What metal is this and how should I mess with it?

DMS General
#1

So I have these medallion wedges that I would like to modify and make into a custom piece. (Basically, I would like to remove some of the existing designs/lettering and add my own.) There are magnets inside two of the three wedges that make all three fit together into a circle. I think they are steel, but I’m not sure.

The tricky part is that the existing design is engraved/recessed into the metal. I can of course grind/sand that away, and I’m assuming I can then polish the remaining material to smooth out the surface…

… but after that, what tools would you think of for decorating these things? Is this a job for lasers? A hammer and some letter stamps? One of those fancy engraving pens? And after doing that - how would I go about filling in the new letters / shapes with color? (I expect that is some kind of resin or enamel they have in there right now, but I’m not sure.)

Suggestions welcome!

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#2

Based on the color, and the way those things are usually made, I’d say that they’re probably cast bronze with the magnets glued in. Maybe the guys will know more about them, but cast bronze does not lend itself to further changes. It’s fairly brittle and doesn’t braze well.

#3

What Metal? First step is to figure out what kind of metal they are.

Details

I agree with Beth @dryad2b that they’re likely cast something-or-other - possibly “pot metal” (a cheap, high zinc alloy that melts just above 400 degrees). They all look different. IIWM, I’d show up to the Machine Shop committee meeting tomorrow (Saturday) with your parts in hand and ask the various attendees what metal they think they are. Machine shop has some files to test hardness and that will give some clues.

You may get some clues from doing a water-displacement test. Weigh them (in grams), immerse them in water and measure the displaced water, and then you can get the specific gravity. You’ll have to be precise to be able to distinguish them.

Grinding/Sanding

Comments about how-to

The castings may have a lot of porosity in them so grinding may actually make them worse.

Bronze files fairly easily (as metals go) because it’s mainly copper. If you plan to use a DMS grinder, please check what metals they allow. I know that no one allows aluminum on their grinder but I don’t know what other restrictions there are.

A Dremel is a good choice to smooth/polish them. You should check out RioGrande for [silicone polishing disks](https://www.riogrande.com/searchresults#q=silicone polishing wheels). You will probably want coarse, medium and fine. You can also get super fine but you probably don’t need that. You will need mandrels to put the disks on - can get at Rio or at CDC locally (for about $1.50 each if you go do CDC). However, you will be at it for a year or more if you’re trying to remove a deep engraving (OK, probably exaggerated but you get my point).

Bronze Castings

Bronze castings

If you’re lucky they are bronze, IMO. I’ve been machining a fair amount of cast bronze and mine has machined beautifully. However, I admit that I’m using a mill to do it. If you can find a good way to hold/secure them, you could use the Sherline mill to make them flat. However … if you suspect that it’s pot metal you’ll should check with the committee chair @TBJK for permission.

How to Engrave

Engraving comments

  • DMS does not have the type of laser required to engrave metal (fiber laser).

  • You could use CerMark (or equivalent) to laser mark

  • Hammer/stamps will depend on the material type. Someone in Jewelry can weigh in on this, but I haven’t had good success with a hammer stamp except on very very soft metals; i.e., copper or silver. Of course, I’m also a weakling … :grin:

  • Dunno what to suggest as a fill material, but IIWM I’d do the fill and then polish it smooth to remove any excess fill.

#4

Holy smokes! I am egregiously late in saying so, but thank you SO MUCH for taking the time to think this through and reply so thoughtfully. I can’t tell you how much I appreciate having someone with been-there-done-that experience chime in (and that goes for you and @dryad2b too!)

I was out of town during the Machine Shop committee meeting, but I will bring these with me to the TIG welding class this afternoon just in case anyone has a genius notion about what they are. I do have a couple of extra ones that I got to experiment on, so I can cut into one of those with my Dremel cut-off disc and/or give it a smooch on the bench grinder to expose the interior. Thank you SO much for giving me a place to get started!

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