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Sunday, December 30, 2007

Zhumell Mod: OTA Knob


When I first got my Zhumell 10" Dobsonian, I pointed and moved it by grabbing the end of the optical tube assembly. While this works, it can sometimes be hard to operate the scope like this. So I decided to add a knob onto the end of the OTA. This is a pretty common mod, actually. The advantage of having an OTA knob is that it is a consistent place to control the scope from. It will help you learn to operate your Dobsonian more consistenly, by placing your hand always in the same spot.

First, unscrew one of the screws at the end of the OTA. Then, go to the hardware store and buy a cabinet knob. Any knob will do, but I bought a black porcelain one to match the telescope. Check to make sure the screw it comes with is the same size and thread pitch as the ones from the end of the OTA (The screw is reportedly a metric M4/0.7). Taking the small OTA screw to the hardware store will help you determine this fit.

Cut the head off of the screw that came with the knob, and use a small nut to secure this newly made stud into the end of the OTA, where you removed the screw earlier. The nut could be purchased at the hardware store, I just had some laying around the garage.



Now simply screw the knob onto the stud and you've got an OTA knob!

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.


Clear skies!

6 comments:

MiketheChap said...

I did this mod this past weekend. It went well except that I went to Home Depot for the part (did other projects to, and they had none of the parts). When they didn't have anything I went to Lowes. The screw here is a metric screw, M4/0.70 threads - at least on my Zhumell 8". Hopefully, that will help someone.

Sean Welton said...

Thanks for the info on the screw.

March 5, 2008 at 10:27 PM

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