Are C-clamps rated?
- Thread starterpudgeo2
- Start date
I see gaff's point, and I see Sean's. When I was in college, the requirement for every person on an LX crew was to have an 8" crescent wrench. That is what I carry every day, and that is what I tell new crew people here at PTC to carry.
Sean has a very valid point in that if you teach someone how to hang a light and you teach that you only need to go finger tight plus another 1/2 turn with a wrench they should be able to handle that weather they bee in HS, college, or a pro. Otherwise you just drill it into the crew until they do get it.
Sean has a very valid point in that if you teach someone how to hang a light and you teach that you only need to go finger tight plus another 1/2 turn with a wrench they should be able to handle that weather they bee in HS, college, or a pro. Otherwise you just drill it into the crew until they do get it.
I love the fact we are having this debate over an insanely minute detail. I think we all agree that a 6" wide mouth will do the basic C-clamp job and I think we all agree about how tight is proper. No it's more a debate about if the 6" is too restricting for other tasks. We all need something better to do with our lives.
I think it was Ship or Van who a while back told the story of the crusty old T.D. who would take away any wrenches over 6" and cut them off. That'll be me someday.
I think it was Ship or Van who a while back told the story of the crusty old T.D. who would take away any wrenches over 6" and cut them off. That'll be me someday.
JD
Well-Known Member
The disagreement (in my opinion) seams to have to do with the concept that a larger wrench may lead to over tightening. Finger tighten, then half turn with a wrench would apply the same force no matter what the size is, but then there's human nature to deal with. (The bigger the wrench, the more someone is likely to put the same force at the end of it, which results in greater foot-pounds torque if they don't stop at half a turn.)
On fact in rigging, construction, and even auto work, is sometime missed by the novice: The tighter you tighten something, the weaker it becomes! The static force has to be subtracted from the maximum working force of the joint. In other words (simplified), if a bolt had a tinsel strength or 2000 pounds, and was tightened to the point where there was 500 pounds of static force, it would now break under a 1500 pound load.
The compromise has to be in-between what is needed to keep something in position, and the drop in structural integrity.
I can't place the news article right now, but I remember a walkway collapse that occurred a few years ago that was blamed on over tightening of support bolts.
I think this debate is a good one because if one person happens across this board who didn't know about the half turn rule-of-thumb, we may have saved someone a lot of grief!
On fact in rigging, construction, and even auto work, is sometime missed by the novice: The tighter you tighten something, the weaker it becomes! The static force has to be subtracted from the maximum working force of the joint. In other words (simplified), if a bolt had a tinsel strength or 2000 pounds, and was tightened to the point where there was 500 pounds of static force, it would now break under a 1500 pound load.
The compromise has to be in-between what is needed to keep something in position, and the drop in structural integrity.
I can't place the news article right now, but I remember a walkway collapse that occurred a few years ago that was blamed on over tightening of support bolts.
I think this debate is a good one because if one person happens across this board who didn't know about the half turn rule-of-thumb, we may have saved someone a lot of grief!
I believe you might be talking about the MGM walkway collapse.
There was a documentary on TV here a week ago.
Apparently what had happened was they had welded to beams together to make a box beam. The supporting bolts were placed through the centre of the welds. So apparently eventualy the weight of the walkways distorted the beams around the bolts. The beams finaly broke at the weld and the bolts pulled through dropping the walkway.
I remember the back in 2003 when the rig at Broadway-Hall collapsed. Was still in high school at the time, but know a few people who were there and have the pictures still. Pretty scary stuff when you thing about it. Didn't know the 'half turn rule' before, but will remember it for future use. Thanks.
lightbyfire
Member
Not an overtightening incident, but when you said this it made me think of an example given in Structural Design for the Stage, where the 1980 collapse of suspended walkways in a Hyatt Regency. Box beams were partially to blame here too, however it was two stacked walkways that were originally supposed to be supported by one continuous rod, but to save cost the builder used two rods, so instead of both walkways being supported by the ceiling, the lower one was instead hung off the upper one, causing the top walkway to have to support twice its normal load.
I find overtightend C Clamps all the time, I have a technician who insists on using channel locks, and I dont care how careful he is bolts are always overtightened. I myself have bent a number of ETC C clamps by overtightening when overhanging fixutres with scrollers. I have a box of about 20 that are bent.
We have a 24" wrench, but it's a little impractical to carry in your pocket.
I find overtightend C Clamps all the time, I have a technician who insists on using channel locks, and I dont care how careful he is bolts are always overtightened. I myself have bent a number of ETC C clamps by overtightening when overhanging fixutres with scrollers. I have a box of about 20 that are bent.
We have a 24" wrench, but it's a little impractical to carry in your pocket.
JD
Well-Known Member
I am thinking the article I read may have been about a different mishap. It was from a few years ago and involved a contractor substituting three screw-rods for a project where the design was for one long one that ran through all three stories. One rod would mean mean only one floor was supported by the threads, but three rods caused the second floor joint to support 2 floors, and the third to support 3 floors or 300% of the design spec. Another factor was the capture bolts which subtracted strength from the support bolts. I will try to find the article.
Just noticed the post above! I think that may be the one. Been a few years!
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Probably a good idea.
I don't follow, how would these be interchangeable? Aren't beam-clamps for I-beams, while C-clamps are for pipe?
You should get rid of your c-clamps (you can mail them to me for disposal) and replace everything in your theatre with uni-strut.
Uni-strut...please God anything but that.
