Another noob question- delicate/thin part removal from mold

AGE this hobby/side job, can get out of hand really fast if you let it. Hell I came out of retirement to fund my growing need for real working equipment. I didn't buy any premade equipment just the parts to make them like temp controllers, ceramic fiber and heating elements. You can make a burnout oven using a flower pot and an old hot plate (not the new style). There are ways around certain things.

This book helped me greatly. Some of the info just validated I was doing things correctly and some was a real eye opener.
Lost-Wax Casting: Old, New, and Inexpensive Methods Paperback – Illustrated, February 23, 2006
by Fred R. Sias Jr., (Author)

This is what I use for investment.

PRODUCT DESCRIPTION
Prestige ORO is a true premium gypsum bonded investment developed and perfected for the casting of gold alloys up to 22K. To achieve the very best casting surface possible, ORO incorporates specially graded refractory minerals and specialized control chemicals that are proven to out-perform all premium investments currently on the market.
Prestige ORO have proven to be a truly superior investment for gold that far "SURPASS THE INDUSTRY STANDARD."

 

Bill I'm going down the machining road now. The machines were cheap compared to what's sitting in the tool cart. Ever time I turn around it's another $100 and the wife is starting to notice.

 

I know what you mean. You need to make more things for the wife that require the new tools... I just bought a belt/disc sander from HF (I know, not even a $100) because the wine stoppers she wants made needed sanded or filed flat on the bottom. I'm not really sure I could do the finishing without that type of sander.

 

A clever ruse. I like it.

 

When you burnish using a wire wheel, are you using a steel or brass wire wheel?

 

An 8" steel wheel, you have to be careful not to overdo it, too much force and you lose the shine and begin to smear the metal.

 

I use brass course and fine on any copper or copper alloy. I'm afraid the steel will be too abrasive.

 

So my basic procedure for anodizing an aluminium casting is:

1. Work the sand casting finish with a steel wire wheel to smooth over the roughness of the metal to a "brushed" finish.
2. Next it goes into a fairly dilute caustic soda tank for a few minutes to degrease/pickle.
3. Water rinse and into a 20% nitric acid solution made from common 68% nitric acid.
4. Water dip
5. Anodize in the anodize bath.
6. Dye with colour.
7. Seal the dyed piece with nickel acetate solution or wax or steam bath/hot water.

 

For a lot of people here, finding a convenient source of nitric acid is going to be an issue, is it essential or could you suggest a work around?

 

It's an oxidizing acid: it "desmuts" any greyness in the aluminium caused by the caustic exposing silicon and makes it silvery white and gives a starter oxide layer for the anodizing process. Maybe try some aluminium cleaner with the 10% hydrofluoric acid from the auto stores. I get my nitric from a cleaning supplies store that makes up their own product from various chemicals, like alloy cleaner and high strength degreasers.

 

Hold that thought. When I finally get to the anodizing step, I’ll be asking questions.

 

FWIW, I just checked the msds for Caswell's desmut, it's 18% concentrated sulphuric acid, 6% sodium nitrate, the rest is distilled water.

 

I think nitric acid is made by distilling a mixture of sulphuric acid and a nitrate together like in this video at the 1:35 minute mark.

 

Another day, another failure.
Injecting the wax has enabled me get good wax positives pretty reliably and quickly. So...next step-
I previously made a slurry of ceramic clay that I used in an earlier attempt at shell casting. Those results were pretty good considering I had zero idea what I was doing. I now mixed the slurry with some plaster of paris because...oh hell, why not?
I made it way too pasty, but continued on to see what would happen. I made the trigger guard molds (2) , and baked them in my little foundry somewhere near 700 F to remove the wax and set the mold.
During the pour, I had a hell of a time hitting the little sprues and got lousy pours.
I am encouraged though having learned a few things. Need to re-think the sprue configuration. Also, I’m going to remix some more of my secret investment recipe, because...oh hell, why not?

 

A for effort!

 

Next load in the crucible, add a dead piston or three. That alumin(i)um is lacking in silicon. I'd almost say you might need to adjust your alloy to get the part to come out good - in addition to the other variables common to Foundry.

Adjust as in, "adjust the amount of silicon, etc. to get the most-free-flowing aluminum you possibly can."

 

Something like this....