Friday, December 24, 2010

Finally finished!

I just got an e-mail from the optician today stating the mirror has been finished. All that remains is to add a coating of aluminum then a protective overcoat on top of that. Sometime after New Year's the mirror will arrive here, and that will allow me to complete the final steps on the telescope's construction. That will be first and foremost determing how long the truss poles have to be, and at what angle the pole blocks will have to be set. To do that, I will temporarily install the primary mirror and use a star to find out how far apart the mirrox box and the upper cage have to be. Once that is determined, I can drill the holes and bolt them permanently to the mirror box after returning the primary mirror to it's storage box. I will have to shim the bottoms of the blocks out, and likely shim the pole seats on the upper cage so the poles will slip into them easily before I tighten the wedges to secure the upper cage in place. I will cut the poles two inches too long to give me a margin for error, then I can trim them to the final length that will allow the eyepieces I now have to focus as well as leave leeway for eyepieces I will buy in the future. This way I'll avoid the risk of having to buy more aluminum tubing because I cut the truss poles too short. After these steps are done, the mirror will be pemanently installed in the mirror box and the sling attached to it with double sided tape to keep the sling from slipping off the edge of the mirror. I will then adjust the sling and side pins to support the mirror in the case of the sling, and to leave a 1/8 to 1/4-inch gap between the mirror and the side pins as well as the mirror clips. They serve to keep the mirror in place and prevent damage to it, they will not touch it normally unless the telescope is bumped or I am driving over a bumpy road. After that, I can then start making the shroud to keep out stray light, and the poles can be covered to make both holding them in the cold less rough on the hands and to supress reflections off of them. Many people use black foam pipe insulation for this, but I am going to try to use shrink wrap tubing that is normally used on large electrical cables to cover the shiny aluminum tubing. After all of these final steps are completed, at long last the telescope can be assembled, collimated then receive it's "first light" on a planet or other celestial object. The much larger aperture will make a big difference in how galaxies look, and the best time to see them is going to come soon. By the time February arrives, the M-81 group of galaxies, along with the clusters of them in Coma Berenices, Leo, Virgo, Centaurus and Hydra will be well placed for observation. There is at least 8,000 galaxies in range of a 15-inch telescope, and of those 8,000 at least 2,000 or 3,000 of them are visible in these galaxy clusters at a good site. The rest are distributed all over the sky including the apparently barren regions near the celestial poles. The massive light grasp will result in brighter examples resembling black and white photos from a dark site, with dimmer ones appearing everywhere wherever there's a galaxy cluster in our local region of the Universe.

Tuesday, December 21, 2010

Solstice total lunar eclipse

Last night's total lunar eclipse was the first to occur on the winter solstice for at least several hundred years, making it a very rare event. Since the weather forecast for my area promised at least relatively clear weather, I set up the 10-inch telescope because it had dew heaters and digital setting circles, which my 6-inch is not equipped with. I recently acquired a new dew heater controller called a Dewbuster, a device that pulses the current and also uses a temperature probe to prevent too much heat from interfering with the views due to heat blooms in the telescope. It also conserves battery power, a big plus for long observing sessions when the dew is extremely heavy like it often is here in coastal Alabama. As soon as it began to get dark, I set up the telescope, and turned the dew heaters on.

I was planning to look at Jupiter, Uranus and Neptune before they dropped behind the trees, but the seeing turned out to be horrible and Jupiter was a large, bright squirming blob. The moon looked like I was watching it from the bottom of a swimming pool. I also discovered the digital setting circles were acting in their usual temperamental manner and thin clouds were passing through, so I left the telescope outside and did other things until the eclipse began. It turns out there was a stationary front near my area, and weather fronts create bad seeing and annoying thin clouds. Had it not been for last night's eclipse, the telescope would have stayed inside last night and I would have been reading a book or watching television.

By 12:30 a.m. the moon was entering the umbra or dark inner shadow of the Earth, making it look like a cookie with a bite taken out of it. At last the horrendous turbulence let up somewhat  but the view was still shimmering from time to time. I opted to use a 32mm and a 21mm eyepiece that gave  magnifications of 41X and 63X respectively, until the coma corrector lens started to fog up. After taking it out, I was looking at the moon at 36X and 57X respectively, which is very low power for a 10-inch Dobsonian, but I had a nice view of the increasingly eclipsed moon. At first, the portion that was eclipsed was a dark grayish brown but as the moon passed deeper into the umbra, the moon took on a dark brownish red color. Around the edge of the umbra, the moon took on a bluish gray color. By 1:15 or so the moon was almost entirely in the umbra and by 1:30 it was completely immersed.

During this time the bluish gray color faded and most of the moon took on shades of brownish red. The stars that otherwise are washed out both to the unaided eye and the telescope came out and I looked at the bright star cluster M-35, which was only a few degrees away from the eclipsed moon. I also stopped to look at the sword of Orion, at the heart of which is the great Orion Nebula. As for the moon itself, it took on a three dimensional appearance as it drifted in front of background stars, dozens of which were visible. Normally the full moon is a whitish, glary object that looks flat and two-dimensional to me through any telescope. The huge light gathering power of a 10-inch Dob makes it almost painful for me to look at without a dark gray filter to dim the moon to a comfortable level. I was able to see with ease the moon's orbital motion as the eastern limb approaches then covers up star after star while others pop back into view on the western side.

By this time a most unwelcome visitor appeared for sky watchers like me, clouds. Few in number, they became steadily more numerous as the  eclipse progressed. By 2:00 a.m. the moon was past mid-totality and the eastern limb was beginning to brighten again. The moon made a wonderful sight as it was at the juncture of the constellations Taurus, Gemini and Auriga. The bluish gray color was starting to return as the planet Saturn was finally climbing above the tree line. Then the weather completely went down hill, and the entire sky rapidly clouded and fogged over. By 2:30 it was time to put away the telescope but as I carried the base back into the house I watched the eclipsed moon appear in a break in the clouds. I was most happy to had the opportunity to watch this rare event.

Sunday, November 7, 2010

Southern galaxies, northern nebulae

Last night was one of the clearest, and driest nights to come along in months. After arriving at the site before sunset and setting up my 10-inch or 25cm Dobsonian telescope, a friend and her family came visiting along with folks who own and fly aircraft out of the airstrip where I observe. Once it became dark, I gave a tour of some of the better show piece objects for them such as the Andromeda Galaxy, Dumbbell, Veil and Swan Nebulas. These are all spectacular through smaller telescopes if the moon is absent and the sky free of haze and heavy light pollution. The airstrip I use as an observing site is at most thirty kilometers from the edge of my city, and therefore subject to quite a bit of light pollution. However, the Milky Way was plainly visible and numerous stars were in evidence except near the light domes from my city and others that surround the area. I also assisted my friend with her telescope, and looked though it as well. The air temperature fell swiftly after sunset, and it soon grew cold, enough that I bundled up under a heavy German army field jacket after they went home and got down to the business I came there to accomplish, observing and sketching galaxies and nebulae visible through my telescopes. Dew was mercifully minimal but the seeing was turbulent. Stars often appeared as fat blobs and they twinkled furiously near the horizon. At least the wind was light and few clouds existed to spoil the view, and the cold was tolerable.

First on my list was the Pegasus galaxy NGC-7814, a precisely edge on spiral galaxy that has a very thin dust lane along it's length. However, it did not appear and the galaxy itself was a softly glowing object shaped rather like a double convex lens turned edgewise at 150X

Next was the large and fairly faint Cetus galaxy NGC-908, a very large spiral galaxy that appeared as a dimly glowing oval glow that was vaguely patchy with a brighter center at 150X. A trapezoidal formation of foreground stars lied along one side. It was an easy object, comparable to some of the dimmer Messier galaxies in fact, but not as well known as they are.

The next object to be observed was the small and face-on spiral galaxy NGC-309, which at 188X has a slightly brighter core. No sign of the spiral arms was seen, but it was fairly easy to find and fairly bright despite the low elevation it has from my area.

Next was the spiral galaxy NGC-428, a massive spiral galaxy 70 million light years way that just finished merging with and absorbing another smaller galaxy. It showed no sign of the peculiar split spiral arm at 188X that is plainly apparent in photographs, but it did show the prominent nuclear region. This galaxy resides in a perfect right triangle of foreground stars, like a diamond set on a ring. No doubt a larger telescope will show hints of it's disturbed structure at a dark site. It's galaxies like this one that led to my efforts to build a much larger telescope to better see them.

A short distance away can be found the elliptical galaxy NGC-430, which was flanked by two smaller and dimmer elliptical and lenticular galaxies at 188X. NGC-430 was small, faint and round with a bright core, whereas the other two were dimly visible with averted vision. NGC 426 is also small, oval and has a brighter center, while NGC-429 is more lens shaped with a brighter core. The trio makes up an isosceles triangle with the lenticular galaxy being canted at an angle that points away from the longest side of the formation, with NGC-430 being the brightest member of this small galaxy group.

A short hop led me to another Cetus galaxy, NGC-448. This object was bright and very elongated oval that has a very bright core at 188X.

Along the way, I paid a visit to several galaxies in the southern constellation Sculptor. First and foremost I stopped to look at NGC-253, the largest and brightest of the Sculptor Group, which consists mostly of more than two dozen spiral and irregular galaxies spread across 20 degrees of the southern skies. NGC-253 itself is known as the Silver Coin Galaxy. Very bright and nearly edge on, this galaxy has shown hints of the dark dust clouds that litter it's disk from very dark sites through my 10-inch. At 63x it spanned a greater length than the Moon. More than ten degrees farther south led me to another large member of the Sculptor Group, NGC-55. This is an edge-on irregular or barred spiral galaxy that appears as a patchy, long and very  bright streak, again at 63X. These are among the closest galaxies to us outside of our Local Group, but they are very low in the sky even from the southern United States. For people in the southern hemisphere, they are among the brightest and most spectacular galaxies in the skies visible to them. Even a 6-inch or 15 centimeter aperture telescope at my location has no problems revealing them.

Then I turned to NGC-289, a galaxy that is much father away than the Sculptor Group and is therefore a background system. It's bright inner core was surrounded by the much dimmer spiral arms of this oval galaxy at 188X. Another oval galaxy with a brighter center was the very patchy NGC-7793, which displayed a large oval disk at 150X. Subtle patchiness was seen intermittently in this nearly face-on spiral galaxy.

Before packing up for the night and returning home, I looked for and found the reflection and emission nebula NGC-1579 in Perseus. This object apparently demands very clear skies to be seen, because it eluded detection until now. It's patchy and irregular form was easy to spot even at low power. While an Oxygen III filter obliterated it from view, it showed up easily with no filter and was a nice sight at 150X.

Other objects along the way that were visited included the companions to the Andromeda Galaxy M-32, M-110 and NGC-185 in Cassiopeia. The galaxy NGC-7331 was a small but bright object that is a twin to M-31, but more than twenty times farther away from us. The other large spiral galaxy in our Local Group, M-33 was also observed, though it's dim glow is not as easy to see as M-31's.  Other bright objects I looked at included Orion Nebula and the planetary nebulae M-57 in Lyra, NGC-7008, NGC-7048 and NGC-6826 in Cygnus were also observed. Two others I stopped to look at were NGC-7009 and NGC-7293, also known as the Saturn and Helix Nebulas were also visited. The bright globular and open star clusters M-2, M-15, the Double Cluster and NGC-6709 in Aquila were also showcase objects.

Monday, October 25, 2010

The mirror is coming along.....

I've just received word from the optician that the mirror has been ground and polished, and that he's now in the process of the most important step, figuring it. That's put simply, turning a spherical mirror into a parabolic one so all the light that reflects off of it comes to a single focal point. He'll have to test the mirror to see both the shape of the surface and the progress he's making, and this can require many cycles of figuring then testing to get it right. Although it's taken considerably longer than I expected, figuring a large, short focal ratio mirror is not an easy task for even a professional optician. I would have made the mirror myself if I had a place where I could do the work and had I made several ten or twelve inch mirrors before trying to take on a 15-inch mirror. I opted to leave the job to someone who has the skills I lack, it was quite a project so far when it came to the wood working and welding I had to carry out. I expect a month or so to pass by before the figuring and testing is complete and then the mirror can be coated. Once that is done, it can be shipped and I can then determine the length and angle of the truss poles, pole blocks and pole seats the telescope requires. Then I can make the shroud for the truss poles and then I'll be ready for the moment that has been nearly two years in coming, the first views through a dream telescope I mostly made by myself.

Tuesday, August 31, 2010

Got some good news

Recently, I contacted the optician to see how the mirror was progressing. He reported that the mirror could be ready as soon as the middle of next month, which will place first light at the end of September or early October. Figuring the mirror is critical, so it may take considerably longer than that to complete. With that in mind, I will be buying the materials needed to make the shroud for the truss tubes, fasten the pole blocks in their final positions as well as shimming them and the pole seats as required. I've added high density foam to the case after varnishing it and welding handles for it to facilitate handing. However, I plan to add threaded inserts so I can roll it out just like the mirror and rocker box units. A steel lip was also made to keep the top from sliding around on the bottom because I opted not to use hinges. With any luck, the telescope may be ready before this year's Deep South Regional Stargaze, which I may try to attend this year.

Saturday, July 17, 2010

Case for upper cage

Now that the upper cage is complete with the exception of installing the secondary mirror, I had to build a case for it to keep dust and inquisitive little kitties from getting into it. Nose prints and cat hair all over the secondary mirror won't lead to the best views I could get from a premium quality set of optics, so I bought a sheet of high quality softwood core, hard wood veneer plywood. After taking careful measurements of the cage, I made a box with inside dimensions of fourteen and a half inches deep and twenty three and a half inches on a side. After all six sides were glued up, I carefully split the box into two parts on the table saw, then made a support to rest the cage on. I cut an radius to accommodate the inner shell of the upper cage, and drilled two holes in the cross pieces for the struts. Alas, the assembly turned out a little too big, so I split it into two and glued two more cross pieces, then glued them together before gluing them to the bottom of the case. I then uses a trim bit to knock off beads of glue followed by a 3/8-inch round over bit on all outside edges. I plan to finish the case with three or four coats of exterior grade, glossy polyurethane. In the bottom will be foam padding in which the Telrad and computer for the digital setting circles will be stored. I will make a lip of 12-gauge steel flat bar to keep the lid in place, and skids will keep the cage from bumping the sides of the case. I'll be using padding on the bottom support, lid and skids to keep the upper cage in good condition for many years to come.

Friday, May 28, 2010

Mirror box flocked, finder scope arrived.

Last weekend I flocked the interior of the mirror box with my usual flocking material, flat black oil-based paint mixed with saw dust. Using a foam brush, I dabbed it on the inside of the mirror box to create a rough textured surface that will help suppress stray light. After waiting for several months, the finder scope finally arrived. Apparently after contacting the vendor they realized that it was never shipped. It arrived yesterday in perfect condition and it's a nicely made finder scope, complete with a long dew cap. With it and one of my Stratus eyepieces in the focuser, the upper cage weighs 14 pounds or so, about what my calculations predicted. I may have to tweak the balance after I get the primary mirror, but assembly and testing my telescope should be straight forward.

Monday, May 17, 2010

Cooling fan now operational

 In preparation for the arrival of the primary mirror, I made a bracket for a sealed 12-volt lead-acid battery I bought to power the cooling fan. I located one small enough to fit in a corner of the rocker box without interfering with the mirror box, tail gate or the primary mirror itself. I MIG welded four pieces of 3/4-inch wide steel strap to make a bracket to hold the battery in place during transportation, yet allow easy removal for recharging. I made a cable from some leftover 16-gauge wire and crimped on connectors for the battery on one send, while I soldered the other end to the leads then covered the connection with shrink wrap tubing. Tie wraps anchor the leads to the tail gate and I left enough slack so I can raise and lower the telescope without pulling on the wiring. The fan's power source will be independent from the power source for the dew heaters and digital setting circles, which will draw much more current. I am considering the use of two 12-volt 18 amp-hour batteries wired in parallel to power them since the dew is extremely heavy here and the secondary mirror and finder scope dew heaters will require a lot of current. At the very least, one 18 amp-hour battery will be used which will be enough for several hours of observing, but to go all night will require a lot more power here if I have to keep dew off the finder scope, secondary mirror and coma corrector all at once. I've also replaced the nuts on the mirror clips with all metal, stainless steel lock nuts to ensure the clips will never loosen during transport.

Monday, April 19, 2010

Mirror ordered!

Two weeks ago, I placed an order for the primary mirror with Optic Wave Laboratories. It will be a 15-inch, F/4.5 mirror on standard low-expansion glass with standard aluminum coatings, which is more durable than many of the enhanced coatings. According to the owner, the mirror will take perhaps three months to complete, which will place first light in July. I have constructed everything as far as I can without the primary mirror in hand, when the mirror does arrive construction of the telescope will be complete.
I also built a cart for my welder to hold a gas cylinder so I can MIG weld any additional parts, such as a steel bracket I made this weekend for the digital setting circles' altitude encoder. Now that I can MIG weld, I may make any additional parts from 6061-T6 aluminum alloy instead, and if anything else needs to be remade, it too may be made of aluminum alloy.

I am very excited and looking forward to the night when I turn my telescope to the stars for the first time. If all goes well, I plan to attend a regional or national star party this year with it and my 10-inch telescope too.

Tuesday, February 16, 2010

Winter Objects

After more than a two month hiatus from sketching deep sky objects due to cloudy or very cold weather, I took the opportunity to sketch these objects last Saturday night while observing at a local airstrip. NGC-1199 is a galaxy in Eridanus, one of many I wanted to sketch that night but sky conditions were not very good and this was the only one I was able to see. As such it was small, round and it's bright inner core was visible. Eridanus has numerous galaxies that are visible in modest telescopes that can be seen from the United States and along the border with Fornax is a rich galaxy cluster as well. Also located in Eridanus is the very bright double shell planetary nebula NGC-1535, also known as Cleopatra's Eye. The larger but faint outer shell surrounds the very bright and younger inner shell, which has a hole through which the central star gleams. It's a great object for small telescopes and it takes high powers and light polluted locations very well. It's definitely the best deep sky object in Eridanus.

NGC-972 is one of a number of moderately bright to faint galaxies visible in the constellation Aries. It's fairly bright and appears as a faint oval object with a brighter core at 150X. The Canis Major galaxy NGC-2207 also was observed as a faint very elongated oval with a slightly brighter core. This galaxy is anything but easy from the hazy and light polluted sites I make do with, but it was evident despite the curious difficulty I had seeing galaxies in Eridanus that were easy objects the last time I looked for them. The sky was very patchy transparency wise.

The open clusters NGC-1220 and 1245 in Perseus were also observed. NGC-1245 was a fairly large swarm of faint to very faint stars and made a pretty grouping of stars embedded in the rich Milky Way star fields that dominate Perseus. NGC-1220 on the other hand was a lot more difficult to find, and at first glance it looks like a distant unresolved globular cluster. Even at 188X, only a few stars appeared surrounded by a hazy glow of other stars too faint to see individually, but their collective glow was visible in the telescope.

Besides these objects, I observed the Orion nebula and the planetary nebulae  NGC-2438, 2440 and 2452 in Puppis, along with the emission nebula NGC-2467. In Gemini I located the faint but very rich open cluster NGC-2266, and in Orion the nebulae NGC-1788 and 1999 were also observed. In Monoceros I observed the planetary nebula NGC-2346 and the reflection nebula NGC-2261, also known as Hubble's Variable Nebula. Finally, I looked at the brightest galaxy in Aries, NGC-772 and the galaxies NGC-1023 and NGC-1161 in Perseus.

Wednesday, February 10, 2010

Focuser and finderscopes

After a short wait, the focuser, Telrad and the bracket for the 50mm finder scope arrived and I got to work installing them on the upper cage. However, I found the focuser board that I made originally to be all wrong for the focuser, and worse yet I botched the job of mounting it. So I took a piece of Brazilian cherry and made a new one, moving the hole for the focuser 3/4-inch farther back to allow some space for adjusting the position of the secondary mirror and it's holder. The board was made wider to accommodate the focuser better and I made a spacer from left over 1/4-inch aluminum used to make the tail gate so operating the focuser would be easier and there would be a thrust plate for the leveling screws to push against if their use is required to square the focuser with the optical axis. The Telrad fit right into place on it's base, but the bracket for the 50mm finder needs a riser for the finder scope to clear the rings of the upper cage. Ideally, I will be able to leave the finder scopes on the upper cage even when it's in the storage box I will be making to keep it free from dust, dirt and getting damaged. At present the focuser is just held temporarily in place until I can get a nut driver for the nuts and  notch the baffle to allow me to finish inserting the screws for it. Once the finders and focuser are mounted permanently in place, the only operation left to complete for the upper cage is to adjust the pole seats, which will not take place until the primary mirror is delivered and I can determine the length and angle of the truss poles. I am in the process of coming up with the money for the primary mirror, when I do, I will contact the optician I've chosen to make the primary mirror.

Sunday, January 31, 2010

Pole block problem resolved

After making and then staining and varnishing new pole blocks, they were placed on the mirror box to see if the poles all align in the same way. Unlike the previous set, they do and thus my previous problems were resolved. That still leaves the issue of getting them to fit in the pole seats, or possibly making new ones altogether but for the present I will leave them as they are until I get the primary mirror and determine the length and angle the truss poles and blocks must have before the blocks are bolted to the mirror box.

I've also ordered a Telrad and a 50mm straight through, non-illuminated finder scope after finding that straight through 80mm finder scopes are scarce. The smaller aperture will not be a problem because ultimately digital setting circles will be my main means of locating objects anyway. The focuser has already been shipped from the manufacturer and will arrive here soon, with the finder scopes soon afterwards. When they arrive, they will be attached to the upper cage assembly and an accurate weight can be derived for determining how the telescope will balance and what, if any corrective measures I will have to take.

Sunday, January 24, 2010

Secondary mirror and holder arrived

After adding the knobs for the pole blocks and inserting the poles, I discovered that the pole bores were tilted in opposite directions and thus I was forced to make new pole blocks after my attempt to correct the problem merely made things worse. I was able to test fit the poles and see if the pole seats are even close to being workable. It's clear that shims will be needed on both the pole blocks and pole seats, but I found some thin sheet aluminum that would make excellent shims that will be nearly invisible once installed. To prevent the problem with crooked pole bores from cropping up again, I made a jig where I took great care to ensure the fence to which the blocks are clamped while drilling the pole bores is at 90 degrees with respect to the plywood bottom of the jig. While drilling, I drilled four blocks with the pole bore on the left side, then four more with the bore on the right side as seen from the front. I then beveled the edges, then with a spade bit I made four circular recesses where the bolts for the block will be. In the center, I drilled and countersunk 9/32nd inch holes for the 1/4-inch machine screws that will eventually permanently anchor the blocks in place once I acquire the primary mirror and determine both the length of the truss poles and the angle of the pole blocks. Since I chose to use red oak instead of maple, which is very scarce locally, I stained the blocks with red oak stain then varnished them as before. I would have preferred to use maple, but since the poles are smaller than usual, and there is a greater thickness of wood left on both sides of the pole bore, I have little reason to worry about the strength of the pole blocks over time. Obsession is using plywood to make the pole blocks on their smaller Dobs with apparently no problems with durability, so I have little reason to worry when the truss poles are going to be less than four feet long. The blocks are now fully varnished and ready to attach to the mirror box once I can determine the length of the poles and the angle the blocks must be set at so the poles mate with the pole seats on the upper cage assembly.

I've also ordered over the holiday season the secondary mirror and it's holder, which arrived a week ago. I've also placed an order for a dual-rate Crayford focuser from Moonlite and next week I will purchase the finder scopes, which will be a Telrad and probably an 80mm finder telescope of some sort. I opted for the Moonlite focuser because it is adaptable to any telescope and is a high quality focuser that is built to last of high grade materials. Most likely if I choose an 80mm finder, it will be a correct image finder because I have not been able to find any straight through models that do not cost as much as a small Dobsonian. The bigger aperture will be helpful for hunting down faint objects, but I may have to add strips of steel to the tailgate to balance the telescope. So far the cost of the components to complete the upper cage have come to 500 dollars. All told, this telescope will probably cost me 3,500 dollars to build, if not more and that does not include the cost of acquiring a welding machine and other tools needed for this project. Once I have the finder scope, the next goal will be to get the money together to purchase the primary mirror, which will take at least a couple of months for the optician to produce. I expect first light for this telescope will be in the late spring or early summer at the latest. Before it will be truly finished, I will have to make a shroud for the truss-tubes, a case for the upper cage to protect it from damage in storage and transit, and fit the telescope with batteries, digital setting circles and dew heaters. With some luck, I will be able to attend a major regional or national star party and try the telescope out on some faint galaxies and nebulae.

Saturday, January 2, 2010

Keepers and knobs added

After planing a piece of Brazilian Cherry left over from the construction of my dresser, I made two "keepers" to prevent the mirror box from sliding from side to side when the telescope is pointed near the horizon. After planing, I ripped a piece one and a half inches wide, then cut two pieces six inches long. I then bobbed the top corner and drilled two holes then countersunk them after reducing their width to 1 and 1/4-inches. Two holes 5/16ths of an inch were drilled all the way through for the 1/4-inch machine screws to pass through. On the rocker box, I made two pairs of blind 3/8-inch diameter holes to accept threaded inserts, which were installed with a bolt and nut after dabbing epoxy on them to keep them from coming back out. The keepers were varnished with three coats polyurethane and before finishing I notched out the sides of the tops facing the altitude bearings to prevent them and the keepers from scuffing each other.

The knobs for the pole blocks were ordered from Woodcrafters, a very good company for any woodworker to deal with. Among their numerous products are knobs with an internal threaded insert which are used to make jigs and other fixtures used to build furniture. I ordered eight of these knobs, one for each pole block. When tightened on the carriage bolt, they press the middle section of the pole block inwards, gripping the truss pole tightly without crushing them. However, the ends of the poles do not for some reason don't all lie in the same plane, the left hand poles are farther out than the right side poles by about three quarters of an inch at the ends. Since it is consistent on all four sides, I'm going to shave a small amount of wood off the left hand blocks to bring them in line with the right hand poles. The pole seats on the upper cage also need to be altered so the poles will slip into the seats. Apparently an angle of one or two degrees is all that's needed to rectify this problem.

I've also begun to order the components necessary to complete the telescope. I've already ordered the secondary mirror and a holder for it, and soon I will purchase a focuser and a finder telescope. I am planning to also install a Telrad. While I made the assumption the upper cage will be quite heavy for a 15-inch Dobsonian, I can add strips of steel to the tailgate if the telescopes turns out to be top-heavy.