Dobsonian mount for 300PDS ?

[wisedraco]

btw, you bolted alt bearings to tube rings, as i understand? in result, alt bearing discs is parallel each another?

in my case  -not. looks like there need a some ?wedge? for got that discs parallel each other.

also interesting about ventilator for primary mirror - what one you used? looks like, a mirror support is designed for 80mm ventilators?

[8kids]

You are correct, I placed a thin piece of plastic between the bearing and tube ring.

I have a fan from an old computer case attached to mine but I never use it.