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  1. #16
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    Quote Originally Posted by bob ward View Post
    The short answer is fill the fire extinguisher with water and put it in the freezer.

    The longer answer is as above but be cautious about how much water you put in, you don't want to create a volume of ice larger than that of the extinguisher or create too high an air pressure within the extinguisher.

    Water expands by around 9% when it freezes, filling the extinguisher to 90% means the trapped 10% of air will reduce in volume to 1%, Boyles Law comes into play.
    Hi Bob,

    I understand the physics of it but how will it concentrate the force at the dent where it is needed to push it out? Isn't the force per square in/cm going to be the same throughout the tank? Have you used this method yourself?

    The tank has rivetted and soldered seams which may not withstand the pressure created. Just checked my info and they are designed to take 350 psi so maybe OK.

    The soldering also works against using too much heat nearby in the case of heat and rapid cooling to shrink the metal.

    I like Droog's bullseye pick idea but commercial ones wont work in the available space. Perhaps a homemade one- the famous fireplace tongs could be sacrificed and modified.

    Will try some of the ideas put up here. As they say in medicine "do no harm" so if I have to live with a couple of dents I will. My truck's roof was taken to with a ball peen hammer by a previous owner to remove a small dent and caused more damage I reckon than if he left it alone.

  2. #17
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    Jun 2007
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    Ipswich QLD
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    Gents the age oif this copper vessel means it is more than 20# thick copper tube it does not deflect like sheet metal. So freezing water will have a different reaction the copper will shrink before water freezes.. Not omly the copper but joints of solder the brass qs well as rivets.

    It is a pressure vessel meant to withstand internal forces.

  3. #18
    Join Date
    Nov 2011
    Location
    Melbourne
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    102

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    You could fabricated a raising stake similarly too the this one.
    You slide the cylinder over the stake , an push down the cylinder down hard over the stake,while using a Planishing Hamer around the edge of the effective area.
    Similar to how panel beaters raise a dent using a dolly and hammer.
    Or a dolly an slapper(yes there’s a tool called a slapper)

    Cheers Matt

  4. #19
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    Nov 2011
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    Melbourne
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    Quote Originally Posted by Jacqualos View Post
    Hi Bob,

    I understand the physics of it but how will it concentrate the force at the dent where it is needed to push it out? Isn't the force per square in/cm going to be the same throughout the tank? Have you used this method yourself?

    The tank has rivetted and soldered seams which may not withstand the pressure created. Just checked my info and they are designed to take 350 psi so maybe OK.

    The soldering also works against using too much heat nearby in the case of heat and rapid cooling to shrink the metal.

    I like Droog's bullseye pick idea but commercial ones wont work in the available space. Perhaps a homemade one- the famous fireplace tongs could be sacrificed and modified.

    Will try some of the ideas put up here. As they say in medicine "do no harm" so if I have to live with a couple of dents I will. My truck's roof was taken to with a ball peen hammer by a previous owner to remove a small dent and caused more damage I reckon than if he left it alone.
    Bullseye picks are really only for raising small dents, once you get to the level we’re you would start to use a body file.

    Cheers Matt.

  5. #20
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    Aug 2008
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    Charlestown NSW
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    How about a flat steel washer (maybe more than one). Bent in the middle to make an "L" shape. Soft solder to the edge of the dent so it can be used as an anchor, then use a small slide hammer with a hook end to gently pull dent up. Work your way around it.
    peter

  6. #21
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    Sep 2013
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    Melbourne
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    Quote Originally Posted by bollie7 View Post
    How about a flat steel washer (maybe more than one). Bent in the middle to make an "L" shape. Soft solder to the edge of the dent so it can be used as an anchor, then use a small slide hammer with a hook end to gently pull dent up. Work your way around it.
    peter
    Thanks Peter, That may be the way to go. The brass is tougher than I thought. The hot glue just pulled off without any movement of the dent. I have heard of that method too for dents in fuel tanks but you would want to have it inerted fully beforehand. No problem with an extinguisher however.

  7. #22
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    Nov 2011
    Location
    Melbourne
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    Quote Originally Posted by Jacqualos View Post
    Thanks Peter, That may be the way to go. The brass is tougher than I thought. The hot glue just pulled off without any movement of the dent. I have heard of that method too for dents in fuel tanks but you would want to have it inerted fully beforehand. No problem with an extinguisher however.
    Body shops use this method a lot(well they did when I was a beater)
    It’s “ok” if you can’t get in behind the dint,such as in a sill.
    But it can make a mess,
    We use to have an attachment that went on our spot welder, it would weld a copper washer onto the panel, we would then use a hook on the slide hammer to pull the dent out.
    But really it was last resort.
    I know that’s not kind of helpful!!
    Cheers Matt.

  8. #23
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    Sep 2013
    Location
    Melbourne
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    Quote Originally Posted by Simplicity View Post
    Body shops use this method a lot(well they did when I was a beater)
    It’s “ok” if you can’t get in behind the dint,such as in a sill.
    But it can make a mess,
    We use to have an attachment that went on our spot welder, it would weld a copper washer onto the panel, we would then use a hook on the slide hammer to pull the dent out.
    But really it was last resort.
    I know that’s not kind of helpful!!
    Cheers Matt.

    Thanks Matt,

    Will give it a try, soldered on washer method. Any solder residue left will help to fill in the scrape marks on it. Saw on You Tube a quarter panel repair using a stud gun to weld studs onto the damaged area to pull it out. A lot of bog was still required afterwards, Grrr!

    Cheers,

  9. #24
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    Jun 2007
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    Ipswich QLD
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    When you remove the cap how far into the cylinder to the damage can you get with you hand?

    I'm struggling to see the damage in the photo other than that around the lower rim?

    If you can get your hand & arm in the a heal dolly internally used while warming the exterior and also cold water wetting the dent will help. Light tapping the heal dolly or rubbing should suffice.

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