Young machinist here. How did we make precise instrument from something supposedly less precise and how did we calibrate it? We have machines that can machine things within .0001 inches or less of tolerance. Wouldn’t that require the machine to be made with at least the same precision? This applies to the measuring equipment as well. In order for say a micrometer or CMM to measure down to .0001 or even .00001 of an inch, how did we ensure those firsts were accurate?
In: 4
The machines are designed in such a way, that once they are build they hold their properties as much as possible. As soon as something fixed in place and doesn’t move anymore, you can just calibrate them. Which is a reason why we’ve moved to derive measurements from physical experiments.
Due to the calibration they can achieve vastly higher precision as their singular parts. As long as you account for stuff like deformity and the precision in repetition,
I’m pretty sure I could make cube within +-0.01 mm using only hand tools, despite not having anywhere near that sort of precision in my hands. I can always just remove a little bit at a time with sandpaper. It’ll take time, but I could get there. Then I’d need a measurement reference. A micrometer is ideal of course, but even a ruler would suffice. Even if the ruler only goes to 1 mm increments, I could use a simple mechanism to create a 100:1 leverage, where 1mm on the ruler is 0.01 mm as measured.
The same principles are applicable for machining equipment.
There are processes that will get you something more precise than the tools you started with and one example sticks out in my mind
I’m taking this from a video that I’ll link at the bottom.
You’re in the wilderness and don’t have any tools. There are lots of rocks around, though. You find 3 of them that have approximately flat faces. They can still be bumpy, just need to be flat enough to rub against each other.
You start by rubbing a pair of them together to make both surfaces a little flatter. Then switch it up and use a different pair, then the last pair, then rinse and repeat
If you only used 2 rocks, you would eventually get 2 surfaces that fit together snugly but aren’t flat. Bumps in one would be valleys in the other. But with 3 rocks, a flat surface is the only way each rock will fit snugly against each other rock.
So after much rubbing, you’ll be left with flat surfaces. You’ve probably got one of these in your shop that’s calibrated. Having a known flat surface lets you make more complicated stuff. And you didn’t even need a tool with a rated precision!
It starts with making repeatable and consistent parts. Specifically screws/bolts that are interchangeable with each other. Every rotation of the handle moves the tool 1/4 inch etc. If you can make a set of consistent screws/bolts you can use the magic of fractions and gear ratios to make an even finer screw. Where one rotation of the handle is 1/64 of an inch and so on and so on till you get to the smaller fractions. Now instead of the handle turning the screw, have the screw turn the handle and replace the handle with a red arrow that points at some numbers that mean something.
Forty threads per inch, 40TPI.
so…if you spin the threaded item 4 times, it measures 1/10th of an inch. Then, around the barrel, you make 25 even marks. Four times 25 = 100. So, each hash-mark is 0.001″
One full spin is 0.025″, right? so, four spins is 0.100″…so 40 spins is 1.000″
This is why a micrometer uses 40TPI…
Latest Answers