Alt bearing height

[griff44]

Hi, I'm currently building a dob base and just trying to get hold of the height of the altitude bearings from ground level on the 200p skywatcher dobsonian before I proceed further with the project - could someone kindly advise or measure it for us if you own one ? Thanks

[griff44]

Come on guys someone must know ?? Need to get the project off the ground ASAP so I can start stargazing

[scogyrd]

Do you mean on the tube or including the base? If just the tube the distance from the floor to the centre of the original bearings is 475mm.

[griff44]

Thanks for the reply, its including the base, is it 475mm? (from ground level to altitude bearings - to the screw in handles at the side?)

[scogyrd]

475mm is the height from the bottom of the tube to the centre of the bearing, eg the hole the side handles go in. unfortunately my original base is in the attic so I'm not too sure of the height including that, if nobody else replies I'll have a look for you tomorrow.

In the meantime, if it helps, the side panels on my DIY base are 525mm.

[Moonshane]

is there a reason why you are replicating the skywatcher base if building one yourself? I'd say that you could improve it substantially with a square rocker and larger alt bearings which would mean a lower 'cradle' height. you would still have a round groundboard.

e.g. if you made a 12" square rocker box and your tube is balanced with 12" on the bottom end, and you made 12" diameter alt bearings (which would give smoother and more uniform motion) then you could have a rocker which is a 12" cubed box. this would be a lot more compact. obviously you can increase this at will to say a 14" square box with 12" high sides and this would increase the stability noticeably.

just a thought.

if you need further info I have recently made a dob base for a 6" scope and a 16" scope and can link you to my threads.

[griff44]

I'm just after a general size from ground to the alt bearings and if anyone has the diameter of the SW 200p dob base that would be great !

Once i have these sizes i will tweak them so i will not replicate the SW base

I'm using PTFE bushes for the alt bearings with brass threaded inserts, a M8 bolt will fit through the mount and into a tube ring that i have which i will re-thread to M8. The bushes will then run against a formica alternative to ebony star (i have formica uk technical on the case for me)

The az bearings will also be PTFE on formica