custom drill bit diameter

[LCHIEN]

thanks, tom, that's the kind of hint I was looking for.

[LCHIEN]

Well, I modded my bit today.
(First I tried Larry's suggestion about forcing the .710 pipe into a smaller hole - 11/16 or .680" but .030" dia. diff. was just too hard. Couldn't get it started and couldn't drive it in with a mallet.)
I took an Irwin 3/4" Spade bit bonus bit from the $8 pack of 5+1.
I marked one side with a dot from my centerpunch so I could keep track of which side I was working on.
I marked the edge with a sharpie and used Tom's suggestion about scratching it with the caliper. .016 is not a lot. Turned out to be marginally useful.

I used my stationary belt sander with 80 grit belt and a stop for keeping a side vertical, I placed the edge against the belt.

I took what I though to be about 0.016 off one side, it was hard keeping the edge aligned with the belt.
Then I flipped it over and took off some from the other side. I had the sides a bit out of parallel.
I drilled a hole and it vibrated like crazy - so much that the laser guide battery door popped open and dumped the batteries on my table.
I took a dial indicator to check the run out and one side was about .020 out more than the other. I took most of that side off on the sander trying to make it parallel with the smaller side and it ran quite smoothly after that. I calipered it about .715 at the leading part of the flute and .705 at the top of the flute.
The holes measured about .715-.720. So it not perfect straight up and down the bit but it tracks smoothly and cuts a hole about .005 over size.
The pipes go in with no force required but have no wiggle either. The pipe is plugged with a wood dowel and a couple even made a popping noise when I pulled them out of the hole quickly.


The sander took off .005 pretty quickly, it was easy to overdo it. It was also tricky to grind it parallel to where I needed it. If I had to do it again, I'd make a jig to hold it maybe. The best thing proved to be checking the runout with the dial caliper. Regardless of how the bit was originally centered, and whether you grond it evenly or not, you can make it good with the dial indicator. The centerpunched dot proved to be quite helpful in identifying the side i needed to work on.

After I was done I took one of those vibrating engraver pencils and marked the bit 0.720 and 23/32 right below where it was originally marked 3/4.

Overall, it was a success, fits just like it was custom fit.