[von]

One thing that no one mentioned in this thread is something which I believe is a worthwhile little safety item. This takes only seconds, costs very little, and provides a fair measure of "just in case" redundancy for those who are using the GM method (which I like and have used.)

I loop a slightly loose piece of steel wire safety wire through the spring and A frame assembly. I use something like this;

http://www.markertek.com/Lighting-B...Lighting-Background-Effects/Lighting-Safety-Cables/Fehr-Brothers/39312-30.xhtml

These are typical grid safety wires, and are rated for shock impacts of 1800 lbs.

The cable routing must contain the spring and sturdy component like frame or upper A frame, etc. The length must be sufficient to allow for removal once the spring is relaxed, but not so loose as to allow the spring to truly escape should the A-frame or jack somehow slip.

I learned this from working on theater style lighting grids. We use steel safety cables all the time on big lighting instruments...just in case something slips. It is scary to have a big light fixture slip off the grid and hang free over a live crowd, but the steel safety cable keeps scary from becoming tragic.

A spring stores a lot of potential energy when compressed, but in the case of a slip, the release of that energy occurs within a very small dimension and in a very short time period. If one contains the spring's behavior during the first few milliseconds of slippage with a steel wire safety cable, the energy will be dissipated without further damage to one's person, car, and surroundings. The steel wire is only 1/8" diameter, and does not get in the way of the work.

This provides a small additional measure of security which I believe makes the GM method just a tiny bit safer.

Of course, the rod method already contains the spring...that is, unless the rod breaks or a bolt shears.

Just my opinion

Keith

I always use a chain through the coil and A frame shock hole, bolted together. I leave just enough slack in the chain for the spring to decompress.