The Home Machinist!

I have a piece of 1/4" steel bar stock that I am trying to make a gib/shim out of.

As it is .. its too wide. To try and get it narrower .. I tried to mill
the edge with a 2f endmill. I have a set of endmill holders coming ... but for right
now ... I again tried to use the damn drill chuck .. lol .. and it again .. came apart.

But before it came apart, I had trouble keeping the endmill on the edge of the bar stock.
it would wonder off. And it really chattered . Was this because I used the drill
chuck .. or .. because you just don't do what I was trying to do .. or .. because
my machine just isn't ridged enough to do this ?

There's no delicate way to say it. Wise people don't use a drill chuck to mill. Not for any reason.
If you continue the practice, you're most likely to discover that the chuck will not stay on the shank, so you'll have to replace both of them.

Don't remove material from only one side when machining bar stock---especially cold rolled materials. Internal stresses will cause the part to bow, with the convex surface being the side machined. Take small and equal cuts from both faces, alternately, to help keep the piece straight.

The end mill wandered off? Which way? If the cut became shallow, as if the end mill was pushing away from the cut, I'd suggest that the chatter you mentioned was allowing the screw to back off. That's what table (and saddle) locks are for. They prevent that from happening.
Why the chatter?
Hard to say. Could be the machine simply isn't rigid enough to machine steel without issues---but not using a drill chuck, alone, will make a huge difference. The closer to the bottom bearing of the spindle you can hold a cutting tool, the greater will be the rigidity of the setup. Simply hanging a cutter from the drill chuck is more than reason enough to have the problems you're experiencing. I'd even suggest you not use end mill adapters---collets hold things much closer to the bearing, and are, as a result, far more rigid.

It's simple. Be patient, and lose the idea that you can mill with a drill chuck. That, to me, is driving in to the garage by driving through the closed door. Not exactly how it's supposed to be used.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Ok .. I got that I shouldn't use the drill chuck .. just chalk it up to " can't wait "

I guess my question is .. if you had to narrow a piece of bar stock .. would you
entertain using an endmill to .. as you said .. take a little off each side.

Sure. And, if finish was an issue, I'd use it by clamping the piece to the table and use the side of the end mill, not the end. By taking light cuts and climb milling, you can achieve a very nice finish, even in mild steel. That's not so easy using the end. These things will all start making sense to you the moment you take a few cuts with a proper setup.

You can usually use some snug fitting blocks in the key slots to locate items when machining them as we're discussing. I use a pair of 5/8" parallels. Once inserted in the slots, you can then use parallels on the table to space the part the required distance so the part hangs off the back side of the table (or the front side) enough to take the cut without touching the side of the table. It's fast and quite reliable, assuming you're not trying to work to tenths. That's generally beyond the capability of a mill, anyway, so that shouldn't be much of a concern.

Be patient. You can do a lot of damage to your equipment employing poor practices, to say nothing of the possible risk of injury. Learn to to things properly, and don't take chances. That can get quite expensive. The most important thing to consider is that you build bad habits that way, and they're hard to break. I've had no end to the discussions with folks that have poor approaches to machining---insisting that there's more than one way to skin a cat.

Yep, there is! But, there's often an optimum way to approach the project. It generally provides a better outcome, with less risk to one's safety and a better chance of a job completed properly. That comes home to roost quite quickly when a poor decision comes home to roost by the project going south.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.