How to drill larger holes?

At 1.5" in diameter in 1/4 mild steel you really don't want more than 50-70 RPMs unless you have flood coolant.
In addition you will want to have a hole larger than the central web between the cutting edges of the final sized drill. This central web only displaces material so the cutting edge can remove it. Once the web is dull, it does not mater how sharp the cutting edge is.
 
I have used hole saws to cut more than 100 2" diameter holes in 3/16" steel plate. I have cut 2.5" diameter holes in 1/2" steel plate with a hole saw. I pre-drill the pilot holes and use a HSS arbor for a guide. If possible to modify the punch , I will use a larger diameter arbor to increase rigidity. I save the cutouts for heavy duty washers.

It does require some torque to do this effectively though. My mill drill will develop 100 lb-ft. of torque at 95 rpm.
 
One other method is a trepanning tool. You can get an adjustable one. It has to be used in a mill or lathe, though. Nice smooth holes. Very weird tool shape.

If you go with hole saws get a good arbor!

Annular cutters rock: smooth, accurate holes, right where you wanted them. Overlapping is ok... expensive, but if you need a bunch of holes ;-)

Sent from my SM-G892A using Tapatalk
 
I use hole saws in the lathe and drill press.
They screech but do work.
Here I'm removing the centre from a cross slide dial

cross-slide-4.jpg
 
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