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To cut! ..... or not to cut?

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bobthebuilder

Well-Known Member
Joined
Feb 16, 2012
Messages
183
Location
Johannesburg, South Africa
Hi Guys,

I am doubting my understanding of the outer sleeve tube splicing method given in AC43 4.96
The outer sleeve i'm reffering to is the one used at the undercarriage point.
I chose to splice the 12ft longeron there.



Should the two tubes butt up against each other inside the sleeve?
Maybe I'm being a bit frugal, but to save weight, can I cut the pieces of tube away that are illustrated in the picture, or are they supposed to be welded before the sleeve is fitted?

AC43 4.96 shows that 1.5 x the diameter should be left withing the tube.
Am I reading this out of context?

What are your thoughts?
 
From memory of a repair I made on tubing structure a couple years ago, I believe you are correct that the inner section of the smaller tube can be removed, as your photo shows. This allows a section of damaged tubing to be repaired on an existing frame.

Tom H
 
Bobthebuilder...what tool are you using to cope the tubing? Very nice job!
 
Ok yea I got that part! I was talking about all of the other copes to the longerons etc...should have been more clear!
 
Thank you kind sir!

I started out using a Dremel tool with a 5/8 sanding drum. It didn't take long to figure out this would take years to notch all of the tubing. Some very neat notches can be achieved with patience though.

Next .... I bought the "Ol Joint jigger" from ACS.
I found that the teeth on the hole saws were too course and ripped the thin walled tubing up with ugly results.

I figured there must be a faster and neater way, so I built this:



I actually bought a cheap belt sander for the motor, drive and switch and built my own notcher. I have the drawings, or 3D models rather if anyone would like to use them to build one.

The principal is based on clamping the tube in a lathe chuck. You can rotate the tube in the chuck to any angle you like, and then swing the tube, which is clamped into the chuck, to the desired angle relative to the belt sander.

I must warn you though, it took me around three months to design and build it. One could have notched all of the tubing with a pair of tin snips in one or two evenings.

Personally, I wanted things to be as accurate as possible, with as smaller gap between the tubes as possible to fill when welding. I figure, the bigger the gap, the more filler rod required, which adds weight.

This is my first build, so I do lack the experience that other builders here have. Any comments and suggestions are welcome.
 
I'm one of those thinkers too my friend! The 2-3 months is irrelevant if you come out with a tool that produces consistant results. I've been in the fab/machine shop business for over 10 years now and love to see tools that are made job specific.

And I think more important than the weight of the "weld" added due to the gaps from imperfect copes, a tight and secure fit will allow for less heat when welding which yields a true(er) assembly after everything cools off. In the TIG welding world, the smaller HAZ (heat affected zone) while maintaining the proper size weld is key. Many of these guys weld these fuselages with oxy/acet setups so the welds come out larger than they need to be but if it works it works. With your copes and a good TIG machine, your fuselage will be a masterpiece!
 
Ah! Somebody else isn't happy with the ye'ol joint jigger. I tried the belt sander with the variable size rollers and that worked much better until I took the torch to it and those razor sharp edges disappeared in a flash! Now I just cut with the aviation snips. I imagine using TIG it would work but with Oxy-Acetylene you are wasting you time making pretty coping. With Oxy-Fuel I am actually happy with a gap between pieces.

What I really want it a stand nibbler. The Piper factory used nibblers to cope the tubing using pattern tubes. Very effective and fast. The problem is the cheapest stand nibbler I found was built in 1938 and cost $4,800.00 and weighed over a 1000 lbs.

Anyways, anyone want a ye'ol joint jigger for cheap? ;-)
 
I found that the easiest method for cutting tubing is with a miter saw with a metal cutting abrasive blade in it. I shaped a grinding wheel for the radius of the tubing and fish mouthed the cut made with the miter saw. The cuts at the ends must be in alignment with each other. To keep them straight, I would use a marker and lay the tubing in a piece of angle iron and used it as a straight edge. Mark a line down the length of the tube to help keep the fish mouth cut outs in alignment. The other big help was to make a stand for the grinder that I could roll around so it is close to the job. With a little practice, parts can be made very quickly. As for the tube with the sleeve, the inner tube should be butted. It's designed to take landing loads. Two wall thicknesses won't crush under load. I hope this helps. Pat Mc
 
Hi Pat,

I think the best way to cope tubing, is to find the way that works best for you. All of us have different tooling at our disposal, so we try to use what we have.

To be honest, I have no idea how to shape a grinding wheel. It sounds like a relatively easy way to get the job done, and fast too.
 
Well I have no idea how you guys are using tin snips on this 5/8 .035 tubing! I'm no weenie and there is no way my snips are going to cut this stuff especially anything resembling a cope. ???
 
There is a grinding wheel facing tool that can be used to shape the stone. As for cope in tubing using tin snips, go to EAA website for building tips. Earl Luce has a segment on that very subject that will help. Patmc
 
Racegunz, its actually very easy to cut with aviation snips. It does take a little practice but once you get good at it it is very fast. I see why many like John Monnett, Steve Witman and the Tinman use them. They are cheap, fast and very inexpensive compared to the following...

This is a video from Piper Aircraft showing how they cope tubing back in 1943;

The Construction of a Light Aircraft (1943): http://youtu.be/Q6q1VKsTeKQ

The link below is like what was used by Piper and is the hands down best way to cope tube, period. Its at the bottom of the page and is called the TB400 and will run you about $2,500;

http://www.heckind.net/Trace-A-Punch.htm

The new tool you can use thick plastic cut out as the pattern so you shape the plastic to fit and then wrap it around the tube and zing! Perfect cut! No thin edges to burn off either.
 
I use tin snips up to 3/4" x .035, which gets the fish mouth started, but then the grinding wheel does most of the actual shaping. It is difficult, but can be done...
 
I also use tin snips to rough cut acute angles, but 95% of my work is done with a 6 inch bench sanding disk to get the angle, then a grinding wheel for 3/4 and 5/8 inch tubes. Occasionally I use an angle grinder mounted flapper sanding disk with the edge rounded off for other tube diameters.

I also tried the cheap Harbor Freight joint jigger. It took about 30 seconds to realize that was not the way to go.

And I also use an abrasive cutoff wheel in my miter saw, but I had to make a spark deflector for it. Man, does it ever put out the sparks, but it is quick and easy.

O'Bill
 
Okay so I went and fishmouthed some 5/8 .035 this morning, it is do-able but my snips are not quality enough to last doing it this way, and compared to the grinding wheel too slow. I suppose if I was going to cope tubing for money I'd spend more money and time but I'm not, so moving on to building planes, instead of building equipment.
 
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