Sweet! So refresh my memory, how long are you estimating before you have cast prototypes? And is your real business now sold and behind you?
Real business is sold!
Sort of. I’m on a four year payout, so I’m still tangentially involved, but day to day, I’m FREE!!!
I should have cast my first prototype by now, but between the kiln troubles and the basement remodel project, I’m behind schedule.
God willing, end of the month.
Very exciting week here. God willing, the first test pour will be finished by this time tomorrow.
Recall that it starts with wax molds, sprued up like this:
First thing was to place the flask around the mold, fill it with investment, let the investment harden (about an hour or so), then remove the base, revealing the pouring cup molded into the investment:
I realized last week that one hole in my process was that I had no solution for lifting that flask out of the kiln. It is going to be at 1000F at that point, so something was required. That resulted in me putting this thing together:
Then I tested it with the flask (in it’s full state), which proved that just squeezing force wasn’t going to be enough to lift it. Too heavy. I ended up adding some fingers to the lifter, and some tabs to the flask.
Next step in the prototype was to put the flask in an oven (just an ordinary household range) upside down, set it at 275F, and let the wax melt out onto a cookie sheet. No pix of that step. It’s boring anyway.
From there, it goes into the kiln. The purpose is two fold: First, burn out any residual wax. Second, “fire” the investment so it becomes a true solid.
The schedule is to ramp up to 1350F linearly over five hours. Then hold (“soak”) at 1350 for for another five hours. Then allow to cool to 1000F, and hold there until you’re ready to pour.
(IE, the flask has to be hot for the pour, lest the molten metal freeze prematurely and not fill all the nooks and crannies.)
At this moment, there are about two hours left on the soak cycle.
I programmed all that into the PID controller I set up. I don’t remember if I’ve mentioned this yet, but I had the Devil’s own time getting that working. Turns out the first controller I had was defective, and wasn’t sending enough voltage to the solid state relay to fully activate it.
I couldn’t help but take a peek inside the kiln:
When the time comes, I’ll use the beer keg foundry to melt some bronze. Once that is ready, I’ll use the tongs to lift out the flask, and place it on this vacuum table:
That red stuff is a sheet of high-temperature silicone. One of the points of failure I’m concerned about is if it is up to the task of handling the temperatures I’m working with. We’ll see.
This is called “vacuum assisted investment casting”. The idea is that the investment material retains a certain degree of porosity. The vacuum will draw the air out of the mold, ensuring that the metal reaches into all the fine details.
That’s where it’s at.
The deed is done!
Everything went exactly as planned. This is what things looked like immediately after the pour:
One of the things I was worried about was the ability of the silicone sheet used to seal the flask to the vacuum table to take the abuse (heat). Looks like it came through like a champ:
Next step is to wait a half hour or so for the bronze to freeze, then dump the flask into a barrel of water. In theory, the bronze will still be plenty hot to boil the water, and in the process, boil away most of the investment.
Once all that is done, we’ll see if I’m made anything useful, or made a lump of scrap metal.
Absolutely glorious result!
The one mistake I made was miscalculating the amount of investment I needed to mix to fill the flask. Came up just short. Went back and added some more. Turns out, you can’t do that. The bronze slipped into the joint between the two layers.
But overall, I couldn’t be happier. These two may even be usable. We’ll see how well that “flap” of extra bronze comes off.
It cleaned up reasonably well. It’s not a keeper, so I’m not going to put any more time into it.
Still, for a first effort, I am beyond delighted.
One thing I’ve decided based on this is that there is no way to have a cast surface on the back side. Going to have to find someone with a CNC who can machine those.
One advantage of that is there is a limit to how thin I can make the shell for casting. I settled on 0.175″. That’s thicker than it needs to be, and as a result, this thing is pretty heavy. Just about exactly three pounds.
If I cast it, then have someone carve out the back side (it’s basically concave), we can reduce the final shell thickness down to at least 0.125″ or even 0.100″.
Took a fair amount of doing, but I just finished my first casting using the revised process.
Had to go back almost to the beginning.
In order to do the machining, I need to cast in some “ears” that the CNC operator can use to hold the piece. That meant that my molding frames (the MDF pieces I use to hold the rubber molds) needed to be modified. And my flask needed to be resized. And therefore the lid to my flask needed to be remade. And my wax sprue system needed to be re-engineered.
All of that to get to this:
One of the nice things about this modified process is the ears are all going to be at the same outer diameter. That will help out in terms of casting different sizes at the same time.
Those two are pretty much fresh out of the mold, with only a light sandblast to clean off the investment.
Next step is to get the sprues cut off and get them down to my machine shop guy and see what he can do with them.
Your machine shop guy? I though you were the machine shop guy. I still think that. They’re both killer gorgeous. You’re going to need a bigger bank. And a lawyer. On retainer.
I have a question, and don’t taze me, Bro, but what are those circular indentations, if indentations they are? If it’s to accommodate a screw, the one at the top in that 12 oclock position might impinge on one of the little turrets on the crown. I don’t want a screw to even partly cover that turret.