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  1. #1
    Join Date
    Nov 2020
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    Daisy Hill
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    Default Astronomical observatory roof roller steel u channel

    A few years ago I recovered an astronomical observatory. It consisted of a 3 meter square wooden structure on on which a 3 three meter rotating steel dome stood. I have recently started rebuilding it and have laid the concrete slab, telescope pier foundation, and walls to ceiling height but to cut a long story short have decided to forego reassembling the dome and instead opt for a simpler and lighter roll off roof.
    For the rolling mechanism I have some industrial stainless steel pallet rollers which I plan to use upside down rolling in a U shaped steel channel. The U channel steel would need to be 50 mm wide and 40 mm high and 2mm thick to accommodate the rollers.
    I have been unable to find anyone who can supply U section of this dimension but I can get 50 x 50 x 2 square section. I would however have to cut off one side of the square tube to give me a height of 40mm.
    My thoughts are to do this with an angle grinder with a metal cutting disc but because I would need to make two lengthwise cuts into 12 meters of square tube (24 meters of cut) it seems a daunting task and am wondering whether there is an easier option.
    Open for any suggestions.
    Geoff

  2. #2
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    5,945

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    Hi Geoff and WELCOME to a TOP FORUM.
    If you have a decent sized compressor available, you could hire a Plasma Cutter. Set it up with a guide so that you're able to cut a constant 40mm wide section. That's about the easiest way i can think off. If you get your pressure and speed right, there should be very little cleanup required.
    HTH
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
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    Aug 2010
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    Toorloo Arm, VIC
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    Default

    I wouldn't be too keen to take that approach myself.... RHS can take some very interesting shapes sometimes when you cut one side of it out, you might end up with a badly warped track, which I assume is undesirable. Depends on the luck of the draw as to how much stress is in the bits of RHS you buy.

    All depends on the tools you have of course. I'd sooner weld my own profiles out of 40mm and 50mm (or wider, depending on attachment design) flat bar, but that does bring some challenges in avoiding warpage too, and of course requires a welder. Not too sure about getting flat bar in less than 3mm thickness either, if that is a fixed constraint.

    Ideal solution for the profile exactly as specified would be to find a decent size fabrication shop with a guillotine and pressbrake to make up that profile out of 2mm plate - preferably with an owner very fond of beer.

    Without knowing the space and design constraints you have, bit hard to offer much else...

  4. #4
    Join Date
    Dec 2005
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    South Australia
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    As said above cutting would be the stuff of nightmares, far simpler to fabricate from flat bar.

  5. #5
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Hi Geoff, Guys,

    I would have thought at 2 mm thick it would be screwed to a timber support. Though there are UPV plastic sections that might do the job.

    One thing that would bother me is the wind ripping it off. But without knowing the design details difficult to advise.
    Best Regards:
    Baron J.

  6. #6
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    No, that’s the easiest option. You can cut it with a grinder reasonably easily, and consistently if you make a guide or rest to support the grinder. Not overly difficult at all, just needs to be a block of timber or something that holds the grinder guard at the correct height and not allow it to rock or tilt. Use a 1.6mm disc and remember to cut the face with the seam off.

  7. #7
    Join Date
    Oct 2011
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    Norwood-ish, Adelaide
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    How about some commercial C channel, with either bigger rollers or two small rollers, one for each flange? I agree with all those comments about cutting RHS - it will not work well.

    These guys have hot rolled 100x50
    https://www.orrconsteel.com.au/produ...-steel/channel

    Or there is cold rolled
    http://www.bluescopesteel.com.au/fil...rtiesjan10.pdf

    Michael

  8. #8
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    Mar 2011
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    Southern Flinders Ranges
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    Default

    Interesting, I’ve sectioned RHS and SHS on quite a few occasions and never found it difficult or challenging. Everything presents differently to the individual I guess.

  9. #9
    Join Date
    Dec 2005
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    South Australia
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    Yeh! for short lengths maybe, we are are talking "12 mtr cut"

  10. #10
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    I think it was 24m, I’m imagining being a 3m structure, the lengths are 6m each to allow the roof to slide back so the top can be fully opened.

    Random suggestion.. what about a roller door for the roof?

  11. #11
    Join Date
    May 2013
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    Rockhampton, QLD
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    454

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    Welcome to the forum Geoff.

    Ross

  12. #12
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    Dec 2005
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    South Australia
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    Roller door would need fixed supports this would create obstructions at some point, this is why the preferred method is a dome can be moved to to any position giving unrestricted view, the are some designs with a square type roof although these are normally mounted on a circular bearing of some configuration, it seems like Geoff has chosen to just slide the entire roof from the top of the building, not ideal for many reasons, but I am sure he has researched this and come up with his own compromise.

  13. #13
    Join Date
    Nov 2020
    Location
    Daisy Hill
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    78
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    4

    Default

    Thanks for the welcome all. Very much appreciated by an old codger trying his hand at metalworking and welding for the first time.
    The original dome was made out of a steel rhs geodesic frame covered by sheet steel rotating on a huge 3 meter steel ring. We managed to get the steel ring home but had to cut the dome into three sections. I decided against reassembling it as it was just so heavy and would have been difficult to use without also investing substantially in precision power assistance. I also briefly considered a garage panel door but I had concerns with waterproofing, overhead obstruction, and condensation whereas a simple insulated roll off Could avoid all those issues.
    So committed now to the project, I purchased a short piece ( 0.6m ) of 50 x 50 rhs to practice on.
    it took me about 20 minutes and one cutting disc to turn it into a 50 x40 channel.
    I was happy the way the roller fitted into the newly made channel and how easily it ran.
    Calculating things out that equates to roughly 6 hours of cutting time and about 20 cutting discs for my small grinder. I think can do that if I set the job up up well and not try to do things too hastily.
    Just some pics of the work.

    .7071809C-1B1D-44A7-A18E-9FF60AF584ED.jpg65BED89F-3CBC-4964-BD67-B7E6538E8F0F.jpg

  14. #14
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Quote Originally Posted by Swagman105 View Post
    Thanks for the welcome all. Very much appreciated by an old codger trying his hand at metalworking and welding for the first time.
    The original dome was made out of a steel rhs geodesic frame covered by sheet steel rotating on a huge 3 meter steel ring. We managed to get the steel ring home but had to cut the dome into three sections. I decided against reassembling it as it was just so heavy and would have been difficult to use without also investing substantially in precision power assistance. I also briefly considered a garage panel door but I had concerns with waterproofing, overhead obstruction, and condensation whereas a simple insulated roll off Could avoid all those issues.
    So committed now to the project, I purchased a short piece ( 0.6m ) of 50 x 50 rhs to practice on.
    it took me about 20 minutes and one cutting disc to turn it into a 50 x40 channel.
    I was happy the way the roller fitted into the newly made channel and how easily it ran.
    Calculating things out that equates to roughly 6 hours of cutting time and about 20 cutting discs for my small grinder. I think can do that if I set the job up up well and not try to do things too hastily.
    Just some pics of the work.

    .65BED89F-3CBC-4964-BD67-B7E6538E8F0F.jpg 7071809C-1B1D-44A7-A18E-9FF60AF584ED.jpg
    Hi Geoff,

    If you edit your pictures, I just crop and rotate mine, then save them, they will come out the right way round on the forum.
    Doing this removes the data stored by the camera with the picture which includes orientation.

    HTH.
    Best Regards:
    Baron J.

  15. #15
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
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    59
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    Quote Originally Posted by racingtadpole View Post
    ...I’ve sectioned RHS and SHS on quite a few occasions and never found it difficult or challenging...
    The difficulty is not necessarily in the cutting but because it is rolled into a square and welded, there can be stresses in there that make it twist/ bend if a side is removed. It will depend on the brand/ material and origin, but it can happen.

    Michael

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