This is a fairly long post. I worked on the details over a week and didn't think it would make any sense until you could follow the whole path to a working process. At the end of this I'm making ferrules.
Based on the
International Spec. for Ferrules and NACA Report #3 the ferrules need to be a close fit to the wire loop (0.002" clearance). At the same time the tighter the fit the higher the load the ferrule can resist because it is mostly friction which prevents the hooked over end of the wire from pulling out. They had some suggestions for how to improve the strength, which we'll cover when I make the actual wires.
A perfect ferrule would be a snug fitting oval. Some ferrules were made with 8 turns and some with 10 turns. To increase the friction I'll use 10 turns.
The obvious way to make the ferrules would be to wind the wire around an oval mandrel. Fortunately for me
John Gaertner tried it before I did and saved me the embarrassment of missing what I hadn't thought about. The spring back of the wire means, each loop springs back in such a way, and with so much force that you will never get the wound ferrule off the mandrel. The way John makes these, as recommended in many books, is to wind a round spring of the correct diameter and then he flattens it in a hardened steel die. The books claim you can flatten them in a vise. I can only assume the authors never actually tried it.
John sells ferrules if you would like to avoid a lot of work.
Jim Wilson made the ferrules for his Travelair by winding them around 2 wires which solved the problem of getting them off the mandrel but he still had to adjust each loop to make a straight path for the wire.
For a couple years I've been saying there has to be a way to wind oval loops that are all lined up without any secondary operations to flatten or straighten them, so that was my mission.
I found that when you make a 180 degree bend you have to over-bend about 20 degrees to allow for the spring back. As you can see from the drawing below that means an oval mandrel would be in the way of bending far enough to allow the 2 sides to spring back to be parallel as you as you make all the bends. To get the 2 bends spaced to allow for the wire you need a mandrel to hold the first bend away from the wire as you make the second bend or you will just end up with a round loop, not an oval loop, which happened by accident several times. To create a mandrel I borrowed from Jim Smith's method. I wound around a wire and used a second loose piece of wire as a pin to create the spacing. It will make sense farther down.
To start with I borrowed Rich Wilbur's
Porter Spring Winder. I really need to trade him something so I can keep this useful tool. It allowed me to learn about winding the wire.
It's rather simple. You thread the wire through the holding disks. Bend an end to lock into the handle. Tighten the wire into the handle and the handle onto the mandrel of the size needed to the inside diameter you want.
There is a lever to adjust the pitch of the spring, in this case zero pitch so it's clear of the winding. Then just wind the number of turns you need. The loads on the wire help hold the mandrel from bending as you wind. It really works great.
The Dremel Tool with a cut-off disk works for cutting such hard wire.
There was just no way to use the winder to make make the oval ferrules. I needed a surface to wind against to use my 2 wire method. It's a Righty-Tighty world so I'm winding clockwise. This would work fine in either direction but my brain would explode winding counter-clockwise.
The wire perpendicular to the block is the wire (mandrel) I'll wind the ferrule around. I found that this mandrel wire slowly gets bent up and needs to be replaced after several ferrules. I cut it about 6" long so I could switch ends when the first is bent up and then make a new one the next time. The spool of wire feeds in from the right and touches the bottom of the mandrel.
I started out trying to use the handle from the winder. The first bend is made around the mandrel with a tab turned out to be held by the handle.
The bend is moved slightly to the left to leave room for the spacer pin to be inserted so that it is touching the block face.
With the mandrel (on right) and pin held in the handle (on left, touching the face of the block) the handle was then rotated to make the first 180 degree bend. The pin is then moved to the left of the mandrel, touching the block and the next 180 degree bend made. This process gets repeated until the desired number of turns are wound. I found that it helped to grind off the tip of the pin after a few ferrules to assure the diameter didn't get reduced. I also put a very slight chamfer on the end so it would slid in better. It has to be less than half the wire diameter.
Unfortunately because of the angle the wire comes into the block the turns are widely space,
You can see the angle the wire enters is the angle forming the widely spaced pitch.
The good new is we are making oval loops.
The next change was to cut away the block to the wire feed hole to create a slot for the wire. The slot was at first cut with a slight angle on the bottom and the wire easily slipped out.
A little work with a small rat tail file provided a ledge which held the wire very well.
The process starts the same with the only difference being the wire is in the slot so it can be wound tightly to the preceding wind.
This time the winds are tight. This is cool. We have something which looks like a ferrule. The problem at this point is that by applying the winding force from the starting end there is always a twist. I had assumed you could control this by where you stop each turn. It never worked, there was always a twist. It has to do with how the force is transmitted through each bend to the one you are making. The turns will need to be made by gripping the turn right behind the bend you're making.
To grip the coils, my idea was to make a handle with a hole the shape of the coil so it would just ride on the existing loops.
I started with a 10" piece of 1" x 1/4" bar stock. Any reason for a trip to the hardware store is always a good plan. The oval is about 5/16" by 1/4". Without a mill there is no way for me to drill 2 holes 1/4" in diameter with the centers only 1/16" apart. The first hole wipes out the center for the second hole. As an alternative I drilled a 1/8" hole and then 1/8" from it's center I drilled a 1/4" hole with a center drill.
I clamped a block to help keep the bar from sliding as the hole progressed.
The result is sort of a key hole shape.
To finish shaping the hole, I used 3/16" and 1/4" chain saw files. The nice thing about them is they are sold in 1/32" increments and they are the same diameter for the full length. They are also a very fine cutting file so they leave a smooth finish unlike a much coarser and tapered rat tail file.
To control the filing I inked the small hole. That way I could see how deep I had cut the hole. I could also see that I was going perpendicular to the face, if the edges were parallel. I switched between the 2 files, using the 3/16" file to deepen the hole and then the 1/4" increase the radius. Just slow and easy until the ferrule just fit snugly.
Here are the various pieces of the tool. I'm using the base from the spring winder. I'll have all my parts made before Rich gets his winder back. It would be easy enough to make a base from angle iron and clamp it to the work bench. Hmmm, I think I have some scrap angle iron that would work.
Clearly the winding bar only works once you have some coils started so how do those happen? The process starts like with the handle.
The bend that got inserted into the handle just gets another bend to wrap it around the bar. That way the bar can be used like the handle for the first few winds. This is only needed at the very start. Once ferrules are being wound and cut off you just always leave a few winds to grip with the bar and keep on winding.
The first turn isn't real tight but after that it's easy to keep them tight.
Enough turns to use the hole in the bar.
Pull the pin out and slide the mandrel back to remove the bar.
A notch is cut in the first bend to weaken it so the starting wire can be broken off. The cut-off wheel is narrower than the wire but you have to be careful not to nick the adjoining turns.
To clean up the cut end I dulled a Stanley Knife blade, after cutting myself, and pressed it between the coils with a pair of pliers. The blade protects the coil behind it while you put an angle end on the wire.
Before removing the blade do a light de-burr with a file.
A drop of light, #10, oil (sewing machine oil) helps the pin slide in and out as the ferule grows.
I thought I could control this by where the bar stops, but it doesn't grip the coils that tightly. As a result I start with a few turns sticking out past the bar so I can put a pointer on the free end of the ferrule. After all if that end always stops at the same angle while making the bends then all the loops are aligned for a good tight fit.
The first pointer I made was from another piece of scrap with the same oval hole. It worked but like the bar the hole was a little loose and you had to hold it snug to get a consistent stopping position. You also had to re-position it after each bend since it only points one way. It also lined up with the bar so it got in the way.
I was trying to figure out a way to grip the coil better for the pointer when I remembered my wife's nice tap handle, from her tool and die maker days. It clamps on perfectly because of the vee block shaped jaws. A light twist of the handle snugs it well.
Because it sets horizontal its easy to see if it's level after each bend.
Move the pin to the left, make a bend, repeat. It's easy to make 2" of loops all lined up for a nice fit.
I figured out, after mis-cutting several ferrules, that I can't count to ten. I made a simple gauge with notches punched at each wire (like a thread pitch gauge) so you can see you're marking the right wire to cut.
I stop winding with the cut end on top so I can cut the coil with the sparks going down. Trim and de-burr the end of the ferrule and the start end of the next ferrule and you're done.
One nice ten turn Ferrule with all the loops aligned for a good fit. Right now I'm making 8 per hour so I'll be at this for a while. I need 68 of these for the fuselage. I also found it takes 7" of wire per ferrule, which means it takes 40 feet of wire just to make the ferrules not counting scrap and wire for making mandrels and pins. I hope this same process, with new tools, will work for the much heavier 0.125" wire.
It's fun to have an idea and see it work out so well despite all the details changing along the way.
Here are the tools I used:
Dremel Tool with cut-off wheel
Length Gauge and Permanent Marker
Pliers
Hammer to Push blade between coils
Stanley Knife Blade
Oil
Winder Bar
Awl for tightening Tap Handle
Needle Nose Pliers for Start Bend
Channel Lock Pliers for pushing blade between coils
Winder Tap handle
I made a video of winding a ferrule. It runs just under 6 minutes. Unfortunately that's to long to upload to the blog so I split it into 2 videos. The first covers winding the 10 - 1/2 loops. The second covers cutting and finishing the ferrule.
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