Re: Rear Gin Pole Question


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Posted by Sherman in Idaho [108.162.246.17] on Thursday, October 20, 2016 at 15:51:55 :

In Reply to: Rear Gin Pole Question posted by Greg Coffin [172.68.34.169] on Wednesday, October 19, 2016 at 18:32:12 :

The general scheme with a gin pole, if it's to be movable at all, is to use something like a lever-type chain fall, or even block and tackle, to pivot the boom up and down, while using the winch to actually lift the load. I built one that way and used it before I got the wrecker, but it wasn't very good. The problem is that you can't really move the gin pole very much without either flipping it over backward, or having the anchor line run so close to in line with the pole that the strains become enormous. Sketch out the geometry and work out the loads and stresses and you'll see that the stress in the anchor line goes to infinity as it approaches the line between the block and the boom pivots. This is not good.

A-frames and gin poles are best used in a static configuration. That means two trucks -- one to hoist and one to haul. That's how they did it in the old days, and it wasn't because they'd rather buy two trucks. The best old-time (non-hydraulic) self-loader trucks have an I-beam mounted as high above the bed as feasible, with a trolley and chain fall running on it. The military version is commonly called a "bomb hoist". I have one on an M35 and it's simple and adequate for small heavy things like engines and other machinery. You still see them occasionally on trucks used to install concrete septic tanks and even mobile slaughtering services, but they're disappearing.

What you're wanting to do is something everybody probably wanted to do in the old says, but figured out wasn't really very practical. It's also kind of a waste of a winch. A winch is really meant for long pulls. Lifting one heavy thing up to truck-bed level is easy enough to do with s simple chain fall and muscle power. The old telephone trucks did have a pair of bed-mounted winches and an A-frame on front that carried the augur, but they were "luxury" vehicles intended for all day use by men who were getting paid by the hour. One drum did control the height of the boom, but only with a few feet of movement. The other lifted either the augur mechanism or the pole to be set in the hole. The auger itself was driven by a shaft from a pto in the front bumper. The scheme worked, but it had a lot of fabricated parts and would be overkill for just wanting to occasionally load something heavy into the bed of the truck. Plus, it was in front.



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