[TowerTalk] Cutting tubing
jimlux at earthlink.net
Fri Dec 28 15:35:38 EST 2007
>From: "Richard (Rick) Karlquist" <richard at karlquist.com>
>Sent: Dec 28, 2007 12:28 PM
>To: N7KA at comcast.net
>Cc: TowerTalk <towertalk at contesting.com>
>Subject: Re: [TowerTalk] Cutting tubing
>This paper technique is also useful if you have to drill
>two holes at 180 degrees apart. Simply mark two lines
>on the paper spaced apart by pi/2 times the diameter.
>For a 2 inch mast, this would be 1.571 inches.
An even easier scheme that doesn't require calculation or measurement... Since it's hard to accurately measure (and make marks on paper) to thousandths of an inch, and it requires knowing the diameter of the pipe to that accuracy and that it's actually circular and not ovaled..
To cross check, you'd put three marks, one at 0, one at pi/2*diameter and one at pi*diameter, and when you wrap, you make sure the outside marks line up. However, this is where you can be clever and save yourself the measuring:
Make evenly spaced tick marks (a printed tape measure works, as long as the ticks are even) and wrap that around, lining up one hole with one tick mark. You then visually estimate the center between two ticks (one on each side) on the other side of the tube. If the center mark is numbered 0 and all the other marks are numbered 1,2,3,4 in both directions, you'd center between two like numbers.
Hard to describe, but if you try it with a piece of lined paper, you'll see how it works, and it easily lets you get within 1 mm of the true opposite.
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