Tag Archives: measurement

Props for the Weekend

Turning a Realistic Harry Potter Wand on a Wood Lathe – Make Magazine has pictures and a video to show how easy it is to crank out a wand from Harry Potter in less than a day.

Faking It: How Outlander Got That Battle Scene To Look So Real - Outlander is a time travel story set in the 18th-century British Isles. Jim Elliot, props master and resident arms expert, talks about how they recreated the historic 1746 battle of Culloden for a recent episode.

Creating Evenly Spaced Intervals with Dividers or a Sector – Learn how to create a number of evenly spaced marks within a length of material using a sector. I haven’t heard of a sector before this, but Lost Art Press wrote about how to make one last year, and even included a downloadable template.

OMG…I Had a Productive Production Meeting – Finally, Jenner Butler talks about the importance of keeping a production meeting on topic and under three hours.

Sandpaper Grits

We all know about sandpaper grit. The lower the grit, the more coarse the sandpaper is, while the higher the grit, the less material it removes (and the smoother you can make your surface). You may have noticed that sometimes the grit has a “P” preceding the number. What does that mean?

It turns out sandpaper grit is measured in two different scales. As with most types of measurements, you have the US way and the European way. The US scale uses the bare numbers and is known as CAMI (Coated Abrasive Manufacturers Institute). The European scale is the “P” grade, and is known as FEPA (Federation of European Producers of Abrasives).

Both scales are based on the diameter of the average particle size in micrometer (µm), also know as a micron (one millimeter equals one thousand microns). Below is a chart comparing the two.

Average particle size CAMI FEPA
15.3 P1200
16 600
18.3 P1000
20 500
21.8 P800
23  400
25.75 P600
28.8 360
30.2 P500
35 P400
36 320
40.5 P360
44 280
46.2 P320
52.5 P280
53.5 240
58.5 P240
65 P220
66 220
78 180 P180
93 150
97 P150
116 120
127 P120
141 100
156 P100
192 80
197 P80
260 P60
268 60

You can see that the two different grit scales are fairly comparable at the coarser end of things.  In fact, 180 and P180 are exactly the same. But once they start getting finer than about 240, the two scales really start to diverge; 600 and P1200 are nearly identical.

Most sandpaper sold in the US uses CAMI, but you can find some brands with the “P” scale; Klingspor is one that comes to mind. The two scales can get tricky at the finer ends of things. If you read a tutorial that says to sand something at 800 grit, but you grab a sheet of P800 sandpaper, you’ll be using something far more coarse than what was intended.

But now you know.

How to Draw an Ellipse

I have three new videos up on my Prop Building Guidebook companion website. Two are on painting techniques (spattering and sponging), while the third shows a quick method for drawing an ellipse. I’ve attached that below. My book comes out next Tuesday, so that is it on the videos for now. But if you want to request a video for a specific technique, or demonstrating a certain tool, let me know, and I’ll see what I can put together.

A Practical Guide to Friday Links

Mother’s Day is this Sunday. Bill Tull, the prop master on Conan O’Brian, has some Mother’s Day gift ideas for those on a budget.

Here’s a blast from the past: an Interview with Anna Marchant, who was a prop maker on the two Matrix sequels. It’s a great interview because it really cuts to the heart of what kind of materials she works with, how the prop department interacts with other departments, and all the other day-to-day details that other interviews forego to talk about “cool props” or “what it’s like to work with movie stars”.

Dallas Poll, a prop maker on Lord of the Rings, had his house burglarized recently, with a number of props and memorabilia stolen. To make matters worse, one of the items stolen was his Stormtrooper costume—and the thieves struck on Star Wars Day!

Rich Dionne’s latest post is about working together in the theatre. This isn’t just about how a playwright works with a director; this is about collaboration within the production department itself, and how important it is for props, costumes, lighting, sound and scenery to occasionally work together on tasks and not just throw walls up around their individual departments.

Robert Lang does a nice job summing up the advantages of not measuring your work. Relying on measuring devices introduces inaccuracies into your work. Sounds counter-intuitive, right? Check the article out.

A case against Metric

Suppose you want to divide one foot into four parts: that is three inches. Divide a foot into three parts and you have four inches. Divide a meter into four parts: each part is 25 centimeters. Divide it into three parts and you are left with 33.33… cm.

The same is true with liquid and dry measurements. Take a cup. Now double it and you have a pint. Double it again and you have a quart. Take a gallon and divide in four; that’s a quart. Divide a liter into four parts, and you have to call it either 2.5 deciliters or 250 centiliters.

Look at a clock; it has sixty seconds in every minute, and sixty minutes in every hour. You can divide a minute in half, thirds, quarters, fifths, or sixths and in every case, you are left with a whole number of seconds. No fractions or decimals.

Metric may be good for scientific and technical measurements with things that increase by orders of magnitude. For example, hard drive memory started out with bytes, than kilobytes, followed by megabytes, gigabytes and now terabytes. But when dealing with carpentry and recipes and other measurements used in the construction of props, you are not having to convert between units which are one hundred or one thousand times larger than other units. You are dividing things into halves and quarters and thirds. You want to be able to take a measurement with a ruler which gives you one or two whole numbers and a fraction. It is so much easier to say “this prop is one foot and three inches tall, two feet and five inches long, and three quarters of an inch thick” than it is to say “this prop is 38.1 centimeters tall, 73.7 centimeters long, and 19 millimeters thick.” Furthermore, when you look at a tape measure, the hash marks for the fractions of an inch are all different sizes, so you can easily see whether you are at 1/4 or 5/16. With a metric tape measure, you have ten tiny divisions per centimeter, all at the same height. Is that .7 cm or .8? Who knows! (Of course, the greatest sin is a tape measure with both metric and customary units.)

The system of inches and feet were developed from commonly experienced physical objects, like a human thumb and a human foot. Their subdivisions were developed to measure commonly constructed objects for everyday use. This is what we deal with in props; the construction of everyday items on a human scale. A meter, on the other hand, was derived as a fraction of the Earth’s diameter. How much more sense does it make to say “this bench should be as long as three of my feet” than it is to say “this bench should be large enough so that 3,187,000 of them will fit end-to-end from one side of the planet to the other, going through the center”? Balderdash!

Metric is a centrally-designed hierarchical system which is applied to the measurement of everything conceivable, while customary units are a collection of localized systems specifically altered to the items and entities being measured. It may be funny to dig up archaic names of measurements to ask rhetorical questions like “how many hogsheads in a morgen”. In reality though, you will never need to convert the measurement of a cask of wine to the measurement for a plot of land. As an aside, archaic units are not limited to the customary system; does anyone in metric still use a stère?

It may be tricky to calculate how many inches are in a mile, but you rarely need to use that conversion in day-to-day life. Finally, despite the often touted ease of converting from nanograms to kilograms to megagrams, scientists have settled on essentially using the kilogram to measure the mass of everything, from the sun to an electron. No need to convert anything!

This is not so much a case against metric, but an appeal for hybrid systems and specificity in measurements to the task at hand. There is no harm done if I build a bench using inches and feet while biologists measure the volume of a cell in micrometers. I don’t wear the same outfit as a biologist, and a biologist doesn’t use the same tools and machines as a props artisan. That would be absurd. Neither of us have to convert the volume of a cell to the height of a chair. That would be even more absurd. Both of us using the same system of measurements? That’s the absurdest.

Tape measure