Step Down drill bit

This is a follow up of a previous post about deep drilling and especially step drilling for roughing out a conical bore :
http://www.homemadetools.net/forum/%...out-bore-67249

In this article, I explained that the best thing to do was to first establish a guiding hole with the smallest diameter.
I used to do that with a long and thin 4mm diameter gun drill.
Unfortunately, maybe I was too much in a hurry, but I ended up breaking this gun drill.

So here is how I do it now :
-1) I use a 1/4" gundrill, as deep as I can, but not all the way through.

- 2) Here comes the new tool : I use this "stepping down" drill bit extension, in order to establish, after the 6.35 hole, a well centered 4mm diameter second level guiding hole.

-3) If not long enough, I finish the hole with a 4mm D-bit, which is much more easy to drive at this depth thanks to the 6.35 initial bore in the first part of the hole.

-4) I use the second setp down head to get an intermediate 5mm diameter step, between the 4 and 6.35.

It is basically a brass extension shank, silver brazed on the shank of a standard good quality metal drill bit.
Once brazed, I put the drill bit in the lathe chuck, and turn down the brass to 6.35 mm. Doing so, I am sure there is a perfect concentricity.
Then I tap the end of the brass to M5, in order to screw an extension rod, which is threaded M5 at the end.

http://www.labellenote.fr/file/homem...drill_0001.jpg

http://www.labellenote.fr/file/homem...drill_0002.jpg

Thanks Christophe Mineau! We've added your Extended Drill Bit to our Drilling and Drill Presses category,
as well as to your builder page: Christophe Mineau's Homemade Tools. Your receipt:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="http://www.homemadetools.net/homemade-extended-drill-bit-3"> <img src="/uploads/213357/homemade-extended-drill-bit-3.jpeg"/> </a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="http://www.homemadetools.net/homemade-extended-drill-bit-3">Extended Drill Bit</a> <span> by <a href="http://www.homemadetools.net/builder/Christophe+Mineau">Christophe Mineau</a></span> </div> <div class="tags">tags: <a href='http://www.homemadetools.net/tag/drill-bit'>drill bit</a> </div> </div> </div> </div>

Nice, thanks

Ralph