/diy/ - Do It Yourself

To place your 'anvil' you want to get it on something that won't shift when you hit and won't crack either.

If you stand naturally, arm at your side, the heigh of your hand is wear you want to top of your 'anvil'.

I used some bolted timber, this one's up to you, what ever works.
If you used the I-beam path then you have the problem of making it stand well. All I can say is good luck coming up with something. I should say you want to stand it like this...

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The top is your 'anvil'.