Steel Soldiers::Military Vehicles Supersite - View Single Post

gringeltaube · 06-14-2009, 02:16

Not that handy....

Had to do some measuring & testing first, with real size parts and “sacrificing” half a dozen of my pins to determine their actual strenght...

Found following:

1)Most of the (rebuilt) winches I checked have the hole in the input shaft already re-drilled to the next common size 5/16”!, same for the corresponding drive shaft yoke; probably during depot rebuilt?
2)The shear pins I used for this are home made, out of brass which already had proven to have a shear strength very similar to some old AL pins I once found hidden in a tool bag. (I’m positive these were OEM)
3)Two 7.1mm (nominal 9/32”) diam. pins sheared each at about 250ft-lb, inserted in its stock size 7.2mm diam. hole.
4)Surprisingly it took more or less the same torque (245ft-lb) to break the same diameter pin but in a hole enlarged to 8mm (5/16”+)! Tested for a second time to confirm this! Wish I had AL pins to compare in this case!
5)A 7.94mm (5/16”) diam. pin in a 8mm hole shears at 350ft-lb! I repeated this test too, to be totally sure. So certainly size makes a big difference here!

Having this data its simple math to at least estimate the real capacity of our 10K-Garwoods:
Not taking into account friction losses and the minimal force to overcome the internal band brake, we have a minimum of 250ft-lb multiplied by 23 (23:1 reduction ratio), makes for 5750ft-lb on the drum. The drum itself has a diameter of 5” so if we started with the wire rope all out, the center of the ½” rope would be winding in at a distance of approx. 3” from the drum’s axis, for the first layer. Since 3 inches = ¼ of a foot, and to maintain the same torque figure our force needs to be multiplied by 4 and that means that we actually could pull over 20,000 pounds, single line!!! (pretty tough job for a ½” rope… imagine with the larger pin or even a steel bolt!)

Now lets say we only pulled out the first 10 meters (last layer) for a light duty winching job only: then it would be pulling in at about 5” from the drum's center, so we have 5750 times 12, div. 5 = 13,800 lbs.!

Conclusions:
Are our winches under-rated? YES!
Do we need much stronger shear pins? NO! (IMHO)

G.