Music wire question

[Jim Svitko]

The 3/32 wire that has 4-40 threads on one end is soft material.  Is this wire too soft to use as pin material to connect a clevis or ball link to the control horn?

[Perry Rose]

I use it exclusively and I haven't had any problems with it. I run a tap down the ball links first and measure the depth of the hole so I don't bottom the rod out in the hole. I use steel clevises and put a bit of thread locker, medium or less, on the threads to absorb vibration. I use 4-40 threaded rod for the bell crank to flap horn so I can put a clevis on the flap end and screw it into the ball link. Up to 65 ounce planes.

[Jim Svitko]

About the 4-40 threaded rod from bell crank to flap horn:  do you stiffen it in any manner?  I know it is a rather short length but it could still buckle a bit.

I don't remember why I bought this wire some time ago.  Probably because the hobby shop was out of the regular music wire and this looked to be a substitute.  But, I did not consider how soft it was. I suppose the wire had to be soft to form the threads on one end by rolling.

I have some concerns about using it.  As I mentioned, I was wondering about cutting off sections of it to use as the pin to connect a clevis or ball link to the horn.  This wire might not be any harder than the brass tube I use to make horn bushings.  When used as a pin, I was wondering if it would wear quickly due to being so soft, even if lubed on assembly.

I am not too concerned about the threaded end.  The threads should be good enough if I wanted to thread that end into a clevis or ball link.

[Bob Reeves]

Hi Jim,

I use the rods you are talking about but only on 35 size airplanes, not real sure I would trust it on a 60 size stunt ship. On my big airplanes I use Tom Morris carbon push rods with his inserts. Our controls are really put to the test in Oklahoma and Texas winds.

[john e. holliday]

If you shop around you may find carbon tubes to slide over the wire.   But I use a larger carbon tube with just enough wire to go into the tube a couple of inches.   Put a short L bend on end of wire going into the tube with a hole drilled in the tube to receive it.   Small piece of hardwood to hold it in place and glued with CA.   Don't forget to wrap the end of the carbon to keep it from splitting.

[Tim Wescott]

Hey Jim:

After reading your question and the replies, I'm thinking that I don't understand what you mean by "using it as a pin".  Do you have a picture you can post that explains it?

I think all of us are (or were) assuming you meant to use it as the rod between two ball links as, for instance, between a bellcrank and a flap horn.

(my take on what I thought your question was is that for the bellcrank to horn I'd rather use music wire, with threaded brass ends soldered on, and for the flap to elevator rod I'd rather use CF with 4-40 bolts at the ends.  That's worked well for me).

[Perry Rose]

I don't stiffen the rod.

[Steve Helmick]

Some people have used 4-40 socket head machine screws as inserts at the ends of CF tubes, after grinding the heads down to be a loose slip fit. Don't forget to rough up the inside of the CF tube, use real JB Weld (not the quick JB Weld), AND either wrap the end of the CF tube OR
epoxy a slip-fit aluminum tube over the end 3/4" or so...to prevent splitting, as The Doctor suggested.  Steve

[Tim Wescott]

Some people have used 4-40 socket head machine screws as inserts at the ends of CF tubes, after grinding the heads down to be a loose slip fit. Don't forget to rough up the inside of the CF tube, use real JB Weld (not the quick JB Weld), AND either wrap the end of the CF tube OR
epoxy a slip-fit aluminum tube over the end 3/4" or so...to prevent splitting, as The Doctor suggested.  Steve

I use arrow shafts which usually have a big enough OD that I can make an aluminum plug to go into the tube (lots of gluing area), with a screw threaded into the plug.  Regular old epoxy has worked fine for me.  Using a bit of Al tube over the end for split prevention is probably good, although I haven't had problems, even on planes that I've crashed regularly.

[Bill Johnson]

I was in my LHS looking at control system parts. Next to the $35, titanium / CF tube set-up was a simple CF tube with 4-40 All-Thread. Grabbing a piece of 4-40 All-Thread and wandering around, they also has carbon tubes next to the K&S tubing. The 4-40 slides perfectly into a 5mm OD / 3MM ID tube. 2 pieces of 48" CF tube and a 12" 4-40 rod was about $10 out the door.

It seems like the 5mm/4-40 control rod should be plenty strong enough for anything up to, say, a plane with a .45 engine. I haven't done any testing yet, though.

[Jim Svitko]

Hey Jim:

After reading your question and the replies, I'm thinking that I don't understand what you mean by "using it as a pin".  Do you have a picture you can post that explains it?

I think all of us are (or were) assuming you meant to use it as the rod between two ball links as, for instance, between a bellcrank and a flap horn.

(my take on what I thought your question was is that for the bellcrank to horn I'd rather use music wire, with threaded brass ends soldered on, and for the flap to elevator rod I'd rather use CF with 4-40 bolts at the ends.  That's worked well for me).

What I mean is a small section of this wire, about 3/4 inch long or so, one end bent to an "L" shape, the other end going thru the clevis and horn to connect the clevis to the horn.  This could be either flap horn or elevator horn.  The other end of the wire would have some retainer on it, such as a wheel collar.  In this case, the wire is used as a connecting pin, for lack of a better term.

Also, it could be used as a pushrod between flap and elevator.  The threaded end would have a clevis, the other end simply bent to go thru the flap horn.

My concern is that with this wire being rather soft, it would wear quickly in the horn bushing when used as a small, separate pin or if simply bent and going thru the horn bushing.

[Dan McEntee]

   Just want to point this out: The  push rod material you see at the hobby shop that is threaded on one end IS NOT music wire!!! YOU CAN NOT RUN A DIE DOWN A LENGTH OF MUSIC WIRE TO CUT THREADS ON IT! If you notice on the push rod material that is threaded 4-40, the threads are LARGER diameter than the diameter of the rod! How do they do that?? The use a special device that "rolls" the threads into the rod and that raises the material. It does not "cut" threads like you may be used to seeing or perceive. I have used the longer threaded end push rod stuff on .35 and 40 size planes but always use a fair lead half way back to the stab to prevent flexing. Simple but effective and on some models looks cleaner than a black carbon fiber push rod.
   Type at you later,
    Dan McEntee

[Jim Svitko]

   Just want to point this out: The  push rod material you see at the hobby shop that is threaded on one end IS NOT music wire!!! YOU CAN NOT RUN A DIE DOWN A LENGTH OF MUSIC WIRE TO CUT THREADS ON IT! If you notice on the push rod material that is threaded 4-40, the threads are LARGER diameter than the diameter of the rod! How do they do that?? The use a special device that "rolls" the threads into the rod and that raises the material. It does not "cut" threads like you may be used to seeing or perceive. I have used the longer threaded end push rod stuff on .35 and 40 size planes but always use a fair lead half way back to the stab to prevent flexing. Simple but effective and on some models looks cleaner than a black carbon fiber push rod.
   Type at you later,
    Dan McEntee

Yes, I am aware of what you said.  The 3/32 wire that is threaded about an inch long on one end has rolled threads.  So, that threaded end is, of course, a bit larger in diameter.  I do not know what the material is but could not think of any other name but music wire.

[Tim Wescott]

Hey Jim:

I think I'm still not entirely envisioning what you're doing, but I think I know enough.

I would recommend that you use good quality ball joints throughout, thereby side-stepping the whole issue.  I use Hanger 9 ball joints (wait, didn't I just say good quality?  Oh well -- I use 'em anyway).  Use them anywhere there's a pivot, and your question becomes moot.

Some recommend (and I have done) using a brass bushing on the horn to provide more bearing area and so that you have dissimilar metals moving against each other.  I couldn't say how well this lasts, because I was just learning how to fly stunt at the time -- the ground kept jumping up at my airplanes, so they didn't last long.

[john e. holliday]

Sounds like he has a clevis missing the pin that goes through the control horn.  I would never use a clevis on a bell crank.  Also is the clevis soldered in place?    I my self if that is the case would use music wire with the L bend and wrap/fix it to the push rod.   

[Phil Krankowski]

Those push rods are a common "mild" steel, as in not much carbon in them, and not hardenable. 

The ones I have are galvanized, coated with zinc, and care should be taken if you wish to heat them as zinc fumes are bad to breathe (all soldering fumes are bad to breath).  The zinc does mean the wire takes solder very easily.

On RC planes the control loads are actually less than with CL planes so the soft wire push rods are generally fine.  This is mostly due to slower, larger maneuvers than what we ask of CL planes.

Phil