Tiny anvil knob for forge - video

[tonyfoale]

A word of caution. Using diodes in parallel to increase the current rating does not increase the rating in proportion to the number of diodes.
Diodes are not born equal and when connected in parallel some will do the lion's share of the work and some will just loaf along. So the one doing most work will get overloaded and fail, that will put more load onto the remaining ones and so the one that is now most heavily loaded will fail quickly and the effect will quickly cascade through the whole diode pack.

So to avoid these problems you have two options.
1. Use more diode bridges than you think that you need, I would suggest double. They are cheap so there is no need to skimp on the number.
2. Use diodes with a sufficiently high current rating. In the past these were expensive but now they are not. This would be the preferred solution.

I do not know if you are aware of it, but if you add an Argon bottle and a TIG torch you will have everything that you need for a scratch start TIG welder for steel. You could add a solenoid valve in the gas line for greater operational convenience.
40 or 50 years ago I bought a thyristor controlled DC only welder which I used for TIG welding. It worked well. HF or lift start would have been better but I put up with scratch start. That welder is still my favourite for stick welding

I would second NortonDommi's suggestion to be able to switch polarity. I would disagree with the suggestion to fit capacitors, instead use a choke (inductance) in series if you want to smooth the current more.