Gold wedding ring with Mem-Gem design project

Intro

If you want to place your Mem-Gem in a unique and beautiful piece of jewelry, you have come to the right place! In this blog article I'll be describing my processing of getting a gold wedding band made using a Reflection-type Mem-Gem and all the details to consider.

To start with, a sketch of the desired design:

In this design, the laser bounces off the Mem-Gem to form an image, and the Mem-Gem is flush inside the ring for a very minimalist look. You can choose any design you like. Just make sure the laser can bounce in and out (nothing blocking path - with nominal angle 30 degrees), and make sure the metal-coated side of the Mem-Gem is somewhat protected from scratching of daily wear.

Getting quotes

If you are busy like me, you can start by getting some quotes from local jewelers for your design. To my dismay, the jewelers I talked to quoted me between $2200-$2500 for the white gold ring that I wanted. This probably would have been a reasonable option since the process would end here, but I like to save money, so I figured that I'd abandon the traditional jewelers and try to design and build my own instead. It's a lot more work this way, but saves some money. So if you have the money to hire a jeweler, you can stop reading here. Just pay a professional! Or order a pre-designed Mem-Gems compatible ring from the Mem-Gems website :) If you want to do the work to make your own, keep reading below!

3D printing a ring

There has been incredible progress in commercialization of 3D printing technology in the past decades. There is a technology called lost-wax 3D printing, where a ring design is first made out of wax, then plaster is cast around that, the original wax melted out, and a precious metal is cast (poured while liquid) into the hole left by the molten wax. Although the lost-wax technique has been used for centuries, the advent of 3D printers for making the wax opens the design possibilities considerably. From my brief research, the two main companies doing this are Shapeways and imaterialise. From what I could tell, the latter was more friendly towards jewelry and technologists like myself, so I chose to try working with them, although I'm sure either would work.

Designing a 3D ring

In order to design a ring in 3D, you need to use some 3D design software. There are dozens of options to choose from. I have a degree in Mechanical Engineering, but the Solidworks software that I learned with more than a decade ago is too expensive for my personal use. I started trying Sketchup (free), but couldn't figure out how to extrude a part. I happen to be familiar with Autodesk Fusion 360, so I chose to work with that one. I managed to get going pretty quickly. There were some hiccups along the way (blue means solid, orange means sketch - that distinction cost me a couple of hours of confusion), there's a bar at the bottom that tells you what step you're on so you can go forwards and backwards, and new parts are created using the "Data Panel". Within a day, I was able to create this rendering of both my desired ring with the Mem-Gem inside it:

 

 Mem-Gem in gold wedding band

I verified that my design met the 3D printing and casting guidelines https://i.materialise.com/en/3d-printing-materials/gold/design-guide which wasn't very difficult because my design is simple.

Dimensions and tolerances

There are few subtleties to designing with Mem-Gems. For my design, I'm going to try a flush "gypsy" set. There are lots of tutorials that talk about this, here's one: https://www.ganoksin.com/article/basic-gypsy-flush-mount-setting/

The Mem-Gems have a reflective ellipse of 2mmx4mm on the center of a nominally 2.5mmx4.5mm sapphire disk. I measured the Mem-Gems from the last batch with calipers and found the following outer dimensions:

# x y
1 4.43 2.45
2 4.45 2.47
3 4.45 2.48
4 4.45 2.47
5 4.48 2.47
AVG 4.45 2.47

 

So let's call it 4.48mm(+0,-0.05) and 2.48mm (+0-0.03). Traditional tolerancing would call for a "Sliding Fit" in this situation. Not too tight that it won't go in, and not too loose that it can't be securely fit. I had to look it up and found (G7/h6)  https://en.wikipedia.org/wiki/Engineering_fit#Clearance_fits

(see http://theoreticalmachinist.com/IsoTolZoneCalc for details). This will allow the Mem-Gem to fit into a corresponding hole, so that we can subsequently fit it in. Usually this is done with round holes, but I'll extrapolate the results to an elliptical hole for the reflection-type Mem-Gem. So let's use 4.48 as the h6 shaft. So then the hole needs to be: 4.484-4.496mm. So let's aim for 4.496mm. And in the other dimension we get (using 2.48 as the h6 shaft), 2.482-2.492mm.

 

The Gold casting process

There are two main things particular to the casting process that can mess with dimensions:

  1. Shrinkage during cooling
  2. Polishing

The shrinkage after molding is complicated. First, there's a density change from liquid to solid, and next there is the thermal contraction as the piece cools. The specs on the i.materialise website are pretty vague:

Accuracy: ±5% (with a lower limit of ±0.35 mm). Well, that throws all the dimensional analysis into question! Because things are vague, we'll just have to print one and see. 5% of 4.5mm is 0.225mm. So if we do 4.7mm that should be good. That's 100 microns on each side. The Mem-Gem should fit in the hole. If it rattles around too much, I'll make it smaller. After I print it, I will report the measured dimensions to see since I think this information will benefit others also!

 

I'll make the first time out of Silver. i.materialise has a great website that allows you to get quotes in different materials. After creating my 3D design in Fusion 360 I could export as a .STP file and upload directly to i.materialise, and even get quotes in different materials. Amazing!

Alright I received the silver 3D print cast, it looks great!

The Mem-Gem fits in. 

 

I did some measurements and found: 

Length (mm) Nominal (mm)
Ring 4.786 4.7
Ring 2.636 2.7
Mem-Gem 4.478 4.48
Mem-Gem 2.399 2.48

 

So the piece came out to the same dimensions as the drawing (within the measurement error of 100 microns).

I bought a "burnisher" online, made a DIY jewelry setup by taping a wooden spoon to a table, and then used the burnisher to bend the silver over the Mem-Gem.

 

 

Overall, it worked, and I think it looks pretty cool! My custom flush Bezel set was pretty good for a first try! One thing I'll change for next time is to make a little bit more material on the far edges of the Mem-Gem so it sits a bit deeper and the flush set can go around the entire perimeter, not just the two short axis edges.

Mem-Gem Silver men's wedding band



If there is interest, I will consider offering rings as an option in future Batches of Mem-Gems!

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