Creating a Sterling Purse Charm, Part 4 (Final)

Here’s the final purse charm, taken from a design on my computer, printed with a $400 3D printer, cast in silver, and then cleaned up and finished:

The charm installed!

The charm installed!

This, from a design I created:

The purse charm as it is being designed on the computer

The purse charm as it is being designed on the computer

If you want to see the whole process of creating this, you can start at Part 1 and read forward from there.

It’s pretty amazing that on a home computer you can design something and take it all the way to a final form!  There is a real revolution in manufacturing coming with the advent of cheap 3D printers…


Some additional views:

The purse charm + the purse

The purse charm + the purse


The final purse charm by itself

The final purse charm by itself



Creating a Sterling Purse Charm, Part 3

With the charm cast at the end of Part 2, it was time to turn it into a thing of beauty!

Out of the mold, though, it was not so pretty:

Kind of charm free at this point!

Kind of charm free at this point!

The basic problem was that there was excess metal all over the place.  Some is unavoidable — the large knob on the back is from the funnel the silver was poured down.  The bumps around the side are where the air vents were in the mold — the metal flowed past the edge of the design.  Other places were just as a result of the mold being flawed: I found it very hard to get the “delft clay” sand casting system to hold together inside of the letters.

So the process of finishing the charm consisted mostly of removing the excess metal.  I used a small grinding wheel on my flex shaft to remove the metal on the outside edge:

Grinding away the excess metal!

Grinding away the excess metal!

Then I had to work on the inside of the letters:


This is a a ball burr, which is small enough to get inside of the letters and quickly remove the extra silver in them.  

You might notice the cross hatching pattern on the surface of the charm — this is actually from the 3D model itself.  And while it’s charming to see the 3D model faithfully reproduced, it’s not something I want to see in the finished product.  I’ll end up losing a fair amount of thickness when I file the surface flat.

In additional to the ball bur, I used jeweler’s needle files to clean up inside the letters:

It's looking better!

It’s looking better!

When the letters were cleaned up, I went ahead and removed the “button” on the back of the charm:

Closer to its final shape!

Closer to its final shape!

All that was left was to file down the front and back to a flat surface and then polish it up.  That starts with sanding:

Getting very close!

Getting very close!

From there the process consists of sanding/filing with progressively finer grit and then lastly taking it to the buffing machine for the final finish.

I also soldered on a short length of chain and a lobster claw clasp to complete the charm.  The final pictures will be in the next post!

Continue on to Part 4!

Creating a Sterling Purse Charm, Part 2

In the first part of this series, I wrote about some unsuccessful efforts in casting a sterling purse charm.  I’ve got a good cast at last, and want to walk through what that process was like.

As a quick recap of Part 1, I’m trying to use new 3D Printing technology as a way to create items in precious metals (for the moment, sterling silver).  3D printing doesn’t do it all, but it automates a very important part of the process: the creation of a wax/plastic model that can be used to create a casting.  After the unsuccessful cast (actually, several unsuccessful casts), I decided to reduce the size of the model to try something a bit smaller.  Since I had received and assembled my 3D printer, a Printrbot JR, in the interim, I was able to reprint the model smaller without having to use Shapeways.

I started out by designing a fairly simple design in Blender 3D, the free 3D design program:

The heart made 3D

The heart made 3D

This gets exported into a format the 3D printing software can understand (“STL”), and then the charm gets printed on my Printrbot JR printer:

It ain't pretty, but it gets the job done!

It ain’t pretty, but it gets the job done!

The end result is the design I created rendered in plastic:

I (heart) Printrbot...

I (heart) Printrbot…

I did some clean up of the model — mostly with needle files to remove burrs and other large imperfections,

But can only get it so good in plastic...

But can only get it so good in plastic…

and then it was off to cast it in silver.

The first part of this series talks about unsuccessful castings, and I finally have a good one. There’s a couple of challenges I had to overcome to get there.

First, the design I have doesn’t work as well as I hoped with the Delft Clay sand casting system. The system consists of two aluminum rings as a frame and a special fine grain sand (the clay) that you make the mold with, and is conceptually simple.  You fill one ring with compacted clay, put your model in the middle, and then fill the other ring with clay:

The mold being created

The mold being created

At the bottom of the photo you can see a line around the outside of the mold frame — that’s where the mold separates. The next steps to finish the mold are

  • fill the remainder of the mold with clay
  • compact the clay
  • pull the mold apart at that separation point
  • remove the model
  • put tunnels from the surface of the mold to allow the molten metal in and air out

It was at the “pull the mold apart” point that I kept running into problems.  For whatever reason, it was very very hard to get a perfect imprint of the inset C+K letters — the clay would stick to the model when I pulled it out.  I used talc to coat the model.  I even teflon coated the model. But the mechanical compression of the clay into the letters just made it too hard to separate cleanly.  I eventually decided that the ratio of the size of the openings to the depth of the openings was problematic for clay, and when I got a “good enough” mold I moved on.  I knew I could remove excess metal afterwards.

The next step is the pour of the metal:

Molten Metal!

Molten Metal!

And this is where my choice of metal saved me!  Because although this is a linear narrative, the process was not linear — I ended up (re-)casting this piece several times.  Argentium® silver saved me!  While ordinary sterling gets firescale (a pernicious kind of tarnish) every time you torch it, the Argentium stayed perfect through my repeated abuse of it.  The very small incremental cost of it over ordinary sterling is trivial compared to the grief it saves me in casting.  Maybe if I did everything perfect, quick, and once I wouldn’t care so much, but when you’re experimenting with new technologies having a metal that is extremely forgiving is just wonderful.

The final result was “good enough” — A little excess metal I’ll have to remove, but it will ultimately be more or less perfect when finished (fingers crossed!):

Close up on charm right after casting...

Close up on charm right after casting…

In Part 3, I’ll detail the finishing of the charm.  Lots of elbow grease involved …

It may seem like there’s a bit of “stone soup” involved with creating precious metal jewelry with 3D Printing, but I don’t want to diminish the value 3D printing provides or the revolutionary nature of it.  It is the same kind of CAD/CAM approaches that have cost 10 to 100 times as much beforehand, and the opportunities it offers artisanal and amateur (in the best sense of that term) jewelry manufacturers are phenomenal.

Continue to Part 3!

A couple of 3D prints

Two interesting prints today from my Printrbot Jr.  

The first for the inlaws:

Pat & Larry Easter 2013

Pat & Larry Easter 2013

I’m lucky that their names intersect well!  For some reason, I got globs of burnt looking plastic here and there.  Maybe the nozzle temperature was too high (I’m running PLA at 205c to try to prevent extruder jams).

This one was surprisingly hard to create — I didn’t realize at first that Blender cubes (which is what this is made out of) end up being hollow when they print.  Slic3r kept complaining about the model.  Eventually i just created a 2D cross and extruded it; I have to go back and figure out how to print solid Blender mesh cubes 🙁

The second print was the logo of the company I work for, done in miniature:

Wonder who I work for ...

Wonder who I work for …

I already had the logo in 3D in Blender for graphics work, and so I just printed it. I think that if I print the logo a bit larger it will look better: this is pushing the resolution of the printer.  technically, this is about 20 point type — you can see how a 3D printer has much lower resolution than a modern ink jet! (to be fair, though, the 3D printer prints one dot at a time, so to speak).


Quick update on Raspberry Pi as application server

A brief status update to my earlier post about running a Raspberry Pi server:

It’s rock steady running MySQL and a custom Java app (that generates Twitter statistics).  The CPU does get pinned to 100% at times, but since it’s keeping up with the Twitter data I’m collecting  just fine that’s not really an issue for me.

The last time I rebooted it was when I changed the amount of memory available to the GPU: since I’m running headless, I only need enough for the character mode console for emergencies.

Here’s a view of the system in operation from “top”:

Click to enlarge

Click to enlarge

Funny that the Java app is talking up so much more of the computer’s  CPU than MySQL.  I think I have some optimization to perform in my code 🙁