I am in the process of designing a plane body for a custom profile, dedicated plane that I will make this week. I was sent the following image from the customer and we're trying to come up with a plane design that will create the profile.
Take note of the bead above: it's a full 180 degrees. If he decides to have this full bead in the final profile then the plane must not be sprung.
There are two major disadvantages to not having this plane sprung. 1. The high point of the cutting edge of the iron will be much higher in the plane. This will result in a mouth that is not as uniform, well beyond the wear angle of the body and wider than necessary. 2. The iron itself will be vertical. This will result in less of a shearing cut and more of a scraping cut--think edge retention. The difference in cutting action won't be a deal breaker, but it does change things.
There are two planes illustrated below. The plane that is vertical has no spring. (This is the one from above.) The other plane, the left, has a spring angle of 22.5 degrees. The mouth will be more uniform and the cutting edge will have more linear feet in it.
Take note of how far up in the body the cutting edge travels. I can make the entire cutting edge inside of the plane's wear angle.
The disadvantage to the sprung plane is that I have to reduce the bead from 180 degrees to what's illustrated.
A few frequently asked questions:
Q. How do you make dedicated planes?
A. Hollows and rounds. There is no tool better for producing small amounts of very specific profiles. This is a perfect example. I will make 10" of this molding and likely never make it again. Increase the size, decrease the size, whatever. It makes no difference to me. (We are also deciding the actual dimensions below.)
Q. Why are there no spring lines on hollows and rounds?
A. Hollows and rounds have no spring lines because there is no predetermined angle at which the plane must be held.
Q. How will the plane be maintained?
A. The plane's sole will be flattened with hollows and rounds or poor man's hollows/rounds:
Sleep on that.