How To Ruin A Perfectly Good Silver Ingot (or: Surfacing Silver Using A Fly-Cutter on a Taig)

I decided to start using 1 ounce fine silver trade ingots as my raw material. There are some reasons for this due to my location and experience (or lack of it).

Between reading the Ganoksin forums and the PMC websites, I wanted to strike a compromise between cutting sterling and using Precious Metal Clay (PMC) for my first few real projects:

1) I wanted to avoid the problem of firescale that I would eventually encounter once I started melting the silver or soldering pieces together. Firescale evidently only because a serious problem with sterling (92.5%) silver due to the 7.5% copper content. PMC artists avoid this by using fine silver exclusively.

2) The main disadvantage to using PMC is of course the cost, PMC with shipping is at least twice as costly as the spot price of silver! So while I liked the idea of beginning with fine silver to avoid the problem of firescale, I also wanted to avoid having to pay so much for PMC.

3) The ingot is already work hardened, rolled, stamped, what have you at enormous pressures, so annealing becomes unnecessary (I hope!).

4) These trade ingots are nearly always a standard shape, possibly allowing my crafting processes to be repeatable and less prone to error (just about the most important point I came away with from my Six Sigma Green Belt training from the aerospace firm I once worked for).

5) I realize that fine silver is unsuitably soft for many applications of silversmithing, but one of the PMC artists at New Mexico Clay persuaded me that the difference between fine silver and sterling was negligable for many other applications, such as pendants, that I could begin to create.

Fortunately, my wife and I shop at a Sams Club about 250 miles away once per quarter year for bulk canned and dry supplies, and there’s a coin store not too far away where I can pick up those few ingots as I can afford from my allowance. I know the owner and he’s agreed to buy chips off of ingots I buy from him in exchange for new ingots.

Here’s one I bought from him:

1 ounce fine silver ingot before I ruined it with a fly cutter on a Taig

Using my calipers, I have determined that the thickness of the ingot is 0.10 inch (I am willing to speculate that my ingot is a far more accurate standard than these calipers!)

My tool for casual measurments down to .01 inch

My objective for this self-taught lesson was to remove the artwork off of both sides of my ingot using a fly cutter:

Fly cutter purchased from DeArmond Tools

Typically I will set my pulley speed flat out of 10,000 revolutions per minute (RPM) to take best advantage of my endmills. But this speed is not appropriate for fly cutting, at least on a Taig, and on other Taig user had recommended a speed of “about” 3,000 RPM. Here’s the pulley arrangement:

Taig pulley settings appropriate for fly cutting on silver ingot

I originally took a page out of the A2Z CNC site and tried sticking the ingot to an aluminum block using double sided carpeting tape, and then mount the block in the vise. Evidently the tape was not sticky enough, because the fly cutter pushed the ingot right off of the block. I had to settle for the tried and true backup method of holding the ingot in the vise on wood spacers:

Taig after having fly cut a side of silver ingot

After a few false starts I got the artwork on both sides of my ingot effaced, so that I can now use the ingot for other purposes:

1 ounce fine silver ingot after ruining it with fly cutter on a Taig

Lessons Learned:

1) Trust my touch off! Trust the numbers!!! I didn’t, I went by the sound the fly cutter made as it contacted the silver. Very bad idea. I faced off a LOT more silver than I wanted to this way on both sides. I started with 0.10 inch thickness, I wanted 0.09 inch thickness, and I wound up with 0.04 inch thickness (and I faced off a little bit of aluminum from the top of one of my vise jaws as well)! In other words, I wasted at least $10 of silver off of a $15 ingot!

2) I need to indicate my vise, and shim as necessary. I have a slightly uneven thickness to my resulting piece, which would not be very good for finished work. I’ll use this piece though for testing my sanding and polishing process, later.

3) I need fixtures for solidly clamping my ingot into the vise. Spacers under the stock might have been all right for crafting in bismuth and tufa, but I need much better accuracy.

4) My chips flew just about everywhere in the shed, necessitating the use of a broom and dustpan for recovering. I need to construct a chip catcher so that I can more easily recover the silver for later recycling.