Hougen mag drill with Broken Spindle

[metric_taper]

It's clear what degree of trust metric_taper places on thrust, with amount of thrust his post carries..
Bad puns aside, that mechanical aspect is so often neglected or not even considered. I've lapped hard washers to gain that security on torqued fasteners; those being repeatedly loosened need it most of all. Any burr or dirt scores mating surfaces, requiring increased tightening for retention. Easily cured with various efforts of lapping, and a bit of high pressure lube.
My long-time go to mill wrench are double box ends, 3/4" and 7/8" in the case of running a Bridgeport pattern. 3/4" does the drawbar and sometimes handy operating the vise, along with convenient parking between operations, and 7/8" for clamping hardware, another handy parking spot.
A neophyte operator watched me, next day had same wrench as I........, but lacked some discretionary finesse.

But I've never sheared a drawbar. I told him so, adding that wrench lengths are coordinated to sizes of related fasteners; not the requirement to use all of it!

The previous owner of the mill abused the hell out of the original OEM drawbar assembly. The Wells-Index has a thread spigot on the end of the spindle where the sliding quill splines end. This threaded end is where the thrust flat plate is threaded on, for the drawbar bolt, washer to pulled against. I had to make a new one, and made it to fit the thrust bearing diameter. It's worked well, I've not had any of the end mill adapters, face mills, boring heads or collets ever let the tools spin. I did design it that if needed I could put a hex on the assembly, but found it was not needed.
You making a living doing this, see the need for the use of more torque.
A bigger issues is the spline is worn, and that will make pounding sounds in some sections of the quill travel where the wear is worse. I really only ever use the mill to repair things, so it's not a production used machine.
I do have a good sense of torque vs fastener max stress. It's been a long time since I twisted any bolt hardware off.