I made a wobbly dob base for my truss converted 8" f/4 newt. I'm getting pretty sick of this project. I've been working on it few hours every night this week. End result is a wobbly base that will be useless for observing.
The A frame sides are sturdy and the altitude bearings work very well too. But the vinyl LPs (2 glued together) and aluminium base are way too flexible, making the mount very wobbly.
I'll try again with plywood. I did not want to use wood, because of all the restrictions on bringing plant based stuff into the country.
The bearings are not the issue. They are very nice and smooth. Vinyl bumpers on PVC flange for altitude, and furniture sliders on vinyl LP for azimuth. These work great. It's flex in the base that is the problem. It supports a lot of vibration with little damping.
I tried replacing just the base plate with 20mm plywood. A little better, but the vibrations are still way too much. The vinyl flexes very easily, so that needs to sit on something solid as well.
Portaball would not pack up too well and would need a lot of counterweight to balance, that's why I didn't go that way.
I decided to chuck the whole thing and go all plywood (12mm). This will eliminate the wobble in the base, and using plywood for the sidewalls as well will let me get away from the straight edges, so I'll be able to drop the scope right down and still brace the mount properly. atm the scope is sitting 5-6 high to leave room for the bracing elements.
I'm thinking thin high tensile strength wires/cables & small turn buckles to tension the frame up to stop the vibes, but looking at the overall design I'm not sure where these could be placed to work effectively.
Hi janoskiss,
I've made quite a few mounts for my scopes..EQ's and Alt-az..more duds than goodies..and it is a learning experience..at first you don't succeed..etc
But at least you tried to build something bold and diffrent!!.so full marks for that!!
i did mean to do it once you have it up and running satisfactorally
Sorry about my smartypants comment there...
I don't want to complicate it more with cables, more braces etc. I wanted to keep it simple, so it's fairly quick to disassemble/reassemble. Mark 2 will be all plywood.
I wanted to keep it simple, so it's fairly quick to disassemble/reassemble. Mark 2 will be all plywood.
Just to throw another idea your way
I have also contemplated doing this with a base consisting of a number of flat panels secured to each other with dowel pins and spring loaded snap catches.
That sounds very sophisticated Geoff. I wouldn't even know where to look for the parts needed.
Anyhoo, plywood + L-bracket idea was a disaster. The execution was anyway. Probably could make it work - if I bought stiffer (thicker) plywood and thought more about how to stiffen the joins between panels too.
So I went back to my Meccano Dob after all. Added plywood to the swivel base, and plywood for ground board. Big difference. Rubber feet in pic had got to go - they are a major source of vibrations. I replaced them with steel bolts - much better. Bigger ground board might be good idea for better AZ stability when near zenith. I'll also add ALT friction control tomorrow. Otherwise it's not looking too bad. Might even get to try it out tomorrow night.
8" f/4 travel truss dob - arrgh not good enough!
