How to make a Newtonian Telescope part 3

In this part we make the Mirror Mount and install the mirror into the tube

I do have a video showing this whole process. You can watch that at the bottom of this page. Here is a picture of the completed assembly. This is what we are making in this part.

This part is really not very hard. You can do this with just a couple of pieces of wood, a few tools and a little bit of common hardware that you can get at any home improvement store. (nuts, bolts, washers and a few springs. You should read through this whole process. Things will become clear as you see how we make this.

Cut yourself two disks of wood. One of them is the same size as your mirror and the other is the same size as the inside of your tube. That one should slide easily into your tube with just a little bit of snugness.

The wood I used is 1 x8 pine. The 1 inch refers to the thickness of it but that’s a woodworking inch. The board is actually 3/4 inch thick. When you buy it the board will be labeled as 1 x 8.

Doesn’t matter a whole lot what kind of wood that you use. Just as long as you can get nice round cirlces in the right size.

Now place the small wooden disk on top of the large one and get it nice and centered. You might want to drill a hole right through the middle of them to help you keep them nice and centered.. Do a good job here. the more close they are to exactly centered the easier it will be to collimate the telescope later.

Once you have them nice and lined up clamp them down and drill three holes at 1, 2 and 3. They are approximately equidistant apart and these do not have to be that accurate. drill a little over 1/4 inch because you will be sliding 1/4 -20 bolts into them.

While it is clamped you want to drill right through both disks. This way those holes are lined up nicely between the two disks.

Try to drill them very straight down. If you have a drill press then use that. We want to minimize any angling.

Insert bolts into each of the holes of the smaller disk. These are flat head bolts that are three inches long.

Notice that they sit very flat in the wood. Countersink those holes so the bolts sit down inside. The mirror will be sitting flat on this disk so we don’t want the bolts sticking up!

On the other side of the disk add washers and nuts. Tighten them down so the bolts are nice and tight. Be sure to add the washers. They help keep it tight.

Now cut and add some springs right over those bolts. The springs should be a little more than 1/4 inch so they spring freely. They shouldn’t be snug on the bolts.

Now put another washer right on top of each spring. That’s not shown in this picture but you will see them in the next picture.

Now slide the bolts of that assembly right through the three holes of the larger wooden disk. You can see how this causes a nice spring action. The small disk now floats on the large disk. Held up by the springs.

Now add washers and wingnuts to those bolts. And this assembly is done. We just need to install it in the telescope.

These wingnuts are for adjusting the angle of the mirror. You can turn each one as needed to align the mirror. This process is called collimating and we will cover that once the telescope is built.

Now let’s make some clamps and mount the mirror to the assembly. I just used some sheet metal to make three clamps. I bent them into L shapes like shown here. And I glued a little piece of foam onto the flat edge. This foam protects the mirror from scratching.

About these clamps. They have to hold the mirror in place nice and securely. We of course don’t want the mirror to fall out. But we also don’t want the mirror to move at all in the assembly.

And about the little part that actually holds the mirror down. Keep that size small. That part blocks the mirror so we want to block as little as possible. If you use a strong metal you can make these tabs pretty small while still holding the mirror nice and tight.

Now drill holes and mount the clamps with screws just like you see in this picture here.

Now one more thing we need to do before we install this mount. Measure the distance from the back side of the big disk to the flat surface of the mirror. We need this measurement so we know where the mirror sits inside the tube. It doesn’t have to be exact and of course we can change this number by tightening or loosening the springs. Mine came out to about three inches.

Now insert that assembly into the back end of the telescope tube. Make it nice and flush. This will insure it is pretty straight and you won’t have to adjust the wingnuts too much.

And because of the measurement we made we know how far from this edge the mirror sits. (3 inches).

Now drill four pilot holes through the tube and into the wooden assembly and secure the two together with wood screws. You can do this mounting now or you can just set the assembly aside and do it later.

If you mount it now you should take it back out and set it aside. The reason being is that you will continue working on this tube and you don’t want to keep the mirror inside while all that drillling and work is going on. Just to keep it protected.