Tom Gardner wrote:

I have to make four identical 1/4" plates that have 15 holes. 11 of the
holes be countersunk for 1/4" socket-head countersunk screws that will
be used to mount fixture parts, 4 of the holes are for #10 SHCS for
mounting to the machine. These fixtures will hold wood blocks in a
machine. I need .005" difference between hole placement in the plates.
The plates are 8" x 6"

My question is: Can I stack all four plates, tack weld them together
and drill all four plates at once in the mill using the DRO to position
the plates and have the top plate and the bottom plate be within .005"?
In other words, will the drill wander more than .005"? I will use a
combined drill countersink to spot the holes then drill undersized, then
drill the 1/4" hole using all new drills.

I'd ream them; it shouldn't be necessary to tack them together if you have
a decent set of clamps for your mill. Put them on top of a couple of cutoffs
so that the drills and then the reamer can go all the way through. (or
on top of a sacrificial piece of something softer than the parts.)

Have Fun!
Rich