Undergrad Torque without a torque wrench

[HRG]

I need to tighten the nut for a trailer hitch ball to 250 ft lbs but I don't have a torque wrench that can do it.

I read on a different forum that an alternate old school method to get 450 ft lbs of torque is:

• Torque = Force x Distance
• So in that forum's example, have a 180 lb person stand on a 2.5 ft breaker bar. The calculation is 180 x 2.5 = 450.

Is that a correct way to get 450 ft lbs of torque?

If so, then since I weigh 142.3 lbs, 250 ft lbs / 142.3 lbs = 1.76 ft.
0.76 ft is about 9 inches. Therefore 12" + 9" = 21".
So I would have to stand on a breaker bar at 21" from the nut to exert 250 ft lbs of torque.
The breaker bar would of course have to be horizontal while I stand on it for the 250 ft lbs of torque.

Need confirmation from physics gurus whether this is correct or not.
Thanks!

 

[.Scott]

Your math is correct. I would practice my technique before standing on the breaker bar with the nut attached.
You don't want to bounce the bar or have your weight shifting +/- an inch along the bar.
Plan and Practice.

 

[jrmichler]

Yes, it's right. Plus what @.Scott said. And you get a +1 for actually properly tightening the hitch ball.

I once designed a threaded connection that needed 3000 ft-lbs of torque. So we bolted a 15 foot length of pipe to the part, attached a deer scale, tied a rope to the deer scale, and had two men pull on the rope until the scale read 200 lbs.

A deer scale is a spring scale used by deer hunters for weighing deer. Like this, but 300 lbs full scale:

 

[berkeman]

We need to close this thread now, since there is liability involved in helping you do something dangerous to save a few bucks. Especially if you are going to be changing trailer balls very often, you should just invest in a new torque wrench. Also, you may want to invest in an extension for that wrench so you can get the nut back off again...

As a safety tip, since you will likely be turning the hitch 90 degrees in order to be able to use your weight vertically to turn the nut, also put a box or other platform under the part of the wrench where you will be applying your weight, so if you do slip off, you only slip a couple inches onto the box/platform.