Forming a round domed crystal.

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441victor
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Forming a round domed crystal.

#1 Post by 441victor » Thu Jul 03, 2014 1:07 pm

To refine my crystal making techniques I chose to make a replacement for one of my A-11's. The advantages to the round shape are its symmetry and the ability to use the bezel to help form the domed shape. For these simple round crystals I use light bulbs that closely match the radius of the dome. For more complex shapes, if I'm lucky I have the old crystal to use for a mold. Otherwise the search for a surface to mold against can take more time than the actual production. In the future I will be experimenting with shaping the mold from epoxy or clay or another suitable material. The surface must be smooth as the concave inside of the crystal is difficult to shape and polish. The material I use is acrylic sheet used for picture framing. You can buy it in large sheets and in various thicknesses. I use small picture stands made of folded sheet and shaped to slip in a photo and set on a table. They are about 2mm thick and have enough material for 8-10 crystals for $.99. Holding the blank in a pair of forceps, I use a heat gun to bring it up to temp so its floppy but not melted. Then I place it on the bulb and press it down with the inverted bezel as shown.
Crystal Military 1.jpg
Crystal Military 1.jpg (240.87 KiB) Viewed 2315 times
When it cools you have a piece that looks like this. If it's not fully formed you can reheat it and mold it again.
Crystal Military 2.jpg
Crystal Military 2.jpg (275.29 KiB) Viewed 2315 times
All that remains is to cut the blank out and shape it to fit the bezel opening. The bezel in this case leaves a handy ridge that defines the edge of the crystal. I use various cutting burrs and sanding drums in my Dremel grinder for most of the work. Just work slowly as you approach the final shape. The edges can be worked down to taper the crystal profile or rounded and polished. Using a thicker stock will allow you to contour the top surface to match the original more closely.
Crystal Military 3.jpg
Crystal Military 3.jpg (258.72 KiB) Viewed 2315 times
For square or rectangular crystals you can't use the bezel to form the dome. I have used another piece of acrylic with a same shaped hole in it to press down on the edges of the heated blank. This works for relatively simple shapes that curve in both directions.

Things I'd like to try:
Holding the heated blank in a frame that would allow it to be pulled down over a raised mold.
Molding round crystals which change curvature at the edges or have vertical edges.
Molding shaped crystals that curve in only one direction and have vertical sides.

Joel

retroworx
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Re: Forming a round domed crystal.

#2 Post by retroworx » Thu Jul 03, 2014 4:47 pm

Thank you for posting your technique, Joel!
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Paleotime
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Re: Forming a round domed crystal.

#3 Post by Paleotime » Fri Jul 04, 2014 7:55 am

Wow...pretty cool. I have read about doing this in the Chicago watchmaking school materials, but never really considered trying it. I might have to change my mind.
"Percentage players die broke too..." - Fast Eddie in the Hustler

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Re: Forming a round domed crystal.

#4 Post by retroworx » Wed Nov 04, 2015 3:54 am

In the future I will be experimenting with shaping the mold from epoxy or clay or another suitable material.
I wonder if this stuff would be useful for this application. It can be molded and dries in 24 hours to a firm finish:

https://sugru.com/
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indyago
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Re: Forming a round domed crystal.

#5 Post by indyago » Wed Nov 04, 2015 10:43 am

Thanks for sharing Joel. I have created a square crystal that didn't have to be hollowed out to allow for hand movement. But, could never figure out how to hollow out the back side or, polish it clear either.

This method for round makes a lot of sense, especially using the case for marking the ridge.

I count myself a patient person but, it takes a gift sometimes to not get in too big of hurry when shaping and polishing a crystal................Good show!
Rob

"Tomorrow hopes we have learned something from yesterday." (John Wayne)

441victor
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Re: Forming a round domed crystal.

#6 Post by 441victor » Wed Nov 11, 2015 7:16 pm

Even shaped crystals can be cut from a sphere or are close enough to make a suitable replacement this way. Here is an Elgin model that shows the kind of curvature on the long edges and side to side that might make it possible.

Image

I would find a form that touches all four edges as close as possible and try it. Sometimes I can work on the back side of the corners or under the edges and get it to match the bezel. A little heat can also make it pliable enough to conform to the opening closely enough to fit with the help of some crystal cement. I know I have a square case that I was successful with. I try to find it for some pics. Joel

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