16 Holes

P.S. I cheated and went with only 60% thread form.

OHMIGOD ! The ones that don't strip right off are going to gall and seize ! Oh , wait , did you say 4140 ? Never mind .

I'm sure it's just pure coincidence that you're doing this just as those up-and-coming machinist/engineer/ etc kids are in need of just such an apparatus ... I was going to say something sappy , but I'll just say good on you and keep it up .

----------------------------- That's a mark of an experienced professional.

I go the taper, plug, bottoming route for difficult ones, like holes in grade 5 and 8 bolts.

When building custom machinery we had to tap the pre-punched mounting rails in shop-made 12 gauge steel relay racks. I used a Milwaukee drill freehand and retired the 10-32 taps after each 1000 holes.

Now they are called server racks. The hole pattern spacing alternates between 1/2" and 5/8" apart, lots of holes per rack.

Custom machined RF-tight enclosures for microwave circuits were somewhat like molds. They may have shelves part way down to mount the circuit board, and inner walls to isolate circuit sections, avoid unwanted resonant cavities or heat-sink power components. The screws were small and closely spaced because areas where the box and cover don't make good contact can radiate as antennas.

I've got one in my living room that I bought from a work colleague whose wife didn't like it, I use it as my drink and glass cabinet. It has a front door with polycarbonate? window and ball bearing runners for all the shelves, I replaced the metal shelves with laminated glass and fitted mirror panels to the sides and rear panel, and a lock for when friends visited with their younger kids. Not to everyone’s taste but it works for me.

I have my old Milwauke drill on the back bench with a 1/4-20 machine tap chucked up all the time. I've lost track of how many holes it has tapped.

Fixed side: