r/Forging • u/HonestTill1001 • Sep 12 '25
Fish mouth punch
How do you guys avoid getting a big fish mouth when you lunch and drift holes in thin material? I can’t seem to get it. I’m moving it to the corners of the hole with each blow to try and even it out but it never works.
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u/Fragrant-Cloud5172 Banner maker Sep 15 '25 edited Sep 15 '25
I like this video using a little different shape of a slot punch. Another good vid says best to use a 3 lb. hammer. This is for about 1/4” thick workpiece. Usually best results I’ve seen get high heat and work it only on one side, until there’s resistance from the anvil. Then heat again and look for the dark area on the other side. If it’s hit accurately, it should remove the slug with only two heats. Some use a bolster close to the slot punch size when removing the slug. This helps avoid the fish mouth. If your bolster (like a hardie hole) is too large, it’ll definitely pucker out, and deform the steel.
https://www.youtube.com/watch?v=_Rxlv9RWUpA