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C8 Conversion

I love my C8 – the optics are great and it is such a nice compact package. But as I began to push the boundaries, I realized that the plain fork mount just wasn’t going to do it for me anymore. There was just too much flex on the forks, and the tracking was less adequate for visual use, but not for photographic exposures of more than 15 seconds. So when one of my fellow RASC members put his HEQ5 mount up for sale I jumped at it. This mount, which is the same as the Orion Sirius mount, has a good reputation for being reliable, sturdy and economical. The 30 pound load capacity is more than enough for the C8 OTA, which is quite light once freed of its forks.

Since the C8 can be purchased with a dovetail for mounting on a GEM mount, I naively thought it would be easy to find a C8 dovetail that I could buy and plunk on my OTA. Not so much, as it turns out. Celestron and Orion do not sell the dovetail separately (Celestron went so far as to direct me to the Losmandy website). There are a couple of aftermarket rails one can buy, but neither was quite right – one was raised up on spacer blocks, the other had a short rail mounted on a plate, limiting the range of mounting positions. So it looked like I was going to have to make one myself.
Another issue that arose was actually attaching the mount to my pier cap, which was designed for a wedge. I realized I would need a wide based cylinder that would sit on the pier, and which could accept the mount. Again this called for some custom work.

The new pier cap (or maybe it’s a mount base, I’m not quite sure what to call it) was fairly straightforward in that it was a straight cylindrical job on the lathe. The learning curve part was that it was a 30 pound block of 1045 steel, which I had never machined before (I could have used aluminum, but the steel was ¼ the price). I made a small brass post that threads into the block for the azimuth adjustment screws, which works well. The biggest hassle was the central mounting bolt, as it is an M10 thread. I never did find a long M10 bolt, but I did find a small metric tap and die set that I used to make my own.

Mounting this steel cylinder to the pier, I placed an 8"x ¼" steel plate on three red rubber washers (for vibration damping), and then the cylinder on top of that. The central bolt goes through the whole package and locks on the top plate of the pier cap.

One problem solved.

The dovetail was not so simple, and is best explained using this video.

The end product is eminently serviceable, and far more steady than my fork mount ever was. I am even able to observe and image when the breeze is blowing, which used to grab the fork and shake it annoyingly.  Though frustrating and time consuming, making the parts for this conversion was ultimately a rewarding learning experience.

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