DaveS's Obsy Build Thread

[DaveS]

I'll have a think about that, but it may be that the studs are integral to the design. Also getting 19.5 kg of ODK12 plus 45 kg mount plus 13 kg cwt bar plus 15 kg cwts off the pier isn't going to be a trivial job. I had to rig a gantry to get the ODK on the mount, and had help to get the mount on the pier.

The aperture in the pier is for accessing the nuts holding the studs to the top of the pier, there is another, larger, one at the base for accessing the bolts holding the pier to the concrete slab. The mount bolts down on to the top ring.

[Rusted]

When I need to lift a lot of weight in a tight space [10' dome] I use two folding, builder's stepladders.
The ones with the wide foot braces. The ladders are straightened out and lashed firmly together at the top.
Then I use a chain hoist supported from the top crossbars with an 'approved' 1T strop.
I may have mentioned this arrangement before but somebody else might find it useful.
I lifted my massive mounting up to my second floor observatory and then onto the pier this way.
The total cost is quite modest and the folded ladders can be stored compactly for future use in decorating, hedge clipping, etc..
Or they can be hired from better DIY stores and builder's merchants.

Edited August 21, 2020 by Rusted

[DaveS]

Thanks for that tip @Rusted. I do remember now seeing that arrangement in your dome thread ages ago. I'll give it a go if I need to demount the OTA or mount at any time.

But for the time being the OTA / Mount / Pier are staying as they are.

[DaveS]

While waiting for the weather to settle down I've been making a door for the obsy. Not strictly necessary just yet, but might as well, while I'm waiting.

[Gina]

WOW!!  That sure is a lightweight roof framework!  I have a pair of 100x25mm each side with the wheels in between.  The main roof framework is mostly 4x2 with some 6x2 (dropped back into Imperial!).  Studding to support the 6mm plywood is 2x2.  EPDM on top of the plywood.  OK so I'm into over-engineering!  🤣.  But it was that same roof that was lifted off by wind and dumped onto the fence upside down several years back.  It too 4 blokes to lift it back on!!  I have some very helpful neighbours.

[Gina]

Incidentally, that roof with 4 x 120mm wheels and steel track from FH Brundell, can be pushed with one finger.

[Chris]

I've just had a flick through your obsy build Dave and I think it's really classy! I Really like the raised position on those ornate bricks too, and I'm straight up jealous of your mount  

[TerryMcK]

Looking fab so far Dave.

On the metric versus imperial front. I think I was in the crossover years of metricfication (is that a word?) and for a couple of years was taught both inches and centimetres at the same time. That was about 1969 to 1971 (I think as my memory is not good nowadays). So 4x2 or 2x4 for our American friends works just as well as 48 x 96 (50 x 100 allowing for machining) for me 😆

Mind you 1 gallon is definitely 8 pints not the silly 7 pints as in the USA.

[JamesF]

28 minutes ago, TerryMcK said:

Mind you 1 gallon is definitely 8 pints not the silly 7 pints as in the USA.

An American would probably tell you that their gallons are eight pints, too

But their pints are only sixteen fluid ounces whereas ours are twenty fluid ounces.  The story doesn't end there though, because a US fluid ounce is slightly bigger than a UK fluid ounce.

This sort of thing probably drove some people mad.

James

[DaveS]

1 hour ago, Gina said:

WOW!!  That sure is a lightweight roof framework!  I have a pair of 100x25mm each side with the wheels in between.  The main roof framework is mostly 4x2 with some 6x2 (dropped back into Imperial!).  Studding to support the 6mm plywood is 2x2.  EPDM on top of the plywood.  OK so I'm into over-engineering!  🤣.  But it was that same roof that was lifted off by wind and dumped onto the fence upside down several years back.  It too 4 blokes to lift it back on!!  I have some very helpful neighbours.

I definitely have made the roof too light, the question now is what to do about it.

F H Brundle have some 25mm square by 3mm thick steel tube, and offer a cutting service from the 7.5-7.6 metre lengths, so I could get 5 x 2.27m sections from 2 lengths, with a bit spare. This would be a straightforward reinforcement job and could be slotted straight in without having to touch the rest of the roof structure.

Alternatively, strip the roof right back and use heavier gauge timber for support. This would put me back by a couple of weeks at least allowing for weather interruptions and the vagaries of Wickes's delivery system. It could also push me beyond the "Permitted Development" limits for height.

Will have to give it some thought, but I may give Brundle a bell tomorrow.

[DaveS]

53 minutes ago, Lockie said:

I've just had a flick through your obsy build Dave and I think it's really classy! I Really like the raised position on those ornate bricks too, and I'm straight up jealous of your mount  

Ha, thanks Chris.

Those "ornate bricks" are slabs / chunks of Portland Stone, in keeping with the local buildings, similar to the facing of the smaller platform that has my 130mm 'frac on it., and help to raise the level of the mount enough to get a slightly better view to the south.

There's over 8 tonnes of "stuff" in that platform.

[DaveS]

@Gina, I remember the saga of the disappearing roof, and the struggle to get it back on. Unfortunately I don't have any strong blokes I can call on, so have installed four 600 kg toggles to hold the roof down, plus I'm looking into passive measures to keep the roof secure in ordinary wind. Given the height of the walls getting the roof back on would be a non-trivial job.

[fifeskies]

I engineered some catch plates that engage as the roof closes.

Normally I just have a single locking pin elsewhere that locks the roll off track and hold it closed , but if high winds are expected I lock down the catch plates with wingnuts for additional security.

There are 4 corners that engage as the roof reaches the closed position , so even if unexpected winds appear when I am not around the pins hold the roof down since the roll off track lock prevents the pins from disengaging.

 

[DaveS]

That looks similar to the arrangement that Sara (Swag72)'s builders used when she had her obsy reconfigured. Unfortunately I am, at present, without a workshop as such and without engineering tools. I can probably work something out with wood. As things stand the 3 metre long rack is attached to a 3 metre long wood bearer that carries one side of the roof and runs through an opening in the rear wall, and the opposite bearer fits into a pocket in the same wall. The rack motor will stop the roof from rolling off of its own accord.

[fifeskies]

I purchased the aluminium blocks pre-cut. (from a friendly auction site).

Drilled the aluminium with an electric hand drill for the screw holes.

Screwed plate on , marked the bolt position , with black marker ink on the end of the bolt through the wood bearer just let it touch the plate.  (I did use a sander to give the bolts a cone shaped tip to help them align)

Took plate back off to drill the through hole. (pilot the bigger hole with a small drill to keep it true) , made it slightly bigger than the bolt pins.

(if I remember right its 10mm bolts and a 12mm hole, drill the hole up in stages rather than going too big too soon , that helps it stay aligned.)

Just a simple job as its fairly easy with a decent drill bit in the soft aluminium , its also rust free.

 

[Davey-T]

You can get a metal cutting blade for your chop saw Dave, I use mine all the time.

Dave

Be sure to clamp the ally down.

Edited August 24, 2020 by Davey-T

[DaveS]

Thanks Dave.

I will have to check, but I think my saw is spec'd for wood only as it's single speed. I think metal cutting saws need to be variable speed?

[Davey-T]

47 minutes ago, DaveS said:

Thanks Dave.

I will have to check, but I think my saw is spec'd for wood only as it's single speed. I think metal cutting saws need to be variable speed?

The one I use for aluminium is only a cheapo from B&Q sale, single speed.

Dave

[DaveS]

I've been up that long river place looking at blades that might work with my saw (3800 rpm, 305mm saw dia) and found This. Their search is pretty dismal, turning up loads of irrelevant stuff, even with key words.

[Davey-T]

Last one, 305mm is a bit of an odd size

Dave

https://www.ebay.co.uk/itm/Bosch-2608640452-305mm-x-30mm-x-80-Teeth-Multi-Material-Circular-Saw-Blade/274264940302?epid=2254464043&hash=item3fdb76df0e:g:V14AAOSwRfNeRRx9

[Rusted]

I have regularly used my 12" DeWalt sliding mitre saw for aluminium up to 20mm thick sheet.
I bought a fine tooth, inexpensive, blade listed specifically for aluminium.

Odour free lamp oil [UK paraffin] is a good cutting fluid for ally.
I just run a wet brush along the cut line.
Repeat the wetting sometimes to stop build up on the teeth.
Don't push too hard. Just let the blade find its own pace without loss of revs.

As Dave says, you really must clamp the work down for safety.
I use Bessey F-clamps with the original plastic 'feet' to avoid marking.
The long jaws allow safe clamping under the mitre table casting.
It makes a hell of a mess with the swarf flying everywhere!

The DeWalt mobile bench saw has a clear warning to use it only for wood. NOT METAL.
Which is a shame because it has the potential for much longer cuts.
However, if the blade should dig in it would send the work flying backwards and probably slice the user in half!
I never stand behind the work on the mitre saw for exactly the same reason.

[Davey-T]

1 hour ago, Rusted said:

t makes a hell of a mess with the swarf flying everywhere!

All gets stuck in your socks 😂

Dave

[RAR_MI_USA]

On 23/08/2020 at 17:28, DaveS said:

@Gina, I remember the saga of the disappearing roof, and the struggle to get it back on. Unfortunately I don't have any strong blokes I can call on, so have installed four 600 kg toggles to hold the roof down, plus I'm looking into passive measures to keep the roof secure in ordinary wind. Given the height of the walls getting the roof back on would be a non-trivial job.

 

Edited August 27, 2020 by RAR_MI_USA
wrong person

[RAR_MI_USA]

On 24/08/2020 at 09:02, DaveS said:

I've been up that long river place looking at blades that might work with my saw (3800 rpm, 305mm saw dia) and found This. Their search is pretty dismal, turning up loads of irrelevant stuff, even with key words.

Nice going Dave and looking good. Hey regarding your hold downs, those top blocks of wood you have the hold down screwed onto.... well, they may not hold up under any stress from wind lifting on the roof. One should never drive screws "inline or with" the grain, but rather, perpendicular or against. I fear you may find those wood blocks will split easily. That should be an easy fix for you.
As to your roof frame, from what I gather, it is much too light to hold up very long. And additionally, not sure if you experience snowfall where you are, but here, that roof would fold under it's weight. I suggest full 2x4 framing for the roof.
And I hope you don't mind my suggestions, because that is all they are, and I want to see you get years of enjoyment from your observatory after all that hard work you have put in!
Ray

[DaveS]

Not at all, happy for any suggestions.

Two of the hold-down blocks have been replaced, just a matter of finding time in between doing the other obsy work to do the other two. They have been cut ready, now to fit them.

We don't get much snow here, last year it was just a dusting, and no snowfall this winter.

The roof is, as you say, much too light. I should have had a look back at my original plans which *did* call for heavier timbers when I was putting the orders in to Wickes. I was also trying to keep the height below 2.5 metres for the "Permitted Development" rules.

I think I can use 45 x 70mm beams on end. Will investigate the geometry.