Thursday, April 23, 2009

Now for the bolts

Now that I made the bars and triangles, I had to scour the area for stainless steel fasteners to hold them together and to the steel tailgate, as well as hold the mirror in place within the mirror box. The salt air here is also laced with corrosive pollutants from local industries and power plants, so I chose to use stainless steel fasteners, which will look good for many years. If I'm going to pay over $2,000 dollars just for the primary mirror, it makes no sense to use cheap fasteners that will rust or worse yet, rust together. So far the mirror cell has cost me over 100 dollars, but it will be money well spent because it will support the mirror very well and look good too.

After obtaining the threaded rod, washers and nuts, I cut and installed the bolts for the side pins, the sling and collimation. I found ordinary hex nuts to be fine for the side pins and the split bolts for the sling, but nylon insert lock nuts to be useless for attaching the bars and triangles to the collimation bolts. So I special ordered some all metal lock nuts for them. I had wanted to use fine thread levelers used on things such as large appliances but they were not to be found anywhere I looked, so now I have to make some disks to attach to the other end so I can turn the collimation bolts by hand. So I cut out some disks from the left over aluminum I used for the triangles and drilled out the holes in the center to slip over the collimation bolt. With a nut on both sides of the disk, it will stay secure and I won't have to weld a disk to each bolt. I cut the collimation bolts much longer than the book I'm using as a guide recommends because of the bars being 1/2-inch thick and the space the lock nuts holding the bars will take up, plus room needed for collimation. That will leave enough on the back of the tail gate to attach the knobs plus leave some in travel that may be necessary later.

I then bought three feet of black Nylon webbing and inserted it into the split bolts. When I assemble the telescope for the first time, I will use a pair of 9/16th wrenches to turn the split bolts until the sling raises the mirror off the side pins. For now, it will be left slack. The next steps will be to finish the side pins, add a circle of Kydex or thin plywood to keep the triangles aligned in the correct positions, add pads to the triangles to keep the mirror from touching the screws that hold them on the bars and adding mirror clips to catch the mirror if the telescope tips over. Finally a cooling fan will be mounted on the tail gate with another thin piece of plywood along with a switch to control it. At that point, the mirror cell will be complete.

Wednesday, April 15, 2009

Flotation System

After making a few telephone calls and trips to various shops around my area, I found a business that sells 6061 aluminum bar and strap metal that is the right size for the bars and triangles for the flotation system, as well as the drill bits to make the necessary holes for it to pivot properly. The total cost for the material came to about 44 dollars. Moreover, the business where I obtained the aluminum carried it in other shapes and thicknesses so I can get what I need to make any other aluminum alloy parts I choose to fabricate for the telescope. Eventually, I will have to acquire a cylinder of argon gas for my welder, a spool gun and welding wire for aluminum if I choose to weld brackets and other parts to connect the trusses to the mirror box and the secondary mirror cage. I already have a regulator and flow meter, so setting up to weld the aluminum if I choose should be fairly easy. But for now, I just have to find stainless steel bolts or all-thread, nuts and washers to finish the tailgate so I can determine the weight. This is necessary for calculating how deep the mirror box will have to be so the telescope will not be extremely bottom or top heavy. I would rather not have to put 20 pounds of steel on the tailgate to make the telescope balance correctly if I can help it, because I'll have to lift the rocker and mirror boxes, with the mirror inside into and out of my car when I take the telescope to a dark site.

After obtaining the aluminum, I calculated the dimensions of the bar and the triangles that the mirror will rest on and made a plywood template. I then traced out the triangles on the 1/4-inch flat aluminum and cut them out with my heavy duty hacksaw. It was slow but I was able to cut them slightly over-sized. I then took them to my table saw and used a sanding wheel to shave them down then round the corners so they matched the template. Then I cut three bars from the 1/2-inch by 1-inch bar stock. The result is I now have six identical aluminum triangles and three identical aluminum bars. The next step will be laying out and drilling the holes for the collimation bolts and machine screws.

Thursday, April 9, 2009

Now for the rest of the mirror cell

Now that the tailgate has been finished, the next steps are building the flotation system that will support the primary mirror and making the side pins to keep it captive on the tailgate without chipping or worse yet, breakage. I cut 3-inch long sections of 1/2 and 3/4-inch dowels and hammered them into a wood block so I could drill a hole through them while keeping my fingers away from the drill bit. That turned out to be a more difficult proposition than I expected, and it took a number of tries before I got a set of side pins I was satisfied with. After drilling out the side pins, I sprayed them with flat black paint. Another task will be adding a pair of split bolts on on which a sling will be place to support the primary mirror when the telescope is pointed near the horizon.

Finding fully threaded bolts of the correct size is looking to be a chore, but they are a must for all the bolts that will be added to the tailgate. Because of the corrosive atmosphere here in my area, I want to use stainless steel bolts, washers, screws and nuts so they will look new even after years of observing. I would prefer to make the bars and triangles for the flotation system out of stainless steel, but the cost of stainless steel sheet metal and bar stock is bound to be at least several times that of ordinary mild steel. So I'm going to try to find 6061 series aluminum alloy plate and bar stock instead because it doesn't need painting and I can cut and shape it easily with the tools I now have. If that is not feasible, then I'll use mild steel and prime and paint it in the same manner as the tailgate.