Is 50 inches too big?

[ianaiken]

I've read pier recommendations at being around 43 inches high, as this is a suitable height for refractors and reaching the EPs etc... I've did some measuring up and I think 50 inch is what I need to clear the OBS walls (once built), with the head (NEQ6) on top of that and two refractors.

Is 50 inch too big for a water pipe concrete filled pier? I am thinking about 30 inch into the ground too for stability.

There's a lot of debate and discussion on this forum and I just can't make up my mind.

[ASIGN_Baz]

It's all a matter of rigidity and resonance. If it is too tall and thin, then vibrations will resonate and you may have some flex as the telescope and weights shift through the night. If you need to go taller, then go wider. Just narrow it off or step it down at the top where you need clearance. Tapered steel stabilizing fins welded full length will also help. There's also some merit in filling it with sand, rather than concrete. Concrete is rigid so vibrations can travel full length, where as vibrations lose energy as they transfer from one grain of sand to the next.

However, all arguments aside, when you are imaging, the idea is to let the gear do it's job and you don't move! No movement, no vibrations.

Something to think about.

Baz.

[ianaiken]

Baz - Good point, when imaging I will be in a different building so it will be just the scope and the elements, so there shouldn't be any movement. I wasn't going to use Steel for the pier so I couldn't reinforce it with stabilizing fins. I had plastic in mind, like water the gas and water use underground (purely as they are doing gas works nearby and I was going to see if they had any off cuts).

[ASIGN_Baz]

Baz - Good point, when imaging I will be in a different building so it will be just the scope and the elements, so there shouldn't be any movement. I wasn't going to use Steel for the pier so I couldn't reinforce it with stabilizing fins. I had plastic in mind, like water the gas and water use underground (purely as they are doing gas works nearby and I was going to see if they had any off cuts).

What is the diameter of the plastic pipe Ian?

[ianaiken]

Don't know yet, it depends on if the workman have any spare otherwise I will have to purchase some from somewhere or go down the steel route. My target diameter is 8 inches based upon no calculations or theory but I think it might be a problem getting one long enough with a large diameter.

[ianaiken]

Maybe something like this http://www.plastics-express.co.uk/product/200mm_%C3%98_3m_Pipe_Single_Socket_P-DL195

[ollypenrice]

One thing to remember when working out the height; when you go past the meridian, which most of us want to do when imaging, you end up with the saddle plate below the top of the mount. It's easy to forget that, as you track into the west, the scope gets lower and lower and soon points at the observatory walls if they are too high!

If you do use concrete I'd run plenty of rebar down it.

Olly

[pete_l]

I expect you've already sorted out your local horizons, so that the obsy walls are the highest obstructions your 'scope will see.

However, it's worth bearing in mind that imaging (or eyeballing) at low angles has its own limitations. For a start, everything gets dimmer as you approach 0 degrees. At 10° everything is already 1½ magnitudes dimmer than at the zenith - and objects get much dimmer more quickly as you go lower. Add on to that as you go lower, seeing / twinkling gets worse for the same reason and the effects of distant LP becomes more noticeable.

Exactly what the lower practical limit is for any given site depends on the specifics of each case, but it may mean that your telescopes wouldn't need to "peek" over the obsy walls, as the low-angle targets wouldn't yield satisfactory results.

Also, the higher above the walls your scope is, the greater the clearance you'll need for the roof.

[ianaiken]

Thanks everyone for the pointers. The walls are 6ft 1 with two walls against my boundary fence the other two are sufficiently low that they don't block any horizon that the buildings don't anyway. I won't be pointing too low anyway because of LP etc... I'm spending a long time looking and checking the positioning and measuring up. The scopes park position would be on the side parallel to the floor.

The only problem with 50 inch is my wife would need a stool to see through EPs. So I may go lower for that to say 45 inch.

[laser_jock99]

Pier height should be determined by the height of your equipment in it's lowest 'park' position, plus say a 4" allowance for sliding roof clearance. So you could measure your current tripod head to top of scope distance and work it out from that. You might need to allow for any bigger scope upgrades, but it makes no sense to make the pier shorter than necessary as you will loose out when needing to look at low horizon objects.

My current pier was designed to allow low horizon viewing with refractors up to 150mm and still close the roof.

I can just about look at low horizon objects, though I'm limited by mountains in some directions.

[ianaiken]

Thanks for the input. I've measured and there are 4 inches above a horizontal park to the height of the walls. I need to check the plans to see where the roof is in relation to the wall height so I can be sure it opens. This is with two scopes on a side by side arrangement on an NEQ6 so I could go up to single 16 inch scope if needed.

There are buildings and other boundaries to consider so I cannot go too low anyway, so it will ultimately be a balance. I've got the spot where I think the pier will go so I need to take the mount out later and double check horizons.

[Gina]

Very good advice! I made a miscalculation on my pier and made it too short. Ended up putting an NEQ6 Extension on the top and the mount on top of that. Still, thankfully the stability is still adequate.

[Starblazer]

Around the base of the mount, but not touching. Build a small set of steps that go all around the pier, This way you can have the pier higher to clear the obsy walls, but also still be able to step up and see through the eye piece. If it's fixed in place, less chance of toppling over onto your scope if it moves too

[ianaiken]

Good plan

[laser_jock99]

Around the base of the mount, but not touching. Build a small set of steps that go all around the pier, This way you can have the pier higher to clear the obsy walls, but also still be able to step up and see through the eye piece. If it's fixed in place, less chance of toppling over onto your scope if it moves too

I just use a small step ladder as occasionally need to access parts of the scopes away from the pier.

[Daniel-K]

i used concrete my only down fall is i never used enough rebar i do get some vibration but not much and you have to whack the pier to get them, if i was doing it again i would buy a fabricated pier and fill it with sand as olly said maybe in 5 years time i will take the floor up and dig out the concrete and pour a new block in for a pier that's bolted into the block and fill it with sand, make sure you do lots of research and measurements i had to cut my walls down in my obsy cause of miss calculation luckily it was only 6inch's but im over the moon now with mine just need a warm room putting in

[ianaiken]

Thanks for the input Daniel, sound advice. I will be using concrete, my pier head has to be cast into concrete. If I have to whack it to get vibrations then I am very happy with that. I'm going for 8 inches and we will be using a lot of rebar. I did think about a fabricated pier but the price puts me off. I check measurements daily. Going to get my builder friend to double check them too. Can't wait.

[fwm891]

Hi Ian - just measured my new pier and that's 52.5" to the top plate with the NEQ6 still to add! This will give me a clear view over the 4' Obsy walls

[ianaiken]

I think that will clear those walls for sure thanks for the input Francis.

I'm measured to 50 inch from the floor to the top plate with 6ft walls. No point putting the walls any lower as there are houses and trees in the way.

I am currently still planning. I think we have the materials list now and its a case of getting some foundations down, a hole, and cracking on with that. Then fabrication of the frames then the cladding with the roof last. I expect it to all start sometime next week at which point I will start to take pictures. Unfortunately I don't have pics of the area prior to ripping out plants and bushes but I got 20 bags worth of garden rubbish. All clear now bar some stumps that are hard to get rid of.

I've also opted to have 50cm between the boundary fence and the OBS for maintenance reasons. I'll summarise this up later with some other considerations.

[Earl]

My pier is low as I use the walls of the obsy as a light shield, this does restrict my view but keeps it dark in there.

I would recommend taking that into account if you have any street lights etc to consider.

[ianaiken]

Earl - actually there is one street lamp that could cause some issues but I believe it to be blocked by the wall already. However.... I'll measure twice and cut once because now I am not absolutely sure. Thanks for the recommendation. I need to get the scope back out into position and check this out with string at the right height.

[fwm891]

I think that will clear those walls for sure thanks for the input Francis.

... I don't have pics of the area prior to ripping out plants and bushes but I got 20 bags worth of garden rubbish. ...

I've also opted to have 50cm between the boundary fence and the OBS for maintenance reasons. I'll summarise this up later with some other considerations.

Same for me loads of rubbish to remove first. I've drawn up a materials list and got a reasonable quote from a local supplier - who is great because they will deliver things in stages for me (have to pay up front though) So I'm lifting old paving tomorrow and starting to dig 'THE PIT'. Once their up I can peg things out and dig the wall foundations. These will be quite light - about 5-6 inches of concrete with a layer of Theralite blocks which will bring me 50 mm above ground level and keep the worst of the moisture away, the DPC and moisture barrier will do the rest.

Good luck with your build

[ianaiken]

Sounds good and good luck too, I know I need it.

I'm putting down blocks on top of the old 4x3 slabs that are down. They are quiet solid been there for years. Its not level so some of the concrete blocks I'm putting down will be cemented up. Basically it will be 4inches above ground level at the lowest point.