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Any tips for fitting pushrod ends into torque tubes?

SabreFlyr

Well Known Member
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Working on my aileron torque tubes. With reasonable effort, I was able to get my torque tube collars to fit into my torque tubes. However, it took 90 minutes effort to fit one of the pushrod ends into the other end of one of the torque tubes, that is AFTER fully deburring the rivet holes. The remaining three are giving me much more trouble. Mostly, I've been using Scotch-brite on both the inside of the torque tube and the outside of the pushrod end. On the inside of the tubes, I have sometimes been using Scotch-brite wrapped around a dowel, otherwise just a finger. I can't get any of these remaining pushrod ends more than 1/8" into the tubes so far. It seems it's going to take a couple full days of work to get this done.

Any other suggestions?
 
measurements

Ray,
Have you by chance used a micrometer to measure the inside diameter of the tube versus the outside diameter of the fitting? And are you having difficulty getting the parts to fit before or after priming the inside of the tubes?
 
Measure

Yep. Measure carefully. Which is the issue. Tube out of round? Fix that first.
The rod end can be chucked in the bench drill and polished down with some fine emery.
It's important they fit. On the other hand, lots of builders get them in and weld them.
 
Ray,
Have you by chance used a micrometer to measure the inside diameter of the tube versus the outside diameter of the fitting? And are you having difficulty getting the parts to fit before or after priming the inside of the tubes?

Yep. Measure carefully. Which is the issue. Tube out of round? Fix that first.
The rod end can be chucked in the bench drill and polished down with some fine emery.
It's important they fit. On the other hand, lots of builders get them in and weld them.

Haven't primed yet. That has me more worried.

Not a machinist but have a micrometer. Not sure how to use it to get an inside measurement. I'll see what I can see with my calipers.

I DO have a slight suspicion of out of round.
 
Ray,
Your thinking is correct. Micrometers do not measure inside diameters. However, there are a couple of ways to use a micrometer along with other tools to get an inside diameter.
The most common is to use a tool called a telescoping gage. Google it for an image. You will need to be instructed in their use because there is user technique involved in obtaining an accurate measurement. Its easy but the technique must be followed.

Alternatively and less accurate is to measure the tube outside diameter with the mic and measure the tube wall thickness. Do the subtraction to get ID. If using mic for wall thickness, a known dowel against the inside wall curvature would be needed.

As a side note, ovality can be determined by measuring the outside of the thin tube and by confirming the wall thickness is not wildly out of spec with your calipers.

Lastly, measure the end caps to make sure they are cylindrical and not cone shaped. I doubt this since distorting the entry of the tube is fairly easy (giving you the 1/8" entry).

I does not take much interferance to become a PITA. You are looking for a mismatch on the order of 0.002. I don't think ovality is the issue if you have already been tapping this with a rubber mallet. The aluminum tube should easily conform to the circular shape of the end cap.

If you have scrap tube left over from fabrication, it might be worth playing with that and a cap.

Oh yes, if the tube is oval, measure twice at 90 degrees apart and average the diameters for comparison to the end cap diameter.
 
...ovality can be determined by measuring the outside of the thin tube and by confirming the wall thickness is not wildly out of spec with your calipers...

Oh yes, if the tube is oval, measure twice at 90 degrees apart and average the diameters for comparison to the end cap diameter.

That finally came to me late last night (a little mental molasses, I think). Haven't checked yet.
 
I'm not a builder, but the gorilla in me says put the rod ends in the freezer and heat gun on the tube. I would think it would drop right in.
 
On my 10 I ended up making a fixture and turning them down to be a light press fit. From memory it was about 0.002” I had to remove even after removing the primer from the torque tube and the insert. You’ll be there for days trying to remove that much with a scotch brite by hand.

You could use a screw with a jam nut and chuck that up in a drill press with some emery cloth to reduce the diameter.
 
I used a small cylinder hone from one of the local auto parts stores. Worked well.
 
If we're talking about the powder coated bellcrank to aileron pushrod, I had some fit issues as well. I did remove most, if not all, of the primer inside of the pushrod. I sanded the inside of the tube slightly, but didn't want to remove much of the tube wall. I leaned towards removing material from the fitting instead because it's pretty beefy. Not too much though. Still wanted a nice snug fit inside the pushrod.
Here's some pics of how I reduced the fitting diameter.
 

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I seem to recall removing the primer on the insides, starting the end fittings, using a piece of carpet on the concrete floor, and a couple "pile driving" moves. I know that's how I did the big pushrod ends. Can't remember the small bellcrank-to-aileron pushrods, but if I did I probably put an old rod end on first.

They were snug for sure, but no splits.
 
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