Tricks To Weigh Heavy Things

Do you need to weigh something really heavy but don’t have access to an industrial scale?  How can I weigh heavy things — like a trailer frame — without a special super heavy duty scale?

When we look at “Where Does The Axle Go” and other build objectives, often it is not convenient to haul things down to a truckers scale to measure them.  Sometimes the item is not mobile enough to easily haul it.  So what can we do to weigh these heavy things? There is always some way or hack to help.

Here are some tricks, and though they are not super accurate, they yield a reasonable answer without needing a special industrial scale.  The catch?  They require some some math, and accuracy of the answer is subject to your care in setup and measurement.  We’ll use two examples, including a video showing us weighing a trailer.

What Resources Do You Have?

When I first got married, my in-laws sometimes called me McGyver.  I suppose it fit somewhat because figuring out how to accomplish something with whatever you have laying around is just part of what I do.  I grew up in farm country, and farmers don’t run to the store for every little thing.  They figure it out, and make due with what they have.

So, the first thing in being able to weight heavy things is to find resources.  Westley from “The Princess Bride” did the same thing when he asked “. . . And our assets?  Inigo:  Your brains, Fezzik’s strength, my steel . . .”

Weigh a Heavy MachineHopefully your resources include some lengths of steel (or wood beams) along with a push-button brain (calculator).  Hopefully too, a scale of some sort — like a bathroom scale, or maybe something bigger (strength).  A typical bathroom scale goes up to somewhere around 300 lbs, and that can be enough with levers and tricks.  We’ll use it with the same principle as a wheelbarrow . . . “I mean if we only had a wheelbarrow, that would be something.

Measuring or estimating weight is a pretty big part of finding weight proportions — like for calculating axle position.  For things like tongue weight, load weight, axle load on trailers, and even shipping weight (as the example we’ll use here).  It would be great to have a big scale as the right tool, but that’s not common in a DIY shop.

Levers To Weigh Heavy Things

Like the wheelbarrow, there are tricks we can use to weigh heavy things with a smaller scale.  It’s setting up a lever system to support the weight then calculate portions using a something cheap like bathroom scale.  Yes, some math, some careful measurements, and some logic are all here.  And some tricks, like to weigh a trailer, measure one side of the trailer (then double it) can give a good estimate.  (If things are symmetrical.)

See the photo above.  The big blue thing is a machine for a customer, but I need to know what it weighs.  A guess of 500 lbs is not accurate enough, so we make something to weigh it.

The starting weight guess puts us in the ballpark, then we choose levers.  We’ll use a simple case first for easy understanding, then expand the discussion below for other applications.  So, first, let’s look at the theory with the help of this diagram.

Setup to Weigh Heavy Things

If the load is center (meaning D1=D2) between the supporting points, then each end holds half the weight.  If one end is a scale, then we can read the weight, and double the number for a total.  This works because the scale goes to more than half of the total weight (guess of 500 lbs) for the machine.

The Process

So, we set steel bars with a fulcrum at one end (C), and the other end (B) on the scale.  We can use a simple straight beam, or in this case, an “A” shape allows the machine to balance with less risk of tipping.  It does not matter that the two beams are not the same length, what matters is the length from point “B” to each “C” is the same on both sides.  Also, that the machine is centered on both beams.

I have used steel angle iron pieces placed V up, to more accurately measure to the point of contact. Both ends.

Once the beams are setup with the weight scale, take note of the value showing on the scale.  This weight is now the “new Zero”.  In our example, the beams without the machine weigh in at 41 lbs.

Loaded ScaleNext, we place the machine at center on each beam, and see the measurement.  With the machine on the beams, the scale indicates 259 lbs.  Subtract 41 from 259 and we get 218 lbs.  Assuming the setup is correct, 218 lbs is half the weight of the machine.  Double it, and we now know the machine weighs about 436 lbs.

The accuracy to weigh heavy things with this method depends on accurate measurements for the beams, and placement of the load.  The more careful we are with setup, the better the final result.  Also, a longer beam increases accuracy simply because any error we might create in setup becomes a smaller portion of the total.

Weigh More Complex

To weigh things that are much heavier than the scale can measure, we need to change our setup and do a little more math.  Basically, as we move the load closer to the fulcrum end (C) it will put more weight at C and less at B.  More leverage.

We can use a simple single beam, or the “A” shape as illustrated with the blue machine above.  Either way, we’ll use this new diagram and these equations to make the calculations:

How To Weigh Heavy ThingsEquations For Weight Measurement

Though it seems more complex by using formal equations, it’s really the same as above.  It’s a method to weigh things that are much heavier than what the scale can directly handle.  Like how to weigh a trailer.

Weigh A Trailer Measurement Example

In the video you can see the setup to weigh a trailer.  This uses the more complex method as described above, then the “Weigh Things In Parts” section that comes later.  We’ll show the example, then describe what we did and why.

The Video does a pretty good job of showing what we did, and why.  But here are some points to notice.

  1.  The object heights to support the beam — and the part contacting the trailer — are set at a length that makes the beam effectively level.  You need to know where the contact is made to get the best accuracy.
  2.  Before lifting the trailer, we made sure it cannot move.  You don’t want things moving when you start picking them up.
  3. The wood blocks under the wheels are to give space for the beam under the suspension, with the beam up on the jack.  They don’t change anything with the measurements.
  4.  The point of lift for the trailer was the center between the wheels.  Always put the heavy weight at a point you know.  Don’t let it spread out.

For me, I try to lift carefully to make sure I’m not exceeding the scale at any point.  By putting too much weight on the scale, it can cause damage.  If you see the scale going too high, just reduce the distance D2.  Making D1 longer and D2 shorter will allow you to weigh a bigger heavy thing.  The down side comes if the distances become too short, then you loose accuracy (or you have to be super careful with your measurements).

Side Note On Tongue Weight

Tongue weight and it’s % of the trailer was noted in the video.  See the article about tongue length, and note that this tongue is quite long.  A longer tongue allows a lower % of trailer weight on the tongue.

Weigh Heavy Things In Parts

The above example shows a few techniques.  First, using levers.  Second, dividing the problem into manageable parts.  It would be near impossible to weigh the whole trailer all at once, but like in the video, we can do it in pieces.  Most importantly, we can extrapolate that to many different variations — like in the video where we weigh one side of a trailer, assume symmetry, then weigh the tongue load.  Add them all up, and you have a total — like in the video.

It works in cases like to weigh a trailer because we don’t need to be super accurate.  While we know that it’s not perfect, yet to give us an idea of the accuracy, let’s just re-do the calculations.  Let’s say we were off by an inch in measuring D2.  We measured D2 = 35.25″ and that gave us a side weight of 535 lbs.  But, what if we made a mistake and it were actually 34.25″?  Then the answer for the side weight of the trailer would be 546 lbs.

A 1″ mistake is pretty big, yet, because of the long beam, the one side weight answer difference is 11 lbs.  In terms of total trailer weight, 22 lbs (we have to double it for both sides) is not really very significant.  Just food for thought.

The keys here are:  1) Take your time and measure carefully.  2) Use a long beam of an appropriate size and strength as your lever to minimize error.  3) Lift slowly to assure you don’t overload the scale, beam or other items.

One More Word

As I have used these methods to weigh heavy things, like a trailer, the hardest part is often getting the lever under the heavy thing.  In the case of the blue machine above, I had to work the machine up the lever, carefully.  I needed my gantry crane, but didn’t have it there.  Be creative (like using the wood under the wheels), and be safe!

Good Luck As You Weigh Your Heavy Things

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