Pier Mounting

Hey
I've taking a look at some of the previous posts on pier mounting a scope. I notice that a lot go for the semi-permanent steel pillar mount. If i had the option of going for permanent is sinking the steel post into the ground better then bolting the steel post down in terms of vibration?

I have lengths of 6 1/2" steel round posts (which from other suggestions can be filled with sand), i also possibly have the option of using a 10" Timber electricity pole, between these which would be the best in terms of stability, flexure or vibration damping?


Thanks
Mike

Hi Mike,
I built a steel pier many years ago for my scope (12" LX200) in the dome.
I was determined that I'd go to some extreme, no corners would be cut so that I'll end up only doing this once and not end up fixing it in the future.
I have fairly good drainage in the back garden so I decided to dig deep for the pillar foundation. In the field behind my house is a filled in limestone quarry and I had heard from some of the older neighbours that there was bedrock not too far below the grass.
So I decided to build a 3x4 foot hole (smallest area I could physically work in) in the center of the footprint of where the dome was going to be and kept digging and actually hit bedrock at about 6 feet, I then filled the bottom 3 feet of it with concrete which if memory serves me right is about 2.5 tonnes.
I then got a 10 inch steel pillar 6 feet long where the steel was 0.5 inches thick, then I got 2 16x16x1 inch steel plates welded to each end and had a 3 inch hole made near one end so I run cables up the center of the pillar.
I had 8 holes made in the lower plate and 6 inch rawl bolts to secure it to the foundation, this was plan A.
Plan B was that if I found that the thing vibrated then I could bury 2.5 - 3 feet of the pillar in concrete to make it more secure, however I found that this measure was not needed thankfully.
I had 4 1inch holes drilled on the top plate of the pillar and using 4 1inch thread bars put a further top plate above the pillar, I figured I wouldnt be able to accurately level the pillar but could easily level a third plate above it. Looking back, 3 bars would have been abit easier,
I had originally filled the pillar with sand but later removed it as it seemed to be a mecca for spiders for some reason. It turns out this pillar is so massivly heavy, removing the sand had no effect.
I can lean against the pillar looking through the scope and it takes a hard thump on the plates to see vibration in the eyepiece, so I'm happy.
I had it hot dipped galvonised and then I painted it with black hammerite, so it'll probabily last longer them me.
So yes, this is a rather drastic solution, but in my mind practically any mount/scope combination out there that will fit into the dome can be easily carried by this pillar. At the time I was thinking I'd get the 16" SCT eventually, but that plan is history now.
Here's a pic of the pillar in my front garden before it was "shipped" to my back garden and painted.
farm4.static.flickr.com/3459/3960873032_b04b667476_o.jpg

Hope this helps.

Hey Dave
Thanks for the reply. Just to clarify you ended up just back-filling
the top three feet of the hole? The picture does give the impression of something that could be nothing but stable, it s an impressive pillar!! I think i will go with the 61/2" pillar and do something similar just on a smaller scale I have a couple of lengths of the 61/2" steel so can afford to go pretty deep and see how stable it is as i go.

Thanks

Mike

Hey Mike,
I ended up not burying the bottom half of the pillar in concrete, 8 rawl bolts on their own did the trick, nor is the pillar filled with anything but air.
Its a beast of a thing, a major job to lift at the time, but it is a job for life.
The pillar you describe sounds good, what do you intend putting on it?

Keep in mind that you cant over engineer this thing, but you certainly can under engineer it resulting in troublesome consequences. I would have used a wider pillar could I at the time have gotten my hands on one.

Hey Dave
I can only imagine the work involved in getting it into place! I plan to put an Atlas EQ6 with 11KG OTA and necessary counterweights, i'd say in total just over 20kg (also a guidescope). I definitely dont plan to put anything bigger on the pillar. From what i have seen 61/2" steel pillar is reasonably generous for the mount (but that really remains to be seen). It was only in the last few weeks that an ESB pole landed in the yard and it got me thinking!!! (to be honest even if a 10" timber pole was better then a 61/2" steel pillar i can't see a solid way to attach the mount)

I reckon also that i will go for good heavy plates on either end of the pillar. Now that you've said it I definitely dont want to under engineer this, i will keep an eye out for a wider steel pillar.

How have you found vibrations traveling up from the ground they must surely get damped down with the sheer mass of the pillar?


Thanks
Mike

Mike --

I load up about 60 lbs on an Astro-Physics 6" pier, but it's got tensioned rods to keep it rigid:

Ed: oops, forgot the counterweights: that's probably closer to 90 lbs all in.



Without those, I think it would be under-spec. So I'd be inclined to look for an 8" pipe. I also think the ESB pole would be fine, if you could devise a reasonable attachment method.

Cheers,
-- Jeff.