Tuesday, May 5, 2009

Walking the dog

Fortunately, common sense and better engineering criteria have become more prevalent in stage rigging, however, I still find many brand-spankin'-new facilities with equipment suspended on dog chain.

Some of the stuff I see is really scary. This batten at the left is just a smidgen from falling out of the rigging. Fortunately some one put a (pot-metal) screw through the bent wire chain so it would (hopefully) stay-put.

Here we see a dog-chain wrapped around an old loft block rope sheave. It too, secured with a pot-metal bolt.

This is a good example of multiple failure points all in series:
Bolted joint (at least this one was an SAE Grade 5 Bolt).
Open ended hook (if the batten snags on something and the line goes slack, then this can disengage).
Pot-metal Turn-Buckle with closed eye at bottom, but not a one-piece forged eye (it could bend open under load).
Bent wire S-Hook connected to track (no load rating for this either).
"Dog chain" is nothing more than a piece of bent solid wire. It is not load-rated for overhead lifting or suspension of loads over peoples' heads. Only Grade 63 or Grade 8 alloy steel chain is rated for that purpose. The next time you see bent metal parts holding up your rigging, or find open eye hooks, or non-graded bolts, or pot-metal turn-buckles, you might think about getting that fixed ASAP.

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