Slotting body tubes

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Sooner Boomer

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Just had an idea for cutting slots in body tubes for TTW fins.

I had a couple of years drafting when I was in high school. I learned how to work in pencil and ink media. We had pens with fixed tips, but the less expensive drafting kits had pens with nibs that could adjust the distance between them to draw wider or narrower lines. This is the compass from my set:

compas.jpg

I was thinking this would make a great way to be able to cut variable width slots in body tubes, if only these were knives.

What I came up with is adjustable, but not as easy as turning a thumbscrew. The basses of most hobby knives have a slit cut in them. A #2-56 machine screw will just fit through the slit. I didn't have an appropriate piece of thin metal to use, so I used a different style blade for the center piece.

blade1.jpg

blade2.jpg

blade3.jpg

As you can see, I put the screw through the blade, tightened a nut down on the blade, followed by a second blade (the different type), another blade and nut.

tip2.jpg

tip3.jpg

You can go as close as the two cutting blades together (other blade would be bolted on the outside)., or you can use a combination of blade placement or nuts/washers/shims to get the width of cut you want. BE CAREFUL - THESE BLADES ARE SHARP!
 

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Typically, I make my first cuts by using the alignment guide, and a piece of angle aluminum to ensure a straight cut. I then press the fin I'm going to glue into the cut, and using a mechanical pencil mark the other side of the slot. I then use the angle aluminum again. My slots tend to be a little tight, but a few swipes with an emery board usually tends to remedy any problems. I can also use the removed material to fill gaps if the slot is too wide for some reason. I only apply it to the side that was cut second (the first cuts were aligned properly remember?).
 
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