My Personal Site

Coin Project - (again)

Well...! Over the Christmas holiday I started over with the coin. I had intended to plan ahead and get some sculpting wax. But I used the same type of wax as I did before. It's patching wax. It's a translucent, cloudy white. Patches of white, and dirt, show through the clear parts, which makes it hard to tell where the surface really is. I bought a fluorescent desk lamp, which helped.

I did a better job this time because I wasn't so rushed. It's hard to stop. The more time I spend, the better it looks - but it's never really good enough. Those block letters were real hard. I'd scrape with a straight edge, and the wax would deform unevenly. Afterwards, the surface would be white crystalline. I'd pat with my finger and find a bumpy surface, and the edges would be deformed. Argh! But as time went on, the thing did look better. This time I included the school year.

I built a wall of clay around the bottom of the coffee mugs to hold rubber. Yes! I have time to make a rubber mold this time!! I didn't have time for this step before the homecoming game. Back then, I put the original pattern right into the investment mud and hoped the first one worked - which it didn't. When people ask what the mark under the chick's armpit is, I say, "It's an enigma". I've found that sometimes that answer suffices. In fact, it's my personal mark. That's the first, and distinguishing, letter in my signature.

So, here are the two new patterns, ready for rubber.

I haven't used the rubber in over a year, and the rubber I have is three years old. I've taken care of it, but I was uncertain about its quality. I also pretty much forgot the procedure, too. I would spray a coating of release agent on the pattern first. That might cause problems if it's too deep or not deep enough. I decided to try the process on a scrap pattern, in order to test things. I didn't want to risk my new originals yet. As it happened, things went real smooth, (figures, right?) So, one day later (that's how long it takes for the rubber to set up) I bathed my new patterns in rubber.

Here they are, all smothered in rubber. This is after they've been setting overnight in the spare room - at 65 degrees. They are already set up, in this picture. Here, I am about to open them up for a look.

This is what I found. It's hard to tell if it's good or bad, by looking. The only way to find out for sure is to pour some hot wax in there and let it set up. That doesn't take long at all.

Here's the hot foundry wax. I cooked it up in the garage, then brought the crock pot inside and spooned out the wax. I like the way it smells. My old, unacceptable coin is there on the table, too.

Here's what I found. I am very pleased. The dark and light spots you see in the chick background are only from the film of mold release that was left over from making the rubber mold. It wipes right off. I only have a very little reworking to do on these patterns. Then, I'll stick them together and put them in the investment. Since I have a rubber mold now, I can turn these things out by the hundreds! And, my original patterns are still as good as new. I'm happy.

(time passes)

Well.. I made a cashe of bird cash. I was having a great time. What fun. (Little did I know..)

This is what I envisioned for a spru. I was thinking that the coins would shrink noticibly, since they're so think this way (both sides being poured together). I thought that a big fat spru would help keep pressure on the freezing metal below. I intended to build the spru's thickness right above the coin.

This is how I made the sprus. I jammed some clay between the coin and the sides of a small box. I propped the box up to get an increasing dept to the wax.

The problem was in getting the wax coin sides thin and flat on back. You'll recall that the first time, I poured each side seperately and machined them down, then welded them together. I decided that that would be best again because it is real hard to carve foundry wax thin and flat. Also, I can save investment by pouring in pieces. My flasks can be smaller. I also like the idea of pouring into an open faced mold.

My very cool wife, Michelle, held this up to the light and had me take a picture. It looks cool.

This looks cool, too.

Here's a close up. I intended to fill voids with patching wax, but that is too much trouble.

You can see voids where air bubbles were (look at the 2 and 5). There are other small voids. I decide to scrap all my wax and cast again. I'll run a tool all around inside the rubber mold after pouring the wax, to get the bubbles out. I think I can make patterns with (almost) no voids. Defects in the smooth background are hardest to hide with patching wax.

Coin Project - (even more)

Well, I was optimistic, but I had nothing but trouble when it came to casting.

These are just some of the rejects. I have more at home and in the car. I started out casting two at a time - a Chick and a Duck. But after a few bad ones, I started doing one at a time.

Early on, I suspected the real problem was that I was pouring them "open faced". That was different from anything I'd done before or seen in books. It seemed possible that I needed to bury the pattern in the mold and pour through a spru. The metal in the spru, above, would add pressure in the mold.

This casting is not typical in that several turned out better. But this one clearly shows the trouble I had with all of them. The distortion is worse in the low parts of the background. In the mold, these would be the high spots that the hot metal laid over. I suspected that, rather than moisture expanding into the metal, hot air or some gas from the investment was the problem.

This one looked different. I suspected that the smaller voids in the background were from slag. Maybe I didn't skim well enough. The dent at my pinky is from the welder. I was practicing and learned to be more careful. The dark color is from the stainless steel brush.

This one turned out just fine (The only distortion is to the knee above the "C".). I still don't know why. I tried to get others to turn out like this. I called the people who supply the investment and asked them. I called a real art sculptor. I read books and articles on the Internet. I tried hot metal, cool metal, hot molds, cool molds, and every combination.

I decided to attach sprus and bury the patterns. This is a hurry-up job to make sprus.

I also sent the guys at Ransom & Randolph (investment supplier) some wax patterns. They agreed to try casting some, after my desperate plea.

We only had three weeks of school left.

With this one, I went so far as to attach a vent, so that the air could escape from the bottom instead of having to bubble through the metal.

I suspended the pattern and spru on heavy wire. This was awkward.

The patterns wanted to float out of the investment. I had to weight them down with steel, being careful that they didn't rotate away and tough the side of the flasks.

I needed more metal than what I could ladle, so I welded up a way to hold a small crucible.

This is the result. It's an improvement, but there are still defects in the background.

The defects are small, but unacceptable.

I thought of flawless castings in the world around me and wondered, how in the heck do they do it?

The guys at R&R sent me a couple nice castings and pictures of how they did it. Although they had told me on the phone that pouring "open faced" was not suspect, they did make and used sprus. I called them and asked what the picture above showed. His answer, "A vacuum table". ! !!!

A what? !!!

He said, that to be save, they used their vacuum table to draw air out of the mold while the metal was poured in. Of course!

I made up some more molds, but ran out of investment. Above, you can see that gating system is exposed and I didn't reach the top of the flask - no spru.

I welded up this spru and placed in on top of the investment. I would pack sand around it.

Here it is, ready to pour.

I drilled holes in the bottom, to suck air through.

This is the hurry-up job vacuum table. A student, Brett Tiggelman, threw this together for me. We had two weeks of school left.

It's hard to see, but I hooked a shop vac to the table and turned it on. The hose collapsed, but I decided to go with it anyway.

I also had some old molds left over, with no sprus. I was waiting for delivery of more investment, so I decided to cobble sprus above the best looking one. I put it in a sand flask.

Then I put another welded up spru on top and covered with sand.

Here it is on the table, with hot metal in place. The ingots are to weight down the cobbled spru. Brass is heavy. I could imagine it floating the lid off and leaking all over.

This is what happens when real thick metal freezes and cools. It shrinks. A little tunnel formed that reached all the way down. It didn't cause any problems.

Getting the brass out of the steel spru wasn't easy.

When the new investment arrived, I had time to make a couple more molds. (One week of school left.) You can see that I've learned to leave the bottom off the flask, and to simplify the spru.

This is also real smart. Rather than suspend the patterns, I stuck them to the steel sheet underneath. I also filled the crack with wax, to keep the investment from leaking out.

This is what it looked like. (The wax only sticks real good if you clean the steel with a solvent. Otherwise, it breaks off and the pattern floats up into the investment. I learned that earlier.)

I wanted to add vents, to help suck the air out, but forgot to make wax vents. I stuck pencils in one mold and pens in the other. (I ran out of pencils.) I was able to pull the pens out afterwards, but the pencils broke. They burned out in the kiln, except for the lead. I left the investment below the "top", so that it wouldn't rest on the vacuum table when I turned them over.

This is what they looked like before going into the kiln.

This is the result. They look fine, except for this discoloration and small texture defect. I was able to clean this off easily with a wire wheel.

The same discoloration and texture covers the casting. I think it might be avoided with cooler metal. I'm not sure.

This one also has a couple beads, where bubbles in the investment stuck to the wax, (bottom and thumb). Those came right off with a chisel.

This is the first hurry-up job of welding and machining, along with the castings from R&R that I machined. This is the last day of school. I got this done at 6 pm. I handed it off to our superintendent at the 6:30 pm farewell meeting.

These are the R&R castings that I machined. They are bronze.

I used brass. I sand blasted mine, to clean it. Then machined it.

Here they are again. I came back during the summer to weld and machine two more of these coins. I gave them to the principals at our two high schools. I'll hand the bronze castings to our superintendent to go in a display.