Saturday, 11 March 2017
I recently purchased a new SCT optical tube assembly to replace my lovely orange tube C8 that I retired from action. I’m pleased to say that the Old Girl has found a new home with a collector who will look after her.
So, this new SCT needs a mount.
I purchased this scope knowing that I have a German Equatorial Mount (GEM) that can take it. However, GEM mounts do not place the eyepiece at the most convenient location. There is also the meridian swap in order to keep the motor drive loaded appropriately without undue stain. Yet a fork mount has a much more limited range of eyepiece placement, and is not affected by the strain of meridian shift.
So, I’ve got a new OTA, but which set of forks?
One reason that I bought this particular OTA is that it has screws on it that would seem to correspond with the coupling holes on the fork mounting plates. I have an old set of forks from the same brand as the OTA, so why not look at seeing if I could couple this OTA with these old forks? I’ve been using these old forks as my video astronomy rig, having made a platform that spanned the forks.
Alas at first glance not. The OTA appeared to be wider in diameter than the span of the forks and the coupling holes did not match. The latter was by just 1mm, but enough for the screws not the fit.
So begins the search for a set of forks to match, and an interesting saga of near misses, useless sources of information, wonderful people willing to help, and pigheaded, devil may care, try it and see try to fix it attempt.
So, after the question asking, frustrations, and fruitless searching, the promise of finally a clear sky and the chance of finally doing a sketch of the Moon, I decided to have another go at fitting the OTA to the old forks. I mean, how hard could it be, right? So after dinner, I disappeared into my workroom and let the Devil take over!
I decided to take the arms off the mount, modify the holes to allow the screws to fit the OTA. This was very quick and easy to do as it was just a minimal amount of material that I had to adjust. To my joy, the third hole in the coupling plate was a perfect match to the corresponding hole on the OTA. Bonus! This allowed me to first couple the tynes to the OTA with this third, leaving the two other holes easier to deal with.
Once both tynes were fitted, I lowered the OTA onto the mount. I expected there to be a gap between the mount and the tyne attachment points, and had thought of a way to deal with it. But to my surprise, there was no gap! It was a perfect match! Perfect!
Finally I have a brand new SCT OTA with the convenience of the fork mount that I preferred. I am overjoyed that I have been able to once again re-purpose the old forks. The wedge I made some time ago and my kids decorated it, and the tripod is a surveyors’ tripod. So my “new” scope is a real Frankenstein, made up of old and new, DIY and re-purposed. And it all works brilliantly 😎
Now, to get scope time once again. I’m hoping that the sky finally clears this weekend. The forecast is promising. I’m now all dressed up, and nowhere to go until the clouds clear. Oh, well, that’s how things go with astro…