Quote:
Originally Posted by benklerk
Just need some help and advice.
I'm planning on putting in a 3m x 3m shed to house a GSO 14" RC with either a mesu 200 mount or a JTW mount.
Anyway, Im going with a slab. - Slab first or pier first
- How deep to I go with the pier
- How high do I make the pier
- What is a good size diameter for the pier
- How much of a gap do I leave from pier and slab
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Do the pier first - that's the important part. The slab can be poured later with a gap sufficient that the two are not touching - it doesn't have to be large. I left about 15 mm between the concrete pier and the concrete floor of my obs, and filled it with a strip of foam from Clark Rubber.
The pier needs to be 'rock' solid, so your particular circumstances will dictate how deep you need to go. I poured mine in a Formatube cardboard pipe, which is made for the purpose. I dug a 2 cubic metre hole, put in plenty of reo and and had the reo continue up through the tube for the concrete pier. Metal piers are very popular and work well, provided that they are stiff enough. Stiffness comes primarily from the pier diameter, not the material thickness. I used some 6 x 275 mm dia pipe that was readily available. Plenty of others have used smaller diameters, sometimes using tapered gusset plates to provide additional stiffness and also to avoid the pier having a strong resonance at a particular frequency.
The height of the pier needs to be calculated for your particular circumstances, as it depends on your scope, mount, and wall height for a RoR observatory. You need to do some sketches to show how how low and how high the eye piece (or camera) will be over the full range of telescope positions that you will be using.
Good luck with your project!
Chris