Sizing of cast rings?

[Icarleug]

Hello everyone!

I have a question (or two) for those of you more experienced with casting, since I have never had any done before.

Background is; I am making wedding and engagement rings for me and my girlfriend, so naturally I don't want to mess up too badly.
Since we are both not too fond of golden things I thought I'd have it cast in Palladium. So naturally I need to get it cast at a professional caster since I don't have the equipment to solder or cast it at home.

The rings themselves I will design using CAD, then let the caster print and cast it. (I have no experience of working with wax either, plus, it saves shipping costs). Since I know our measurements in mm it is also easy to adjust it in CAD.

According to a caster I spoke to there would be almost no shrinkage due to wax model and casting in Palladium, so that is good.

Now for the actual questions:

1) I will be using a court shaped ring (shallow curved on the inside) for all rings since it is more comfortable. However, my question is how this affects measurements. Since fingers are quite soft I would guess that the measurement would be using the maximum inner diameter more than the minimum inner diameter, since that is what will be pressed against the finger and it will become too loose if only using the minimum diameter.
So, would I make the rings a little bit smaller to match the maximum inner diameter, use the minimum or somewhere in between?

2) Finishing. I have seen a bit of reference that you will lose a bit of material to finish up a cast. The question is, how rough do they usually come out, how much do I need to polish away, and will it affect the size to a degree that I need to adjust for it?

I know I can make it a little bit smaller and then size it up a bit, but I don't want to make it too small or too big to begin with since it is the first time casting, and it will be a fairly expensive one at that.

Do anyone have any (other) advice?

/Andreas

[Dennis]

As the caster says, although the tendency is for a casting to shrink into itself, so in theory it would end up a tiny amount bigger, in practice there is little in it. Also the inside finish will be pretty smooth, but will enlarge very slightly on polishing. So all in all you would make it no more than a half size smaller.

The real crux is that you must take the size with a sizer of the same profile and width as the final ring. Also it is wise to leave this test ring with the wearer for a week or two to be absolutely sure that they are happy with it.

As a result I recommend that you make a plain silver ring first to confirm the sizing, or risk painful resizing later. Dennis.

[Icarleug]

Thank you.

Pretty much as I thought, the biggest issue is that my fiancee is located in Russia and I am in Sweden, so we don't see each other that often. I guess I will need to spend a bit on postage, both from the caster to me and then to Moscow.
She has tried on a few rings over there (and they do size in mm, so it is quite easy to make a CAD model out of it).
Still I would feel better if it was tested (and I can see how much I need to clean up the cast) before making the palladium ones.

/Andreas

[josef1]

I always make the model half a size bigger and it depends on how you have the model made for clean up of its grown allow 0.1 to 0.2 mm for clean up depending on the how big the grown lines are if it's milled you won't need as much extra metal in my opinion on

[Dennis]

Well we have hit a snag in hat I was sure that the ring would end up a fraction big, but joseph who has more regular experience of cast rings says that it will end up a little smaller.

We need someone out there to adjudicate. Dennis.

[Nick martin]

Great idea, and romantic too.. top marks.

I'm by no means an expert on such matters, although I do tend to cast a lot of things from wax models I make.

In my humble opinion, I reckon it'll shrink a little.. or at least thats my experience. Delft clay casting, and of course the more advanced centrifugal / lost wax casting methods should not leave too much clean up to do I would have thought. Casting into something like cuttlefish which is of course textured, does however require quite a bit of clean up on surfaces that are designed to be smooth.

Cheers,

Nick

[Nick martin]

That's turned out nice Andreas, and you've got a good shine on it too.

Quick question though, why did you feel the need to have this ring cast when ( judging by the design of it ) you could have quite easily formed it yourself from the wire?

Nick


Sent from my iPad using Tapatalk

[Icarleug]

Ah, it is made of Palladium 950. She didn't quite like the gold color of gold, and wanted a white shiny ring. Since white gold is mostly grey and need to be plated I figured we should go all the way and make it from Palladium instead. There will be a wedding ring cast as well (these are engagement rings (old Swedish tradition)) later, also in Palladium.

There is no way I could have soldered it at home, I don't have the equipment for it.
I am not entirely sure my landlord would like me to store hydrogen or acetylene bottles in my apartment.

Plus, wire + solder + equipment would cost a lot more than having it cast.

/Andreas

[enigma]

Nice finish!
Incidentally have you seen the 9ct white gold that Cooksons do? its far less grey than 18ct, actually has a very slight yellowish tinge to it.

[Icarleug]

Yes, I saw it and considered it for a while.
I would still need to buy solder and wire, and manage to make a nice shape ring out of it (basically a court shape with flattened sides) + a wedding ring (same style) later, with settings for stones.
This way it is a lot easier to make the wedding ring since I can adjust the thickness to be a little bit higher on the gem side which will make it fit well wit the other.

Plus, it is light and strong, won't oxidize and is a really nice color.
Since it is light it does not cost much more than a regular gold ring, and I still get to work at it a bit.

/Andreas