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Pinched End Support Rods

tjyak50

Well Known Member
Anyone seen a thread or tips / best practices for making this type of pinched end support rod?



I have to hang an oil cooler off the motor mount (non Vans, but you guys are the only ones actually doing actual stuff). The inboard side is mounted directly to the engine mount, but the outboard edge needs a couple of support rods to triangulate it back to the mount for support in roll and pitch.

Figured you just take a stainless 1/2" tube, smash the end, drill a hole, round and dress up the end and voila?
* image courtesy of another thread.
 

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I do not recommend this approach.

I gave up on such exhaust system support rods years ago as they always broke off at the pinched end. I changed to 3/8” solid aluminum rod, one end drilled for the the Adel clamp bolt, the other end with a grove(s) cut around the circumference to better hold the hose under the hose clamp.

But for your application I would not do this at all as you have no need for the rubber hose to account for engine movement. I suspect Adel clamps supporting 3/4”x3/4” aluminum angle is a better way to hang your oil cooler if for whatever reason you can’t just bolt it to the firewall.

Carl
 
I have used .125-3/4"x3/4" aluminum angle to support oil coolers in the past, never any issues.

If you do the squashed tubing approach, I'd suggest upsizing the tubing to 4130 .049x5/8". Squash the end in a vise - note, use something inside the vise jaws to radius the pinch.
 
I have used .125-3/4"x3/4" aluminum angle to support oil coolers in the past, never any issues.

If you do the squashed tubing approach, I'd suggest upsizing the tubing to 4130 .049x5/8". Squash the end in a vise - note, use something inside the vise jaws to radius the pinch.

Ahh thats smart, thanks.
Like a piece of thinner AL sheet in the jaws to smooth the pinch area.
 
I made this oil cooler support brace by pounding some 0.058" wall 4130 tube over the round edge of an anvil, annealing the ends with a torch, and painting:

20110621_brace.jpg


(note: fasteners shown in photo are temporary)
 
I made this oil cooler support brace by pounding some 0.058" wall 4130 tube over the round edge of an anvil, annealing the ends with a torch, and painting:

20110621_brace.jpg


(note: fasteners shown in photo are temporary)

Yep that's exactly what I need to do more or less. Thank you.

What I should probably find is some Titanium tube...
But I have a chunk of good Stainless I was going to use.
 
Been there - done that

I made this oil cooler support brace by pounding some 0.058" wall 4130 tube over the round edge of an anvil, annealing the ends with a torch, and painting:

20110621_brace.jpg


(note: fasteners shown in photo are temporary)

I originally braced my oil cooler exactly the same way, except I made mine from a solid steel rod with flat stock welded on each end. For the first 3 annual inspections, I found the brace fractured at the flat connected on the oil cooler end. I remade the brace a bit heavier twice trying to solve the problem before finally giving up and reinforcing the cooler another way by basically stiffening the aft baffle with some aluminum angle. No further problems.
 
Here is mine. 1/4" solid rod - heated and used kinetic shaper to reform the thermally softened rod. (2015)

Brace to head.jpg
 
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pinched end support rods

Anyone seen a thread or tips / best practices for making this type of pinched end support rod?

Use something like this in the vice jaws to give a rounded transition from round tube to flat end.

IMG_0171.jpg

The jaw guards are so old I don't even remember where I got the material. But is nothing more than aluminum angle stock (window frame grade) with a rounded over edge, about 3/16" radius. Make something like this out of aluminum (aircraft grade or not) and round over the edge with a router bit. Or use hard oak or maple blocks. Point is, this produces a gradual transition to the flat part.

All of my stainless steel Vetterman exhaust hangars are made this way, as is my 4130 steel oil cooler diagonal brace. The 4130 steel was heated cherry red and allowed to cool in air after forming. None of my exhaust hangar ends or oil cooler brace has cracked in just over 1000 hours service.

Simply smashing the ends in the sharp jaws of a vice (as in the OP's photo) will clause a stress point in the material, that may lead to a cracked/broken part right at the round to flat transition.

FYI: yea, I know that is a piece of aluminum tubing in the photo.....only think I could find in my scrap bin. :) Sorry no photo of my oil cooler brace, but it looks like the one mburch posted in his photo....same material, same thickness, same configuration except the cylinder head end mounts to the side baffle through a 1/16" x 3/4 AL angle , above the head, using a 3/16 bolt. Seems to work. NO cracks in the aluminum stack up on the back right corner of the baffles.
 
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Back when I was building, stories about cracked #4 baffles by the oil cooler and cracked stainless steel tube exhaust hangers were legion.

I had a bunch of 3/8 OD x (somethingorother) wall thickness 4130 chrome moly tubing lying around from other projects. From decades of non-aviation experience with the stuff, I had learned to be suspicious of any 300 series stainless steel that had to live in a place subject to heat and cyclical vibration, so I happily substituted the 4130 tubing for exhaust hangers plus an oil cooler brace.

Like others, I heated it cherry red first, but then simply pounded it flat with a hammer. Worth noting is that it would've been impossible to flatten without heating first- the edges would split. Drilled holes, done.

I duplicated the Vetterman supplied exhaust hangers, then set about making an oil cooler brace, shown in the photo below (note: photo was taken 2 years before first flight so many other details are irrelevant). I painted the oil cooler brace but left the exhaust hangers bare. I was warned that corrosion would be a problem, but so far it's been a non-issue.

1200 hours and 10 years later, no cracks or failures in any of the tubes, or the #4 baffle. 4130 is good stuff.
 

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Very helpful, thank you.

Mine is a 540 (angle valve) with the cooler going behind #5 and it’s kinda suspended in mid air in and around the motor mount arms which all go in different directions and angles.

The final solution hasn’t quite “come to me” yet. But getting closer.
 
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Swaging tool

Here is what I use for forming a swaged end on tubing to prevent stress fractures at the flattened area:
 

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I just reinforced the baffle corner really well with aluminum. 850 hours and no cracks.

Larry
 
I see the issue with the stainless tube I had, its not seamless and the seam exposes itself. Switching to seamless 4130 as suggested.

Or maybe even rod ends and threaded rod.

This one task is roadblocking a million other tasks and I'm boresight locked-out of other things that need done.
 
If you do the squashed tubing approach, I'd suggest upsizing the tubing to 4130 .049x5/8". Squash the end in a vise - note, use something inside the vise jaws to radius the pinch.

Thanks Sam for the vice jaw pinch tool pictures, exactly what I was trying to describe!
 
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Heating the tips to cherry red with regular seamless steel tubing did the trick.
Once hot I could use my Knipex to work down the ends and finish on the anvil.
Turned out great. Strong, fairly light and easy to do.
 
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