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  1. #16
    Join Date
    Oct 2015
    Location
    melbourne
    Posts
    473

    Default

    Rather than abrasive disks, you can get long life metal disks (diamond or carbide type chips) which will last a lot longer.

  2. #17
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default

    Quote Originally Posted by Michael G View Post
    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.
    Can't remember what it was for, but I once tried halving some 50x50x1.6 SHS Duragal lengthwise. The resulting 2 bits of warped, unhappy metal were utterly useless.

  3. #18
    Join Date
    Nov 2020
    Location
    Daisy Hill
    Age
    78
    Posts
    4

    Default Sliding observatory roof

    An update on my sliding observatory roof project. I just couldn’t find any commercial 50 x 40 u steel channel and in the end decided to bite the bullet and despite worries about warping etc, make my own by cutting a 15mm strip off each wide side of some 6 meter x 100 x 50 x 2 gal steel box section to leave me with two 6 meter x 50 x 40 channels.
    it was a lot of cutting (24 meters) and I used nearly 30 cutting discs with my 115mm angle grinder but managed to finish the job and am pleased with the outcome. A few times the discs got jammed when the cut relieved stresses that caused the cut gap to narrow. Although there is a slight inward slant on the sides of the finished channels they are perfectly straight and will be suitable for their intended purpose.
    I experimented with a jig to keep the grinder running straight during the long cuts but found the easiest solution was to screw a bolt into the grinders opposite handle hole. By loading a heap of washers of appropriate size on the bolt to act like rollers on the side of the steel, the grinder blade could be run down the length of the work at exactly the right spacing.
    After welding a few brackets on the side to attach them to the top of the wall plates will now turn my attention to the roof itself probably shallow angle insulated roofing panels.
    468E1816-8EA3-4D22-B79F-1C4EECCD2E63.jpg8CEB234A-07B9-439B-871C-C889ED00574A.jpeg

  4. #19
    Join Date
    Nov 2020
    Location
    Daisy Hill
    Age
    78
    Posts
    4

    Default Observatory roof sliding mechanism

    Just an update on my observatory sliding roof.
    just couldn’t find any 50 x 40 channel for my roof sliders, so bit the bullet and bought some 100 x 50 gal rhs. The idea being to remove about 15 mm lengthwise down the middle of each 100 mm side to end up with two 50 x 40 ish channels.
    The channels need to be 6 meters long so the job involved four lengthwise cuts (24meters in total)
    Fortunately all went off well and despite a few discs jamming when stresses were relieved the end result looks straight and will be perfectly useful for my purpose
    In order to keep the cuts straight I found the easiest way was to screw a bolt with a stack of appropriately sized washers into the grinders opposite handle hole. The washers acted like a roller which could be run down one side of the 100 x50 to keep the cutting disc at a constant distance from the edge.
    I used a lot of discs for the job some better and longer lasting than others but overall the cost is about the same except you have to change out worn cheap ones more often. Basically you get what you pay for.
    Next is to weld some brackets to the channels to allow them to be fixed to the top plate of the observatory Into which the roof bearing rollers can be placed.
    Attached Images Attached Images

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