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How to cutting tube angles while minimizing scrap

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Joined
Jan 3, 2014
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Location
Wisconsin
Seems lately there's just not many "how to's" or educational posts on scratch building so figured I'd post something fresh.

Goal: Cut accurate fuselage tube pieces with the correct angles while minimizing waste and eliminating excess labor.

Like any task in life there's a million ways to accomplish it. This is my way and I find it to be really fast and extremely accurate.

A typical fuselage has longerons with various small pieces connecting them together. These short small pieces are either the same size as the longerons or smaller. These pieces are cut, shapped or coped to make welding strong and efficient. A strong and efficient joint is the result of accurate cuts with minimal gaps to fill by the welder.

Before the pieces can be profiled to shape they must first be cut from long stock. Straight cuts are fine but there's waste involved. But there's a larger issue with straight cuts, it's harder to shape and time consuming. You'll find the profiling later on is much much easier if you cut the pieces with angles on them.

You probably heard stories of guys in the old days using files to shape tubing. Well, that can be easy or difficult depending on how much material needs to be removed. Ideally, once the piece is cut with the proper angle and almost exactly the right length, the little bit of shaping left is incredibly small. In other words, the hard part isn't shaping the ends, it's in cutting the pieces.

Here we go.

Let's look at a cross section of a 3/4" longeron and a 5/8" tube running perpendicular. In the photo below you can see a straight cut won't work. We need some overlap to account for the material used to "cope" the joint tighter. (Minimize gap).
20170126_190031.jpg
Clearly you can see how we need the end to be about a 1/4" longer, as indicated by my dial caliper.

No problem. With the fuselage table set and the jig block in place we have everything we need in that jig to help up figure that out. The longerons on this particular section of the fuselage are 3/4". I need to make marks a 1/4" in so I just throw some 1/2" material in the jig where the longerons would go. Look at the photo below.
20170126_190235.jpg

These 1/2" strips are just a depth gauge. You'll see why shortly.

Buy the cheapest tape measures possible. Cheap tape measures have crappy flexible steel so they are perfect for patterns. About $3 each in the barging bins. The smaller 12' - 16' tapes have the ideal width. Too wide is a problem.
20170126_190102.jpg

Pull out the tape and detach it.
20170126_190205.jpg

Now you have this.
20170126_190252.jpg

In the photo below the circled area is the piece we want to cut a pattern for.
20170126_190418.jpg

Slide a tape section UNDER the 1/2" strips. Mark with pencil. Both ends.
20170126_190459.jpg

Cut with a snips. Here it shows what the pattern looks like with the 1/2" gauges removed. Label the table and the pattern. Move on to the next one.
20170126_190523.jpg

As you can guess it's real easy to lay the pattern on a tube, mark, and cut.
20170126_190544.jpg

Close up of how it wraps around the tube.
20170126_190327.jpg

So, this is my way, my idea and my method. I started out with files so I learned quickly that if the angles were cut accurate with absolutely minimal excess material the coping or shaping of the ends become so easy a kid can do it.....even with a file. I know, because I was a kid when I first did this.

Good luck.

Scrapper
 
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