Having trouble with this

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When I bought my mill it came with this chuck and for the life of me I can not get it to stay. I've done what I've always done before is too just put the chuck on the shaft and hit it on the bench. What am I doing wrong, do I need to press it on?

[Dr Stan]

Is there a hole though the center of the drill chuck?  If not you're probably compressing the air causing the shank to pop right off.

Take a piece of 1/2" round stock, mount it in the lathe then put the drill chuck on.  Drill a hole (1/8" or so) through the chuck to allow the air to escape during assembly.  You can also grind a small flat on the side of the Jarno taper shank to allow the air to escape, but I prefer the preceding method.

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There is a hole all the way through the chuck.

[Mayhem]

Is the end of the shank threaded?

[rleete]

Chances are, the shaft is just a little too long, and is bottoming out on the chuck before it seats. You may have to grind some off the end of the shaft to get it to work.

[pepi]

Paint the arbor with layout fluid insert and check interference/contact that will indicate if the arbor length needs to be shaved

Greg

[dallen]

check to see if the length is ok, and that the arbor is the correct one for the chuck, by painting the whole end of it with dykem

Then if you don't want it to come loose, put the arbor in the freezer over night and drive the chuck and arbor together the next morning.

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Thanks for the ideas everyone, I'll try them out and see what I get. I'm not saying that the arbor is the correct one but it came with the chuck.