The Prototype
Wow, Has it been busy lately. Let me tell you, its much easier to grind/polish/figure than it is actually build the scope assembly. Actually the scope was pretty easy, just a lot more physical work.
So let me start by saying that the
dang thing actually works!! J Here’s a picture that will save some words:
The whole thing packs up rather small, but it does require the use of a Philips screw driver and a block of wood to assemble. Here it is packed into the back of my Caravan.
How about a time-lapse video
showing the complete process of assembly? It’s a 45 second 1.4 Meg file, but
here it is.
Now, If your wondering about that block of wood in the video…. That was a design idea which is actually working well so far. For truss tubes I’m using ½ Galvanized metal electrical conduit (Cheap 12 cents/foot) The mirror base has a 11/16th inch hole bored at the just the right angle and depth. The truss tube is held to the mirror base by friction fit into the bored hole, and thus the need for the block of wood to ‘seat’ the tube into its hole. To remove, just twist and pull and it reluctantly slides out. Its probably the weakest link in my design so far, but at the moment its working surprisingly well. Here’s a picture of the mirror base/tube joint.
And one of the other end of the Truss tube, which is made from two pieces of ¾ inch MDF (Medium Density Fiber board)
How strong is the completed assembly? Strong enough to do this J
Since I’ve only talked about the
frame of the scope, lets continue on that theme. The bino scope consists of 2 completed Triangular scope assemblies
bolted to one common alt/az mount.
Looks like this:
Out near the points of each of the triangle is a ¼ - 20 threaded rod which attaches the scope to the alt/az mount. 2 of these rods have extensions added to them so they can be adjusted while viewing thru the scope. So far, once adjusted it seems to hold the binocular collimation fairly well.
The alt/az mount is pretty
simple basic Dobson design, just a lot wider.
Here is a picture of the altitude bearing which is a MDF disk wrapped in
aluminum metal (roof flashing) and uses “Floor Glide” Teflon? pads from home
depot.
The azimuth bearing took a little work. I tried using Teflon pads on plate of galvanized 24guage metal secured to the bottom of the altitude base, but do to either the weight of the completed package, or the less than efficient use of metal instead of Formica, it didn’t move very well. Since I already had the metal base, I picked up a 16 pack of roller blade bearing from Target for a measly $14.00. After thinking of many HARD ways to mount the bearing to the base, I came up with a really simple answer. On the base (the part that actually sits on the ground) I routed a 3/8” deep 1” long groove, then cut off a 2” length of steel rod , slide the bearing on with some washers on each side, sat the bearing in the grove and epoxied the shaft to the base. Like this:
The down side to this idea, as you can see in the photo, the metal was rather thin, and the bearings are causing the metal to deform, so far its working good, actually a little to good, I need to add some large washers to the center shaft to give it some friction, as it turns a little too easily J
Now for the good parts. Let’s start with the spider and secondary
(secondary is from Orion and 1.61” diameter) .
The spider is built from a piece of 1.5 inch poplar wood handrail
material. Center bolt is nylon, with
three collimation screws, and metal box strapping for support.
The end of the metal supports have a piece of ¼ - 20 threaded rod, split partially and epoxied to the end and supported in another block of MDF
Tertiary and focuser is constructed from a 1.5” PVC tee, with a similar tertiary mirror support as the one for the secondary, and a 1 ¼” threaded reducer bushing for the ‘helical’ focuser.
Now, about that focuser. As we know, PVC threaded parts are done with Pipe thread, which is tapered so the farther you screw it in, the tighter it gets. This is bad for a focuser J To fix this problem was rather simple. I took a metal 1 ¼” threaded extension tube which uses a washer and compression joint (go look under your kitchen sink for an example) Anyway the threads on the end of the pipe are the same as Pipe thread, just much shorter. I used a file to cut several grooves into the thread portion of the metal pipe to turn it into a thread tap. I used my improvised thread tap to rethread the female pipe thread into straight thread, then used a piece PVC threaded extension tube for the eyepiece receptacle.
Inter-pupilary distance is done by rotating the secondary / tertiary assembly like this
Being that I’m on the frugal side, which turned me into an ATMer, I obviously refused to pay the price of commercial eyepiece, so I made my own J
(7mm, 12.5mm, 26mm)
The eyepieces are made from Surplus shack Rini lens sets and are housed in one inch PVC couplers with lexan spacers/retainers and a piece of 1 inch pipe for a tail piece to hold the lexan spacers in place. The only down side is the OD of the one inch pipe is a little over 1 ¼” so I turned the completed assembly (minus lenses) down to the appropriate size on a wood lath. I now have 3 sets of identical eyepieces that work amazingly well and only spent less than $38.00 for materials!
OH yea, the mirror cell. Another fairly simple affair, once constructed J
The cell is a six point ‘plop’ designed cell. The cell starts with a (again) another ¼ - 20 threaded rod, on the end of which is a ball and socket leveling bolt. The ‘foot’ of the leveling bolt is epoxied to a piece of aluminum flat metal which is in turn siliconed to the back of the mirror. The mirror held its collimation on the ride from Florida to North Carolina just fine, its easy to adjust, and the leveling bolt can be removed from the treaded rod so as to afford easy removal of the mirror for silvering and cleaning.
So far I’m VERY happy with the scope and the primitive views its afforded so far. The moon is absolutely incredible when viewed with binocular vision. It goes from a 2D flat ‘coin’ like image when viewed with one eye, to a 3D ball floating just in front of you. The detail presented is stunning to the few novices (family) that have looked thru it so far.
Tomorrow we silver the mirrors and prepare for the Mars star party next weekend, I’m getting REAL excited.
Best wishes
James