Apr 30, 2018, 05:41 AM
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 :
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.
The Following 4 Users Say Thank You to Christophe Mineau For This Useful Post:
blkadder (Apr 30, 2018),
Jon (Apr 30, 2018),
PJs (May 2, 2018),
Seedtick (Apr 30, 2018)
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:
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