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Hi Richard
I have a 16" lightbridge. However I can't see it for a couple of weeks as it is still at Wiruna. The bearing assembly is about 18" for memory but I haven't looked at it since last July.
It occupies a space of about 5 mm. I had it out last July because I had dirty/sandy water flow over the base in a rain storm and it was full of grit. It still is not right.
That drawing was lifted from a drawing of another dobsonian I modified years ago and edited slightly and I would probably make a special bearing housing for the rocker box rather than recess it. That drawing is for 1" thick ply. At the moment I just use a thrust washer and pull the bolt down with the underneath retainer assembly.
My lightbridge also has a different centre bolt. I have an old Magellan 1 and its replacement centre bolt with the encoder was an exact replacement except I had to make a new sleeve to remove the slop in the base. I also modified the altitude bearing to take the other encoder. These encoders are now used with an Argo Navis. Making specialised centre bolts is no problem on the lathe.
I have only used the lightbridge on DSO's at around 70 Mag. I did manage to see the flame nebula clearly but have not got the horsehead yet. To get 300 mag I would certainly need to beef up the base and azimuth pivot.
Barry
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