Lifting the Lid

[hughgilhespie]

Hi,

I need to lift off the dome of my 2.2 metre Pulsar observatory so I can smooth out the joints between the 4 sections. They are causing problems when the dome is rotated. When I bought the dome it was installed by Pulsar so I have no experience of lifting the dome on or off the walls. My plan is to use 4 Acrow props to do the lifting so I can do it as a one man operation. I assume that it is best to place the props outside the dome and lift using the edge of the dome. Can I ask anyone with experience of these Pulsar domes if this is the right way and are there any snags?

Thanks, Hugh

[Peter Drew]

I've no experience with Pulsar domes but make sure that any provision for preventing the dome from blowing away is unfastened before you progress much further.

[Davey-T]

Sounds a bit dodgy, not much purchase on an acrow, you can get wall supports that fit to the top of acrow props which would get better purchase and use more props but still sounds a recipe for disaster.

Not a one man job anyway if only from elf & safety point of view, one gust of wind could topple it and the edge of the dome may not be strong enough to take the weight anyway.

Dave

[Demonperformer]

47 minutes ago, hughgilhespie said:

When I bought the dome it was installed by Pulsar

Don't know how long ago you purchased it? But surely, if installation was included (so you were paying for it as part of the price), I would have thought that they have a responsibility to do the job properly and if the dome is not rotating properly it is their responsibility to correct their inadequate workmanship.

[Gina]

I too don't think you should risk it on your own - your personal safety is more important than any dome after all.  From what I've seen, it takes four strong men for that job.

[Mick J]

If its the dome in your avatar then it may be worth a go with acrow's........  as Davey-T wall supports on the top of acrows will give a bigger foot (strongboys).  You need to lift the dome and keep it down on the acrows at the same time and stop the acrows wobbleing around - lots of rope would be a possible way to go.

Dome has to be stable when up, not unlike working under a car on the jack - you need to be safe as well.  Good luck with it and stay safe.

[Gina]

This is definitely dangerous and I don't think we should encourage it.

[hughgilhespie]

Hi,

Thanks for the comments. I agree with Demonperformer but the dome's been up for about 3 years now and it's probably too late to complain. After it was erected the instructions were not to try and rotate it for a few days to give time for the caulking to set.

I had already thought about how to keep the acrows from moving about. If I go with an outside lift, I will either bolt the acrows to the concrete base around the obsy - it's about 12 inches wider than the plastic bit or I will make a plywood circle in 4 segments and bolt an acrow to each segment. Then when in place, I can fix the segments together with some screwed battens. Using 19 mm ply would keep everything stable. I didn't know about wall supports but I was also intending to make top plates that will bolt onto the top of each acrow and that give a secure engagement with the dome rim. 

The plan would be to raise the dome by about 6 inches, take the measurements I need then lower the dome again. I would then make up a couple of tapered brass wedges that will let the support wheels run freely. The brass wedges will be fixed by a combination of glue - my beloved CT1 - and countersunk screws. So, one lift to get the measurements then another to fix the wedges in place. 

My real nervousness is not about the whole thing blowing over - I would pay a lot of attention to the weather forecast before starting - it's more that I have never seen a dome lifted off it's walls and I don't know how easily they come apart.

Hugh

[Oddsocks]

17 hours ago, hughgilhespie said:

it's more that I have never seen a dome lifted off it's walls and I don't know how easily they come apart.

Hi Hugh.

I helped the Pulsar team lift my 2.2m dome into position, there is a time lapse video of the whole install attached below.

(I'm the weedy looking one with the checked shirt).

The dome is not heavy, it was just awkward for two people to lift and guide into place at my site because access around the dome walls was so restricted so was I asked if I wouldn't mind helping.

The dome is lifted on the walls at around the 5min 38 sec point in the video.

Dropping the dome into the walls just needed all three to keep the dome level while lowering it into position and giving a bit of a shove to flex the dome if the skirt caught on any of the lateral guide wheels.

The only thing that secures the dome against blowing off in the wind is the short skirt that drops down inside the walls. The lateral guide wheels and support wheels have no adjustments, the wheels just gently push against the dome skirt and underside of the dome lip. When gales are forecast and I am home I manually apply the optional security clamps inside the dome, if I am away A neighbour does this for me.

I can't remember how heavy it felt now, certainly not more than my carrier bag of groceries from Sainsbury's, around 10-12Kg perhaps per person.

Three people can easily lift the dome, walk it sideways and place it down, four people would make it easier to lift and lower but obviously a fourth person can not walk through the dome when the dome is taken away so a forth pair of hands is just useful for the actual lift but not really essential.

The problem you would face with jacks is that once the dome is lifted the wind can get underneath and blow the dome away very easily, it will act just like a yachts spinnaker and be half way up the English channel before you know it.

I once tried to work on a water leak on the dome of my old SkyShed POD (shown in stills in the early part of the video) and lifted the dome single handed using wedges and planks to slide the dome of the wall. Needless to say, getting it off the walls was the easy part, getting it back on proved much harder, I just could not slide it back up the planks and manoeuvre it into position, it is just impossible to maintain any sort of control over a heavy round object while pushing and pulling uphill on a pair of planks at a single point on the circumference. I had to recruit a couple of willing helpers from the pub opposite my home (for the price of a pint each) to help lift the SkyShed POD dome back in position. The SkyShed Pod dome was around 25Kg heavier than the Pulsar dome, being filled with insulation, and a few years of water ingress that had soaked into the insulation did not help.

While the Skyshed POD is quite tough, being made of polyethylene (disposable milk bottle plastic) and can take a lot of flexing and abuse, the dome of the Pulsar is made of GRP and you risk damaging and cracking the gel coat if the dome is flexed too-much or lifted and lowered crookedly.

If using jacks around the edges of the dome you would certainly run the risk of damaging the dome skirt and lip unlesss you could be certain to spread and cushion the weight over a large area and lift the dome equally all around, and to do this the jacks have to be a fair distance from the walls so that the Acrow's lifting collars can spin, this makes it all a little unstable. You would really need to lift the dome first, slide long planks between the dome and the walls and then lift using Acrow's on the ends of the planks to give you room to swing the Acrow's collars and jack up the dome.

Now that my dome has settled I too have a few points during dome rotation where the dome catches against the wall joints and gives a loud 'crack' and a lurch as the small moulding imperfections in the dome joints and wall joints brush against each other and catch.

The plan I came up with was, because the dome is so light, I would remove the scope and mount from the pier, place a pair of jacks inside the dome strapped to the pier for support and place a piece of circular cut 15mm ply, ~600mm diameter on top of the jacks, padded with foam and securely tied to the jacks and then lift the dome on the jacks centrally until it was clear of the walls and work on realigning and resealing the walls and joints could be done, then lower it back down until the skirt was engaged but not taking the weight of the dome while the joint sealant repairs had time to set. Obviously if lifting the dome internally on a central jack the shutter chain would need to be removed. As long as the skirt is dropped back down inside the walls then the wind can't get back under the dome to lift it and a mesh sheet thrown over the dome and pegged down would keep it stable while any joint sealant used had time to set. You would certainly need help guiding the dome skirt back into the walls as you lowered the jacks because the dome will flex and change it's shape once the forces acting on it change their positions. 

But then I thought this is an awful lot of faffing around, and will most likely just enlist the help of neighbours, relatives, or hard up pub goers who can spare ten minutes for the price of a pint and just lift the dome off as it was installed, work on the dome while on the ground, cover the dome walls with a tarp while any re-sealing dries and then lift the whole lot back a few days later.

Let us know how you get on, I hope to learn a bit from your experience before tackling mine later in the summer. 

HTH

William.

 

 

[hughgilhespie]

Hi William,

Excellent reply! And excellent video!

Maybe I am over-thinking this. If the dome is easily liftable by 3 people then perhaps that is the way to do it. The problem then is that I would have to build some sort of structure to put the dome on while it's off the obsy because I need access to the underside of the flat ring on the base of the dome. I think trying to put it down 'upside down' would almost certainly over stress it and possibly cause damage.

Or - going back to Plan A - I add a lightweight mesh into the equation as you suggest and have a couple of volunteers keeping the mesh taut while the dome if lifted. Then when it has sufficient clearance - say about 150 mm - the mesh can be tied off onto the acrow bases. I will still have good access from inside the obsy for measurements and for fettling any high spots and attaching the brass ramps where needed. 

I have been looking at how to attach the acrow props to the concrete base around the obsy and concrete screws look like a fairly easy answer, they are cheap, removable and you only need to drill 6 mm holes. I do have an SDS drill and that shouldn't be too difficult.

The only thing I'm not sure about is the design for the plate that will fix on to the top of the acrow prop and will give a good engagement with the lip of the dome over a fair length - say about 150 mm. Something with a curved groove would be ideal, particularly if I stuff some foam rubber in the bottom of the groove.

More thinking needed!

Thanks again, Hugh

[Oddsocks]

4 hours ago, hughgilhespie said:

The problem then is that I would have to build some sort of structure to put the dome on while it's off the obsy because I need access to the underside of the flat ring on the base of the dome.

I think the simplest way to do this would be to knock up (or hire) four A-frame trestles and a couple of planks/boards from scrap timber, chopped branches etc, anything that is lying around or inexpensive. With a couple of willing helpers, lift the dome off the walls on a calm day and walk it across to the trestles then lay the dome on a couple of boards or planks placed across the trestles, use a few scrap wood blocks placed on top of the planks to support the dome on the flat part of the dome lip (where the support wheels normally run) to keep the skirt away from the boards, then throw mesh/netting or a tarp over the dome and tie it down with guy ropes and tent pegs.

You can crawl under the dome just as easily as if you were entering the observatory normally as the dome will be at the same height as it usually is and you can position/rotate the dome on the trestles/boards so that the dome quadrant joints are all freely accessible to work on. Once the work under the dome is finished for the day and if the repairs need time to set/cure and there is even the remotest chance of windy weather then the dome can be securely pegged down using the mesh tarp and guy ropes.

Work on the dome walls can be covered at the end of the day with a waterproof tarp supported wigwam style from the pier and tied down with guy ropes and tent pegs.

Doing the job this way would keep the dome unstressed and level.

If you have nothing to hand to make your own trestles you could hire the adjustable height steel A-frame trestles and a couple of scaffold planks from most tool hire shops you only need to make up some tent pegs out of scrap timber and supply some guy-rope, mesh/netting and waterproof tarp.

Since a sketch paints more than words (if only I could ) see attached:

[hughgilhespie]

Gosh! A man of so many talents!

 

[Mick J]

What great reply's, well done Oddsocks

[Rusted]

I would avoid multiple acrow props due to their weight and instability. They seem like complete overkill to me.

Imagine a prop falling sideways and seriously damaging the dome walls. T_I_M_B_E_R!

I've lifted cars, engines, lathes, tanks and boulders [the latter the size of a mini] working entirely alone, using just levers and packing.

Have lots of timber or plywood packing pieces to insert and protect vulnerable edges.

Profile the packing by adding battens if they are to rest on narrow edges. Don't damage upstands!

 

If it was me, I'd use a pair of folding builder's stepladders, opened out and tied together at the top.

[Between £30 and £50 each or hire]

Then lift the ladders up over the dome as a tall and stable A-frame. [Manageable by one 70 year old I could name.]

Then use a pair of blocks and tackle to lift the dome by its center top via load spreading timbers across the inside of the observing slit.

Or use multiple ropes with suitable [flat] hooks under the dome edges.

But that would require some investment in equipment you might never use again.

Though the ladders are handy for decorating, or just cleaning the dome. Or sell them on?

Note the sturdy crossbars at top and bottom. These are the secret to their extraordinary stability.

The images show me using a chain hoist suspended from a pair of stepladders to lift my 300lb mounting.

I use ratchet strap guy-lines when lifting up on my 10' high obs. platform for extra safety.

A chain hoist might damage the dome cosmetically.

So pulleys are safer for this and you don't need the greater lifting capacity.

You MUST pull the rope IN LINE with the ladders. NOT facing the A of the A-frame!

[hughgilhespie]

Hi Rusted,

Lots of good advice but I already have the Acrow props so I am still intending to use them.

After all the comments about the wind catching the dome and sending it flying I have just ordered some cargo netting and tent pegs/guy ropes to keep the dome firmly attached to mother earth. See wonderful drawing from Oddsocks for full details!

My latest plan has three Acrow props inside the observatory. The bases of the props will be attached to the apexes of a timber triangle that spans the width of the observatory and I will fit clamps to the tops of the static parts of the props and use more timber struts to fix these to the timber triangle on the obsy floor. This 'should' keep the props secure. I will test everything as well as I can before starting to lift the lid!

I will make wooden 'plates' to fit on the tops of the props with 200 mm long channels that will engage with the vertical rim of the dome. Foam rubber strip in the channels to even out the lifting load. The advantage of having the props inside the obsy are that the props can be placed exactly under the lifting point and still have room to turn the handles to screw them up.

So - me inside turning the handles, half a turn each at a time. Her indoors is now her outside, adjusting the guy ropes as the lid lifts. Perfect! What could possibly go wrong!

Regards, Hugh

 

[tteedd]

Hi

All this seems highly complicated to me.

I bought my old Pulsar 2.7 m Ob's online. It was in Yorkshire and we had to move it to Hertfordshire. My daughter, son in law and myself easily lifted the dome off when we were diss-assembling it. I got two neighbours to help lift it back on when I had re-assembled it.

I went through this procedure twice as I decided to drop the height by taking a ring of sections out. Later, when I wished to take the dome off again, I got three golfing friends to help.

It sat on the lawn for some time and showed no sign of lifting when it was windy.

I'm contemplating access to the rollers and surface but intend just to lift it up onto wooden blocks and expect to accomplish this on my own.

Last time I had anything to do with Acrows they were nasty heavy things, necessary for supporting the roof while part of the wall was taken away, but not the sort of thing I want anywhere near my glass fibre pride and joy.

If you were near me I would offer to pop round and lend a hand. How about asking at your astro' society?

Ted

[hughgilhespie]

Hi Ted,

I agree that this is a complicated way of taking the dome off. Unfortunately I can't do any of the lifting myself and while I could round up 2 extra people to help I don't think I could ask them to come back the 3 or 4 times that would be needed. So, I have - hopefully - come up with a method that Janet and I can manage on our own. I will finish installing the Acrow props today. I will do the first lift to have a look at the segment joins and see what needs doing as soon as the weather forecast is good for a rain free day.

Regards, Hugh

[Mick J]

Sounds like a plan Hugh, I can second the comments regarding Acrows, they can be heavy old things with a mind of their own (hang on, sounds like me!) but they are designed for lifting (no that's not me).  A bit of grease on the threads may make your life easier - builders will hate you, and do double make sure they are secure, base, middle & top, would you want to screw the base to the floor? I am thinking twisting when winding.

What could possibly go wrong 

[Gina]

As an engineer, I can think of lots of things.  I have an image in my mind of a twisted mess of fibreglass and iron ?  Please take care.

[hughgilhespie]

OK- The lid has lifted!!

Well - only by about 30 mm as an experiment then back down again but I am pleased with the way it went. Minor problems with the dome flange binding against one of the 6  horizontal rubber wheel that centre the dome to the base but it did eventually move. Next time I will put a bit of Vaseline on the wheel to help it slide off more easily.

For the 'proper' lift I will put netting over the dome and peg it down before starting.  Gina - thanks for your concern and I do promise to be careful. I have been working on getting this observatory ready for over 3 years now and it would be a tad irritating if I trashed it at this stage.

I did a quick check of the segment joints whilst the dome was raised. I had thought the problems were due to a height difference between segments but actually the problem is that two of the segment joins have a ~3mm gap between them with and the filler doesn't fill right to the end of the join, leaving a sort of top-hat profile hole. These should be easy enough to fill with epoxy putty. I will wire brush first to clean and key the fibreglass, fill with Milliput epoxy putty, let it cure for 3-4 hours then sand down smooth. The only snag with this plan is that we now have a Met Office yellow warning for rain for Saturday and Sunday!! I think I need two consecutive dry days to do everything so everything is on hold until ???

Regards, Hugh  

[ACross]

Hi Hugh,

It sounds like you and I have the same problem. My dome was purchased second hand and I thought the rotating "bumps" that I was getting were a result of my over-excitement at fitting stage. After partly lifting the dome I realised that the panel gap on the dome underside is the culprit, I would be interested to hear how your fix works.  

As to lifting the dome, my obs is fitted to a 600mm high table, which didnt help but my wife (nicknames incl Debbie McGee and Pit-Pony) and I were able to lift the complete dome into place by hand. That said, I will be calling Brother-in-law to help take it off again soon.  My plan (at present) is to lift the dome a side at at time and insert two parallel timber beams on foam cusions that sit on the walls. The dome will then rest in a raised position on the timbers. Four clamps will be used to hold the whole assembly still while I work on the rollers and running surfaces.  As to wind lifting, Pulsar carried out extensive wind tunnel tests and had a very boring time watching nothing happen; I dont expect this to change much even with the dome inner flange lifted above the rim of the walls - the clamps will be there for lateral stability, more than wind lifting.  

What can possibly go wrong?

Cheers, Anthony

[hughgilhespie]

Hi Anthony,

Sounds like a good plan but hey - what do I know!

I will take some pics of my repair work and report on how successful it is. I think it will probably be OK at first but I wonder how long it will last. However, if it lasts for a reasonable time, say 12months, then it’s not too arduous to repeat.

Regards, Hugh

[hughgilhespie]

Well, to all those who said my method was too complicated all I can say is........

.....you were right!

In the end, four wooden blocks, one strong neighbour, lift an edge, pop in a block, repeat 3 times. Took absolutely ages - well at least 60 seconds. The blocks were roughly cubes about 5 inches a side. Plenty of room to get at the offending gaps and height differences. Clean with a wire brush, mix up some Milliput epoxy putty, force it into the gaps with a small screwdriver, final shaping with a high-tech wet finger. Then list, remove block, repeat 3 more times. Bit of jiggling to get the dome flange to fall inside the horizontal guide wheels and job finished. Well - not actually tested yet - the putty will be left for 24 hours to fully harden before trying the dome rotation. Worst case it may need sanding down a bit.

Regards, Hugh

[ACross]

Well done Hugh, sounds like a satisfying days work.

[Gina]

Great - well done ?