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Hi Arief,
What is your intention with the scope, photo or visual? If visual, dob mount or eq?
While designs for both photo and visual require a rigid structure, the way you go about designing an OTA is influenced by the mount. Designing an OTA for a dob mount has different requirements to that mounted on an eq mount. Each style of mount subjects the OTA to a different set of forces, and makes different use of the centre of gravity.
There are also subtle differences in the way you set up the optics in a scope for primarily photo as to visual. This even influences the choice of secondary mirror for each, though at f/6 it is touch and go, so you need to make the appropriate calculations to determine this.
Glen came up with a very novel way of building a Newtonian for eq mounting. It is a very rigid design and makes use of ultimately a massive set of poles in a great 'cage' arrangement. By 'massive' I mean their collective rigidity is enormous in the way they have been arranged. For a dob mounted scope, it is would set the centre of gravity too high within the OTA and would need a very high rocker box to mount it. For an eq mounted instrument, this higher centre of gravity is a better suited. Different purposes brings a different set of requirements.
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