wax ring sizing

hallo, hoping someone can share their wisdom with me here. I've been asked to make an engagement ring, by my brother, for his girlfriend. Its to be platinum, and after some thought I decided i would carve it from wax and get it cast.
She's given me her ring size, K 1/2, but I'm a bit confused as to what size I should make the wax version to allow for shrinkage. I've seen conflicting advice as to whether the final ring ends up slightly larger or smaller than the wax one. Since it's platinum, and I don't have the equipment to work in it at home, I'd like to avoid having to resize it once it's been cast. So should I make the wax ring a wee bit larger or smaller than a K 1/2??

(also have to make a setting for a diamond, so that'll need to either be a really tight fit or a bit loose)

sorry if this has been asked before!

cheers.

Hey madsally, go for size K in wax, that should give you a cast ring of slightly below K and leaving you enough buffing and polishing to get to K1/2, it's allowing easier to go up than down. Also use a tried and trusted caster for your platinum if your don't have the equipment to rectify any problems caused by bad casting.

Hi madsally,
You are correct in saying that there is shrinkage when casting from wax, so make the ring smaller than the ring size required because when the wax is cast the shrinkage of the metal will make the actual ring size larger than the wax was as it is the volume of the ring's body that will shrink slightly.
I would make the ring smaller than needed and then increase the ring to the correct size by hammering round the ring shank on a mandrel.

James

I find most shrinkage occurs when using rubber molds to reproduce waxs if your casting straight from a carved ring ( I do this with cad rings) it should be minimal approx 1-2%

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Originally Posted by josef1

I find most shrinkage occurs when using rubber molds to reproduce waxs if your casting straight from a carved ring ( I do this with cad rings) it should be minimal approx 1-2%

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Thanks Josef, I've been looking at casting too, so what does this mean if I am making a specific ring size, how do I work out what size to make the master for casting??

hi guys, thanks for the replies. There seems to be a bit of confusion on this topic, as the whether the final rings ends up being larger or smaller than the wax original. I'm having it cast straight from the wax, no rubber mould. I suppose it's possible to make the final ring slightly larger through finishing and polishing if necessary. I don't have platinum equipment, so I have to rent someone else's workshop for that bit.
I'm carving the setting into the ring, for a marquise diamond (it's very pretty!). Should the setting in wax be very tight, with walls thick enough to file back if needs be? I assume this is better than it being too loose.

Also, can anyone recommend a caster? The prices seem to bounce around, but I'm looking for someone who's going to send it back with a decent finish. One that I heard of was Weston Beamor, though their platinum price seems a little steep compared to others I've asked.

cheers again for being helpful, i appreciate it!

The apparent confusion as I see it, is that the metal shrinks into itself as it cools so giving a slightly larger shank. No doubt the casters can give you further advice on this.

I have used West One Castings Hatton garden, and their finish was perfect. Dennis