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Casting hollow balls with decorative cutouts - Advice needed!


I must say that this is my first time asking a question on the Orchid. Usually if I have any queries workshop related I find everything, but this is something I would love and really appreciate some advice or tips on…

End result needed
hollow ball with decorative cut outs.

My process up to now
I have two silicone moulds with each half of the sphere which is wax injected. These models I lost wax vacuum cast in silver. I then have to solder the two halves together at the end which is extremely time consuming.

My question
Is there a way where I could join the two halves of the sphere wax models together prior to lost wax casting as to avoid having to solder them??? Of course without losing any of the decorative wire rim details.

Thank you in advance for any help!

You could join the two halves with small dobs of hot wax prior to investing, but you’ll have great difficulty cleaning the insides after casting.
If you add a couple of keys to the halves so that they mate without slipping, soldering them will be much easier. You can use any sort of locking tweezers to hold them together when soldering, and the keys will keep them from slipping.

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Thank you Elliot.

The dobs of wax would probably ruin the details. The spheres are only 8mm in diameter so the insides are small and wouldn’t need much or any cleaning up apart from getting the investment out. Could one half of the wax model be touched on a hot plate and then quickly joined to the other?
The keys are a great idea and would definitely help with soldering if that is still what I would have to do in the end.

I agree with @Elliot_Nesterman adding keys is essential. However I don’t think using the keys fo alignment is the most productive. I would recommend the keys be used to align the wax halves then spot weld with wax. I would use a simple dental tool. Locate your sprue as you would if casting the halves, in fact the halves joined with the sprue may be sufficient. Depending on your equipment you can remove the investment by ultrasonic, vibration, or tumbling. Or with a dental pick as a last resort. Hollow objects are FUN.
Regards RLW

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If you are doing many hollow balls, set up your bench with partial hemispherical holes that support the lower half. sand the halves to be flat, the put the bottom half in the hole in your block, flux the inside edge and the joining edge, but not the outside, lay 3 very thin pieces of sheet solder in a triangle on the lower piece edge, place the top half and heat gently - the solder will pull to the seam. You can do many in a hour. It’s a good technique, but requires finesse at the outset, then speeds up with practice.

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I don’t cast, but 8mm isn’t that big. Why not cast them solid?..Rob

Thank you for your input.
This is the same way I have been doing them up to now. I think I did over 200 of them the other day (uff). I would ball bur out many holes on my charcoal block. I made some powder solder and mixed it with powder flux. I dip one half in water, touch the solder powder (it sticks to the wet half) and place it on top of the other half while introducing the flame. It solders quickly as the powder is easy solder. I am always eager to find a more efficient way of doing things that’s why I was hoping to have a solution in casting them already joined.

The design wouldn’t be the same if it were whole without the cutouts. When you make many of them it makes a difference in weight. I can do them in gold too with the same mould (we know how much that would influence on the cost).

Thank you for you input. I will try spot welding with the wax. I am afraid it will get messy and ruin the details, but Ill give it a try. I usually remove the investment with my power washer out in my garden. I do get investment all over me, but it gets the job done. I only put it into my ultrasonic if there is a little investment left on it. My ultrasonic is on a 3l one so I can’t fit much in it.

Sorry, I didn’t catch the cutout part. Looks like you cast in two halves unless the cut outs can be just depressions that you oxidize or color in some way. Good luck…Rob

Cheers Rob!

Hard to say exactly without seeing the part, but it sounds to me like a perfect application for a water soluble wax core.

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I have heard of this and am considering looking more into it @bgober1. I think another wax injector is needed in the process. I think I’ll have to do some more research and see how much this stuff costs.

It’s a tricky process and difficult to describe how to do it but essentially it would be like this:
Make a sphere the diameter of the inside of the ball. Drill a hole through it with a .050” drill bit run it in and out a few times to barely enlarge. Mold it with the wires in place. Inject with water soluble wax You may be able to run them through your cut outs. You’ll need to bend the wires on on opposite sides. What I’m getting at is that you want to have a way to make a mold with the two halves of the model
In place on the sphere with the wires in place. You could probably just glue them on. What you want is a way to “suspend” water soluble wax core in the cavity and shoot the was around it. Of course you’ll need to re use the wires for each step. I would go with a fairly high durometer low temperature cure silicon or urethane mold. BTW-cold sodium bisulfate will dissolve the core much quicker - you could grow old waiting for water to do it!

I saw this video from Rio about using water soluble wax to create hollow core wax models such as beads. I have not done it, but it looks interesting. It may be worth the effort if you do a lot of these.