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3D Printed Pebbled Glass

Started by Sorvan, Aug 13, 2014, 05:12 pm

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Sorvan

As I mentioned in my own build, I've been thinking about using a 3D printer to reproduce the texture of pebbled glass which I'll then cast in clear plastic.  I've have no experience with 3D printing, but can get access to a printer at a local makerspace.

So far, I've downloaded AutoDesk 123D Design (it's free) and made a model:
2014-08-08_1.jpg

Has anyone else done something like this before?  Any suggestions?

Colin

deck5

The model looks good -- you might want to print a few variations, so it doesn't obviously repeat on each of your windows.  The end result will depend on how smooth the 3D printing is; you may want to coat the model in acrylic to smooth it out before casting.

Beware of the clear casting materials; some are soft(ish), and stay that way, particularly when warmed.  When I made my castings, I embedded plastic sheeting in the clear casting material to provide strength, which has worked out quite well.

Sorvan

I was thinking about producing some variations, or perhaps make a larger sheet which I can cut down in various ways. 

I'm expecting that I'll have to run a few prints before I'm able to produce a smooth enough surface.  After doing a bit of poking around, it sounds like using acetone to basically melt a bit of the surface is the way to go.

The casting material I'm looking at has a Shore durometer of 80D - which is similar to the stiffness of a hard hat.

Colin

Volpone

After that, it would be interesting to see if a 3D printed Fresnel lens is practical. 
"My dear Litefoot, I've got a lantern and a pair of waders, and possibly the most fearsome piece of hand artillery in all England. What could possibly go wrong?"
-The Doctor.

deck5

Quote from: Sorvan on Aug 14, 2014, 12:58 am
The casting material I'm looking at has a Shore durometer of 80D - which is similar to the stiffness of a hard hat.


Hardness is one thing, it's how it reacts to gravity and heat that you have to worry about.  Don't want your windows to slowly sag out of shape.

Sorvan

Quote from: volpone on Aug 14, 2014, 01:56 am
After that, it would be interesting to see if a 3D printed Fresnel lens is practical. 


I think it would be far more practical to use a 5-axis or 7-axis CNC router to sculpt some foam and make a mould of that rather than try to print such a large object.  It just so happens that the makerspace I'm planning to join has these.  Since I already have two lenses myself I don't need to make one for myself, but I'm curious to know if it would make sense to make them this way... but that's for another topic.

Quote from: deck5 on Aug 14, 2014, 02:46 am
Hardness is one thing, it's how it reacts to gravity and heat that you have to worry about.  Don't want your windows to slowly sag out of shape.


That's true, it's something I should call the engineers at Smooth-on to ask about.  Where I live, the temperature ranges from -40°C to +40°C (-40°F to 104°F), not including wind-chill or the fact that it'll be on a dark box in direct sunlight.

Colin

galacticprobe

Aug 14, 2014, 05:47 am #6 Last Edit: Aug 14, 2014, 05:57 am by galacticprobe
If anyone is good with a lathe and has some decent wood round stock, you might be able to tool out a Fresnel master, and then make a mould from that. It would certainly be easier to work with than foam (you could just sand the wood once it was carved, seal it with a varnish or something and with a little Pam Cooking Spray as a mould release be on your way, rather than having to first cover the foam with a Bondo-like substance, smooth the surface, and then seal it before getting to the Pam Spray stage).

And if anyone is that clever, then this may be of help:
FresnelProfile.jpg
It's the profile of a standard Fresnel lens that I pulled from an old Lighthouse Maintenance Manual I have sitting on the bookshelf. (And I cleaned it up a little as well.) There are dozens of different lens profiles in there, but this one came the closest to what we've seen on the "Anchor Lamp" style: 3 prisms on top and bottom with "mounting flanges" on each end, and a "bull's eye" section in the middle. (Yes, the wall of the lens is that thick; I've got a 6-inch Fresnel on top of that bookcase; remember, these things were built to take serious heat!)

If someone does cast a mould from a carved wooden lens form like this, keep in mind that you'll need to also insert a "plug" in the center of the mould. So once the "outer" mould is made from RTV rubber or some other moulding rubber, if you don't make a simple cylindrical plug to fill that center then you'll end up with a solid paperweight of a lens. (And don't forget to really lube up that center plug when you cast the lens or you'll never get the plug out without serious drilling.) As to how clear the casting will come out? I have no idea, but I'm sure someone here has used clear resin to cast things and I'll defer that to them (as well as how to polish something like this to get a decently smooth as well as clear finished lens).

Anyway, I hope this is helpful to someone who's planning on making their own lens.

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

matt sanders

I went to Crich this week, and brought some goodies back, which may be of interest to those who need pebbled glass and fresnels...

Check my Build Diary.  (I don't know how to link to the thread...)

Matt

hb88banzai

Link to Matt's build thread at the point where it starts to get "pebbly" (be sure to look at some of the comments as well): http://tardisbuilders.com/index.php?topic=5555.msg65871#msg65871

By the way Sorvan, nice work and some very interesting ideas.

One comment about your model - to replicate the effect of most of the pebbled glass in question there should be a bit more "space" between the pebbles. My impression is that they should just touch at their base, leaving some patches of flat glass in the resulting gaps elsewhere where they don't touch (being round). Also, you don't want perfect hemispheres - they should be less than half of the full sphere to aid in mould release and to achieve the same effect as the originals, as I'm sure they had to do the same for similar reasons.