Mild Steel Fixture Plate for 440

Hello all, I just recently picked up a PNC 440 and have done a lot of reading. I was interested in a fixture plate so I am deciding to make one from mild steel. I got a piece from work for relatively cheap (7/8" X 10" X8"). I’m well aware of what happens to mild hot rolled steel when machined.
Plate design: holes spaced 1.25" apart in either direction. Each hole will be 1/2-13 thd with Half the depth being reamed out for 1/2 dowels. Pretty simple design.
I know people have done it with aluminum or 4140 steel. Has anyone here made their own plate?

I’m case you haven’t bumped into these videos yet NYC CNC did a few videos on fixture plates before they started selling them.

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I am doing the same. Steel should get here today. Wait what happens to the hot rolled steel when you machine it? I am using (mild steel S275JR).

3//8-16 at 1.0 spacing

Hot rolled steel relaxes you machine, so it won’t be flat the first pass.

I’m going to be milling a 1” thick plate with 10mm alignment holes and 8mm threaded mounting holes. On a test piece the workpiece was still cold to the touch afterwards. There is almost no heat going I got he work on this job, do you think it will still relax? Is there a machining strategy for this, like work center out or outside in. Run the job but leave some stock and then go back again with closer tolerance passes?

From what I have been told by the guys in the machine shop that I work with is to machine both sides a little, then check. You might need a few passes each side before it becomes flat.