Regarding pilot holes...
Although this mainly applies to much larger drills, and is common knowledge among the many working machinists who are forum members, many of those new to the trade could use some extra information.
Pickup a drill and point it toward your face. You will notice that in the middle there is a section shaped like a chisel. This center area of the bit is the web. If you use a drill bit to drill a shallow hole you will see that the center of the hole looks a little rougher than the outer surface. This is because that chisel section cuts with a rotary chisel action that works just like it sounds.
Pick up several drills and look at the ends. You will find that the thickness of the web changes along with the drill size. Small drill= small web. Pushing the web through the material takes much of the available spindle torque and with very large drills that is considerable. With small holes most machines have more than enough torque to push the bit through and you just need to use a combination center drill or a spotting drill to get the hole on location. Just keep in mind that what will work in one machine may not work in a smaller machine (or by hand).
In theory, if you drill a pilot hole equal to the larger drill's web thickness, then the larger drill needs less torque to turn (& cut). In actual shop conditions there are other factors in play such as spindle rigidity, material type, set up conditions, drill grind angles, etc. On a large radial drill I can push a 4" drill through material with only a 3/4" pilot hole and get no chatter. But, only up close to the column. When the hole is 6 to 8ft away from the column I then get chatter and have to adjust feed, speed rake angle or all of those. I also may need to "Thin" the web but that is a whole different skill.
Start with the theory and figure out what works for you in each situation.
Some who are new to the trade do not take the time to learn how to sharpen drill bits or how to properly drill holes. With a decent drill press a good machinist can drill holes on size and accurately located. Take the time to learn more about drilling and it will serve you well.
Walter A.