Ferrules - when did they come about?
 

I guess this is a retro grouch question ;). I have a pair of friction thumb shifters that I realized will not actually take a ferrule -- which confused me at first because I've never seen that happen. Someone at the LBS said that some of the older stuff wasn't designed to take a ferrule, so you just run the regular cable housing directly onto the shifter stop...which acts as it's own ferrule.

Is this true? And when did ferrules first appear on the scene?

I suspect that "friction" is the pertinent word. Index shifting requires compressionless cable housing which is much more particular about being terminated properly.

TB, My '80 Raleigh had housing end caps on it's shifters OEM, not both ends IIRC. It was an easy way to square up the housing to the derailleur. When SIS came out (early 90s?) the end caps became more important and the 9 and 10S Shimano have their own unique design.

Brad

Ferrules are as old as transmission cables. Any design needs to have clean square ends to work effectively. Keep in mind that the first use of cables on bikes was for brakes and a sloppy fitting would have made them spongy.

One of the primary functions is to allow for rotation of something like an adjusting barrel, otherwise a stationary fitting can be made tight fitting to the housing and act as it's own ferrule. Whether or not you need a ferrule depends on the answer to two questions.

1- is rotation of the housing or terminal relative to each other involved?
2- is the terminal properly shaped, and of good enough fit to rigidly support the housing?

If no to the first and yes to the second, a ferrule isn't used. (if yes to the second, it wouldn't fit anyway)

BTW- the above refers to slip on ferrules. Many designs use swaged-on ferrules installed on housings at the factory for the same purpose. The trend has been away from that to lower cost for the OEM, and make after market service easier, but many pre-measured kits still come with swaged ferrules.

I assume it's safe to say that if a ferrule will fit, you should use one -- if it won't, then it (whatever the housing connects to) was probably designed to act as it's own ferrule?

Thanks,

Compressionless housing is necessary for brakes, not index shifting.

Well, the term "compressionless" is misused. Brake housing has to be fairly constant in length but not critically so unless it compresses so much that the brake action is spongy or the lever hits the bars. Properly spiral wound housing works fine.

Shift housing for indexing systems s more properly called "constant length", which it must be to make indexing accurate. Index shift housing has the reinforcing strands nearly parallel with the its length. That keeps the overall length constant as the housing bents with the handlebar rotation or the rear derailleur chainstay-to-derailleur housing section flexes.

You have it backwards, not as to the fact, but the terminology.

Brake housing is made of shallow steel coil spring that lays on itself in a fully compressed mode, while "compressionless" index housing has a high helix angle and depends on a ballistic outer cover to keep the strands from buckling.

The functional issue is the neutral axis as the housing is flexed. Brake housing cannot compress so when curved the neutral axis is in the inner wall with the outer end opening. This means that the center (where the wire runs) lengthens slightly. High helix index housing flexes with the neutral axis in the center so there's no change in the effective length, preserving index trim.

Unfortunately Shimano chose to call index housing compressionless when they introduced it, though a more apt name would have been expansionless, since the low helix housing it replaced is the one that's truly compressionless and suited to the higher load of brake cables.

BTW- a reminder. High helix Index housing is totally unsuited for use on brakes. It depends on the support of the plastic outer cover for strength which will degrade over time with UV and oxidation leading to potential catastrophic failure (burst) in an emergency braking situation.

Low helix (brake) housing has continuous steel on steel support and will function regardless the condition of the cover. It's failure mode is expansion when kinked, which will make brakes spongy, but it won't fail suddenly in an emergency.

Mid-'80s.

Will you please help this novice understand the high and low helix angle thing. Sounds important so I want to understand.

I thought it would be obvious from the context.

The helix angle is the angle of the sloped ramp to the horizontal if it were unwound. Picture a screw in your mind. A fine thread screw makes lots of turns in a short linear distance and has a lpw helix angle. A coarse thread screw advances farther with each turn and has a higher helix angle, and if you've ever seen those twisty masonary nails they turn only a few turns over their length and have a very high helix angle.

Translating that to cable housing, brake housing which is a compressed spring is low helix, while index housing where the strands run lengthwise with a slow twist have a high angle. If they ran lengthwise and didn't twist at all that would be a 90° helix angle.

It isn't the helix angle per se that's an issue, it's whether the strength is derived from direct metal on metal contact, vs linear strands that need to be buttressed by the outer coating to keep from buckling when compressed.

I understand the idea of a helix but when you use the qualifier "high" or "low" there has to be some reference or datum line to measure from. That was my problem in understanding. Is a high helix angle indicating a steep or shallow thread? Kind of depends on where you start counting from or you have to know the official 'standard' nomenclature which I do not know. So I was just trying to get the more precise meaning so my feeble brain can put it all together. Thanks for the explanation.

Just an FYI:
Aztec makes a brake cable housing that uses the "compressionless" type of housing similar to the kind used for indexed shifting. It has kevlar threads wound around the longitudinal strands of the housing then it is has the plastic outersheath like normal housing.

I had purchased some for some folks here in Morocco while I was on a business trip back to the US. I did not reallize until I cut it that it was of this design. I was skeptical and called Aztec to double check to make sure I did not buy shifter housing in the wrong packaging...other than assuring me it was indeed brake housing, they were not really helpful or knowledgable about the product except saying it works and there is no problem with it exploding under compression due to the kevlar strands between the metal and the plastic sheath. Sending it back to them would have been a huge PITA, so I installed it on the bikes I was working on. It has been working as good as normal brake housing.

-j

Re-read this sentence from my earlier post (#11) about high and low helix angles.

The helix angle is the angle of the sloped ramp to the horizontal if it were unwound.

I thought it was clear enough, but if not, lets goback to the example of a screw thread. Unwind one turn and you'll get a right a right triangle. The base is the circumference of the screw, the height the amount the screw would advance in one turn, and the sloping thread is the hypotenuse. The helix angle is the angle between the base and the hypotenuse, or the slope of the helix. A high angle is like a steep hill, an low angle is a shallow hill.

Yes, that's possible, though in my opinion of no added benefit, and possibly dangerous. As I said longitudinal or high helix steel strands, need to be buttressed to keep from buckling or bursting. The normal plastic cover is adequate for gear housing, and if it were reliably buttressed by a structural material such as carbon fiber or Kevlar then it would also be OK for brakes.

But we should also consider the mode of failure. Low helix steel coils are relatively failsafe. If kinked or damaged the housing may cause spongy braking, but that's the worst of it. If the Kevlar supporting winds of high helix housing get weakened by kinking there'll be no early warning before a total failure of the housing, probably during an emergency stop. This isn't a high risk if housings are cared for, but IMO introduces an extra risk, however low, which isn't offset by any benefit.

Wmodavis, to try to add to FB's description try this.

If you strip open some brake housing you'll find that there is small, flat steel banding that is wound tight like a closed exansion spring. With that style when you bend it into a curve the outer spiral wraps will open a little but the spiral steel wrapping maintains contact on the inside of the curve. You can see this if you have a small but long exapansion spring that is totally collapsed and coil bound when at rest and bend it into a curve. The windings open up on the outside but stay in tight contact on the inside. This would be the low helix angle. Or another way to describe it would be tight wound or coil bound winding.

Now if you strip open some shifter housing instead of this spiral wrapping you'll find a bunch of pretty much lengthwise wires that twist around the inner core only about 1/5 to 2 turns over a foot of length foot. I'm a bit foggy on the number because I've never stripped any back far enough to count the turns but from what I've seen it seems about right. This would be a high helix angle of only a few degrees inclination from axial.

From actual use Shimano found that brake style housing did not have quite enough resistance to compressing as they needed for SIS shifting. Hence the development of the stiffer "compressionless" shifter housing that we all use these days.

"From actual use Shimano found that brake style housing did not have quite enough resistance to compressing as they needed for SIS shifting. Hence the development of the stiffer "compressionless" shifter housing that we all use these days."

A bit of an understatement, perhaps.

With age, the outer plastic sheathing can literally "go away", leaving nothing but a bundle of strands, not enough to even apply the brake lightly!

Jagwire sells brake cable kits which include compressionless housing now.
The trick is in the outer covering, it appears to be made of woven stainless steel.
I'm looking foreward to the day that I can buy a bulk roll of this housing by itself!

I think this is part of the problem when I use the terms high and low helix. By convention helix angles are measured from from the norma l or circumference, and not from the axial or or center line. Stated another way the helix angle isn't the angle of twist, but it's complement, or the angle of rise compared to a concentric circle.