[Vodkaman]

Object

To construct a set of weighing scales capable of weighing to 99% accuracy at minimum cost.

I designed these scales 20 years ago. This construction allows you to test out accurate weighing techniques for buoyancy, ballast and construction repeatability, without having to shell out dollars for electronic scales, only to discover that the technique is not for you.

The following description, with the photo’s is lengthy but comprehensive. In actual practice, it is very simple and should not take much more than an hour to complete.

Materials

3 pcs A4 paper.
Paper or plastic cups (identical).
Wire, material not important, stiff enough to hold the cups in place.
Reference weight or coin of known weight.

Tools

Ruler, scissors, pen, pliers, wire cutters, knife, drill, ‘Vmans scales calculator' spread sheet.
PM me your e-mail address, I will e-mail the spread sheet document.

Description

A beam scales construction with a fixed reference weight and fixed beam length. The reference weight in the reference cup at one end, the object to be weighed in the measuring cup at the opposite end. The beam is moved laterally across a knife edge fulcrum to find balance point, weight is read off side off the beam at the knife edge fulcrum.

Reference weight

Object of known weight, as accurate as possible, approximately of 25% weight of the objects that you will be weighing. This is not critical. The important thing is knowing the weight as accurately as possible. If you do not possess such an object, select a suitably sized coin. To establish the weight of the coin, I suggest that you weigh a large number, say 10 or better still, 100, at the post office. Divide the weight by the number of coins and you will have an accurate figure for our purposes.

Here are a few standard coin weights that I found on the web:

British pound 9.5 gram
Swedish krona 7 gram
US dollar 8.1 gram (post 1979)
US quarter 5.67 gram (post 1965)
Malaysian 50c 9.33 gram

A web search will probably reveal the weight of your coin of choice.

Beam

The beam needs to be as light as possible and as long as possible for maximum accuracy and readability. The length and weight are not critical, 1m length would be good, but at least 0.5m. My suggestion is the smallest balsa section that will hold the weight of the object and reference weights without breaking or bending too much.

Alternatively, for lighter lures, a beam can be constructed from three pieces of A4 paper.

Paper beam

Mark a 5mm line down the two short edges of one of the sheets. This line will be the glue guide for the overlap.



Fold a sheet in half length ways, fold in half a second and third time. Open up the second and third folds.



Two of the folds will be in the same direction, one in the opposite direction, reverse this fold so that all three folds are in the same direction.



Arrange the sheets so all the folds are in the same direction and the sheets can be nested together (marked sheet in the centre).

Overlap two of the sheets, so the edge of one sits on the line. Apply a blob of super glue at one edge and press together.



This will hold the sheets together and make them easier to handle while the rest of the edge is glued.



Repeat so all three sheets are joined.



Fold the sheets along the pre-formed folds to make sure everything is working.



Apply a drop of glue near the edge at the centre and fold the sheets in half. Once fixed, glue the entire edge. Starting in the centre greatly reduces any errors. Form the sheet into a triangular section and glue, again starting at the centre.



Drill a hole 5mm from each end, to locate the cup hangers. The beam is complete. Although only paper, the section should be strong enough for 100g or 4ozs with handling care.

Cup hangers

Cut two identical lengths of string, drilled a couple of holes near the rim. I formed a couple of wire hooks, again, equal lengths. The wire hooks were twisted onto the string so the hooks cannot be interchanged. Make the hook wires longer than necessary, for tuning later.



Fulcrum

This can be any object with a sharp corner, a piece of wood carved to an edge or paper triangular section as described above will do the job.



Setup

Calibration

Place the beam on the knife edge fulcrum and find the balance point and mark with a pen and label it “centre”. Label one end “coin”. Always place the ballast coin(s) this end.

Attach the cups to the beam and balance on the fulcrum. Trim the hook wires until the balance point is at the centre mark. This ensures that both cups weigh the same. In any case, label one of the cups “coin” so that the same cup is used each time. Mark the coin and don’t spend it!



Open the 'Vman scales' spread sheet on your computer.



The top line shows the input headings, underneath you will fill in the data as follows.

Length

Measure the length of the beam in millimeters as accurately as possible with a ruler or tape measure. Enter the figure in the box immediately below 'length'. All the boxes have figures already displayed, just click the number and type in your own and press enter. You will notice all the numbers in the output section change as you press enter.

Weight

Enter the weight of the reference weight or coin in the box below 'weight'. You will notice all the numbers in the output section change as you press enter.

coin ctr-bal

This figure will determine the weight of the beam.

With the cups removed, attach a single coin to the ‘coin’ end of the beam.My coin just wedged in the end of the beam. The coin center should be as close to the end as possible.

Place the beam on the fulcrum and maneuver to the balance point. Make a pencil mark on the beam and label with a soft pencil for removal later. Measure the distance from the mark to the centre mark and enter the figure under 'coin ctr-bal' and press enter.Note, all measurements to the coin side of the centre are negative and must be entered as such. Example, my measurement was (-160.5).

In the ref data section, the 'beam wt' has now been calculated. If the beam was made of paper as described above, the 'beam wt' figure should be between 15g and 20g depending on the weight of the paper. If balsa or other beam material was used, the figure may differ slightly, but should be of similar magnitude for reasonable operation.

Cup ctr-bal

Remove the coin from the beam and hang a wired cup at the coin end, the other end of the beam should still be empty.

Place the beam on the fulcrum and maneuver to the balance point. Make a pencil mark on the beam. Measure the distance from the mark to the centre of the beam and enter the figure under 'Cup ctr-bal' and press enter.

In the 'ref data' section, the 'beam wt’ has not altered, but the 'cup wt' is now the correct value and should be around 5g to 10g. again, note, all measurements to the coin side of the centre are negative and must be entered as such.

Start wt

This figure can be altered at any time during calibration at your convenience. It merely determines the start point in the output data. I selected to weigh from 0gm upwards.

Increment wt

This figure can be altered at any time during calibration at your convenience. It merely determines the increment or step value in the output data.I selected to weigh in 0.5gm increments.

Note, If the spread sheet does not have enough output data, you can alter this input and read the data in two sessions. Example, session 1. start wt = 0, increment = 0.5, data = 0 to 14.5gm. Session 2. start wt = 15.0, increment = 0.5, data = 15.0 to 29.5gm.

No of coins

Enter the number of coins that you are using as your reference weight. Normally only one coin is used, but you could elect to use more coins if your baits are heavier or your reference coin is particularly light. You could also create two or more scales on the same beam using different numbers of coins, this would allow you to weigh lighter and heavier loads. You can even enter zero under 'No of coins' to create a scale for weighing the lightest loads. I used a single coin, weighing 9.33gm, most of my stuff is between 18 and 30gm. I also want to weigh as low as 2gm for weighing raw balsa and around 10gm for ballast.

Marking out the scale

The data is now ready. Remove the wired cups from the beam.

Read the first 'ref-mark' figure. Measuring from your measuring line, make a mark the correct distance and write the weight next to it.All the marks are measured from the centre, NOT from each other.

Note, all negative numbers must be measured to the coin side of the centre.

Verification

Attach the wired cups.

Place the reference coin(s) in the reference cup.

Place an object(s) of known weight in the measure cup. Move the beam to the balance point and read off the weight. If reasonable care has been taken, the weight should read with less than 1% error. Even 2% error is very useable.

Errors

There are several causes of errors. Variations in coin weights, glue distribution, human error, humidity affecting the paper and probably a dozen more. But I have used this design many times in the past and it works, at least until you buy the electronic scales.

I measured my lens cap on the above and on my digital scales (12.1gm). The result was pretty much 100% accurate. Obviously a fluke, but demonstrates the potential of the system.

[Spike-A-Pike]

Vman. Thats pretty cool....
What if I already have an accurate digital scale??? I save this to my computer as a reference in case of a thermonucular blast... Ooops, forgot about the electromagentic pulse effects... That idea is "TANGO UNIFORM".

[LaPala]

How about this ancient design? it was used to weight gold

[basskat]

You have way too mych time to think!

[smirkplug]

Just for the record, a dollar bill weighs a gram !

[hazmail]

Dave - Love to see someone making something out of nothing, I spent years going to the post office weighting coins so I could make a balance, to weigh my little 7 gm lures - I have now hit the big time, and bought a little electronic scale ($1, don't know how I got by without it. Great detailed work here.
Smirkplug- does this mean a $1000 note weighs 1 kilogram?????pete

[Vodkaman]

Pete. I too finally bought a set of digi scales. Essential equipment to design. But the first six months of my lure quest was done on the above beam scales.

[Spike-A-Pike]

Dave.
A digital scale... What are you going to do in case of a thermonuclear blast... Did you forget about the electromagnetic pulse effects. How will you weigh lures then??? Ooops, I almost forgot about the original post - never mind.

[DSV]

Originally Posted by hazmail

Dave - Love to see someone making something out of nothing, I spent years going to the post office weighting coins so I could make a balance, to weigh my little 7 gm lures - I have now hit the big time, and bought a little electronic scale ($1, don't know how I got by without it. Great detailed work here.
Smirkplug- does this mean a $1000 note weighs 1 kilogram?????pete

where did you get a scale for a dollar?