"N. Thornton" wrote in message
om...
Harry Bloomfield wrote in message
o.uk...

I fully understand the idea that a steeper cutting pitch and thinner
steel would lead to faster wear, but there is more to it. From using
the traditional bits I know that they get very hot in use - very hot.

Too fast rotation speed will do this, as will too light a feed rate.

So hot in fact that they can even be melted when drilling steel.

Then you are using twist drills that are not up to the job.
The only drill I have ever seen that has burnt out, was one that drilled
into a mains cable.

What can happen with a quality drill, is that the tip changes colour and the
cutting edge gets rounded. The result is a hot drill. The cause is too fast
rotation or lack of push to keep the drill drilling. Or both.

The
result is that one has to go slow to avoid blunting the thing while
drilling just ONE hole. Yes I've done it. Even on wood I've had bits
that have got smoking hot and lost their cutting ability.

Wrong drill angles, that's all that was wrong.
Drill angle depends on the material to be drilled. Change the material and
you change the drill angles to those that work best.

The thing with these sharper bits is they need far less pressure while
drilling, and work well at the lowest speed on the drill. Much less
force equals less chance of breaking on exit. Much less force plus
much less speed equals far less heating, and heat is the prime enemy
of steel drill bits, causing them to blunt very much quicker.

In my time in the engineering industry, I have had to drill some very, very
hard steel. It has been my experience that if the twist drill is up to the
hardness of the metal and has been correctly ground, with the correct angles
for the metal it is asked to drill and the speed is kept down to prevent any
heat generated, then you will produce a hole of the correct size and more
importantly, the correct shape. Not all holes made by the way you describe
are anywhere near round.

So although the cutting edge is thinner, because of the heat factor I
would expect them to still outlast traditional bits. I have yet to
see, I've only been using them a few months, but so far they've
performed very well.

I look forward to your posts about 'How can I remove the cutting tip of a
twist drill that broke on a job I was doing;.

Last holes I drilled were in steel, and the bit behaved impressively,
much better than I had expected. The progress was fast, even at
minimum drill speed, break through was much smoother, the hole was
left neat, and there was no sign of heating or loss of edge on the
bit. So far so good...

Must have been the softest of steels that you come across then.

Dave