Precision Preschmision.

When it comes to manufacturing process, there is a direct relationship between precision and cost: the more precise the product, the more expensive it is.

The reason for this is simple: making precise products requires the use of even more precise tools, and it requires additional steps to measure and verify that the accuracy is within tolerance.

This applies to the home shop as well.

If you want to work precisely, and repeatably, you need to set up your tools perfectly, you need to measure and verify your results, and you need to plan your moves ahead of time, to make sure your plans for assembly and finishing allow you to maintain the accuracy of the components in the finished product.

All accuracy takes time, but there are two different classifications of precision in my mind, and one matters far more than the other.

  • Absolute Precision: making components exactly 3-inches long, or exactly 45-degrees
  • Relative Precision: making components that fit together exactly, with little concern for absolute dimensions

For example: I can make a table with a top that is exactly 6-feet long and 2.5-feet wide, made from 5 planks that are exactly 0.5-feet wide and 6-feet long: this table looks nice, is well made, and is absolutely precise.

OR: I can make a table that is about 6 feet long and about 2.5-feet wide, made with planks that are all the same length and width: The end result looks the same, and has the same quality, but all of my “measurements” are really just making sure the parts fit together. This is relative precision.

Sometimes absolute precision matters: In mass production you need to be able to provide predictable dimensions so that the packaging and usage can be consistent; replacement parts must meet exacting specifications.

But at home it’s often less important that the part be a certain number of inches, and more important that is fits, works, or looks good, whatever the length ends up being.

This is a liberating principle for me. I don’t need to spend hundreds of dollars on Starrett measuring tools to make six cuts of the same length; I can just make the first cut however I like and then keep the setup in place for the next five.

Now, this does require some forethought. If you are planning to repeat the same cut, you need a setup that will allow it. Your bandsaw and tablesaw should have a sturdy fence (but Biesemeyer and Kreg are probably overkill), and you should use stop-blocks and simple jigs where needed.

You may be thinking: “if you’re making something exactly 6-inches wide, isn’t that just as difficultas making something exactly as wide as something close to 6-inches wide?”, and the answer is: …sort of.

You see, I like to start building based on a concept in my brain, and progress through the project adaptively, with the results of each step determining the details of the next.

I don’t want to sit at my computer planning the minutia of the project in Excel when I could be spending valuable time at the bandsaw. And since nothing turns out perfect anyways, my measurements would invariably need adjustment as the project progressed, which then begs the question: Why measure in the first place?

As noted previously, the tape-measure has it’s place, and the blade of any saw should be square to its work surface, but there is nothing magical about hitting the inch within a fraction of a millimeter: These are arbitrary lengths that were made up in antiquity.

The real test of valuable precision is simple: Does it fit? Does it work? Does it look good? If so, it doesn’t matter what the ruler says.


3 thoughts on “Precision Preschmision.

  1. I completely agree…but I usually aim for “precision”.
    Do you find that sometimes the wood that you’re using will dictate how long/thick a piece will be? Sometimes there’s a knot to work around.
    Plans are just that…plans. There is usually some flexibility.

  2. Pingback: Miter Saw Fence | GarageSandals

  3. Pingback: Filling Space | GarageSandals

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