the yesyes observatory - let the planning begin

[yesyes]

I've been thinking about how to make the pier. The original idea was to use 200mm spiral ducting and fill it with concrete.

Now I've been thinking whether I should just build shuttering. Is there any reason why the pier shouldn't be square rather than round? Is round more stable?

Having a pier with flat sides would make it easier to install the box with electronics and sockets and so on....

[fwm891]

No problems with a square pier just watch the size of the diagonals so they don't foul the scope as it rotates. That's where round scores you can have a larger diameter without clearance problems

[Gina]

Square corners could be a personal hazard - sharp edge syndrome.

[opticalpath]

I made mine square(ish) using plywood shuttering and did it all in one concrete pour with the underground base block (1 cubic yard). This has the benefit of being massive and extremely rigid; there are no joints in the concrete and the steel rebar goes right down through the pier into the base. The possible disadvantage is its permanence!

What Francis said is right: the corners stick out a bit further than a neater round section and that can somewhat limit how far past the meridian you can track before having to flip the mount. You can do a few experiments with the mount beforehand to decide if you think it's a problem or not. Just don't make the pier fatter than it needs to be. I made mine a generous 35cm x 35cm section ...... which was no problem with a fork mounted LX200 on a wedge, but slightly annoying when I later changed to a german mount and have to do meridian flips.

Adrian

[Astrokev]

As others have said, can't see a problem with square, apart from OTA crash risk. I'm planning to use 280mm (11" in old money) air duct tube.

[Gina]

I made mine square(ish) using plywood shuttering and did it all in one concrete pour with the underground base block (1 cubic yard). This has the benefit of being massive and extremely rigid; there are no joints in the concrete and the steel rebar goes right down through the pier into the base. The possible disadvantage is its permanence!

What Francis said is right: the corners stick out a bit further than a neater round section and that can somewhat limit how far past the meridian you can track before having to flip the mount. You can do a few experiments with the mount beforehand to decide if you think it's a problem or not. Just don't make the pier fatter than it needs to be. I made mine a generous 35cm x 35cm section ...... which was no problem with a fork mounted LX200 on a wedge, but slightly annoying when I later changed to a german mount and have to do meridian flips.

Adrian

WOW! That's HUGE! My pier is about 170mm (7.25") diameter and is "solid as a rock". I have an NEQ6 and have had that loaded up with 10KG scope plus FW, camera etc. and 2 weights and no problem at all. Most piers are enormously over-engineered

[opticalpath]

........ Most piers are enormously over-engineered

Can't deny that

It just seemed sensible at the time to go big because it was a match to the base plate of the heavy wedge that supported my LX200, and it would be solid enough to support any future scope/ mount upgrade I could envisage. Only later when I changed to a german mount did I see the possible disadvantages of a wide pier.

Adrian

[fwm891]

Can't deny that

It just seemed sensible at the time to go big because it was a match to the base plate of the heavy wedge that supported my LX200, and it would be solid enough to support any future scope/ mount upgrade I could envisage. Only later when I changed to a german mount did I see the possible disadvantages of a wide pier.

Adrian

Adrian - can you fix your mount to the north west corner of your pier that would allow your scope to 'miss' the pier when passing the meridien. It would restrict you for high western views of objects that have already passed the meridien ?

[yesyes]

That's a beautiful pier, Adrian. I think I'm convinced now to do mine with shuttering, not ducting. 20cm square should be fine. The diagonal would be 28cm and shouldn't get in the way of the scope.

[Gina]

That sounds alright Chris Plenty strong enough and not too big. I wonder if you could put some angle or concave curved moulding in the inner corners of the shuttering to provide rounded corners on the moulded concrete.

These are the sort of mouldings I have in mind :-

[malc-c]

Just a couple of comments:

• I would not use particle board for the flooring. 18mm Exterior grade ply or solid timber floor boards makes for a firm flooring that will stand up to the damp conditions
  
• Fixing the floor frame with threaded studs whilst concrete is wet would be difficult. You may be better off drilling the timber and concrete blocks when set and using some sort of expanding bolt type fixings
  
• No need to rebar the footings. A firm mix should suffice.
  

[yesyes]

That sounds alright Chris Plenty strong enough and not too big. I wonder if you could put some angle or concave curved moulding in the inner corners of the shuttering to provide rounded corners on the moulded concrete.

These are the sort of mouldings I have in mind :-

Not a bad idea, but I'm not sure I like it very much... ;-)

The rounded one still has an edge and the triangular one would just end up giving me a octagonal pier. That might be a good idea for the top 30-40cm only though...

[JamesF]

Or perhaps just wrap the pier in an offcut of carpet

James

[yesyes]

Just a couple of comments:

• I would not use particle board for the flooring. 18mm Exterior grade ply or solid timber floor boards makes for a firm flooring that will stand up to the damp conditions
  
• Fixing the floor frame with threaded studs whilst concrete is wet would be difficult. You may be better off drilling the timber and concrete blocks when set and using some sort of expanding bolt type fixings
  
• No need to rebar the footings. A firm mix should suffice.
  

Thanks Malcom. So even OSB would not be advisable...

Regarding fixing the floor frame to the footings, I have already poured the first 2 footings. I've put some strapping in so that I can fix the joists from the side rather than the top. Not sure these metal bits I found and used are strong enough. Worst case I won't use them and I can still drill through the timber and concrete and fix them that way.

Fixing the timber while the concrete is still wet was never an option for me. I have to do the footings and pier first before even thinking about ordering timber. I just don't have the space to have timber and concrete stuff around at the same time.

[yesyes]

Or perhaps just wrap the pier in an offcut of carpet

James

I could also put some of those on.. :-)

http://www.amazon.co.uk/Round-Corner-Protectors-Furniture-Protection/dp/B00BQCFU9C

[JamesF]

Nah, carpet is more fun

James

[JamesF]

Or did you mean in addition to the carpet?

James

[opticalpath]

Adrian - can you fix your mount to the north west corner of your pier that would allow your scope to 'miss' the pier when passing the meridien. It would restrict you for high western views of objects that have already passed the meridien ?

That's a neat idea, Francis. As it turned out, though, I didn't have the problem of the scope potentially running into the concrete pier. The pier height was right for a SCT on a wedge but a bit low for my requirements when I changed to a German mount, so I had to raise the height with a steel mini-pier bolted to the top. This takes the scope out of range of the concrete and movement past the meridian is limited only by the narrower (round) mini pier.

Funnily enough, if I was doing this again I would probably use the same approach. That is I'd pour an underground block and mid-height concrete pier as one piece with embedded studs on top, then bolt a short steel pier on to that ........ rather than the more usual full-height steel pier anchored to a ground-level concrete block. Probably no logic to it - just feels better to me to have a shorter lever down to the anchor bolts. For the same reason I like to see the top plate on short fat studs rather than on four long thin 'stilts' that you sometimes see. In fact, I dispensed altogether with an adjustable top plate on my mini-pier and bolted the mount base directly to a fixed top plate, levelling the mount base simply by shimming the three mounting bolt spacers that the mount rests on. So everything is solid - no stilts, no flexure.

Adrian

[Gina]

I was thinking of something like 20-25mm moulding, just to take the corner off.

[malc-c]

Thanks Malcom. So even OSB would not be advisable...

Not in my opinion, but then again each build is different, and as mine had an enclosed void there was a high risk of dampness (hence the air bricks that Tony recommended). For me 18mm exterior ply gives a nice firm smooth base on which to lay carpet tiles and the interlocking foam flooring in the scope room

[Astrokev]

That sounds alright Chris Plenty strong enough and not too big. I wonder if you could put some angle or concave curved moulding in the inner corners of the shuttering to provide rounded corners on the moulded concrete.

These are the sort of mouldings I have in mind :-

Taking this idea to the extreme - a radical suggestion, but why not use a round tube such as air duct??

[yesyes]

now THERE's an idea...

I would kind of like it square / flat as that would make it easier to install things on, such as my electronics box and power sockets and so on...

[Astrokev]

now THERE's an idea...

I would kind of like it square / flat as that would make it easier to install things on, such as my electronics box and power sockets and so on...

What goes round, comes around, as they say

Yep, I know what you mean Chris. I'm still currently planning on using the duct tube that's been cluttering up my shed for the last few years, though I have to say, a square shuttering design has some appeal for the reasons you've mentioned. I could be swayed....

[yesyes]

If I already had the ducting, I probably wouldn't hesitate using it. But I don't, so I have a choice...

Another thought occurred to me regarding the pier. Would it be OK if I ran 40mm plastic waste pipe up inside the pier about half way up for various cables? It would take away less of the cross section area of the pier than the squareness adds compared to a round pier.

[Astrokev]

If I already had the ducting, I probably wouldn't hesitate using it. But I don't, so I have a choice...

Another thought occurred to me regarding the pier. Would it be OK if I ran 40mm plastic waste pipe up inside the pier about half way up for various cables? It would take away less of the cross section area of the pier than the squareness adds compared to a round pier.

This is what I intend to do with my pier, and which is why I'm going to use a 280mm tube. This is big enough to accomodate a good sized plastic pipe (probably a standard external drain-pipe) up the centre of the pier for any cables I need .