Tom Morris Take apart hardware warning

[Paul Walker]

I have been using the Tom Morris take apart hardware for over 10 years. Until this last plane, the hardware has been bullet proof. Through a miracle, the plane I built for the World Champs in Bulgaria had a failure of the upper inboard joint, yet didn’t crash. Once discovered and replaced, the plane now flies fine. (The story of how I discovered this is more like the three stooges than an experienced pilot. Suffice to say that the plane was flown more than a dozen times with this bad joint. It makes my hair stand just thinking about it).

So what happened?  As with everything, when in a hurry bad things happen. Tom has started gluing one of the cross fuselage fittings in the tube. When it arrived, I noticed a lack of glue squeezing out of the fitting to tube joint. I rationalized that he carefully cleaned it before shipping. I was in a hurry and used it as it was. After the failure, I examined one of the remaining tubes in my inventory that he had glued. I set about to disassemble this joint to see how well it was assembled. To my surprise, it came apart with minimal effort. With a spiral cut, I was able to remove the tube from the fitting BY HAND.  Concerned, I found a similar joint from a crashed plane that I had assembled and did exactly the same procedure to it to test its strength. I found that I had to grind off the tube 100% of the way and no amount of prying with pliers etc. could remove the tube. That was a good joint, and what I expected.

With this information, I contacted Tom about the problem. He stated that he would no longer make any of the glue joints in future sets. If you have a set that is pre glued, and NOT in an assembled plane, call Tom and ask him for another set that is not glued. He will supply that at no cost. If it IS in a plane that you have been flying, be very careful if you have experienced any “weirdness” in its flight characteristics. The problem I have is that I have replaced the upper joint, however the lower inboard joint is STILL a Tom Morris assembled joint. It has held and flown in some bad winds. Based on this, I suspect it is just fine, but plan on replacing it as soon as airplane #2 is in the air (which have 100% PW assembled joints).

How do I assemble them?  Once the tube is cut to length, I use a Dremel grinding stone to rough up the ID of the tube where the aluminum fitting is in contact. Next, I use a Dremel “dangerous disc” to grind in small troughs (round fitting cut with round cutting wheel, see attachment) in at least 20 locations on the OD of the fitting where it attaches to the aluminum tube. Then, the remaining surface of the fitting is roughed up (again, only on the fitting where it attaches to the tube). Then, prior to assembly, the parts are soaked in a 99% alcohol bath to remove any contaminants. While soaking, a batch of JB weld is mixed up. The parts are removed from the bath and dried. Once dry, JB weld is applied to the ID of the tube and the OD of the fitting. The fitting is inserted into the tube and the excess glue on the outside removed, and set aside to cure.

I also noticed on this set that the threads in the male fitting were not tapped deep enough to allow the joint to clamp up properly. Be very careful with this as well. Check and re-check before assembling.

When these joints are assembled correctly, they are strong enough to do the job, and nothing to worry about.

If in doubt, please call Tom.

[John Lindberg]

Thanks for the warning, Paul, just purchased a take apart set from Tom, going to check it out! The Impact is coming along! I did make the plane a take-apart, like the plans show (one-piece wing). 

[Doug Moon]

Paul,

I have a set of these.  I was looking them over and thinkin if the each insert (male and female) were a little longer on the end that goes into the tube then a small hole could be drilled through the tube and the insert and set screw or pin could be inserted through it as well as the JB weld. 

Maybe I am over thinking it a bit. 

[Paul Walker]

Drilling a hole in the thin wall tube is the last thing I would do. It makes it subject to fatigue, and a failure would occur sometime unexpectedly in the future. The crack growth rate in a thin wall tube is very fast, thus not allowing any inspection capability...That is if you could actually see the area of the tube by the hole....Which you can't.

The JB weld as described above works just fine.

[PJ Rowland]

With the addition of the "keys" your getting extra security to the joint which is ideal - have you spoken to tom about changing these to be manufactured this way?

I've been playing around with the addition of the smallest amount of chopped carbon fiber flake to add to the JB weld on my take apart hardware.

[Paul Walker]

PJ,
No, I haven't approached Tom about that. Maybe if he sees this he might.

[PJ Rowland]

Its not a difficult mod to make ; Im curious about this "crash" you speak of...

What model did you loose? The last one I recall was the Mustang in 04. 

[John Leidle]

  This is just like Tom, He stands behind his products no question.
  John

[Paul Walker]

The "crash" was the electric plane headed to the 08 World Champs. It intersected a bird  two days before I was leaving.

There's an interesting story with that as we captured the team gold just a week later.