I was working on my enclosure project and had to drill five holes into 30, 3" x 3" x 3/16" gussets. The five holes were 5/16" in diameters. I had just purchased a new 115 piece cobalt drill bit set, but found the bits were not drilling as efficient as they should.
Originally I was peck drilling with a 5/16" drill bit but it was getting a lot of bit wandering and it was requiring several pounds of force to drill the holes.
I used a 3/16" drill bit to drill pilot holes. I created a set of divots .01" deep with a feed rate 1 IPM at 3000 RPM.
The pilot bit (3/16") then drilled through the 3/16" material in one single pass at 25 IPM and 3000 RPM.
The final size was completed with 5/16" bit at 2500 RPM and at a 25 IPM feed rate.
While these procedures make a drastic improvement on hole quality, I had a feeling that bits were not as sharp as they should be, so I broke down and purchased the Drill Doctor 750x shown below.
To put the sharpener through its paces, I took a couple 3/16" and 5/16" brad point bits like the one shown below and decided to reshape them before messing with my $300 set.
I ground the tip off of the bit and did a first pass on the bit and created the profile shown below. I set the 750x to 135 degrees.
Next I used the 750x's split drill feature and started profiling the back side of the flutes. As you can this bit is so bad that it is slightly off center and the side shown below did not get completely ground.
I repeated the sharpening and spiting process a second time. You need to repeat the alignment process the second time as well to set the grind depth. The result was the profile shown below. The split bit reduces the tendency for the bit to wander as it starts the hole. In addition it causes the drill bit to drill quicker and to reduce the pressure needed to complete the hole.
The image below shows the new profile (Left) and the profile on one of my cobalt bits Right). The new bit cuts much better and requires less force.
How Does it Work?
The bits I purchase were from a 100 piece set that cost $24. One of those sets where you get about 4-10 bits of each size. The were horrible and I was tossing them in the trash by the hand full. Now I can use them in my KRmc01 mill. I cut all 30 of my gussets on the one 3/16" and one 5/16" bits without having to resharpen them.
KRmc01 making gusset