split ring mount

[ponytale]

my new diy project is converting my existing dob to split ring type mount which will allow easier southern polar alignment and easier viewing with a plan to motorize the split ring to sidereal rate for planetary video and photography, after 2 days work with a few snags with angles etc it is almost assembled , the attached sketch is my aim based on the web link below.

Telescope Mount Details

i will take a few photos to post if there is any interest ?

tony

[Glasspusher]

Hi Tony, be interested to see your pics, sounds like a great project. I think the split ring mount is better suited to latitudes lower than here in the UK. Be good to hear from anybody who is using a split ring in the UK.

John

[ponytale]

Hi John , yes i am at 31.4 South just north of Perth, pics soon !

Ps i am happy with my mirror and plan to do my other piece of glass soon ,

and i now work in a tile shop so mosaic tiles no problem , there are broken porcelain tiles with no coating/glaze i may use some of that?

Tony

[skybadger]

Hi tony, I have just about finished.mine. the balance.is.the real.tricky bit, due to the low.swing through size in the ring. Currently rebalancing using lighter truss and counterweights.

Mike

[ponytale]

Photos of split ring mount during construction/conversion,

angles all seem good and ota assembly fits in and is stable at 30 degrees of rotation either side of perpendicular, a total of 60 degrees rotation , balance is not perfect yet but i can fiddle with that , i am more concerned with the polar axis alignment being stable/consistant throughout rotation, which means very accurate bearing alignment especially at the rear/north bearing, i am thinking of making a bearing mount that is eccentric that i can rotate in a cylinder and adjust as required , or even a disc with a bearing in the centre that is spring loaded at 3 points with adjusting screws at 120 degrees ,

any ideas /comments welcomed .

tony

[skybadger]

Hi Tony

how did you work out how close you were going to cut the ring to the edges - looks mighty narrow to me.

Mike

[ponytale]

I cut less than the cutout initially but had insufficient room for scope to reach zenith so out came a bit more!!

it is quite strong as it is 24mm plywood 2x 12mmm glued and screwed together ,

I tried to make from existing dob bases and now know i should have used bigger diameter circles to start with , i have slightly modified the split into cradle type which is stronger and more ridgid ,

I want to try what i have first before i remake to something a bit smarter , but it is an excersize in itself,especially the working out of the angles and joints , i have a rudimentry knowledge of geometry etc so found it a bit hard at first.

here are a few more pics of the set up with cradle it allows more movement in where the scope bearings sit, hence better balance and greater movement, the two rings of the cradle are now on bearings and i am working on a tangent arm and threaded rod setup to test out accuracy .

Tony

[ponytale]

an update on progress so far : tested tracking on the moon during the day and was pleased with the way it worked only needing a slight nudge on the cradle to track the moon after ten miutes of gentle nudges in one direction only the moon was still in the eyepiece which is great, i am happy that a motor on the ring edge will give me what i need for some basic imaging rather than a tangent arm set up which by all accounts has potential for introducing more error. I am going to fit some levelling feet to the base and make it more compactable with the cradle part being the heaviest part i am hopeing to make it out of ally tube if i can get the tube bent into accurate rings for not too much cost, i have thought about using alloy bike rims for the half circles with 18mm ply inserts for the trunnion/brgs to run on , just an idea running around in my head at the moment !! i will sketch it up and see whats involved . Tony