Drill Press Center Finder

This is a simple and inexpensive center finder for drilling a hole at the top of the arc on a circular object, whether a tube or a dowel or a disc. Some commercial units use a pointer and some use a level bubble. This one uses a torpedo level.

Tools

1. Speed square
2. Table saw
3. A torpedo level

Materials

1. A piece of firring strip or wider
2. A finish nail
3. Masking tape

I cut a piece of wood with parallel sides to about 4 1/2 inches in length. I used a caliper to verify the edges are parallel. The wood could be wider than a firring strip.

Notice the markings on the wood. They are centered between the ends of the piece. They look a bit like a chicken foot.

I laid my table saw blade over to 45 degrees. I lowered the blade so the top of the teeth comes to the top of the 45 degree lines where they intersect. (First photo)

I clamped an extension to the miter gauge and clamped the body of the center finder to it to keep my fingers out of the way of the blade. (Second photo)

I aligned the setup so the 45 degree cuts would come just inside the lines. (Third photo)

I want a shallow kerf on the vertical line to provide a channel for a finish nail. I could add a spring to add a little pressure that keeps the finish nail in the channel without the need for my fingers to do it.

The saw in the photo is one I made to replace a keyhole saw I had kept for many years, but the plastic handle broke. I did an Instructable about this one.

For steel tubing I am putting some masking tape on the area where the drilling center will be so I can easily see the mark when ready to drill. (First photo.)

See the second photo. I used a piece of masking tape to hold the finish nail in place. In part that is because I was trying to juggle the torpedo level,* the body of the center finder, the finish nail, and operate the camera on my iPhone all at the same time with only two hands. The intent is to hold the body on the tube while holding the torpedo level on the wooden body. The level could be held in place with tape or rubber bands. With the finish nail in place, let the wooden body slide over the curve on the tube until the bubble in the level is well-centered between the lines on the level's vial. Then press the point of the finish nail into the masking tape or use a pen to mark the location of the nail's point.

This Instructable assumes the level has been tested and is accurate. Use a center punch to locate the hole so the bit does not skate. It is assumed the piece to be drilled is fastened in place so it does not roll during drilling. I would begin with a small drill to make a centering cone to hold the larger bit for the desired hole in place for an accurately placed hole.

*The mount on the level for the bubble vial is a little odd because I borrowed the original for an Instructable on making a long bed level. I improvised a mount for the 45 degree vial and moved it to the location for the longer original vial.