I've seen a fair number of robots with actuators made from attaching a 16mm ball screw to the shaft of a hacked drill motor. I would like to try this out, but I don't know how to securely attach the ball screw to the gearbox shaft. I *think* I have heard of these being made by boring out the ball screw, and tapping the bore so it "screws on" to the drill gearbox shaft. In this sort of set-up, what prevents the attachment between the gearbox shaft and ball screw from unscrewing itself? Is high-strength loctite used?

I was rather more technical than that. AKA, drill/bore out the threaded rod/ballscrew then bash it onto the shaft with a hammer. It never moved EVER.

But yes being more elegant about it just tapping the ballscrew for the same thread then pinning it to the shaft would work just as well.
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Also, the reduction on an actuator like this is (gearbox gear ratio x threads/inch), right?

You need pitch which will tell you how much travel you will get from one turn on the ball screw, not threads per inch. Another ass-backwards facet of the imperial system because most every calculation is done from pitch. (okay ill ease up with the imperial bashing haha, but hey this is a metric forum )

Thankfully pitch is the reciprocal of TPI so you can convert them easily enough.

Once you know that you can work out what speed your lifter or whatever you are making will move at, taking into account the output rpm of a drill which will be either 550rpm or 900rpm.

If you start dealing with acme threads with more than one start then it all gets a bit more tricky but that's the basics of it anyway. Welcome to the forum also ^^;
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