I've never been completely satisfied with the spider design on the telescope, so I decided to read up on the various spider designs and what folks had to say about them. One design really caught my attention because implementing it would be so easy and it has an appealing simplicity - Gary Seronik's curved spider using a stainless steel ruler. The beauty of using the stainless ruler is that it is quite thin, is springy so it retains a consistent arc, and also has tension due to the springiness. Gary's design has a sharper bend and smaller arc than I eventually ended up with. When I first mounted the spider exactly as Gary did, I found out that it had quite a bit of vibration.

I was never able to eliminate the spider vibration when I move or bump the scope, I tried different configurations until I felt that I had it minimized. Now I just need a weekend when it is not raining or cloudy to test it out.

I also replaced my Kineoptics HC focuser with a JMI Crayford. Call me a luddite, but I prefer the two crank knobs to twisting the entire focuser.

Images can be found in this Telescope v.2 Modifications photo set on Flickr.

I periodically browse around for new ATM (Amateur Telescope Making) and DIY Astronomy articles online, because amateur astronomers are always coming up with new stuff and are also always eager to share. And because amateur astronomers, like me, are always looking for new DIY projects.

What I found this time is that my own telescope design and documentation has been featured on Wired Magazine's GEEKDAD blog, maintained by John Baichtal, and cited on Make Magazine online by Phillip Torrone.

Build Your Own Newtonian Telescope on GEEKDAD

HOW TO - Build your own telescope on Make: Online

When I redesigned and rebuilt the telescope, one thing that I didn't change was the primary mirror cell. A few weeks ago I decided to clean the mirror and reached a few conclusions: 1) it was highly inconvenient to remove the mirror from the cell, 2) the cell did not allow for any air circulation at all and 3) the design was just sloppy. So I cast about for ideas and happened upon Gary Seronik's simple design. I especially like that, instead of having springs on each of the 3 collimation bolts to provide tension, Gary's design has the collimation bolts pulling the mirror cell tight against an acorn nut which provides a central pivot point. I didn't follow his plan exactly, but adapted it to the design of my telescope.

Images of my new primary mirror cell are in this photo set.

Gary Seronik's primary mirror cell design can be found on his site.

Done! This week I finished the final touches and the new scope is ready for the field. I painted and polyurethaned the struts and adjusted the focuser's distance from the secondary mirror. Overall I'm pleased with the rebuild; The scope is more functional, looks better, and is certainly a step up in craftsmanship. There are still small things that bug me, but they'll have to wait for the next rebuild - or the bigger scope project. Images documenting my progress on this Flickr photo set.

I calculated the strut length, cut and drilled, and assembled the primary mirror box, secondary cage and struts together. After mounting the reflex finder and putting my heaviest eyepiece in I found the scope a bit top heavy when tilted over to about 25 degrees above the horizon. To lighten up the top a bit I cut out reveals in the upper ends of the struts. This helped the balance a little (but not enough) and helped the aesthetics even more. Ultimately I had to add two pounds to the bottom, which I accomplished with a pair of small metal canisters with eight four-ounce fishing sinkers divided between them.

The extra weight not only helps the balance when the scope is tipped far over - it also improves the motion overall. I measured to ensure that my calculations for the strut length were correct, but I need some clear skies for a 'first light' test to make sure.

EDIT: On 2/6 the skies were clear, so around 9:00 PM I set the scope up just outside the garage in a spot with no direct light from the houses or streetlights. Light pollution is very bad here, but I could see Orion, the Pleiades and Mars clearly with my eyes. Using the 25mm eyepiece I observed all three and discovered that I could almost achieve focus with it turned all the way in. A little adjustment with the spacers on the HC-2 focuser and I had it. The views were very sharp, so the spider design appears to be alright.

I calculated and measured again to be sure I had the secondary mirror in the optimal position relative to the primary. What it appears that I didn't do was account for the 1.25" adapter, which adds a little over a quarter inch to the focuser height. So I moved the focuser in toward the secondary about 3/8". One more test when the skies are clear, one last report and I'll be done.

Then, no doubt, I'll start thinking about how to make this design even better.

Images of telescope v.2 are in this photo set.

The rocker box is complete, pretty much following the original design for it. Instead of cutting a concave semi-circle for the bearing supports, as seems to be the common practice, I mounted Teflon pads on a 22.5 degree angle to support each bearing at two points. With my toolkit and skill level this was more foolproof and, in my opinion, just as effective. I also used Teflon pads against the outer sides of the bearings (see photo set for images) to hold the mirror box steady horizontally. I discovered a flaw in my design - the front two struts will not fit onto the mounting bolts because the bearing is too close to the mounting bracket. I'll need to cut a channel for the mounting boltso that the strut can slide into the bracket from the top.

Dissatisfied with the original lid, which was made from Masonite and hinges that I had on hand at the time, I built a new one with quarter-inch sandply and more attractive cabinet door hinges.

Images documenting my progress building v.2 can be found in this Flickr photo set.

The altitude bearings are complete and attached to the mirror box. I used a bit more of the aluminum stock here to put decorative caps on the ends of the bearings, and also to space the bearings 1/8" from the mirror box to allow some 'slop' in the movement without rubbing between the mirror box and the rocker box. The next order of business is to design and build the rocker box, then cut the struts. Images of telescope v.2 are in this photo set.

This weekend I got started on the altitude bearings. This is fairly easy work, but requires a bit of patience. After cutting the bearings out of .75" plywood, I clamped them together and roughly sanded the out edges to match. I had a bit of excess Ebony Star laminate, so I decided to dress up the top edge of the bearings. Clamping the laminate on the outer edges of the bearings while the glue set was easily accomplished with a tie-down strap, but the concave upper edge presented a problem. The solution was to put the strip in place, slide in the cutout scrap and then wedge the whole business between two nearly full gallon cans of paint.

Next is to find someone with the proper tools and experience to neatly trim the excess laminate. On the previous scope I pre-cut the strips to size with a sabre saw. The results were something less than professional and I want to do better this time.

UPDATE: I discovered a Northern Tool nearby where I bought a rotary tool. The diamond cutoff disc was just right for trimming the laminate very close to the face of the plywood, and I finished off with sandpaper to get a flush, smooth surface.

Images documenting my progress building v.2 can be found in this Flickr photo set.

Only a little work going on lately, but this weekend I made a lid to keep things away from the mirror (dust, small animals, etc.). It's held closed by a magnet mounted in the lid - another magnet on the back strut will hold it firmly open when the scope is in use. The bottom of the lid is covered with craft foam to keep it nicely sealed. Images documenting my progress building v.2 can be found in this Flickr photo set.

Several good coats of polyurethane, some work with aluminum, and the mirror cell mounted makes a complete mirror box. Well, almost. I still need to prepare and mount the altitude bearings. The mounting points for the trusses match perfectly between the mirror box and the secondary cage. Next step is to complete the altitude bearings, then build the rocker box. Images of telescope v.2 are in this photo set.

Today I knocked together the mirror box. It's basically the same configuration as the secondary mirror cage, with three braces to support the trusses. The back is squared off and .75" plywood sides will support the bearings. The primary mirror is mounted inside a 10.5" diameter cookie tin, which will fit inside the mirror box. I need to get a few coats of polyurethane on it and make the aluminum side pieces for the truss supports. Images documenting my progress building v.2 can be found in this Flickr photo set.

This weekend I finished out the secondary cage and mounted the HC-2 focuser. My original plan called for cutting small blocks of half inch plywood to go on the sides of the 3 strut braces to stabilize the struts. But I decided to try aluminum bar and I'm quite pleased with the way it looks and with the weight savings (which I'll need because of the Orion 1.25" adapter I'm going to have to stick in the focuser). Images of telescope v.2 progress can be viewed in this photo set.

The creation of the new telescope inches along slowly but surely. Today I began building the upper cage, which will hold the secondary mirror and focuser. As can be seen from the photo at left, I've got the bare bones of it done. I still need to finish the braces that will hold the 3 struts steady and attach the bolts that will hold the struts, and attach the piece where I'll mount the focuser. It needs paint and polyurethane, as well. Images documenting my progress building v.2 can be found in this Flickr photo set.

After using my home-built Dobsonian telescope for more than 3 years and having time to observe the designs and craftsmanship of other amateur astronomer's scopes, I decided it was time to rebuild mine. Some of the issues I hope to address are: Craftsmanship not good enough Balance is not great Motion is not very smooth Focuser is not the best Does not break down well for transport The first step was to think and sketch and diagram. The second step was to build the secondary holder and spider (seen at left). More posts will be forthcoming as I reach milestones. Images of the secondary holder and spider can be viewed in this photo set.