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The downside to using a 3-jaw chuck, on a lathe or in a drill, is that you are compressing the tube at only 3 points: where the chuck jaws touch the ferrule. In truth, you will not exactly shrink the tube, but rather "deform" it, making 3 points (where the jaws pushed in) pinch in to grab the male.

Other options:

Find a wooden clothespin. At the end of the jaws are the 2 wooden bumps that hold your clothes on the line. Inside of that there usually is a concave area on each jaw. If that rounded concave area makes an arc that just about fits the circumference of your ferrule, then you can put the female ferrule in the pin between the 2 concave spots. Softly pinch the jaws together in a vice. Check often for fit, go slow and lightly. Rotate the female as it is held inside the pin to help spread the "pinching" action all the way around the female. This allows you to compress the tube almost all the way around, instead of just deforming it into a slight triangle, as happens if you use a chuck. The soft wood of the clothespin is a blessing, as it minimizes the chance of crushing the female. I repeat, go slow and softly, check often.

Or: Make a ferrule puller, a piece of hardwood that has had different-sized holes drilled through the longitudinal centerline (for example, 11/64, 12/64, 13/64, 14/64, etc), then split the piece of wood longitudinally with a bandsaw. Attach the 2 pieces with bolts and wingnuts. Now you can select the right-sized hole to put your female ferrule in, put it together and squeeze, either with the wingnuts or in a vice. This is nice because you minimize the chance of compressing the tube too far.

Either way, the thing you have to learn by feel is "how far is too far?" If you compress the tube too far, or unevenly, or deform it in a chuck, you will play heck getting it round again, and fitting well. Given the real possibility of permanently messing up your ferrule, you can always consider the low-impact option of putting a little parafin on the male, although it may not be as "permanent" of a "fix."

Good luck!

Lee