Lastufka Labs - Reference

Handling Lead - How Much Lead

Heavy and easily shaped, lead is great for balancing hobby vehicles. There are a few substances that are more dense than lead, but they are much more toxic by themselves or in compounds that form during their use. Gold is the exception (it's better than lead in every way), but it is too expensive for most people to use. Tungston can be found but is too hard to manipulate if not already in a shape and size you can use. So the question remains "How much lead will I need?" In order to answer this question, you will need to know how much your vehicle will weigh without the lead.

Make a Weight Chart

To begin, make a chart like the following. It lists the parts of the vehicle, their weights and how many of each part there is. Determine the weights of the parts by guessing, weighing on a scale or by Archimedes method (water displacement) to enter in your table.

To allow for a margin of error on the part of your guess, weight scale or the scale at the competition, plan for a buffer wieght. Clay makes a good buffer weight because it is easy to add or remove and conforms to any shape. A tenth of an ounce of clay (density 1.07 oz/in3) takes up about 0.1 cubic inches of space in your well. Clay can also be plastered on your vehicle if there is no room in the well.

For example, you might make a chart like this for a Grand Prix car:


Item Weight (oz) Quantity Total Weight (oz)
Kit Wheel 0.0833 4 ________
Kit Axle 0.0416 4 ________
Finish 0.1 1 ________
Body/Chassis 1.4 1 ________

Multiply each item weight by its quantity and enter the total in the last column. Add all the item Total Weights and enter the result in the TOTAL WEIGHT field.

All filled in, your chart may look like this:


Item Weight (oz) Quantity Total Weight (oz)
Kit Wheel 0.0833 4 0.3333
Kit Axle 0.0416 4 0.1666
Finish 0.1 1 0.1
Body/Chassis 1.4 1 1.4

It's your turn. Here's a blank worksheet for your own chart.


Item Weight (oz) Quantity Total Weight (oz)
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________
________________________ ________ ________ ________

Use Your Weight Limit

Many hobby vehicles are subject to a weight limit of a few ounces. In the example, there is a maximum weight of 5 ounces. For this Grand Prix car, the weight of free lead needed will be 5 - TOTAL WEIGHT or 5 - 2.0 = 3.0 ounces. Use your limiting weight instead of the 5 ounces used in this example. If your limit is a minimum, it is often an advantage to keep the weight down to that value. Use it, unless you are certain another value is better.

Weight of lead needed = Weight Limit - TOTAL WEIGHT.

How Much Space Will The Lead Need?

Lead has a density of about 6.53 oz. per cubic inch. The following table shows how much volume must be carved out to make room for the weight of lead you need to use. You will want to secure your hammered lead or melt and pour it before you put any finish on your vehicle. So remember to account for the weight of all the parts, finish and any other assessories.


Weight (oz) Volume (in3)
0.1 0.015
0.5 0.077
1.0 0.153
1.5 0.230
2.0 0.306
2.5 0.383
3.0 0.459
4.0 0.612
5.0 0.765
6.0 0.919
6.53 1.000

Using "feel" or simple volume formulas for 3-D boxes and disks, determine how much wood to carve out or drill out or reserve for your weight well. Choose the size of the well opening in width, length, radius, or height for the shape you desire. Use the formula(s) in the table below to calculate the depth you need for your volume of lead.

SHAPE Depth (all measurements in inches, volume in cubic inches)
Box volume / (width x length)
Disk volume / (3.1416 x radius x radius)
Deep Triangle 2 x volume / (base width x height)
Deep Trapazoid 2 x volume / (height x (base width + top width))

You may want to make a bigger space for your lead to allow room:

If you are drilling holes to make space, consider drilling away from the center line at an angle with the drill holes meeting in the middle (like tree roots) so the lead cannot fall out. In any case, create the space before you insert hammered lead or pour your lead!

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Lastufka Labs - Reference
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