This mounting plate is slightly warped from the heat of the welding. I have an old 220AMP arc welder and the heat control is beyond my technical capability. There are some slim, sexy welding inverters on the market now, if you can, get one. A 120AMP inverter does the job of a 220AMP oil cooled, and weighs much less. Been meaning to get one for myself for a few years now, and every time I put it off till the the next project. The inverter also gives a much smoother arc, so it's virtually impossible to deposit a welding bead with it that looks like pigeon droppings.

Main difference in the construction between this and the larger black base is that I cut the threaded bar in half, so I used three lengths instead of 6. Make sure you have nuts on the threaded bar before you cut it, because removing the nut past the cut fixes the threads. Otherwise you won't be able to get the nut on from the end you cut.

Also, I never put any fender washers along the threaded bar prior to casting, I just used the 6mm nuts at intervals on the length.

You could use an 8mm threaded bar for this, it'll look cooler with the bigger nuts. Structurally, the 6mm does the job.