This is a page dedicated to the conversion of my old “tube” dobsonian. The new scope is called the “Lowe’s Scope”, meaning, all materials are available at your nearest Lowe’s, except the mirrors of course. Lowe’s seemed to have a greater variety of unique brackets, craft wood and other small items necessary for the construction. This is not a sponsored project by any means. My goal as an incoming science teacher was to make something affordable, lightweight, portable built with parts available to anyone.

I have taken the time to detail as much as possible, and take as many detailed photos to help anyone else trying to make a conversion or simply build a strut or “truss” dobsonian. Don’t be a stranger! If you have questions, comments, email me at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Day 1

Investigating my existing "tube" dob.

Need to find out distance from primary mirror to mounting screws of spider secondary mirror mount. I don’t plan on touching the mount, so I will stick with the distance of 57 inches clean from mirror to mount screws in the new scope. New adjustment !! The primary had 1.5 inches depth from the base so I need to subtract that, so, now the new distance from primary is 57-1.5 = 55.5 inches. Hmmm.. nice number…

Mirror is 15 inches exactly… so, I still have no idea what the focal length is or the focal ratio.

Original mirror cell, if you want to even call it that, was a wooden tube “cap” with holes in it to fasten the cap to the tube. The cap had four wooden dowels that surrounded a piece of carpet wrapped in plastic. The primary mirror was laid onto this carpet-in-a-bag and then was held from slipping by rubber epoxy from a hot glue gun… very low tech, actually, NO tech…

Mirror brand, still unknown. The reverse of the mirror has a pink label on it that says “Hard Beral coating” a description of beral coatings and what looks like a manufacturer name and address, “P.A. Clausing, 8038 Monticello Ave. Skokie, Illinois, 60076”. We’ll look them up and see if they have focal ratio for their 14.5 inch mirrors… Well, that was easy, look up Beral coating and you come to Clausing: http://www.clausing.com/. Apparently Beral is trademarked by Clausing and it’s pretty good I guess, here’s a link to the Beral specs: http://www.clausing.com/beral.html

I’ve looked at many websites and plans and designs, but I need something simple, inexpensive and quick, I’ve narrowed it down to this design: http://www.lefevre.darkhorizons.org/papajoe/papajoe.htm

Has a good snap-latch idea that I like for the secondary cage to attached to the truss tubes. And it looks like he’s got insulation wrapping on the tubes themselves.

Day 2:

Took the old scope apart completely. Now I have a good spider secondary assembly and the focuser.

Day 3

Decided to focus on building the mirror box, and then the mirror cell. Went to Lowes on a whim just because I was tired of going to home depot. I wanted to see what kind of bolts and fasteners, locks they had. I was absolutely amazed to see how organized everything was, to be honest, I rarely go to Lowes even though it is across the highway from home depot. What a shock, I may never walk into another home depot again… There were clerks everywhere coming up to me asking if I needed help, completely opposite from home depot where you can’t find anyone around ever, and the people you do find are generally ex-state workers and have an attitude about working for money...

So, Lowes had knobs that connected to bolts, perfect for collomuation screws for the mirror cell. They had other locks like the snap ones that I found, the type you find on an old tool box with the little metal latch that swings and you lock it down, but I discovered that the latch type requires too much movement with your hand to lock it. Not that I’m lazy, but I’m just imagining myself with only two hands fumbling with the secondary mirror cage trying to put it on. So I think I will go with a curved push type lock, I’m not sure what they are really called, but you just push this little bowl shaped piece of metal and the lip of it locks into the bracket, holds well and one simply movement of the thumb locks it in place tight.

I also found some nice poplar pieces that I could stain and would make a really nice box out of. My materials purchase exactly was:

1x2x6 poplar board

1x4x6 poplar board

1x15 round stain grade pine wood, it’s a round piece of wood pre-cut and perfect size for a 14.5” mirror to rest on, or use as a dummy mirror.

I found some really cool copper pipe guide metal flat rods and I might use them to hold the mirror cell as the frame, I’m thinking of going for a 4 sided cell frame and a 6 point cell itself. Not quite sure how to do the cell but I’m considering using small drawer nobs coated in silicone epoxy.

Day 4:

Construction

I started with the wrong size mirror frame and the wrong size mirror box wood… So this building the mirror box ½ day project took nearly 6 hours and 3 trips to Lowes… But, I got most of it done. Most of my problems were that I didn’t measure the wood from the store first! The labels read 2X2 or 1X2, when they are totally not near 1 inch, they are actually ¾ inch or 1 and ¾ inch… This threw my plans way off, scratching my head why my math wasn’t working… Eventually I got it working using 2X2’s and some nice whitewood 1X6 plank for the outside that I plan to stain a nice dark red.

Day 5,

well, finding truss tubes is a pain in the ass… A local place here in Austin charges $63 for 12 feet of tube, that’s nuts… There’s a few places I’ve found online that ship:

http://www.texastowers.com/aluminum_.htm

http://www.hipco-ne.com/scope.htm

http://www.metalsdepot.com/products/alum2.phtml?page=rndtube&LimAcc=$LimAcc

metals depot has the cheapest so far, shipping is very low price too.

obsession telescopes sells tube inserts, pretty cheap!:

http://www.obsessiontelescopes.com/ATM_parts/index.html

found a place that sells threaded aluminum tube inserts for leveling things, which, don’t have to be leveling, they can be tightening like those I’ll need in several places on the scope:

http://www.jwwinco.com/products/section7/

here are other truss clamps:

http://www.webstertelescopes.com/truss_clamps.htm

Day 7

looking for tubes and clamps… it’s looking like I will need to move on and start designing the upper tube assembly. this needs to be lightweight and somewhat durable. I think the round circular ones are out of my league at this point, something quick, cheap and square but well built is more for me. I have borrowed a router now and that should improve my woodwork for now. I just don’t want to stop the momentum.

Day 8

I have decided to go with ¾ inch electrical conduit. Aluminum poles are WAY too expensive. The conduit is heavier, but the sheer price difference is worth the extra time spent designing and building something stronger to hold them. The aluminum poles at a minimum cost would be $100+ to complete it. The electrical conduit was only $3 for a 10 foot pole… Cut this in half and you have a 5 foot pole for only $1.50… Worth the change, and it’s readily available all over the country. Also, electrical conduit has lots of different accessories available like clamps, joiners, elbows, all kinds of stuff.

Day 9

Now that the tubes are sorted out, I need to finish the rocker box and the bearing. Again, reiterating the goal, this scope must be portable and able to fit in my car truck and carried by one person. I decided that even though plywood is cheap, it’s way too heavy and sticking with the whitewood or low grade pine is a good compromise between price, availability, strength and size. I went to lowe’s and found a large 1” X 12” X 10’ piece that would be good enough to finish the bearings and rocker. I brought the piece back and measured out the length necessary for the bearings, there’s no calculation here, I just eyeballed it from other pictures of other dobs that people had built. It seemed for the mirror box size I had, 55.5 cm, I needed an 80 cm wide bearing.

The next question was, what would my radius be, and how would I draw it? I decided with my limited tools to use the old style “nail, pencil and string” method of drawing circles. I placed the bearing plank on the floor and then placed a scrap board perpendicular to it, touching it. The scrap board midpoint line must be lined up with the bearing plank midpoint of the piece you want to cut, for this case, I had to line up on the 40 cm line since I would be using only 80 cm for the bearing. I hammered a nail into the scrap board at one distance and tied a string around the nail. Pulling the string in a circle, you get the outline of a perfect circle. I tried this a few times with different radii, and came up with one I liked, it worked out to be a 56 cm distance from the center of the nail to the corner of the plank. This may or may not work for other people.

Once the bearing was drawn out, I had to cut it with a jigsaw and then sand it down good all over. Cutting a curve with a cheap jigsaw was no fun, it has to be precise, mine was not, but I was able to sand down a lot of the operator errors.

With the bearings cut, probably the most difficult measurement was figuring out where to place them. I decided to again follow some examples of other big dobs out there and go with an off center placement which would allow the mirror box to swing low or high without stressing out mirror too much. Big mirrors need this, smaller mirrors like anything under 10 inches probably doesn’t need this off-center bearing placement. Anyhow, I decided that one corner of the mirror box should meet an edge of the bearing, and also provide enough room to swing through the rocker box. I have no calculations for where this should go, you’ll just need to eyeball it and measure several times. I must have spent 15 minutes trying to make sure, afterwards I was glad with my decision. The bearings swing extremely smooth through the rocker and there is a minimal 1 inch clearance; meaning, I’ve minimalized the size of this down to a good extreme.

REDESIGNED THE SECONDARY MIRROR CAGE AND STRUT SYSTEM. .  GOT A SEARS DRILL PRESS ON SALE FOR $120.  VERY NICE MACHINE!!!

IT WORKS!!

JUPITER AND TWO VISIBLE MOONS SHOT FROM CAMERA PHONE CAMERA