How does Bowden cable work

If you look at high load situations where you need flexible cables - like say a car gearchange - they generally use two so the load is taken by each as a pull.

If you wish to have one which both pulls and pushes - for low load only - it need a solid inner (so far less flexible) and the outer secured at both ends. That can be with a clamp, or a crimped on ferrule secured to a bracket by a circlip, etc.

Nope, sorry.

Whilst not familiar with such a system for a waste plug I am familiar with Bowden cables in a general sense and I would say they (the outer) have to be 'anchored' with reference to the inner and the force acting on them (with exceptions).

Like, if you had a Bowden cable going a short distance in a straight line between two points it's possible that the inner cable could act like a simple pushrod and so the outer could be considered superfluous.

Of if you have something like a remote (mechanical) shutter release for a camera where it's generally only used for compression and the inner poling out the open end is 'free', but would still need to be activated with regard to the outer (eg, if you just push the inner the other would move as well, resulting in nothing at the output end).

Another exception would be if the outer tube was rigid, then it might get away with only being retained at one place (being rigid means it's then being effectively retained at all places).

So, if we are talking about a plunger that causes a basin plug to 'pop up', I would imagine it could be covered by any of the examples above?

Cheers, T i m

I thought they generally had two for the two planes of movement, one doing the push pull and the other the rotation (to duplicate the 'H' gear selector gate)?

Yup, because the gear change on my Messerschmitt KR200 is 'sequential' it just has a push-pull cable with more rigid 'ends' where it connects to the gear change lever or gear selector arm on the engine.

It actually travels in a open 'Z', from by your right knee, up the RHS of the cockpit, across the back and out into the engine bay and onto the engine.

I think the brand is 'Teleflex'.

Cheers, T i m

Thanks both. It works on a push and pull basis. Essentially when you turn t he knob one way it pulls the inner cable which in turn pulls a lever at the plug end and the plug pops up (or down can't recall which way around). Whe n you turn the knob in the opposite direction it pushes the lever at the pl ug end and the plug does the opposite.

I have both solid and stranded core to try once I get the mechanism working .

Sounds like I have to somehow secure the outer sheath to the brass fittings . Any ideas?

I assume the sheath is plastic on a steel spiral?

The only certain way is to remove the plastic and solder, or crimp the brass onto the sheath. Otherwise glue, possibly using epoxy. It needs to cope with max push.

Since the cable is put in compression solid would be better.

Yes it is a steel spiral encased in plastic. The brass is thick (couple of mm) so no way to crimp it onto the sheath unfortunately.

I wish you would quote the text you're replying to. It is usenet convention.

Bowden cables are best where the sheath is in tension. They really don't work well in compression.

If the steel spiral is genuinely steel, and not stainless steel, I would solder. But only because I'm familiar with the process.

Can you not get a genuine replacement?

Thanks Fredxx. I am using the Google groups forum site so not sure why it doesn't quite the text.

Based on your post, am I supposed to cut the sheath such that it is tight between the 2 end points? I cut it with some slack to give me some room in case I needed to move something slightly.

The brass on the fitting is around 2mm thick around the hole the sheath goes into. . The depth of the hole is around 6mm

Fredxx explained on 09/06/2018 :

Sheath in compression, inner in tension!

I can't put the sheath in compression as it runs from the trap of the bath up to the knob on top of the bath so needs to flex around contour of the bath.

snipped-for-privacy@yahoo.co.uk presented the following explanation :

Usually Bowden cables work with the inner being pulled (tension) against the outer, which is compressed. Outers have limited ability to withstand tension, because if too much tension is applied, then they easily stretch.

I don't think the outer compresses much. It is a spiral wrap so it is flexible but, as it bends, the spiral turns are in contact. I doubt the metal will compress much. The 'gap' between the turns on the outer of the bend may close a bit as the device is operated- typically you see the outer move a bit. As you say, the inner is under tension.

Apologies - spot on for noticing.

Brian Reay was thinking very hard :

I agree, the outer doesn't compress much, but they come under compression when the lever or what ever is operated.

I guess you're using a device with a small screen, so don't get offered quoted text. You can work around this.

Google Groups comes in (at least) two forms - mobile/phone/tablet and desktop - and it decides which form to offer you first, based on how your device and browser identify themselves.

The mobile version doesn't supply quoted text.

My workarounds are:

2 Use the desktop version to get the quoted text and then copy it to a text editor app for full-screen work before returning to Google Groups to paste your edited text.

It's OK to trim the quoted text if it's long. Do keep the name of the person you are replying to and enough of the quoted text to help readers understand your reply or comment.

Bowden cables work due to the core piece having nowhere to go but up and down the inside of the sheath. Its obvious that if the sheath is not continuous then you will end up with just a cable that grows longer and shorter by bulging.

Depending on the design normally the ends are mirror images of each other. However as long as you can hold the two sheaths together you should be OK. Can you not use a small clamp. The ends are normally solid, not the bendy springy stuff the rest of the outer is made of. You need to make sure its stronger than the combined force of the friction in the cable and the force needed to raise and lower the plug. Back many years ago when TVs were dual standard some very long bowden cables were used and the ends often clamped to allow for switch movement adjustment.

Brian

Agreed. The common instance of a push-pull cable, in the good old days, was in car choke cables. IIRC bonnet releases also sometimes had (and still have) a solid inner. But then they have a pretty fixed run and don't need much flexibility.

Looks like soldering the sheath into the fitting is the best next step. Do I use a normal blow torch and plumbers solder? Is also would the fit copper pipe?

Hi all

I have taken some photos and tried to upload them to a public album (hopefully not done this for ages). They show the fittings and particularly the brass fitting I need to connect the sheath to. Hopefully this works

I have tried some searching but can only find examples of soldering the fitting to the wire rather than the sheath to the fitting. They seemed to use "silver solder" which I assume is not the same as plumbing solder

Thanks

Lee.