Fibre optic cable size?

[Bill H]

Group:
I need to move the headlights on a number of steamers from the center of the smoke box door to the top, B&O style. I will need to reroute the light from the light board up to the headlight. Most likely this will call for the use of fibre optic cable. Any suggestions as to what diameter to purchase?

I did a number of searches on RW and there are a lot of divergent opinions as to flare or not flare, polish or not polish, the end to produce a bulb like effect or diffuse the light. Any consensus now or?

Kind regards,
Bill

[nickelplate759]

Definitely polish the finished (exterior) end.  It will look odd if you don't.   

[mmagliaro]

Definitely flare he end.  I hold the end of the fiber optic tube very close to the barrel of a hot soldering iron to do this.
I find it much easier to control than an open flame.

As for diameter, if the fiber strand run is straight with only gentle bends in it, try to fit a piece of .040" in there.  You'll get much better light performance than from smaller sizes.  But if you need to do more than 45 degree bend anywhere, try .030" and .020".  In other words, I'm saying you want 3 sizes, .020", .030", and .040" so you can use the largest one that you can make work for your application.  For a headlight, .020" is really getting down there.  Try to use a larger size if at all possible.

[DKS]

I've moved away from fiber optics and toward 0402 SMD LEDs. It's easier to hide the wires than an optic fiber, and the wires can't be easily damaged like a fiber. Just as an alternate suggestion...

[Bill H]

As for diameter, if the fiber strand run is straight with only gentle bends in it, try to fit a piece of .040" in there.  You'll get much better light performance than from smaller sizes.  But if you need to do more than 45 degree bend anywhere, try .030" and .020".  In other words, I'm saying you want 3 sizes, .020", .030", and .040" so you can use the largest one that you can make work for your application.  For a headlight, .020" is really getting down there.  Try to use a larger size if at all possible.

Thanks Max, any suggestions for a supplier? Neither my local pusher nor my online pusher have any, and I can't find it in the relatively short lengths I need. Trying not to have to buy 100' to get a couple of feet.

Kind regards,
Bill

[Bill H]

I've moved away from fiber optics and toward 0402 SMD LEDs. It's easier to hide the wires than an optic fiber, and the wires can't be easily damaged like a fiber. Just as an alternate suggestion...

DKS:
I have also been using SMDs for some time, but in these applications I really don't want to fuss with figuring out how to disconnect the smd wires when I remove the shell, as the Led will be in the shell headlight.

That's why I was thinking of using fibre optic cables to transfer the light from the exisiting led on the dcc board up to the headlight.

Kind regards,
Bill

[carlso]

Bill,

I'll chime in here with a supplier suggestion : www.thefiberopticstore.com

I have purchased from them and had no problems. Also, check the site as they have a sample pack with several sizes that is $4.00, I think.

Carl

[mmagliaro]

thefiberopticstore (Carl quoted the link) is the place I used the last time I bought some.  I used Edmund Scientific years and years ago, but they split into two stores, and Edmund Optical has a confusing and expensive assortment of fiber optic strands that I don't think will be what you want.

thefiberopticstore has a minimum order of 50 feet for about $13.

Hunting around, you can buy it from Circuitron, Plastruct, and other hobby names, but you end up spending the same amount for a lot less length, so you may as well bite the bullet and buy 50 feet of each type.  I couldn't find anybody selling, like, 5 feet on the cheap.

I do see the benefit of still using these to avoid having wires going up into a headlight housing on a steam loco.  I have been using SMD LEDs on my last 3 or 4 steam loco projects, but on my 0-6-0, I went back to the internal LED with the fiber optic pipe.  It was so much easier to allow boiler and tender shell removal.  And light can look really good if you mount things right.

[nickelplate759]

by the way, is there a good trick for forming a bend in the stuff?  I'm guessing "just enough" heat and form it around a rod (maybe a warm rod)?

[Bill H]

I'll chime in here with a supplier suggestion : www.thefiberopticstore.com I have purchased from them and had no problems. Also, check the site as they have a sample pack with several sizes that is $4.00, I think.
Carl

Hi Carl:
Thanks. I just checked, their sample pack is out of stock at the moment. I will keep my eye on it.

Kind regards,
Bill

[mmagliaro]

by the way, is there a good trick for forming a bend in the stuff?  I'm guessing "just enough" heat and form it around a rod (maybe a warm rod)?

That's what I do.  I get it near (but not TOO near!) a hot soldering iron barrel, and gently bend.  I don't bend it around a rod or anything.  While that seems like it should help, if the plastic fiber optic material is hot enough to bend and permanently deform (which is what you want), then anything that touches it will make a dent in it.

I had better luck just going very gently, and not trying to bend it too much or too sharply.   If you must make a 90-degree bend, try to "ooch" it along, a little at a time, over as much length as you can.

[peteski]

I use fiber optics very sparingly (not much call for them after micro LEDs became available). When I need to bend them, I also use soldering iron for heat source (like Max does). He is correct. if you make the bent to sharp, the photons will literally leak out of the fiber (Just like a car going off the road when a curve is too sharp). 

The plastic fibers we use (which look like fishing line, but are not), actually have a core and a jacket made from materials with different refractive index, and they closely resemble the step index fiber.



Here are few examples of what happens when the fiber is bent too sharply:





I like to understand at least the basics of the materials I utilize, Wikipedia has a good page on fiber optics (no one doesn't need to read all of it - just skim over the contents).
https://en.wikipedia.org/wiki/Optical_fiber

As for sources of plastic fibers, I have accumulated a decent size collection from various electronic surplus vendors (like All Electronics or Electronic Goldmine), but I also bought some from BL Hobby products (I think they became part of Circuitron).  While the price is higher than buying the fibers in bulk, to me it was still worth to buy it in 10 foot lengths.   Here are the part numbers:

800-8020   FIBER OPTICS, 0.020” DIAMETER  30 FT.
800-8030   FIBER OPTICS, 0.030” DIAMETER  20 FT.
800-8040   FIBER OPTICS, 0.040” DIAMETER  15 FT.
800-8060   FIBER OPTICS, 0.060” DIAMETER  10 FT.

See http://circuitron.com/index_files/catalog.htm (page 54 of the catalog).

[Bill H]

Thanks Pete

[Onizukachan]

Hi Carl:
Thanks. I just checked, their sample pack is out of stock at the moment. I will keep my eye on it.

Kind regards,
Bill

Bill the sampler is back in stock, I just ordered 2 of them a couple of days ago.

[craigolio1]

I bend the same way others here have described. I have had success bending SHARP 90deg angles. But you lose a ton of output. Not so bad for a classification light but for a head light you really want to keep as much light in there as you can.

In any case, PERFECT alignment with the light source is key and also flaring both ends of the fibre. If you will be relying on the fibre aligning with the source blindly, where you can’t reach in and poke it around, I recommend making a cone like collar, like a funnel kind of, to capture the end of the lose fibre and direct it toward the perfect centre of the LED. Also you may find it easier to move the LED or change the style of the LED on the board, so that it’s in a better alignment with the fibre. For example if it’s currently facing forward and your fibre would require 2 bends (like a Z shape) then removing and reorienting it 90 deg upward could eliminate 1 bend and make it easier to align.

 Craig.