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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Getting ready to pour our screed in the next few days and I thought I'd just crop down the odd holding down bolt that's excessively long and liable to poke out the top. (Our Structural Engineer said this was fine by the way).

    Having nearly scorched our walls when the angle grinder sparks melted through the rockwool I'd placed as a protective layer, I'm now considering options that don't risk burning the house!

    Realistically, have I got any chance of using bolt croppers (decent length 24"-30"), to cut through 12mm bolts? Or will my weedy arms just melt in the face of an immovable object?

    Any other ideas? I've so far counted 125 bolts...
    • CommentAuthorbarney
    • CommentTimeJul 9th 2018
     
    Acquired from a previous life, I have a pair of 42" bolt cropper that will do 16mm in mild steel and 14mm in tensile steel

    It's bloody hard work cutting a few let alone 125 of the things - I guess with a shorter croppers, you will really struggle. I'm about the square root of bugger all in terms of size - and I can just get the large croppers to cut 16mm mild steel threaded rod even when I'm resting one handle on the ground and using "mass" to assist

    I'd use a zip cutting disk personally speaking - and I'd be worried if you've managed to melt rockwool

    Just use a light wire frame and a soaking wet blanket or bit of sacking to "catch the sparks"

    Wear gloves and goggles and buy a few boxes of disks - enjoy

    Regards

    Barney
    • CommentAuthorSilky
    • CommentTimeJul 9th 2018
     
    it may go better with a larger grinder if you are using a smaller one, i.e. 235 mm, then the edge of the disc will not be as hot and cutting should be quicker
    • CommentAuthortony
    • CommentTimeJul 9th 2018
     
    Hack saw with the correct blade for me
  2.  
    Sabre saw (electric reciprocating hacksaw) with specific metal cutting blade
    New blade for each cut
  3.  
    Posted By: WillInAberdeenSabre saw (electric reciprocating hacksaw) with specific metal cutting blade
    New blade for each cut

    125 blades ???
    liberal use of cutting fluid should increase the blade life.

    +1 for the 235mm grinder if you go that route.

    36" bolt cutters would do the job, especially if you extend the handles by placing a tube over the said handles.

    Bolt cutters would probably be the quickest - especially if you extend the handles by 2 - 3 ft.
    • CommentAuthorbarney
    • CommentTimeJul 10th 2018
     
    Adding leverage to the handles will help you out - but essentially it's the battle between the blade and the bolt that's important - is why I suggested a bigger croppers - you need the blade capability to reflect the workpiece size

    As an aside, that's why you see security fences with asymmetrical mesh profiles - to get at them with a bolt croppers means grinding down the blade beaks - and the size and grade of the wire is designed such you'll probably shatter the blades - you may cut a few but it will really slow you down

    For 125 bolts it might be better to hire a small hydraulic croppers - ideally electrically operated.

    Regards

    Barney
  4.  
    Posted By: barneyAdding leverage to the handles will help you out - but essentially it's the battle between the blade and the bolt that's important - is why I suggested a bigger croppers

    36" bolt cutters will cope with 12mm bolts, its the grunt on the other end that is usually the problem - which is why the extra leverage works well.

    Posted By: barneyFor 125 bolts it might be better to hire a small hydraulic croppers - ideally electrically operated.

    +1
  5.  
    Only 12mm bolts,
    the thin cutting discs in a 4 1/2" angle grinder will make short work of those, this from personal experience, and only need to cut little over 1/2 way through before snapping off with a hammer, if one prefers.
    marcus
    • CommentAuthorgyrogear
    • CommentTimeJul 24th 2018
     
    One could use the grinder, with a (thin) earthenware tile behind in place of the (thick) rockwool...

    gg
  6.  
    As Barney mentioned, how did you manage to melt Rockwool? Are you sure it was not glass fibre? Rockwool, as I understood it, is classed as non-flammable (?but not 'non-meltable'?). It's used above register plates and against flues in solid-fuel stove installations.
    • CommentAuthorJeff B
    • CommentTimeJul 24th 2018
     
    Posted By: orangemannotOnly 12mm bolts,
    the thin cutting discs in a 4 1/2" angle grinder will make short work of those, this from personal experience, and only need to cut little over 1/2 way through before snapping off with a hammer, if one prefers.
    marcus


    Exactly what I would do. Surround the work area with a wet towel to dampen down sparks.
    • CommentAuthorSprocket
    • CommentTimeJul 24th 2018
     
    What orangemannot says
    ie. a decent angle grinder with thin cutting discs should go through those no problem
    If you are trying to use an ordinary thick abrasive grinding disc then that's your problem.
    • CommentAuthorwookey
    • CommentTimeJul 24th 2018
     
    Use an angle-grinder with a metal cutting disc, and just use a sheet of metal or wet cloth or tile or any number of things to manage the sparks.

    Your 'rockwool' must surely have been fibreglass to melt from some angle-grinder sparks? They look impressive but IME it's actually quite hard to set fire to thngs with an angle-grinder. I guess right now your chances are as high as they'll get :-)
  7.  
    Thanks guys,

    It's definitely Rockwool (or at least someone has spent a lot of time faking their packaging etc.). Unloaded some of it myself and it was all baled up with branded wrapping and delivery notes etc. RW3 type.

    Only a 50mm thick scrap piece mind you, so there may have been a localised thin bit or something, but it definitely had a charred hole and my wall behind was burned in the process.

    My Dad's pointed out I should be using something called a plumbers soldering mat to catch the sparks. Think I'll try to get a decent make of cutting disc, thin as possible and give it another go.

    I did find that a decent amount of pressure was also needed before the bolt would 'give', so perhaps I was just making lots of grinding sparks rather than actually cutting anything half the time...
    • CommentAuthorbhommels
    • CommentTimeJul 25th 2018
     
    The types of angle grinder discs have caught me out as well. You need the 1 or 1.2mm thick "slitting" discs instead of the 3-4mm "cutting" discs.
  8.  
    I have heard them described as "Plasma" discs locally, regardless of the name, in reasonably skilled hands, they are a very simple yet very powerful tool, the key is to simply keep the disc aligned with the cut, so that the sparks are ONLY generated at the cutting edge.
    Dont "fight" it.
    I have not burst one yet, despite hearing "horror" stories from other less "handy" individuals.
    Marcus
  9.  
    Oops
    Dont "fight" it.
    Also
    Dont force it, i.e. let the disc find its own way, in terms of cutting speed.
  10.  
    Thank you everyone.

    I've got some 1mm discs and a high temperature resistant 'burn mat' on their way. Will report back!
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