Broaching Question

Hello group,
I am needing to broach a 1/4" keyseat in a hub that's 3" lg. The key will go all the way through the hub. To make it easier for me to make a
broaching collar (I don't know the correct name for the round piece that the broach rides in), I was wondering if that piece could be made out of aluminum or would that be to soft and the broach would want to seize in the part?
Thanks in advance!
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