Saturday, December 12, 2009

Handles completed

After searching area suppliers and the Internet, I found a pair of suitable 8-inch pneumatic wheels with ball bearing hubs for the wheel barrow handles. I painted them with Krylon glossy black enamel paint, then made two bumpers that act as spacers from leftover Brazilian cherry I used to build my dresser. First I drilled a 7/8th-inch hole deep enough to mostly accommodate the lock nuts, then I drilled a 7/16th-inch hole the rest of the way through.

After three coats of polyurethane, I bought some stainless steel 1/2-inch all-thread, 3/8 and 1/2-inch washers, and lock nuts. First I ran the hex nuts that came with the eye bolts all the way to the head of the bolts. Then at each hole in the handles I slipped a flat washer onto the bolt, inserted it through the handle, then the wooden bumper, another flat washer then the lock nut. A socket wrench and deep well socket was then used to drive the lock nut all the way down the eye-bolts until it's just short of tightly holding the bumpers to the handles. The eye-bolts and bumpers are now captive on the handles and will not fall off and get lost in the grass.

Attaching the wheels required first the sawing of two 5 and 1/2-inch sections of the half-inch stainless steel all-thread, then filing the ends to accept lock nuts. Two lock nuts hold the all-thread onto the handle. Next a stainless steel flat washer, then the wheel, then another flat washer followed by a 1/2-inch Nylon insert lock-nut secures the wheels in place on the handles. A pair of 3/4-inch open end wrenches dogged the nuts tightly in place but allows the wheels to turn freely.

Now as a result, I can roll the rocker box and mirror box around with ease, without breaking my back. the finishing touches were the addition of some foam pipe insulation to the ends of the handles to make gripping them in cold weather kinder to my hands. The next steps are to attach the pole blocks to the mirror box with stainless steel carriage bolts, washers, nuts and internally threaded knobs temporarily and to add "keepers" to prevent the mirror box from sliding off the rocker box when the telescope is pointed near the horizon. I will make those from Brazilian cherry still left over.

Saturday, November 28, 2009

Inserts and brackets installed

After painting the handles with glossy black enamel paint, it was time to put the inserts into the rocker sides for the stainless steel eye-bolts. To make insertion of the eye-bolts easier, I bored out the holes with a 7/16th-inch drill bit, then used a magnet to remove the metal shavings that remained in the tubing. I drilled four 1/2-inch holes through the rocker sides using a template to accurately place the holes. Then I used a 3/8-inch by 16 thread per inch bolt and nut to drive the inserts into the holes after coating them with epoxy. This was done to prevent them from coming back out. The brackets were made by welding a 2 and a 1-inch wide by 1/8-inch thick flat bar together. That was accomplished with first an outside corner, than a fillet weld on the inside corner, then rounding off the outside so it will fit in place. A miter saw with a cut off wheel was then used to cut off two sections which were then drilled for the mounting bolts, primed and then painted with glossy black enamel paint. I had a left over hole in the altitude bearings so I used them and them drilled a two pairs of 3/8th-inch holes in the mirror box. I then inserted more threaded inserts, again coating them with epoxy. Stainless steel fasteners hold the brackets in place. The altitude bearings are now braced and no longer are springy while the telescope is aimed near the horizon. Because of paint sticking to the bottom of the mirror box sides that contact the rocker, I sanded the affected areas then applied a thin coat of polyurethane. I've also purchased four 3/8-inch stainless steel eye-bolts and used them to test fit the handles to see if they fit the rocker box correctly, which they do. When the wheels are in place, lifting the handles a couple of inches then pushing or pulling will be all that's needed to move the telescope.

Friday, November 20, 2009

Nebulae recently observed

While my favorite objects to observe are galaxies, I also look for nebulae that are in reach of my telescopes wherever they're found. Recently I came across four lesser known examples of planetary and reflection nebulae that can be observed even from fairly hazy and light polluted regions. The first object is NGC-6813, a very small reflection nebula in the constellation Vulpecula. It was almost hidden among the hordes of field stars as a tiny, fuzzy object that would not focus. At 188X it's nebular nature was apparent and it was quite bright. Instead of a circular or oval outline, it had an fuzzy and irregular shape with a star shining within it.

The next object was much larger and easier to pick out from the background stars. NGC-6842 is a large and faint planetary nebula that was not visible until I screwed a O-III filter into the eyepiece. At 103X it was large, about an arc-minute across with no central hole, central star or brighter rim. NGC-6842 is the only other planetary nebula in Vulpecula aside from M-27. Quite featureless but a good test of one's observing skills and sky conditions.

The next objects is the small and quite bright planetary nebula IC-2003 in Perseus. Small and bright, I observed it from my driveway with a 5mm eyepiece and my 10-inch Dob. It was immediately apparent among the surrounding stars with direct vision thanks to the use of an O-III filter while the central star glimmered in the center. This is a surpisingly easy object to observe from the suburbs.

The final object is the tiny and rather elusive planetary nebula IC-351, also located in Perseus. This tiny and round planetary nebula appeared  featureless with no sign of a central star. It was very difficult to locate among the surrounding stars, and required  a magnification of 262X to identify. It was visible without a nebula filter but the use of an O-III made seeing it easier. A good challenge object but not nearly a nice object to observe as M-76 or even IC-2003.

Thursday, November 5, 2009

Base assembled

After finishing the ground board, I installed the Teflon pads for the altitude and azimuth axis, then installed the locknut and plate assembly. Then I inserted a 1/2-inch bolt and tightened it into the lock nut until a small gap remained between the plate and the head of the bolt. However, I found the rocker box was snagging the mirror box when pointed straight up, so I took my sander and sanded off the face plies along the top of the rocker sides. It wasn't elegant but I sanded it smooth and when the new coats of flat black paint dries the fix will not be noticeable since it will be hidden by the mirror box anyway.

Now that the base is nearly complete, the wheelbarrow handles are next on the to do list. Months ago I measured and cut steel tubing left over from the tailgate, then welded it into handles shaped like a dog leg. This way I won't have to stoop as far when it's time to roll the telescope. I marked and drilled holes to hold the stainless steel eyebolts that will thread into threaded inserts that I will put in the rocker sides. I'll bore them out to 7/16th of an inch to make threading them into the inserts in the rocker box sides easier. The steel handles will be painted with glossy black enamel paint. The eye bolts will be retained in the handles with stainless steel all-metal lock nuts. A larger hole at the end will hold a 1/2-inch bolt that will attach the wheel to each handle. For those I'm going to use a 10-inch pneumatic or air-filled wheel with a 1/2 ball bearing hub, the sort that is used for hand dollies. Eventually I'm going to put some foam rubber on the handles so the steel tube won't be so cold on the hands after a winter night of observing and some bumpers to protect the finish on the sides of the rocker box.

Thursday, October 29, 2009

Fall NGC galaxies

Two weeks ago, a rare break in the cloudy, windy, and rainy weather came just as it started to get dark. At the usual darker sky site the local club uses at a very long private airstrip, I was ready to take advantage of it with my 10-inch Dob, which is equipped with digital setting circles. The two drawings of the galaxies above are just a few of the objects I looked at that night, which included the Lagoon Nebula, the Veil Nebula and the bright globular clusters M-15 and M-2. After giving a couple of visitors a look at some bright showpiece objects, I returned to my main focus, hunting down less well known NGC and IC objects.

NGC-6962, NGC-6964 and NGC-6967 are a trio of galaxies in far western Aquarius. As such they're seen from behind the fringes of the Milky Way, and it's vast clouds of interstellar gas and dust that dim the light of objects that pass through them. Even so, the brightest galaxy NGC-6962 appeared right away in the field at 150X.

When I boosted the magnification to 188X, two other very small, dim and oval  objects became noticeable with averted vision. After scanning the area for a few minutes, it became clear the other faint fuzzy ovals were real and they turned out to be the galaxies NGC-6964 and NGC-6967. These galaxies are very small and faint, NGC-6967 especially with a listed magnitude of 14, which is seemingly too faint given the light pollution that affects the site. The trio seem to be the brightest members of a small galaxy group that nearly sit on the border between Aquarius and Aquila. Two more galaxies of about the same magnitude as NGC-6967 are also nearby, but I didn't look for them. I plan to the next time I return to this field.

NGC-6928 and NGC-6930 are the two brightest galaxies of a small group in Delphinus some 200 million light years away. They are also subject to a good deal of interstellar absorption from the gas and dust between the stars in our galaxy. However, NGC-6928 was easy to spot at medium power. Showing a somewhat odd spindle shape with a bright core, it and the much smaller and fainter NGC-6930 are orientated at nearly right angles to each other. The galaxies NGC-6927, NGC-6927A and several other UGC galaxies are also present in the field, but I saw no sign of them. NGC-6930 was also spindle like, and at first hard to spot among the numerous field stars. Both made a nice galaxy duo at 188X.

Other objects I observed and sketched included the whimsical asterism French 1, which looks like a toadstool from Alice in Wonderland, and at the base was a small but quite apparent elliptical galaxy. The galaxy NGC-7015 in Equuleus, the only deep sky object at all easy to find in amateur telescopes was also an easy mark, along with the planetary nebula NGC-6842 in Vulpecula. A short hop and a few minutes searching brought me to the reflection nebula NGC-6813. Finally, just before I packed it in for the night, I tool a little tour of some of the objects in Perseus. The open clusters NGC-1220 and 1245 made a marvelous view, as did the galaxies NGC-1023, 1275 and 1161. Curiously, the nearby galaxy NGC 1160 eluded me, therefore I plan to return too and redraw the field. The open clusters NGC-6834 in Cygnus and NGC-6939 were also nice sights as well.

Since my web page is no longer available online, I will publish some of my drawings here for the time being.

Wednesday, October 28, 2009

Ground board made.

After assembling the rocker box, I made the ground board from two layers of 3/4-inch plywood cut to the same diameter as the rocker bottom. To make the cut, I used my router, a circle cutting jig and a 1/4-inch spiral bit to cut out the ground board. I then used my drill guide and 1/2-inch Forstner bit to drill a hole all the way through. After that, I used a 1/2-inch rounder over bit on my router to round off the edge. Next I made three feet from a scrap of Ash I found in my shed, and cut them out with a hole saw on my drill press. I then glued them to the bottom 120 degrees apart near the edge. When the glue was dry, I began to use wood filler on it and the rocker to fill up voids in the plywood's edges and repair dings in the surface, then sanded the rocker box with a random orbit sander and 220 grit sanding disks.

I also drilled a 1/2-inch hole in the center of the rocker box bottom, then applied contact cement to it and the Formica that will slide over the Teflon pads. After the cement became tacky, I pressed the laminate into place with a roller then removed the excess using a rotary tool and a laminate trimming bit. Then I primed the inside of the rocker box with Kilz primer and followed that with two coats of flat black paint. On the outside, I did a final sanding and followed that with the first coat of exterior grade glossy polyurethane.

To secure the ground board and rocker box together, I will use a 1/2-inch stainless steel hex bolt and two three by three-inch steel plates I made from flat stock. In the center of each, I drilled a 1/2-inch hole. At each corner I drilled a hole for a #8 screw. To one I welded an all-metal lock nut. When the bolt is screwed into the nut, it will not rotate and confuse the digital setting circles that will be added later. The other metal plate was screwed to the bottom of the rocker box and will act as a fender washer and bearing for the bolt to prevent wandering. After cutting, drilling and welding, they were primed and painted flat black.

Wednesday, October 21, 2009

Rocker box

After completing the mirror box with the exception of adding the pole blocks to it, I turned my attention to making the rocker box. The first attempt to make it failed because the plywood I used warped in the bottom and side, forcing me to start over. That forced me to cut off an inch from the one side that was still usable, which I used as a pattern to make a new side with my router and 3/4-inch top bearing trim bit. I also cut off the front corner of the mirror box to ensure it would not hit the bottom of the rocker box. However, I had taken into account the fact the collimation bolts could strike and crush the azimuth encoder for any digital setting circles I will install. I bonded the sides to a single sheet of 3/4-inch plywood with a 12-inch diameter hole routed in the center. Then the front and back pieces, made of 1/2-inch plywood were added. To the bottom of the rocker box I then glued a 20-inch diameter circular piece of 3/4-inch plywood. Now I have a stable rocker box and plenty or clearance for protecting the encoder and primary mirror as well from damage. The next steps will be boring a 1/2-inch hole for the azimuth pivot bolt, rounding off all outside edges, adding laminate to the rocker bottom then painting the inside of the rocker flat black. The final steps will be varnishing the outside and inserting threaded inserts into which the wheel barrow handles will thread.

Wednesday, October 7, 2009

Altitude bearings mounted

After installing the threaded inserts and giving the altitude bearings two more coats of polyurethane, it was time to mount the altitude bearings on the mirror box. I used four 1/4-inch by 2-inch stainless steel machine screws for each bearing. On each bearing two of the screws thread into the threaded inserts, while the other two pass through a hole in the mirror box. On the other side is a stainless steel flat washer, lock washer then a hex nut. Both bearings are now in place, clearing the way for the next step, painting the interior of the mirror box flat black. I applied one coat of Kilz oil based primer and allowed it to dry. Then it will be covered with two coats of flat black paint, the second of which will be flocked with saw dust. The bolts for the pole blocks clamping knobs will also be installed before painting. After the box's interior is painted and completely dry, I will then bolt the steel tailgate in place inside the box.

Friday, October 2, 2009

Pole seats and altitude bearings completed

After purchasing some threaded inserts, I installed them in the pole blocks along with a handle with a threaded 1/4X20 stud attached. The inserts tend to pucker the wood around the hole, so I beveled the edge around them to prevent that without complete success. In between the wedge and the rest of the block I inserted a spring. The pole seats are not completed and attached to the upper cage.

After searching for suitable Formica, I obtained a large piece from a local cabinet supply shop. I cut two 1 1/2-inch wide strips and coated the back side and the outer edge of the altitude bearings twice with contact cement, then pressed the Formica into position. A router with a trim bit and a cloth soaked in acetone removed excess contact cement and Formica.

To attach the bearings to the mirror box, I had originally planned to use threaded inserts entirely, but given the trouble I had inserting them into the pole seats, I will only use them where I cannot simply use a nut and washer. I counter sinked each hole throughly, then used a block of wood with a piece of all-thread through it to insert the threaded inserts. That allowed me to ensure they are going in straight, and a dab of marine epoxy glue will ensure they will not loosen.

Tuesday, September 22, 2009

Pole seats

After careful consideration, I chose a method to connect the truss-poles to the upper cage that will not result in the danger of parts dropping onto the mirror or being lost. I made four blocks from Brazilian Lyptus I had left over from the construction of my dresser. After the glue set, I made a jig that would hold them at the angle I calculated to be the best for the pole bores, which was 9 degrees.

After trial and error I got the jig perfectly positioned on the drill press and clamped it into place. A 1-inch Forstner bit was then used to bore all the way through the block, which was clamped to the jig. After the pole bores were drilled, I needed to drill the holes for the bolts that will hold them onto the lower ring of the secondary mirror cage. Using locating pins I marked the exact location of the holes on the blocks, then drilled a 1/4-inch hole with a Brad point bit.

Next, I made a simple jig to hold the pole seats stationary while I beveled the edges just like the pole blocks for the mirror box. Unlike the pole blocks, I routed one side on the back of the blocks to make sure the light baffle doesn't get in the way of them resting flush on the ring.

The next task I did making the pole seats was making two nine degree saw cuts in the front of the pole seat blocks after drilling a hole for a bolt and knob. A third cut will be made to split the seats into two parts tied together by a bolt and a knob. These pole seats will work like upside down buckets when the telescope is set up and taken down. When the knobs are tightened, the poles will be gripped tightly without crushing them. Any forces that try to pull the cage out of position will wedge them more tightly into place and prevent major damage to the telescope from occurring if the upper cage should separate from the truss poles. The final step would be to sand and varnish them with several coats of exterior Polyurethane to protect them from the harmful effects of moisture.

Thursday, September 10, 2009

Baffles and gussets

Now that the mirror box had been made, it was necessary to reinforce it with corner braces and gussets. The mirror box is arguably the most vital component because all of the structural loads converge in it, and that requires it to be very rigid and strong. I places two corner braces in each corner and a gusset made from the leftovers from building the upper cage. Additional scrap was used to make the corner braces, which were cut on on the table saw with the blade set at 45 degrees. Brads and sticks held the corner braces and gussets in place while the glue set.

The next step was to make a light baffle for the front end of the box to reinforce it. The baffle will also help keep the box square and free from flexure as the telescope is moved. I took two thin sheets of birch veneer plywood and glued them together, placing a stack of floor tiles to press them together as the glue set. Then with the router and a circle cutting jig I cut out a round opening a little smaller than the inside width of the mirror box. Brads kept it from sliding on the slippery glue when the clamps were tightened.

I then cut out another circle of plywood from a surplus sheet of birch veneer plywood a little smaller than the width of the box. Using the cut out from the baffle, made a cover for the mirror box by gluing the cut out and the larger piece together, again placing a heavy stack of tiles on top to ensure the glue bonds the plywood together. The cover will serve two important functions. One will be to protect the mirror from any falling objects that can strike and damage it. The other is to prevent sunlight from getting into the telescope and turning it into a powerful solar furnace, which would likely damage the telescope severely, even set it ablaze. After sanding and varnishing, a knob and a couple of door catches will be added to facilitate easy removal and replacement.

After that, a router fitted with a trim and a 1/8th-inch round over bit was used to trim off excess plywood around the top of the box and break the sharp edges. I then used wood filler to fill in damage I did to the veneer next to the light baffle. Unfortunately, I couldn't find Baltic Birch plywood locally so I opted to use a 1/2-inch thick hardwood veneer, softwood core multi-ply material instead. It has seven interior plies a little more than 1/16th-inch thick plus the face plies which are very thin. That means it's easy to sand right though them, and I did in a few small spots. After filling them in and sanding, they're not as noticeable as before. I decided to leave the box as it is, after considering covering it with veneer. So I applied the initial coat of varnish to seal the box and help protect the face plies from getting dirty. Before I completely varnish the box, I'll locate the holes for the altitude bearings and drill small pilot holes for them. This way if I botch something, it will a lot easier to fix a small hole than a large one.

Tuesday, September 8, 2009

Mirrox Box

Now that the altitude bearings are nearly finished, I decided to make the mirror box in order to determine where to attach them to it. After cutting out the panels from the rest of the 1/2-inch plywood I bought and checking them for squareness, I laid out and cut out slots for biscuits to join them together. After applying yellow carpenter's glue to the joints and the biscuits, it was a simple matter to tap the panels together with a rubber mallet, ensured the box was square with a steel framing square, then tightening the clamps. After a final checkout with the framing square, I left the box on the table saw so the glue can set. After a few hours, I removed the clamps and cut out corner braces with more 1/2-inch plywood. After applying glue I used scrap plywood to hold the braces in place while the glue dries. Then it was time to check the box for proper fit of the tailgate, which turned out to be smaller than I expected. There's a 1/16th inch gap between the side rails, a minor problem that can be fixed using washers as shims. Had the box been too small, it would have forced me to build it all over again, so if your tailgate turns out to be a little undersized, don't fret.