With a milling machine, so often the finish on the part is dependant upon the ability of the operator to feed smoothly. Early on when I bought my milling machine (used) I came up with this simple 'adapter' which allows me to use a battery drill as a power feed.
The adapter has had hours of use and was super simple and cheap to build.
The photos are all staged and the embedded YouTube clip probably gives the best description and demonstration of it.
Step 1: Adapter Machining and Stock Selection.
Firstly you will need a piece of pipe whose internal diameter approximately matches the external diameter of the milling machines lead screw.
If it is a little loose this is not a problem.
Secondly; slip the pipe over the lead screw and use a marker to show the high and low points on the jaw so you can see where to machine.
Thirdly; mill slots in the pipe to a little deeper than the depth of the jaws, where there is a high point on the coupling you will need to mill out leaving protrusions on the pipe that engage with the jaws on the coupling.
This doesn't need to be super precise and could probably be done with a drill and grinder with a cutting disc.
Step 2: Coupling to the Drill
Most often the lead screw diameter will be bigger than the chuck capacity.
In my design I pressed a socket from a 1/4" drive set into the other end of the pipe. You do not of course need a fancy press for this step, a simple bench vice can even be used to press the socket in.
You will of course be left with a 1/4" 'square hole', use an off the shelf hex to square adapter to push into this and mount into your drill chuck.
That's all folks, Its as simple as that.
Since using this it has made my life many times easier and I'd imagine you too may find it useful if you have a milling machine without a power feed.
Of course it would be possible to lathe an appropriately sized piece of round stock as the main body rather than using a piece of pipe and a socket but now you have the idea the choice is over to you.
Feel free to have a look at my other Instructables and YouTube videos too, if you like this you may well enjoy some of my others.