Gina's Observatory

[malc-c]

Gina, That's a shame. I would go with the enlarged roll off roof and lower your fixed walls to allow your 15º FOV. You can easily strengthen the run-off roof parts with plywood gusset pieces. They will provide stiffness without increasing the weight significantly. It would be financially cheaper and easier to construct. Francis

Have to disagree. Due to the fact that the roof rolls over the fixed roof of the warm room, any bracing between wall and roof will stop the roof rolling as it will strike the other roof.

Personally I would modify the pier head to gain back the extra few inches.

[Ransu]

Hi Gina, sorry to hear your dilemma.

I thinks that adjusting the mount may be the easiest method.

This is the way I have done it and I have a propensity to over engineer things. I used 4 x 16mm high tensile steel tow hitch bolts which has made my setup very rigid indeed. I have welded one end into the top plate adding that bit of extra rigidity and keeping the top plate clear.

I think the bigger nuts my foul your pier if you go this way, and you may have to do it in reverse.

This has given me about 4" space between plates which I think is about what you've lost.

I think this is good way to lift your eq head. (Just assemble threaded bars and nuts upside down when you look the Freff's picture.)

You are now using M14 bolts and nuts, you can easily change them M16, free hole for M16 thread is 14.5mm, so you propably can jus make M16 threads on bottom plate, depending free size of holes in plate. Then twist threated bars in plate and lock them from upper side with nuts. On upper plate you need to make free holes bigger, maybe 18-19mm is good size, allowing easy adjustment. I have use M20 bars in mine.

M14 is not very commonly used size here, standards recommend M12, M16 and M20. Actually i cant find easily M14 here, M16 nuts, bolts washers you can find from any stores that sells nuts and bolts.

[Gina]

Thanks everyone for your replies Weigh of opinion seems to be in favour of raising the mount.

Hi Gina, sorry to hear your dilemma.

I thinks that adjusting the mount may be the easiest method.

This is the way I have done it and I have a propensity to over engineer things. I used 4 x 16mm high tensile steel tow hitch bolts which has made my setup very rigid indeed. I have welded one end into the top plate adding that bit of extra rigidity and keeping the top plate clear.

I think the bigger nuts my foul your pier if you go this way, and you may have to do it in reverse.

This has given me about 4" space between plates which I think is about what you've lost.

Welding isn't an option unfortunately, though I agree this would be stiffer than nuts. And your 16mm HTS is probably a lot stiffer than 14mm threaded mild steel.

[Gina]

Gina, That's a shame. I would go with the enlarged roll off roof and lower your fixed walls to allow your 15º FOV. You can easily strengthen the run-off roof parts with plywood gusset pieces. They will provide stiffness without increasing the weight significantly. It would be financially cheaper and easier to construct. Francis

The problem with gussets is the clearance past the warm room roof. Darren overcomes this in his design with strong steel L pieces, though he tells me he hasn't actually found a source of these. A steel fabricator could probably do it but I don't know one and would prefer to try other methods first.

[yesyes]

I think you should either raise the pier top or change your floor design. Could you not use smaller cross section joists? Or maybe you could lay them flat and gain a few inches?

[Gina]

Have to disagree. Due to the fact that the roof rolls over the fixed roof of the warm room, any bracing between wall and roof will stop the roof rolling as it will strike the other roof.

Yes, that's the trouble. I'm planning to use 2x5 (or maybe 2x4) uprights at the ends with two coach bolts into the 3x2 roof frame. Maybe glue as well.

Personally I would modify the pier head to gain back the extra few inches.

Yes, you're well in the majority there. It would also improve the westerly view - I've already got the roof as low as I can while preserving a 6ft high entrance door in the end of the warm room. An entrance door in the end of the obsy part isn't an option due to space. The north side is limited by the roll off rail which wants to be low enough to allow a good view northwards. Even if I did have the door in the side I could only reduce the roof a little due to head height within the warm room. Although I'm quite tall I'm not quite 6ft tall but I don't think I want the entrance any lower than the 6ft.

Another option of having the roof run-off southwards I rejected due to the difficulty of arranging guttering.

[Gina]

I think this is good way to lift your eq head. (Just assemble threaded bars and nuts upside down when you look the Freff's picture.)

You are now using M14 bolts and nuts, you can easily change them M16, free hole for M16 thread is 14.5mm, so you propably can jus make M16 threads on bottom plate, depending free size of holes in plate. Then twist threated bars in plate and lock them from upper side with nuts. On upper plate you need to make free holes bigger, maybe 18-19mm is good size, allowing easy adjustment. I have use M20 bars in mine.

M14 is not very commonly used size here, standards recommend M12, M16 and M20. Actually i cant find easily M14 here, M16 nuts, bolts washers you can find from any stores that sells nuts and bolts.

Yes, I guess I could tap the bottom plate to M16 if I bought a set of taps. Holes are 15mm to give clearance including the paint. I would also need to buy a drill to open up the top plate holes. I know I can get M14 threaded rod but not sure of bigger - would have to check.

[Freff]

Thanks everyone for your replies Weigh of opinion seems to be in favour of raising the mount.

Welding isn't an option unfortunately, though I agree this would be stiffer than nuts. And your 16mm HTS is probably a lot stiffer than 14mm threaded mild steel.

Gina I'd be quite happy to do any of the welding, drilling etc for you. Unfortunately, the cost of sending the bits would probably be more than getting it done locally.

[Gina]

I think you should either raise the pier top or change your floor design. Could you not use smaller cross section joists? Or maybe you could lay them flat and gain a few inches?

Raising the pier top seems favourite. I could gain an inch by using 4x2 joists which would probably be just sufficient. Putting joists on their side isnt an option - the strength is in their height, extra width doesn't help that much. I discovered this when I made another suspended floor using 7x3 joists on their side because there wasn't the floor space to have then upright. This floor is decidedly springy in spite of the joists being spaced at 18" and supported at 6ft spacing with concrete blocks.

[fwm891]

Gina - Tracy Tools (in Devon) should be able to supply the tapping drill and taps to suit the metric threads.

(I stand corrected about the gussets should have looked closer at the preceding posts...)

Another thought:

If you are running your roof over the warm room then can you not put either lift off or hinged sections to the top of the wall(s) of the obsy part - they would only need lifting folding down in the area you are viewing when skies allow viewing at low altitude?

Francis

[yesyes]

Raising the pier top seems favourite. I could gain an inch by using 4x2 joists which would probably be just sufficient. Putting joists on their side isnt an option - the strength is in their height, extra width doesn't help that much. I discovered this when I made another suspended floor using 7x3 joists on their side because there wasn't the floor space to have then upright. This floor is decidedly springy in spite of the joists being spaced at 18" and supported at 6ft spacing with concrete blocks.

OK, that makes sense.

Couldn't you suspend these joists between the 3 bigger ones similar to what Malcom has done, see picture in post #90 in his thread:

http://stargazerslounge.com/diy-observatories/140015-observatory-build-underway-4.html

I'm no expert... Just throwing some ideas around... ;-)

[Digz]

Definately cannot lay joist 'flat' they will sag in the middle and be very springy. Joists rely on a good height to width ratio to be stable, just remember that joist will need noggins at the centre of the span to stop any torisional effects taking place and the joists from bowing.

You could definately 'hang' your joists between your main supports, providing there is enough clearance below them i.e. they are not any deeper than the main supports.

[Gina]

Gina - Tracy Tools (in Devon) should be able to supply the tapping drill and taps to suit the metric threads.

Thanks Also, Axminster Tools sell taps etc.

Another thought:

If you are running your roof over the warm room then can you not put either lift off or hinged sections to the top of the wall(s) of the obsy part - they would only need lifting folding down in the area you are viewing when skies allow viewing at low altitude?

Francis

Yes, I had thought of that. The obsy end wall has a fold-down section. A fold-down section on a side wall would be difficult to support in the up position - one end would be free to flop about.

[fwm891]

Like yesyes's idea about dropping the joists, most building merchants sell beam hangers/cradles for just that purpose. So long as your flooring clears your pier base it sounds good...

Engineering Supplies for model engineers | lathe and workshop equipment, Myford Boxford or Taps and Dies | Reamers | Tracy Tools Ltd Uk

Axminster are OK I use them for most of my woodworking kit (making acoustic and electric guitars + DIY) but find they're expensive and have a narrower range of engineering bits - unless you want a lathe or milling machine...

Francis

[Astrokev]

Hi Gina,

Just throwing a potentially unpopular thought into the mix -

Have you considered leaving the design as it is and accept the lost inches? A few degrees off the Western horizon shouldn't be much of a problem. How often will you be viewing that close to the horizon anyway? Lost southerly horizon would be more of a worry, but I think you have a drop down panel to the south?

( ...ducks in readiness for verbal attack....)

[Gina]

Couldn't you suspend these joists between the 3 bigger ones similar to what Malcom has done

Thank you for that great suggestion It has provoked much thought This seemed the answer at first but then when I studied my plans some snags appeared.

If I had the tops of the beams and joists level to provide a level run right through for the floor boards, the floor boards would be only a few mm above the pier base block in one place. That would not allow for flexing. But this can be cured by having the joists about an inch above the beams and put a 3x1 section filler on top of the beams.

There is then another snag. The beams were positioned for the joists sitting on top and overlapping the outer two beams by a couple of inches. There would be no support for the floor boards past the beams. Measurement shows the distance from the east side of beam 1 to the west side of beam 3 as 13'6" whereas I had planned the whole building as 14' overall.

Three possible ways round this occur to me.

1. Make the shed 6" shorter. The easy way out

2. Pour another pair of foundation concrete blocks for beam 3.

3. Reseat beams 1 & 3 3" over on the present blocks. Since the blocks slope off to the sides, this would mean just a small amount of concrete on each of the 4 blocks. It probably wouldn't matter if the load were offset from the centre of the blocks.

The overall result would be that the floor would be 4" lower giving the pier height desired. It would be about at ground level on the north side and a few inches above on the south side. I could slope the ground down to the north to make the floor above ground level again and provide good under floor ventilation.

I shall study my plans again and see if taking 6" off the length has other ramifications than giving a smaller warm room. It would save quite a lot of work if the beams could stay where they are.

I think lowering the floor is a great idea and would solve my problem. In fact the mount would be an inch higher than originally planned and that I've shown to be a benefit. There is plenty of height above to allow a much bigger scope even to park it vertically - and I doubt this would be necessary.

[Gina]

Like yesyes's idea about dropping the joists, most building merchants sell beam hangers/cradles for just that purpose. So long as your flooring clears your pier base it sounds good...

So do I but see my post above.

Engineering Supplies for model engineers | lathe and workshop equipment, Myford Boxford or Taps and Dies | Reamers | Tracy Tools Ltd Uk

Axminster are OK I use them for most of my woodworking kit (making acoustic and electric guitars + DIY) but find they're expensive and have a narrower range of engineering bits - unless you want a lathe or milling machine...

Francis

Thanks for the links I'll make note of them.

[Gina]

Hi Gina,

Just throwing a potentially unpopular thought into the mix -

Have you considered leaving the design as it is and accept the lost inches? A few degrees off the Western horizon shouldn't be much of a problem. How often will you be viewing that close to the horizon anyway? Lost southerly horizon would be more of a worry, but I think you have a drop down panel to the south?

( ...ducks in readiness for verbal attack....)

This thought occurred to me but, as has been said in the past, "If the build is in any way inferior to what was planned you'll find it aggravating. Better to spend a bit more time or cost to make it right (or as right as possible) straight off."

Lowering the whole thing from floor up except for the pier gives a western view of 20 degrees above the horizon instead of 30. I think that's worthwhile. Having higher walls and lower roll off section makes the roll off more rigid whilst still allowing the full viewing angles.

[martin_h]

Could you not have the whole block protruding through the floor? By dropping the whole frame?

Mine is.....

All from 6" x 4" joists supporting 18mm OSB

[fwm891]

Gina, What if you lowered the floor by lowering the joists, you wouldn't have to sacrifice any building length as you could put a piece of 3x3 on the outside of the support beam (at each end of the build) and run your floor over that...

[Gina]

Lost southerly horizon would be more of a worry, but I think you have a drop down panel to the south?

No, the drop down panel is in the east end wall though it's actually a bit south of east.

[Gina]

Could you not have the whole block protruding through the floor?

Certainly could! I did think of that though it's a pretty big lump (and it's not square). It wouldn't stick through the floor - it is lower but not by enough clearance (a Gina booboo). I might have a cut out in the floor for the block - it could be covered by a piece of plywood and if a bit bigger could allow access for wiring. Good thought

[Gina]

Gina, What if you lowered the floor by lowering the joists, you wouldn't have to sacrifice any building length as you could put a piece of 3x3 on the outside of the support beam (at each end of the build) and run your floor over that...

Now why didn't I think of that!? Thank you - great suggestion

[yesyes]

I had thought of that too but I thought the problem with that was that you would have to space the joists too far apart due to the size of the concrete block.

If you just lower the joists you could get the missing 6" back by attaching/bolting 3" wide lengths of timber to the outsides of the outer beams.

[yesyes]

Ah, I see it had already been suggested...

(hard to keep up with all the posts here...)