Scissor jacks unscrewing


Super Active Member
May 31, 2018
After thinking about it, the screw holds the weight, so eaither the screw is worn or distorted , or the hole it goes through is worn, bigger. Or the stop washer , nut . I haven't had a one of these out in a dog's age to look at one. But the weight should be held by the screw but isn't. The tighter the better.


Welcome from New Hampshire
Oct 1, 2014
South Central New Hampshire
Hey JNC! What's happening up in NH? I don't understand all that math? My granddaughter is racking her brain over this! Funny sh/+!!!
It's been a bit boring lately Feeling like a caged rat bouncing off the walls. I'm itching to get out but we dont head north until the 23rd. We're going to VT for 11 days Boondocking on a 40 acre Private lot on the top of a small mountain.


May 31, 2017
Basically what it boils down to is, the quality of metal we get from China. After these Chinese Jack's get "seasoned" the slightest ammout of clearance between the bolt and nut reduces the ability to hold the position of the jack. At this point it may be best to replace or rebuild with grade 8 or racecar quality hardware.


Super Active Member
May 23, 2018
South Carolina
We ran many Acme threads and ball screws on production equipment. Most had manual locks or electric brakes to prevent rotation after setup. If you are into vector diagrams, there are load vectors and friction force vectors. As long as the friction vector is greater than the load vector, the screw does not rotate. Change the lube, and the friction vector changes. If friction vector is then less than the load vector, the screw will rotate. I hope this helps.