The test subjects for this post. 1” mild steel bar and a ¾” slot punch. Now we are looking at the difference between punching from mainly one side as opposed to punching half way through and then flipping over and punching from the other side.
When punched half way through and then half way through from the other side you limit the “bottom spread”. Equalizing the spread, so to speak.
So how does this affect anything? Well, if you need more even and visually appealing holes then punch half way, flip and punch again to make the hole more even.
However, if you need more material in a certain spot, then punch from the appropriate side and flip when the punch meets the anvil . Larger cheeks on the bottom of an eye hole is an example of this. The extra material at the bottom would allow longer checks on the bottom of the eye and shorter checks on the top, for example.
I hope this gives you something to think about next time you need to punch a hole. There is so much more to this craft than what meets the eye.
Nothing is as simple as it seems.
I like to compare forging to running a bulldozer. With a few exceptions of sawing, chisels, etc. dozers do not remove dirt they only move it from one place to another, and yet accomplish amazing feats by simple relocating material. Such is forging, the hard part is to determine when, where, and how to move the material from one place to where it is needed in an efficient manner that results in the desired outcome.