I sometimes have trouble aligning my drill bit with the center of a tube. Especially on larger tubes where you can miss by 1/16" and not realize it until you've already drilled the hole. Enter the Round Tube Center finder! This tool is for use on a drillpress.
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Step 1: Tools and Materials
- Tape measure
- Drill and bits (I used a drill press and this tool is intended for use on a drill press)
- Tread tap (although you could just as easily use a cotter pin or rivet)
- Solid aluminum rod that will fit your drill press chuck (I used ½")
- Sheet metal (I used 3/32" sheet aluminum)
- Screw, cotter pin or rivet
Step 2: Start at the Y
While the central point of this unit is the rod that clamps into the drillpress chuck, the better place to start is with the "Y" shaped alignment device itself. Mainly because most people will make one or more attempts before getting one that is perfectly aligned.
I had a scrap of 3/32" sheet aluminum with a #6 hole in it, so that was my starting point. This project might go easier if you started with a layout and drilled the hole last.
Here's the idea. Designate a pivot point, and from that point extend two arms down at a 45° angle forming a 90° angle. Also at a 45° angle, relative to the two arms, position one arm straight up to be the indicator flag. this results in an inverted "Y" shape. The alignment arms can be any width you want, but the length from the tips to the center of the indicator flag should be the same on both sides. Drill a pivot hole such that the distance from the hole to each tip of the arms is also equal.
The indicator flag should be the same width as the rod you used. It's also a good idea to paint the indicator flag a bright color to make it easier to see. I used red.
Step 3: Make the Guide Rod
Ironically, having a center-finder would be ideal at this point.
In the end of the guide rod, drill a hole of appropriate size for your pivot screw (or cotter pin or rivet). If you are using a screw, thread the hole.
Mark a line perpendicular to the hole and cut a slot down that line. It should be wide enough and deep enough to accept the sheet metal "Y" from the previous step. A single pass from a hacksaw will not likely be wide enough. I took two passes with my bandsaw and still had to do a little sanding with the belt sander (and some filing) to make a smooth path for the Y indicator.
Step 4: Assemble the Unit and Test
Once you have the slot wide enough to accept the "Y" indicator, connect the two together.
From this point, the only thing left to do is chuck it up in the drill press and align the stock to the device. If the flag is poking out on one side or the other, the tube is not centered under the chuck. Once centered, install a drill bit and drill a hole. If the hole is through the center of the tube, you got it right!