Constantly Moving Targets and Dial Indicators
Here are a few things to know about making reeds...
Learning to make reeds is a significant endeavor to undertake and has always been extremely difficult and time-consuming to learn. One reason is that there are several 'moving targets' that we have to hit all at once to make a great reed. Additionally, the process of learning how to make reeds and adjusting to these 'moving targets ' is largely a guess and check process.
These moving targets are constantly changing variables that affect our reeds. Weather affects how reeds work - and not just temperature, but also the humidity, barometric pressure, and precipitation. The venue we are playing in, the specific oboe, and the altitude all affect how you will want your reeds to sound and function. Cane, knife sharpness, and even staples are almost always in constant flux as well. The process of learning to make oboe reeds is not just about learning a specific process, but rather about learning how to adjust to as many different situations as possible. In my own experience, the time it took me to go from being a reed making novice to making my first good reed was shorter than the time it took to go from making that one good reed to making playable reeds consistently.
What you can do...
With all these changing variables, I find it necessary to control as many variables as you can while you are learning. As you become more experienced as a reed maker, you will be able to feel what you are looking for just by looking at the reed or crowing the reed, but while you are learning, you should try only to change one variable at a time as often as possible. You should try to stay consistent with the choice of diameter of cane, gouge measurements, and tie lengths. I say that I prefer the center measurement of my gouge to be 0.58mm, but you should still try out 0.60, 0.62, and 0.56mm to see how that changes the reed in its final stages. You may find those changes are not ideal for you at the moment, but that those changes might become ideal with a change in altitude or if you are playing on a different oboe.
I have found oboists to be reluctant to measure the specific thickness of the tip, heart, and back portions of a finished reed, knowing that these measurements will continuously be different due to any one of those constantly changing variables. The thickness of the heart will always be a little different because of changes in the weather or cane, which turns people away from measuring those dimensions at all.
More information is not inherently a bad thing, but reed makers can draw bad conclusions from more information.
For example: if you measure the thickness of the heart of a great reed and find it is 0.45mm, a bad conclusion would be that all reeds should be 0.45mm in the heart. A better conclusion would be that the heart can be about 0.45mm, but might need to be thinner in high altitude or thicker if you are looking for more resistance or maybe even thinner again if the heart is longer in length. I've made great reeds with a heart between 0.38-0.50mm in thickness, but I know when I'm at home, if the heart is 0.51mm, I will very likely have to scrape more cane in that area. I recommend writing down as much information as possible about your reeds as long as you remember that you will need to adjust your reeds to your specific circumstance. Your specific circumstance happens to be that your cane and the weather are constantly changing, so expect your reeds to fall within a certain range, not a specific number.
Note: One important thing to remember about using these dial indicators is to make sure the cane or the reed is lying flat and isn't hanging down or else you will get a thicker reading.