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.