Interesting with the 4 spru’s. I typically use a single spu and gate to avoid getting any draught as the metal flows causing a fracture. Guess it really depends on the type of metal?
Actually, the way you sprue depends on the model. As in this case, you can’t expect the metal to flow through all that lacy design with a single sprue; especially silver.
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Hi everyone! I want to thank you all for continuing to post about your casting methods and results – we find all of this insight and information extremely helpful, and I’m sure our fellow jewelers and casters on the forum do as well.
@katkramer I’m so glad to know yours prints have been coming out great, and it looks like you’re working through the casting kinks! Beautiful designs, I can’t wait to see the finished product! 
@rclaborne I’ve had a number of clients mention adding boric acid to the investment as a strengthening agent. Are you using Plasticast, Satincast, or something else?
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you dont add boric acid to resin specific investment like plasticast. doesnt matter what std investment you use it can be strengthened with boric. for the record, i use r&r ultravest.
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Thanks, all. I’ll be casting tomorrow around noon, and I’ll keep you posted. @rclaborne, I didn’t realize that the 45° angle was important, thanks for the clarification!
Crossing my fingers! And I’ll try the boric acid with my Satincast. I haven’t had any problems with flashing or cracking in the Satincast, but I wonder if my curing the prints for 2 days is helping avoid that problem?
You’ve got some good answers above, the only thing I would add is to look at the following books:
With an honorable mention to this:
The first book is crucial, IMHO, if you’re doing your own casting. The second is mostly handy for bench jewelers, but has some good info, and is worth the read. The third is strictly optional - it’s a rambling, self-published, tome that repeats itself over and over again. Having said that, it does stress the following points:
- Your casting setup is unique, you have to learn its character
- Always use the ‘wedge’ principal when sprueing (thick items to the bottom, thin to the top, like a wedge)
- There can only be one correct temperature for your metal
- Experiment with flask temperatures - if you get partial fills, raise by 10°, if you get perfect casts, lower by 10° until you find the right balance - the lower flask temp, the lower risk of porosity.
- All your hard-won temperature calculations can go out the window when the seasons change
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I have two of those…and another one on ancient casting techniques. Thanks so much for the reminder!
Anyway, I have good news to report. Today I have successfully (on first look) cast two flasks, and two more are coming out now. I used 1850°F for the metal temperature, and the flasks were at 1150°F. I’ll clean them up and report back. I cast both the four-sprue versions and the other version with the sprue coming into the back of the bezel. I did also use the wet towel method, and I can tell that it forced metal into the gate.
Woot!
UPDATE: There is some porosity on at least two flasks, and I’m guessing the other two as well. I’ll try bumping down the temperature. I am able to grind a little away and it’s not as noticeable since these are small, about 5/8-3/4". (about 20mm).
I do have a question that I’m hoping someone is willing to answer. I would be curious about the best way to clean these up. I usually take a toothbrush to it, brass brush it, and then put it in the pickle, hand finish with silicone abrasives on the Foredom, 3M Radial Bristle Discs, sanding sticks, buff with a muslin buffing wheel and rouge/tripoli/zam, and tumble at the end. Is there a better or more efficient way to do this? Is there a better way to remove the investment and clean these up?
Another one I like, which is where I found the information originally on steam casting, was in this one…
Lost-Wax Casting: Old, New, and Inexpensive Methods
I have a heated ultrasonic cleaner filled with pickle. I heat it to 45 °C, give the cast items a quick brush, then put them in there for 20 minutes, then in a pin polisher for 40 minutes. After that, all the investment is off, and there’s a base shine to work with on the models. After that, like you say, tumbling, 3M discs, muslin buffing wheel, etc.
EDIT:
While I was typing the response above, I actually had a couple of pieces going through this process (a friend has 2 daughters who are really into the Japanese anime ‘Attack on Titan’. He asked me to design and cast them some pendants):
So this is from 20 minutes in the hot pickle ultrasonic, and 40 minutes in the pin polisher with no human intervention. All the investment is gone, there’s a dull shine, and they’re ready to have the sprues filed off the backs and jump hoops. The left one is exhibiting some of the porosity you sometimes get with the castable resin, but it’s pretty shallow, so will polish off.
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Did you print these on a Formlabs printer?
Yep. Done on my form 1+ in castable resin.
I scrub with a stiff nylon bristle brush and water then put in ultrasound bath for 10 mins or so, I then heat with a bushy flame 'til cherry red, quench in water & pickle them in a bath that can get a bit dirty. I take them out the pickle, rinse, re heat then quench and put them in a second, clean, pickle. They come out of that nice & clean. It’s then standard polishing techniques,
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When you cast these flask, did you burnout with the buttom face up? Been reading that with resins the button should be up for better air flow
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@arthurr43, no, burned out face down. I’ve had no problems with doing them that way, although my flasks are on a metal burnout tray with a screen so they are lifted up from the bottom of the kiln. I know that sometimes I have a little investment stuck in the wax button, so I turn them upside down to make sure that melts away and into the tray.
Oh, and I am printing now, and just noticed blue resin around the bottom of the tray…it appears to be leaking! It’s about 1:45 a.m., and I have 32 minutes left. I guess I’m going to wait it out and clean up the machine. I hope it’s not a big mess that does damage to the machine. I don’t want to stop the prints…I paused it and took a paper towel and wiped up a little that I could see. I’ve only had it since late June, so I hope it’s nothing major.
@katkramer I use a burn out tray for wax and remove after 30 minutes at 300 degrees and remove most of the wax residue so i does not smell up the store when it burns. Do you even need the tray with resin? My understanding is that it does not melt but actually burns…
thanks
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The caster mentioned they were using sterling silver, not fine silver. When working with silver, the melting point for .999 fine silver is 1761 degrees F and with sterling silver, it is 1640 degrees F.