I have an Atlas Horizontal probably manufactured in the early 1940's. When I purchased it their were a few broken parts I had to make.
The origional universal joints for table power feed are fragile zinc die cast. Mine are now steel. The motor and jack shaft pullys were missing.
I put on aluminum cone pulleys and use the first 2 steps of 4. The key way, cut into the table screw had sharp edges and burrs that badly wore the nut.
I made a nut and wore that out as well. When installing the second newly made nut I deburred the keyway edges with a wire wheel, NO problems with that since.
In general I am very satisfied with mine mill for the size of work I do.
I have built a lot of tooling which I will photograph and show in the future.
My mill came with a 7/8 arbor and I have built a 1 inch. Keep the cutter diameter down around 3 inch to avoid overloading the gears when machining steel.
Keep cutters sharp, minimize cantilever situations when holding material and vibration will be minimal.
Check setups prior to engaging the power feed. If the overarm support contacts the vise a crash will occur.
The zinc die cast gears and universals in the power feed will not tolerate a crash. They break, then you have to machine replacements.
If an Atlas mill can be obtained at a reasonable cost, it is an excellent choice for the home shop.