The function of this initial scrape is to remove the bark from the lay of the reed, AND to start some pathways for the vibration. Oboe reeds are made up of slopes and stops, or ramps and steps, and my preference is to have a good long slope in place foundationally, so I can start working on my reed from a place of vibration and add stops, rather than working from a stopped place and scraping forever to try to encourage vibration to start.
When I put this initial long scrape in, I have three big factors I keep in mind.
The first is that the reed has two planes on each blade. If you think of the curvature of the cane like the arc of a circle, and picture that the face of the reed you are looking at crowns at 12:00 and ENDS at 10 and 2, you want to focus your scrape at 11 and 1, never directly down the center at 12.
The second thing to keep in mind is that although you can remove bark easily with your knife, you can never put it back. So as you make this preliminary scrape, be conservative with your work near the edges. Although you may ultimately remove the bark in the heart area, at this early stage you can certainly leave bark all the way up to the base of the tip. It's safer that way.
And the third dimension to take into consideration is the overall slope. Although I am not at all trying to construct the rooftop transition into the tip at this point, I do want to go ahead and get rid of as much wood as I safely can. Why kill myself trying to scrape everything off carefully and delicately later when I can hack lots of it off sloppily right now and save the time? So although I am a little bit careful in the heart area, I am not a bit cautious at the tip, and I want everything sloping THROUGH the reed so the vibrations can start right away.
If I do my job right, I should be able to beep the reed right away when I open it, although it will be NOWHERE NEAR A REAL REED YET.
Next week: Cane Preparation and Gouging (Thanks, Anish, for the idea!)