Dave Plowman (News) wrote:
In article ,
Dave wrote:
You can certainly get 300mm long non HSS twist drills - I have a set
(5,8,10mm) bought off a market stall. I'd guess HSS might break too
easily at this sort of length.

To help prevent this happening, just pull the drill back out of the hole
to let the saw dust out. It is the saw dust that grips the twist drill
that lets the torque to go up to the twist drill's breaking point. Just
drill for a maximum of 2 inches at a time and then pull out.

I was thinking more of bending type breaking than twisting with a very
long smallish HSS.

I see what you mean. This is a common problem with a pistol type drill
handle. The way to get round this, if you are right handed. (If you are
left handed, just change hands and follow this with your left hand doing
the pushing.)...

In your normal way, start the hole off. Now stop drilling and change
hands. Hold the pistol grip in your left hand with only your first
finger and thumb, using your finger to press the start switch, while you
press at the back of the body of the drill with only the palm of your
hand, directly behind and in line with the chuck to start cutting the
hole. Do not use your fingers at all while pushing. This puts all the
pressure along the line of the twist drill.

It is the act of holding the pistol grip with your full hand grip that
puts a bend in the twist drill, as the pressure is put on the drill
below the axis of the twist drill.

I'm sure that you knew this Dave, but it is surprising how many drills
are snapped by holding and pressing with the handle of the drill.

Dave