a mirror and throw it in to their telescope. Its the joy and contentment of making
a truely great mirror with spectacular results. Its the strive to make the best error free optics. There is a great
sense of satisfaction that goes with this exsperience and of course some hard consistant elbow greese can temper
the soul. Sometimes I beleive that some grinders don't realy care if there mirror even ends up in a telescope because
they seem to just enjoy grinding the mirror. I suggest if you want to grind a mirror start out small (a 4 1/2 to 6" Mirror)
and check to see if any of your local Astronomy Clubs are having mirror grinding classes or if they know of classes being
offered in your area. There is always of course Books like Richard Berry's "Build your own Telescope" and Jean Texereau
"How to make a Telescope". I have compiled a small list on my Materials and tips page.
This section is basically for those who choose to build a
Truss Tube Telescope like the one pictured. There are many types of this design and all use diferent types of connectors and
clamps to secure the secondary cage to the Mirror Box Base. I choose an off center Camber locking system at the mirror box
and the Typical wedge block clamp at the Top. I found that this clamping process took a lot of reserch and even after I choose the
Type of clamping system I always found others that might have served me better.
It will ultimately
be up to you to deside which will work best for you. I just made sure that I got to one of the major Star Parties and took lots of
pictures of other systems so I had a good understanding of how each design worked. My system was designed by a friend of mine
who is a machinist. He fashioned these Clamps out of high density plastic. He drilled holes through the top clamping wedges to lighten
them up and the base blocks are cut a quarter the radius of the 1 inch aluminum tubing down to just short of the end of the block to
create a seat for the Truss. The off center camber locks just tighten more if you pull on the Truss. The draw back of this system is that you have 8
individual clamps. There are systems that will clamp 2 trusses per Clamp But designed carefully all will serve you well.
Just remember that the main object to these clamping devises is to connect the secondary cage to the mirror box. If you have done the proper reserch and
calculated your angles and length of your trusses in relation to your focal length and required focusing distance your telescope should only at this point
depend on the positioning of the secondary mirror, spider assembly and your adjustments on your primary mirror cell. Last, I would like to emphasize that it should be easy enough
for one person to set up on there own. The trusses should be able to stay upright on there own. Look to this section on this page
for future pictures and information on clamps and connectors of other kinds of truss tube design. I will keep investigating new and creative ideas and try to post them
on this page.
There is tons of stuff I can talk about when it comes to mirror cells. As for which design is best, They all have there place in the sun. This section will try to help you understand
how each design works so the intended result will help you deside which is best for the scope you will build. There is no end to the kinds of things that people
come up with on mirror cells although there are realy only a few principles that all of them are base on. These are 1. Claw and Clamp design 2. A three or four pad adjustable sling cell.
3. Push-Pull cells. All Designs regardless of what they are called are based on these three principle design properties. The first type of cell is one of the most secure and knock worthy cells you can install.
It can take the bumps of those pot holed fire roads and consistant bumps of setting it up and tearing it down without loosing its collumnation. The unit is usually a two piece assembly of which is metal. The first
part attaches to the base of the tube or mirror box. It also runs the 3 point adjustments that will collumnate the mirror. The second part holds the mirror securely in place and is supported by the 3 adjustment bolts
that are spring loaded and threaded up through the first part.
There are a few companys which you can obtain these kinds of cells. Univercity optics sells them and you can purchase 4 1/4 inch to 13.1 inch
cells. There address is University Optics P.O. Box 1205, Ann Arbor, MI 48106. Phone # (313) 665-3575 for cataloge and questions. or call for order 800-521-2828. It is possible to make this kind of mirror cell if you have the
ability to melt down scrap aluminum and make your own mold. I happen to know a few people who are able to do this with pretty primitive equipment. Again, this depends on how serious and committed you are on all aspects of the project. I myself with help
from a friend made a mold and small smelter heated by only a single large propane burner, fashioned 1 pound round weights for my telescope.
The second principle design is the sling. this is a design that incorporates a flotation point system from usually 9 to 18 points. Some larger mirrors,( 30" to 44") go even higher on these points. The mirror is then supported by a large sling on the
down side of the cell which supports the mirrors weight. When the telescope is seriously bumped or in transportation it is almost inevitable that you will need to collumnate the mirror for your viewing session. this takes some time but its not to much problem if the
telescope has a good working adjustment system and a laser collumnator can realy come in handy. This type of principle was seen commonly in most coulter telescopes in a very primitive and cost eficient way. and most large scale truss tube telescopes use them also although
they are far more elaborate.
Spiders,Secondary Mirror Cells
Now this is where some of the more complicated thought processes start to kindle. I think I looked at hundreds of diferent designs. All of them were about the same in functionality but all seemed to be machined
in some way and welded. This presented a problem to me as I did not have this kind of equipment available to me in the beginning. So at this point I had desided that I might buy one from a Orion Telescope company. Orion sells and excellent spider and cell plus secondary mirrors. But
eventually I came up with a solution to have a spider made by another friend. The most complicated part of this cell is the center bracket that must be able to run a piece of threaded rod through it for up-down and rotational adjustment. It must also incorporate channels so
you can pin aluminum slats to it which will eventually attach to the secondary mirror cage. You can also use cut steel flashing from your local Eagle, Home Depot or construction hardware store. Flashing works nicely and its cheap. Again, study other telescopes to help you figure what you
want to do. I have seen them made using Flashing, Aluminum rod, aluminum square commonly used for bathroom towel holders or shower curtains. You can find this stuff where the store keeps all the aluminum extruded products. I have also seen some creative cells made with cut aluminum tube to
hold the secondary mirror and guitar string cable to hold the assembly to the cage.
Mirrors, Rocker Box's and Bearings
It was early on in the planning of my truss tube telescope that I focused on certain aspects of its proposed design. First it needed to be low, no more than 15" high when the mirror and rocker box's were packed together. Second it had to fit in the back trunk of my 94 toyota corolla. The rocker box and secondary cage needed to occupy the trunk space together. My measurements were now coordinated around the car in which the scope was to be transported in and not the scope based on conventional methods of proper balance, fit and finish. You could say I designed it around my Toyota. I drew my plan on a computer cad (Computer Aided Drafting)system. My main profession is a drafter in the areospace industrie. I was able to do most of my focal lenth calculations on a program called NEWT and then use this information to set up the length of my trusses and distance from my primary mirror to secondarymirror to the focusing travel. When I created the mirror box and rocker box I was able actualy rotate the mirror box back and forth on the computer to see that there was plenty of clearence. When the parts were cut out with a regular sears table saw they were real tight. Very accurate. The wood Box's were then glued together, I counter sunk wood screws and cut dowl to plug them. The dowling was then sanded flush and the Box's then stained to finish. I then used and outdoor polyurethane finish protectant. The result was a beautiful stained finish that I could be proud of. This scope was based on my needs and preferences but yours may be diferent. maybe your not interested in the cosmetic qualities or you don't have a small toyota like me. You can then go to the more conventional ways of building these scopes. Just remember, Build what you want and what you will use. You will be proud of it when your done.
I thought I would use my own cage to help picture the certain aspects of the mirror cage. The cage is simply for housing the secondary mirror assembly and the
focusing unit. One of the things that I had trouble with was the four aluminum posts and they were to attach to the top and bottom rings. Believe me, I made a few mistakes here and quite frankly there funny. I was sitting about my kitchen table looking at the parts and the
great job I had done on the focusing board. Ready to get on with installing the posts my friend and I had desided to use threaded rod through the posts to either end of the wood rings and bolt them down. Why we didn't catch our mistake Im not sure but we most definitly goofed. Just the night before we drilled the posts
to accomodate the spider assembly. So here we are bolting down the rings to the posts looking at it for a while when it finally hit us that we were dummys. Because of the threaded rod there was no way for the long bolts to go through the posts. Whoops!
Well of course we had to disassemble the whole thing and make dowl plugs, each end with epoxed threaded rod. We let them sit a few days and reassemble the cage. It turned out perfect. You simply have to laugh at stuff like this when it happens.
Around June of 1996 I went to the Green Lake Star party put on by the Seattle Astronomy Society and noticed a member there
with a home made Dob similar to a Richard Berry design. On it he had a Focuser that looked very much like a Crayford Design. Finally assessing that this was true, with pen in hand I scibbled its design on to a small piece of
paper and showed it to my friend. Within a few days he had the focuser almost complete. It just needed bearings. Where could I find these very small 1/4 inch bearings? Ha! The local RC Hobby shop. They had plenty of small bearings which are used
in the RC cars and dunebuggy's. I went down and purchased two packages each containing 2 bearings. we installed them with 4 small allen cap head screws. He fashioned some Nobs out of plastic scrap and drilled some threaded holes. Threaded inserts were placed here to lock
down the Knobs on to piano wire(Also obtained at the hobby shop which is used for RC Airplane landing gears). Tha piano wire is mounted through posts and covered with plastic fuel tubing. It is then pressed against the focuser with a degree of tension.
The most you will ever half to do is replace the plastic fuel tubing because it squashes after awhile. I have never replaced mine yet so it lasts a while.
Here are a couple of other clamps I photographed at TMSP. Click the light wood truss scope to see the other images. The Bottom clamp design on this light wood truss telescope is a simple split wood square that has been pre bored to the
diameter of the truss. Split part of the way through, the truss is squeezed secure by a Knob bolt tightening down through a T-nut in the mirror box. The clamp it self is secured by 2 wood screws. A closer look at the image on the other page should let you have some idea how it was done. The other is slightly the same but uses 3 bolts to
secure them down when the trusses are installed. Notice the upper cage clamp. See its locking lever. When you look at the diferent methods of designing clamps its hard to choose the one you want. Which will be more effective.
Since I built my scope without following the standard balancing methods I needed to compensate this with a weight system. My unit requires about 35 to 38 pounds of weight depending on weather I put a 1.25 or 2" eye peice in the focuser. My friend and I created a smelter and a 4 inch aluminum mold to make small 1 pound lead weights. I drilled the back board on my scope to incorporate 8 long 3/8 6" bolts to hold the weights. This allowed the scope good balance and stability. It was real rock solid. My scope is definitly heavier than others its size but thats what I wanted. If you want the scope to be lighter, build it with a taller box in mind and use thinner wood. I used 3/4 inch ply all the way around. And of course use the conventional methods of balancing. Weights can be obtained from "the Telescope and Binnocular Company" Originaly called Orion. But these weights are only for certain applications. You will most likely have to come up with something on your own. Try your local Marine outfit stores. Iv seen lead weights in diferent shapes used for sale boat applications. There are also fishing weights. Or visit some local mashine shops and see if they have scrap lead that they might want to get rid of.
One thing that always was a factor in the building of my 13.1 inch telescope was making it easy to set up. I own a LX200 8", Not as big as the 10" or 12" but just as much
a committment to set up and tear down. It takes about a half hour to 45 minutes to hook it all up and be observing comfortably. After an hour or two its time to tear it down. Lots of cables to wrap up and stuff to put away in the dark with a flash light.
And if your like me at all you proably would just throw it all in a box and do it when you get home. All in all you will not get to bed until very late in the winter and even later in the summer. I had all this in mind when I designed my truss tube telescope.
I wanted the telescope to be quick and easy to set up. (less than 10 minutes) and fast and easy to break down and put in the back of my Toyota Corolla. Further more I wanted very little hassels with it at home. I just wanted to remove it from the car and put it in the corner
of my bedroom and forget about it until next time. No late nights putting stuff away, just carry it in and get on with other stuff. You will appreciate this like I do. Its no wonder My wife thinks that the Dob with its large aperature and easy set up time thinks the
LX200 is becoming a hanger queen in the closet. Maybe so but it has its place in my heart also.
