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.
Here are the resulting holes and slugs. The hole nearest the end is punched from one side and the slug knocked out from the other. The other is punched half way from one side and half way from the other side.
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So this tells us the resulting slug, at least in this application, are close enough to not significantly effect the outcome. For all intents and purposes the same amount of material was removed from both holes.
You can see an obvious difference here, but nothing drastic
Here are the holes after drifting to ¾” Now the difference appears more obvious.
And now it is obvious. So what is the difference and why is happening? When you punch from mainly one side you are driving that material down and when the material meets the anvil it spreads out. Resulting in the stock spreading out more at the bottom side than the top where you started punching.
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.
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.
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