Just a couple of words of warning about using magnets to fix things onto machine tools:
While they won't magnetise the iron, they will magnetise any steel swarf and dust, making it stick to the bed and a pain to clean off.
If you knock the magnetically attached thing while the machine is in operation, Sod's laws states that it'll be attracted to the the thing that'll cause the most harm (e.g. the chuck) .
Rigging these things with a clamp might be a better option.
Bill