Apr 2, 2016
In order to understand all of this, I’ll give you some background on my journey to creating this new (tongue in cheek) design. I was working on a new revolutionary commercial aircraft at the time. It was to be 30% lighter than its predecessor and 20% “minimum” more fuel efficient. To achieve this, the use of titanium was paramount, and we had to drill this titanium with 100 year old technology but maintain a -0.002 to a +0.001 tolerance on all holes drilled! My particular part of this process required that I drill 12 holes, at one point through 2 ½ inches of aluminum, stainless steel, and titanium. This was quite an interesting challenge in itself never mind the tolerances which were required. Even if (and I emphasize IF) you could get a nice pretty spiral chip rolling out, it most certainly spelled disaster because the spiral would not stay in the drill flute, but eventually cross over to the adjacent flute causing the drill to wobble, either elongating the hole or blowing it out completely. Then it would have to be oversized to the next available size with reamers, which if you didn’t pay very close attention to, you would pull the steel chips into the aluminum and titanium thus blowing the hole through these metals out again. I forgot to mention 20 to 30 bits to drill one 2 ½” deep 3/8” hole. Yes!! It is nerve racking to say the least!!
Since titanium was a relatively new metal to commercial aircraft, and I was growing weary of these issues, I did some research. Interestingly enough titanium is roughly 80% aluminum, depending on the alloy. This set me to thinking why can’t we drill it like aluminum? (just my back-woods mindset I guess). I then started to inspect my drill tips as I would change them out. I soon realized either the tips were breaking (chipping) the cutting tip or folding it up and over. I’m guessing this was due to either the hardness of the particular bit or maybe speed and heat related. One thing is for sure; if you had a bit get hot enough to glow red, the titanium was as hard as carbide afterwards, then you “got” to ream it out and put in a bushing. One day while I was working on one of these “carbide-ed” hole, I was using a chisel and thought: “there’s the solution!” The perfect chisel tip is 45 degrees for effectiveness and longevity. With this thought I looked at my drill bits, they have a 110 to 125 degree tip. For mild steel and mild aluminum this is close enough to cut nice spiral chips, but we don’t want spirals, small chips would be preferred. HUM?? Small chips + chisel point, how to achieve this?? I started to “hand” regrind my drill bits with a Dotco grinder. Every time my manager caught me grinding bits he would rip me a new one, but soon I perfected the angle. With the right drill speed and pressure I would get holes within tolerance 99% of the time.
I turned my design in to the company for a process improvement suggestion (and cash reward), the response I received in return was that it would cost too much to implement the change and therefore was rejected. Fast forward; I got laid off and was out for 4 years, when I was recalled I went back to work right where I had left off. I checked out new drills, as I was preparing to “modify” them I realized that they had, in fact, implemented my design! So the buggers had stolen my idea!! Hence this article, the world needs to know this little trick.
The modification process:
- Hold the bit straight up and down, focus on the leading edge of the flute, and follow it to the tip. You will notice the 110 to 125 degree point, this is what we need to change.
- Holding your drill bit grinder. (I have a fine stone on a grinder for drill bits only) with the grinder off, lay the flute face at the tip on the side of the grinder wheel see picture.
- Move the bottom of the drill bit to the right, a little less than half way to vertical. Mark that position in your mind, get good references
- Remove the bit from the grinder wheel, turn on the grinder.
- Grind about 1/8 to ¼ of the tip along the vertical axis of the bit, any more will cause trouble with holding the hole tolerances.
If done right, this will drill ½ inch thick steel plate in less time it takes to drill a 3/8 plate with the old method. Plus makes the nicest small chips and cleanest hole you have ever seen.
I modified a 1/2" bit and took it to 1/4" plate steel, with no pilot hole drilled through in less than 45 seconds