A dobson-style refractor mount

For most people, the telescope mount ruins astronomy forever.
That little piece between the tripod and the tube that allows you to steer.
Ruined forever.

I’ll explain what happens to most people who buy their first telescope. They spend a few hundred, and maybe they get something like a Celestron Astromaster. They can’t see anything. But why? The tripod is made of sturdy aluminum. The optics aren’t great, but they’re enough to see moon craters and Saturn’s rings. So what went wrong?

The problem is the equatorial mount. They can’t point the telescope at anything! The mount is heavy, complicated to use, and shaky. A good equatorial mount is expensive. A “beginner” mount gives you a shaky telescope. A shaky telescope is unusable. Frustrated, and not able to see detail on even the moon, they give up. Astronomy is dumb, I’ll go watch TV. At least that stays still.

I will never understand why beginner telescopes all come with an equatorial mount when an Alt-Az is much more appropriate. An Altitude-Azimuth mount is much more straight forward. Up, down, left, right. You just point and look.

But I’m not satisfied with this either. After years of trying different brands, celestron, skywatcher, manfrotto, berlebach, I find that these Alt-Az mounts are also sensistive to vibrations, and tough to make fine adjustments. Above 100 power, it’s tricky to keep a planet in the center.

And by the way, no. I refuse to motorise my telescope to track the sky.
If I do that, people won’t notice that the Earth is turning.

Why do the alt-az mounts have this problem? It’s because the center of gravity pivots around the altitude axis. When the telescope is horizontal, everything is nicely stacked on top of each other. But the ecliptic is not found on the horizontal. So we pitch the telescope up, and we find that now, the telescope’s center of gravity is behind the center of the tripod. Without some other force to keep things still, the weight of the telescope would make things topple. This other force is friction within the mount. That’s why alt-az mounts have all sorts of locking rings. But then you have to fight the friction, and for heavier telescopes, there isn’t enough friction. Meanwhile, everything is shaking. You need to spend hundreds on an alt-az mount before it’s strong enough for a beginner to use.

But why bother with all these forces in the first place? John Dobson solved this problem 70 years ago. If you mount the telescope at the center of gravity, you don’t need friction, and you don’t need counterwieghts. Everything is balanced, and stays balanced. The telescope can be moved with a single finger, and stays put afterwards. There are no vibrations.

Finally, I was motivated to build a dobson-style mount for my refractor. It would be my first ever woodworking project. As a precision engineer, I had only worked with metal and micrometers up until this point. But wood is a fantastic material! It’s lightwieght, strong, and it naturally absorbs vibrations.

I wanted to build a mount for my telescope can be built by anyone. So here’s my attempt at a Dobson style mount for my refractor.

It’s only 5 cuts from 2 different sizes of wood stock. I built it using only hand tools.

The circles sit nicely in the Vees, even though my cuts definitely aren’t square! Even though the telescope is not fixed to the tripod, I was surprised how stable it was. Even when I push the telescope sideways out of the Vees, it fails safe, and just gets caught inbetween them. That’s the magic that happens when you stop fighting the forces and mount things at their center of gravity!

I used three teflon pads for the azimuth bushing. The mating side is bare wood. Works OK, I’m happy with the amount of friction, but there’s room for improvement.

Overall, very happy! Looks nice, feels good, and also fits into the extra space of my manfrotto tripod bag. This 20EUR thingy has less vibrations than any mount I’ve personally used before. I’m just amazed at the performance!

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