Casting clear light pipes- material ideas?

[Lemosteam]

For a future product offering I am looking to cast clear light pipes.

The design is simple, a 1.2mm dia shaft about 4mm long with a domed end about 2mm in diameter.  I have a master made from fiber optic using the "heat the end" process to get the dome as in the pic below.

[ Guests cannot view attachments ]

I plan to make a small blue RTV mold using gasket material, possibly with multiple cavities (very low volume so no need for too many).  I do not want a split mold, i.e no parting line, especially on the domed area.  I think I can get the dome in the pour if I am careful, or add it after cure by adding a drop of the material and letting it flow naturally to the edge (likely with some small flash).

I want to make finished parts as simply as possible WITHOUT any mixing so the material must be pour-able out of the container.

I thought of Micro Krystal Klear, but I have never used it and I don't know if it dries rigid or flexible.  A little flexibility is OK, it is the clarity that I am after.

Any other material ideas?

[Philip H]

if its small batch why not just use the fiber optics to make each one?  Seems to me the time invested in the mold making and getting the just right domed end would be better spent just heating, shaping and cutting.

And Krystal Clear will be too flexible to use for this no matter what your underlying pipe material.

[Lemosteam]

if its small batch why not just use the fiber optics to make each one?  Seems to me the time invested in the mold making and getting the just right domed end would be better spent just heating, shaping and cutting.

And Krystal Clear will be too flexible to use for this no matter what your underlying pipe material.

I don't have enough Fiber optic material.

What about the water products?

[Philip H]

haven't worked with any of them yet.  The clear resin that Will Models was using for some of his cars might work, but your mold making requirements seem like a slowdown to the process.

[Lemosteam]

Yes the parts are so small the resin would harden in the cup after just the first one.

How flexible is the MKK?  is it as soft as the silicone?

[Lemosteam]

Just discovered this- tintable too...

[C855B]

Here's something apparently designed for casting very small items:

https://www.tapplastics.com/product/mold_making_materials/casting_products/easycast_clear_casting_epoxy/386

I'd be concerned about the Liquitex product. From the video it appears to be fairly viscous and might not want to pour into the small shaft cavities.

[Lemosteam]

Here's something apparently designed for casting very small items:

https://www.tapplastics.com/product/mold_making_materials/casting_products/easycast_clear_casting_epoxy/386

I'd be concerned about the Liquitex product. From the video it appears to be fairly viscous and might not want to pour into the small shaft cavities.

Thanks Mike, I came across that too but I really dislike mixing- I stink at it no matter how hard I try.  Was planning on using a bulb syringe to force it down the shaft.  I am going to add a downward vent to the mold.

[Lemosteam]

It also dawns on mt that someone else was casting LED's into Epoxy for ditch lights?

Ah yes, here it is!  https://www.therailwire.net/forum/index.php?topic=35617.msg421750#msg421750

Credit to @craigolio1

[C855B]

Heh. Mixing. I just received a sample kit of slow-curing self-expanding foam to play with for scenery, so I'm about to get into the A-B world myself. Everything I read in the instructions seem to imply the stuff has major odor issues. I guess we'll find that out tonight.

Your light pipe idea has considerable merit and I'm watching closely. I'm thinking of it as an extension of the MV Products lens line, but with better accommodation for illumination. One of many projects languishing on my bench is the C855 trio, and well-formed headlight lenses would be a nice touch. You might think about offering a dome size in ~0.050" to correspond to the 8" size (...I think it's 8"...) common on diesels.

[wazzou]

Look at Gallery Glass by Plaid. 
It is similar in nature to the MKK but dries much more clear, comes in a larger container, squeezes out through a hole you poke in the end of the snout and I think is more rigid than MKK.
The trick as I see it would be mold release and what to use.

[Lemosteam]

Look at Gallery Glass by Plaid. 
It is similar in nature to the MKK but dries much more clear, comes in a larger container, squeezes out through a hole you poke in the end of the snout and I think is more rigid than MKK.
The trick as I see it would be mold release and what to use.

@wazzou Thanks!  I'm thinking talc.

[peteski]

John,
the problem with single-part materials is that they harden by drying (evaporation of the liquid solvent) rather than a chemical reaction which sets the material.  So for a piece like you want there will be long drying time (since there is very little surface for the solvent to evaporate) and shrinkage (just ask George Costanza  ).  Microscale Krystal Klear dries flexible. The other problem will be to keep the liquid material bubble-free for casting.

Also keep in mind that a plastic fiber optic is not just simply a piece of clear plastic. It is made of a core and cladding using materials with different light refraction properties to prevent light from escaping.  But that design is not mandatory (as we witness most model trains use homogeneous clear plastic light conduits which give satisfactory (but not ideal) results.

As mentioned by others, for what you need, making these out of plastic fiber optic would be much less hassle than casting them. 

I Googled for 0.040" fiber optic and found some possible sources.
Cheapest would be the stuff Walthers carries:
https://www.walthers.com/fiber-optics-04-quot-diameter-15
Out of stock but looks to be restocked soon. You could also try dealing with Circuitron directly. Here are some more possible industrial sources:
http://www.ttco.com/industrial/plastic-fiberoptic-light-guides/cut-to-length.aspx
https://buy.wesco.com/Fiber-Optic-Cable/EATON/Terminated-Single-Fiber-Plastic-Through-Beam-Threaded-End/6323A-6501/p/78211382701-1

[glakedylan]

hey John...have you thought about possibility of nylon (acoustic) guitar strings, heating the tip just as you would with a fiber optic rod? just thought.
Gary

[chicken45]

John,
the problem with single-part materials is that they harden by drying (evaporation of the liquid solvent) rather than a chemical reaction which sets the material.  So for a piece like you want there will be long drying time (since there is very little surface for the solvent to evaporate) and shrinkage (just ask George Costanza  ).

Didn't you just make a Seinfeld reference in another thread recently?