How to handle drill wandering

A former coworker showed me this method more years ago than I care to mention. I drill straight, small diameter deep holes by chucking the drill very short and peck drill using very small pecks (maybe 1/32" or less) and high RPMs. The trick is to not let chips build up in the flutes of the drill, chips in the flutes put side pressure on the drill causing it to drift sideways. The high RPMs keep the chip size small. Extend the drill as necessary by small amounts (maybe 1/4") Use an acid brush with oil on it to lubricate and clean chips out of the drill on EVERY peck. Using an acid brush is the official method, I use my finger tip dipped in oil. (DON'T DRILL YOUR FINGER!)

I will spot the hole with a center drill or use very light pressure on my small drill and let it idle on the surface of the work.

I have drilled some very small dia. holes as deep as 4" in steel.

Richard
 
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Everything mentioned, especially the use of screw length dill bits is exactly what I’ve found. The other observation is watching the swarf and often on new bits I see uneven curls. I picked up a Starrett drill bit gauge in a local CL score and it has been instrumental in checking and making sure the angles are correct and the point of the drill is truly centered. It has turned into one of my most used gauges.
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My tip is to use a 3/16" spot drill and drill deep enough to leave at least a 1/8" deep counterbore. Then drill and ream as usual, the accurate counterbore will act as a guide bush for the reamer.
Here is a video demonstrating the method, please turn on subtitles. -
 
Drill undersize . Use a 3 flute carbide end mill to true the hole and ream to size . Depending on size , grind up a broken carbide end mill to a single point boring bar to true the hole before reaming . Drills are going to walk with that L over D .
 
Beat me to it...reading slow...

Drilling thick even with a perfect drill can result in the drilled hole not being straight.

It can actually bend the bit.

So, drill a small hole, in this case, 1/8 or 9/32 just to get through the material

Now you can use 2 or 4 flute end mill to finish the hole.

The end mill will cut a straight hole.

If you need thicker another trick is broken drill bit...

From the shank end of the bit sharpen the bit with maybe 1/2 a turn of flutes or less.

There are spade drills for this, the full shaft less likely to bend.

Sent from my SM-G781V using Tapatalk
 
Here is an explanation how a 1/4" drill cutting 0.252" dimeter can wander 1/32" until it is 3/4" deep. The theory is in the first 4 minutes.
Does this look possible?
 
Just a bit from left field, the problem of unequal cutting edges on two flutes has been addressed long ago by resorting to only one flute. The thing is called a gun drill, and seems to be a cross between a boring bar and a drill. It can't deflect because it gets it's support from the hole it fits, and it has a huge flute that goes all the way along it. They are known for maintaining a straight hole even though they are many times longer than the diameter

I have one of these buried somewhere among my stuff to be re-discovered some day, and I admit I have never used it. For a good while, I did not even know what it was for!

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