Using a bottle jack to determine tongue weight?

[MillWeld]

Seems to me that if you have a bottle jack with a gauge on it and know the diameter of the lifting piston you can get the tongue force. (Pressure=Force/Area). Has this approach been used before? It would be a lot easier than the lever arm and scales.
Bob

 

[Rock knocker]

Very common to do, especially with Enerpac products. Probably mostly used for pulling assemblies to failure in tension, but lots of different things to do with the process and principles

 

[David_Kb7uns]

You can buy tongue scales from Sherline with 1 ,2 ,5 thousand pound capacity, they also make a hanging scales to see how much you are lifting with a tractor.

Sherline Trailer Tongue Weight Scales

David Kb7uns

 

[schmism]

accuracy is an issue with that method.

for instance, on a 1" diam bottle jack.
TW pressure
700 891.27
720 916.73
740 942.20
760 967.66
780 993.13
800 1018.59

how are you going to achieve those kind of pressure readings off of one of these

FYI i used 1500 psi gauge because 1100lbs TW = 1400psi on a 1" bottle jack

meanwhile the bathroom scale version can be clearly read to the nearest pound and then with a x3 multiplication means your only off by 3lbs.

oh and the sherline

is $130 for the 0-1000lb.. vs having all the materials you need (jack stands, 2x4 and bathrrom scale) for free

 

[bcp]

This is easy:

Measuring trailer tongue weight with a bathroom scale

Bruce

 

[schmism]

This is easy:

I know, i have my own post if people would search for it.

 

[Renze]

Stick-slip effect of the piston seals would make the bottle jack not very accurate, most bottle jacks are at least 15 ton and tongue weight maybe 500kg...

 

[MillWeld]

Thanks for the feedback. I have used the bathroon scale method and found it cumbersome. Also I was never confident that I could measure the effective length of the lever arms, i.e., are the weights supported by the tongue and jack stands exactly on their midpoints? Flexing of the supporting board could alter the contact point too and thus the effective length. So, being able to read a bathroom scale to 1lb may be misleading.

Certainly, reading the pressure gauge is not accurate, either and I also didn't consider its stick/slip aspect. Given the expense of the bottle jack I will probably go back to the bathroom scales. Thanks again,
Bob

 

[JimRB]

If you had a 10' board, do you not make a mark 10" from the end, 20" from the end and 110" from the end? You place one jack stand at 10", the tongue at 20" and the other jack stand at 110". Isn't that a simple 10X lever? Using a 3.5"x3.5x120 might not flex a lot. Especially if that board is made from steel. You could shorten using a 5 ratio but then the math is trickier.

 

[schmism]

You could shorten using a 5 ratio but then the math is trickier.

or just use the 1' right, 2' left (scale) and multiply by 3 like everyone else suggests.

as for uncertainty in the above version if ive done my math right, an inch off (23 inch vs 24 inch to the left) results in a difference of 80lbs. you can set it up slightly differently and use the pipe instead (as shown in the other version) as that is a single point (easy to measure to) (or tack a pipe to the top of the jack stands)

point is at the end of the day at least you have a ballpark idea (least to nearest 100lbs) for tongue weight for the load you measured vs everyone else who just eye balls it off of rear squat.