Rebar + duct tape + steel?
My reasoning for the pipe + steel + welder was simply how to attach a heavy piece of steel to a handle without it flying apart when you smash it against something. I didn’t consider the vibration… maybe a duct tape handle would help? 
If it bugs you that much, you can say that the superglue in the game is strong enough to bond a 5-10kg lump of metal to a heavy stick for such a purpose and use:
{
"result": "hammer_sledge",
"category": "CC_MISC",
"skill_pri": "mechanics",
"difficulty": 2,
"time": 20000,
"reversible": false,
"autolearn": true,
"tools": [
[
["hacksaw", -1],
["toolset", -1]
]
],
"components": [
[
["stick", 1],
["broom", 1],
["mop", 1],
["2x4", 1]
],
[
["superglue", 3]
],
[
["steel_lump", 1]
]
]
}