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Are C-clamps rated?

Discussion in 'Lighting and Electrics' started by pudgeo2, Jan 15, 2008.

  1. pudgeo2

    pudgeo2 New Member

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    I was recently talking with a sales rep, who informed me that C-Clamps and Side arms are not rated for overhead use. I can see where this comes from, but I find this hard to believe since C-Clamps have been the standard for ever.
  2. soundman

    soundman Well-Known Member

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    Last edited: Jan 15, 2008
  3. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Your rep is correct. Cast iron C-Clamps are not rated, as cast iron, as opposed to forged, is inherently brittle and thus cannot be load rated. We've had this discussion before, particularly in this thread, regarding hanging SeaChangers from side-arms.
  4. jmabray

    jmabray Active Member

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    Derek is absolutley correct. Cast Iron C-Clamps are not rated.

    But other ones, like the mega clamp or the aluminium clamp from L&E are.
  5. cutlunch

    cutlunch Member

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    This maybe a silly question as we don't use these type of clamps in NZ as much. I understand the rating of the clamp but is there a rating on the bolt or this all together? Why I ask is apart from the teeth it seems the tightness of the bolt is what stops the light from falling off the bar if the centre of gravity does not run directly through the center of the clamp.
    Here we use Hook clamps the same as Europe.
    http://www.blue-room.org.uk/wiki/Hook_Clamps
    These have the advantage in that the light will stay on the bar even if the bolt comes loose unless you have the light over the bar. But these are good in schools etc because the bolt normally has a handle not a bolt head. Also the clamp holds to the lights yoke using a bolt with a wing nut. So as long as someone hasn't come along with a spanner and overtightened the wing nut you don't need tools to hang these lights.
    Getting back to my inital question, if a bolt is lost out of a C clamp and replaced with one from the hardware store does this derate the C clamp loading capibilty?
    I think the last time I used a C clamp was on some old Colortran Fresnels.
  6. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    [user]cutlunch[/user], note the LightSource link above. The specs say:

    Safe Vertical Working Load 600 lb 273 kg

    Emphasis on the word "Vertical." The C-Clamp bolt (as opposed to the yoke bolt) takes no weight and is only for holding the clamp in position on the pipe. The yoke bolt on the MegaClamp I have in front of me is a Grade 5.

    Not sure why your hangers never caught on here in the US, except for PARbars and pre-Series 300 Vari*Lites. I've often heard them referred to as "G-clamps."
  7. Logos

    Logos Active Member

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    The Hook Clamp or G clamp was I believe invented by Strand in the 50's I think there is a wikipedia article.
  8. JD

    JD Well-Known Member

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    Cast C clamps have always given me concern ever since High School (many, many years ago) when I was tightening one and the top just broke off! Wasn't even that tight. Castings are funny things.
  9. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Didn't find anything in wikipedia, but stumbled upon the Strand archive, cited here: 1959
  10. Les

    Les Well-Known Member Premium Member

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    I'm confused. If C-Clamps and sidearms aren't rated for overhead use, where are you supposed to use them? I'm hard pressed to think of any hanging position in a theatre that isn't over someone's head. Is the type of clamp in the picture below what we're talking about?

    Attached Files:

    Last edited: Jan 17, 2008
  11. icewolf08

    icewolf08 CBMod CB Mods

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    Yup, that which you have pictured, is not rated. Take a look at it, you will find that not even the "heavy duty" ETC clamps have an SWL listed on them. As was mentioned it has to do with the fact that they are cast iron, very brittle. This is one of the reasons that it is very bad to over-tighten C-clamps. The angle of force that the bolt applies can bend and weaken the clamp, and eventually, as someone pointed out before, they just fall apart.
  12. JD

    JD Well-Known Member

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    Many things used in theater predate current safety regulations. Heck, theaters used to burn down all the time! Most stuff slowly gets weeded out. Some stuff sticks around... Look around your own home- There is no way in the world the standard Edison light bulb base would ever make it to market if it were introduced today! Most people could get two or three fingers into that one if they tried! Popularity just keeps that one alive. ;)
  13. TimMiller

    TimMiller Well-Known Member

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    When ever i'm buying clamps i look at the side of them and they usually have a working load rated, such as a lot of c clamps have 500 lbs SWL or something like that printed on it, i buy those. If it does not have a load rating printed on it, and this applies from everything from c clamps, to quick links, to shackles, and i also only use graded bolts. They call ungraded bolts "shear bolts" in the farming industry for a reason, when your machine gets in a bind those ungraded bolts are designed to get sheared in half to protect the gears from binding up and being destroyed. And if you have been farming long you learn very quickly how easy it is to pop a shear bolt. Its very scary how easy it is, the bolt will pop before you even hear the engine lug down. Just think of this being a lot of weighht on a light over your head. Also i tell guys think of who you love most sitting under that light, do you feel safe with them sitting there, if not then you should make it where you do feel safe, even if it includes double safety cabling and wrapping a metal chain around it.
  14. gafftaper

    gafftaper Senior Team Senior Team

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    This is a really frightening topic I had never thought about. It's a great reason to preach good safety cable use and to only allow 6" crescent wrenches. I can't believe with all the safety stuff we talk about that one of the most critical pieces of hardware on every stage isn't rated. That's amazing!
  15. Sean

    Sean Active Member

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    I cannot disagree more--especially in younger hands.

    There are several folks that will disagree, and preach the merits of speed wrenches, etc. But I can't even begin to count the number of times I've been asked "hey, can I borrow your wrench? Mine won't fit".

    An 8" wrench will fit all the hardware we deal with on a daily basis. Unless you get a wide-jaw 6" wrench, they often will not fit a scaffold clamp (cheeseborough). And, even if they do many do not have enough strength to tighten down said clamp with a 6" handle.

    As to the cast C-clamps. Though I certainly have seen a few broken ones, I've yet to have one break on me (or have it happen on a call I'm on). I would suggest that you look at the clamps each time they're used. If you see any sort of cracks, or if they seems "out of shape", toss them in the trash.

    Don't handicap your crew, just teach them how to use the equipment correctly.

    --Sean
    Last edited: Jan 26, 2008
  16. gafftaper

    gafftaper Senior Team Senior Team

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    To politely disagree with you...
    If they need it for a special purpose, there's an 8" wrench in the tool box. But I haven't found a high school girl yet who can't sufficiently tighten a C-clamp with a 6" wrench... and I've taught a lot of them. The problem comes when a guy uses the 8" wrench to tighten it and the girl has the 6" wrench to loosen it.
  17. Sean

    Sean Active Member

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    I'm not talking specifically about tightening C-clamp bolts. I'm talking about, for example, the yoke bolts and the nuts on Cheeseboroughs.

    To be fair, I've not spent a lot of time working with HS students (though I do have one as a full-year job shadow right now). I just seems to me making them use 6" wrenches is a short-sighted way to protect equipment. It doesn't actually teach how to USE the tools appropriately.

    My $.02. And seriously, no offense intended.

    --Sean
  18. JD

    JD Well-Known Member

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    The one that broke on me was brand new. It looked fine. Once broken, it was easy to see why- there was a void inside the casting. I would assume (and you know what that spells) that once it has been used awhile, the chance of that happening is very unlikely. Still, I doubt they will ever be magnafluxing C clamps, so it's just something to keep in the back of your mind. I am referring to the old cast iron ones here, not things like mega-clamps which I think have a much better QC. I just remember how surprised I was, and that has stayed with me.
    Last edited: Jan 26, 2008
  19. gafftaper

    gafftaper Senior Team Senior Team

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    Continuing the debate...

    I do have to admit I cheat and use a wide jaw 6" wrench as that is needed occasionally for the yoke bolt. But my feeling with that is you should crank it down tight on the bench and not touch it in the air. Along with that, the last thing you want is someone using a 8" or larger wrench on the tiny pan lock bolt (a.k.a. "Jesus/F-Nut").

    I certainly see your point that other types of hanging devices may require more than a 6" wrench but for conventional lighting hangs my basic point is you just don't need to tighten the C-clamp down that hard on the pipe. Finger tight plus another half turn or so is plenty. If you are digging into the pipe you've gone too far. I suppose this depends a lot on your inventory, if you use a lot of Cheeseburgers and other large hardware I can see the need for a larger wrench, but in a mostly conventional rig, my vote is 6" only.
  20. Sean

    Sean Active Member

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    Hmmm.....

    Tightening the yoke bolt is part of both hanging, and often focusing the unit.

    Attaching a sidearm tee to a unit is a pretty frequent use of 1/2" hardware. And, it happens on just about every hang.

    As for the pan bolt, do you really think it's that much harder to break that bolt with a 6" wrench?

    Do you allow students to use power tools? Power saws can do more damage than a regular hand saw can do any day. Just because the capacity/mechanical advantage is there doesn't mean it will be used incorrectly.

    --Sean
    Last edited: Jan 26, 2008

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