How to mark and drill holes in tubing that
are 180 degrees apart
How? Go back to your school days!
How to use a
protractor for marking and drilling holes
This tip came about when a fellow ham radio operator asked me how to drill holes in the round boom of antennas if you don't have a drill press so that they would be exactly 180 degrees apart. After much searching of my limited mental faculties, this is what I came up with. This should work in most cases where you want to drill holes that are exactly 180 degrees apart on the boom of a Yagi antenna you are building, or for that matter, with any project that requires holes 180 degrees apart in round tubing. If you don't have a drill press or drill guide..... read on.......
Now since tubing is usually a perfect 360 degree circle when viewed from the end, you want to be able to find a way to mark both sides of it for the Yagi antenna element holes we are using in this example that you want to drill. You know that for the antenna to perform as designed these markings must be exactly 180 degrees apart so the antenna elements will all be in the same plane with each other.
A very simple method to mark your tubing using a
protractor, (either version shown above), is to simply lay the protractor
on a flat surface, then set your tubing on top of it while lining up
the exact outer top and bottom surface of the tubing
with the line drawn from the 90 degree mark at the top of the protractor
to the bottom where all of the angles intersect...this forms a 90 degree
angle relative to the base of the protractor.
Instructions: Refer to Figure 1.
Using Figure 1 above in this example, you simply use a fine tip felt marker and mark the outer end edge of the tubing on the top and the bottom of it. See the small black squares in Figure 1 above. You now have one end marked. Do the same for the other end.
Important Hint! Since we want to mark BOTH ends exactly in the same plane, you will need to have some method of preventing the tubing from turning from its present position after you mark the first end. This method will be left up to you but you could use a heavy weight or someone to hold it to keep it from turning while you place the protractor on the other end, etc. This is the very tricky part of marking both ends exactly in the same plane. If after you mark one end AND the tubing accidentally turns, the other marks you make will be out of plane with the other end! The tubing MUST NOT TURN when marking the second end.
If you are successful then these marks on each end should
be exactly in the same plane and you should be able to draw a straight
line between them!
You know have a line on both sides of the tubing down the center of it from end to end on the tubing that is 180 degrees apart from each side where you can mark the holes to be drilled for the antenna elements! Use a small center punch in the center of your element position marks for starting the drill bit. Drill one side at a time and don't attempt to drill both at once..this is the key to drilling the holes without using a drill press or drill guide in tubing that yields you holes that are 180 degrees apart!
This tip will save you a lot of money if you were prepared to buy a drill press or drill guide for your tubing drilling project, but if you can't figure out what all this means and are in the market for either one, then check out those listed below from a good source, Amazon.com!