Friday, May 11, 2007

The Final Cut

Here is an image of grinding the web on a drill bit that is left after grinding the wings. The tricky part about this is that the wing that is pointing down is dangerously close to the grinding wheel and the slightest encounter will send you back to step 1. Not a big deal, but it's better avoided. I avoid hitting it by keeping the wing that is pointing up a little past vertical (towards the grinding wheel). By keeping the wing that I can easily see close to the grinding wheel, I can generally keep the other one in the clear. The other key to grinding the web is that as I proceed to push the bit into the wheel, I let it come off of the block a bit. This happens quite naturally because as I push into the wheel, the amount of metal that is cut gets greater and the bit wants to slide to the side. You can see the result of this in the photo below (how about that new camera!).

There is a small learning curve to grinding drill bits, luckily we all have a myriad of dull beat up twist bits to practice on. Once I started grinding bits, I was amazed at how much steel the actually have! I learned using bits that weren't high speed steel, just my old junkers. Even though they lose their temper, they actually work fine, just not for as long. By the way, I've read that quenching high speed steel is not recommended, when it gets hot slow down and let it air cool.

Here is the resulting hole that the bit made. Notice the shavings. And below is the exit hole. I didn't use any backing, just drilled right through. For me, this grind solved one of the most vexing drilling problems in chairmaking, all of those holes that need to start at an angle and come through a curved piece (near impossible to back). I know that many excellent makers prefer auger bits and simply stop when the screw comes through and come back from the other side. It obviously works fine for them. This is a personal preference. I will post some tips for drilling clean holes soon.

No comments: