Wednesday, May 9, 2007

Bit Grinding

Lots of pictures today (a great way to show off my new camera!) The photo above shows the way that I use my wheel dresser to make a shape on the side of my grinder that will correspond to the wing of the brad point. I alway make sure that the corner is lower than the flat of the wheel that I use for general grinding. The sharper the corner, the deeper the wings. I did some measuring of the angles that I use today because honestly I've never bothered. Experimentation is the key and the numbers that I use can vary depending on the performance and intended use of the bit. I measured the angle of a bit that I use all the time and found it to be about 35 degrees (see below). The steeper the angle, the more aggressive the bit, until at some point, the edge is too thin to be effective. I always use high speed steel because it doesn't lose its temper until it is red hot, a little bluing is fine.

Below is the jig setup that I use while grinding. My measurement for this bit is about 2 degrees off of the axis of the wheel. By adjusting the angle that I clamp the block to the rest, I can adjust the length of the center point. A greater angle makes a shorter point. As you can see, it is the side of the wheel that actually forms the center point.

Below is the first cut that I take. I make sure that the existing cutting edge is horizontal and proceed to grind. After a moment, I judge whether the bit is far enough over to form the proper point.

I switch back and forth between the two sides in an effort to let the bit cool and to keep the wings even.

Below is the bit with the wings ground. All that remains is to remove the web (you can see it in the center of the bit) that has been left by the grinding. I'll post the web grinding and tips for using soon.


Lefky said...

What grit grinding wheel do you use?

Also, what size bit do you use for drilling the leg holes?


Peter Galbert said...

I use my finer aluminum oxide grinding wheel for the bits, I don't know the grit offhand but most grinders come with two wheels. I use a 5/8" bit for boring my leg holes, keeping in mind that they will be reamed later.