Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I had discovered 3D modeling, and had created a model for the green twin oscillator that I built.
My buddy in Canada found a 3D printing place in a nearby city, and so he sent my 3D model to them, and they printed it, and sent the pattern to me.

This is the pattern I received, and I was most impressed with it.
I did not know how to add draft angle in Solidworks at the time, and so I had to glue some wood onto the outside of the rim, and sand it down a bit.

The top of the flywheel casting had some sand inclusions, where the sand mold broke off and fell into the molten metal, and this defect leaves a hole in the casting.
The bottom of the flywheel was destroyed when the residual alcohol burned and gassed as the hot metal ran into the mold.

Lesson #1 learned:  No alcohol/graphite spray on petrobond.

My next casting used a core, and the sand I used for the core was sandblasting sand that was adhered using a sodium silicate binder.
I thought the sandblasting sand would be sufficiently fine, but it turned out to be rather coarse material.

I did not know that the top of the flask had to be weighted, and so the mold halves separated, and the aluminum 356 partially ran out.

Lesson #2:  Add weights on top of the flask before pouring metal.
Lesson #3:  I made the pattern for this casting out of thin balsa wood, and that turned out to be a mistake because after several uses, the pattern broke into numerous pieces.  Don't make patterns from balsa wood unless they will be a one-time use application.

And although the core remained in place pretty well, but was not mechanically fixed in position in the mold, so it probably shifted a bit during the pour.

The top of the casting turned out fairly decent.
The bottom was another disaster.

At the time, I had no idea about how to set up gates, runners, riser, etc. in a more standard configuration that is often used in foundries.
Fortunately the exact setup of gates, runners, risers, etc. is not critcal, and I almost got a usable casting.

My next casting was a demonstration for my brother's friend, and I learned lesson #4, which was use different size pins on either side of the flask.
The flask consists of the upper section called the cope, which is just an open box, and a lower section called a drag, which is also just an open box.

I made the drag mold, then made the cope mold, separated the mold halves, removed the pattern, and then unintentionally rotated the cope 180 degrees when I put it back on top of the cope.

Lesson learned again.
Trial by fire as they say.

My Petrobond (this is a tradename for an oil-based foundry sand) was beginning to dry out, and so I made the mistake of adding oil to it.
This ruined my sand, and ruined the casting also.

Lesson #5:  Don't add oil to your petrobond.  Add alcohol.

So I was just stumbling along, learning as I went.

I was getting close to creating usable parts, but still experiencing lots of blunders, and it seemed like I may be up against an infinite learning curve.

This was my first attempt at an iron pour, and I learned lessons #5 (don't pour iron into petrobond, although some folks successfully do this), and lesson #6, don't open the mold soon after pouring iron into it, because a cloud of smoke will rise up out of the sand, and will combust, and burn all the hair off of your face, and potentially blind you.

I was not wearing a face mask when I broke this mold open, since I assumed the dangerous part was over, and so I was met with a ball of fire in the face.
I saw it coming, and closed my eyes, but burned off some of my eyebrows.

My wife yelled "What the heck just happen?  Where did all that smoke come from?".
"Just a minor scratch" I yelled back (I always say that regardless of the injury; its a marital thing).

The petrobond began to fail as the iron filled the mold, and so I had some sand inclusions in the rim.
I did not know if I would ever succeed with another iron casting, so I decided to repair the flywheel and use it, and it is the flywheel that is seen in my final green twin oscillator engine photo.  I turned the flywheel to hide the repair, and the repair did not affect the flywheel structurally.

So I succeeded with my first attempt at an iron casting, and not because I understood how to cast gray iron, but more through luck and chance.
Casting gray iron involves some procedures that are not necessary with aluminum, and so it can be tricky to cast if you are not aware of exactly what to do, and when to do it.

 Luckily the casting turned out to be easily machinable with no hard spots, in spite of me not using ferrosilicon additive, which I was not aware of at the time.
For iron castings that are thinner than this piece, using ferrosilicon is a must to prevent the iron from becoming very hard like tool steel.
So I lucked out and got a usable iron casting on the first try.

Melting aluminum can be a rather casual affair, and a steel crucible can be used, a temporary brick furnace, a rudimentary burner, propane, and the burner does not have to be fine tuned in order to get aluminum to pour temperature.

Almost anyone can melt and pour aluminum, although it is a step up from pouring the lower temperature metals such as lead-free pewter or similar metals that pour at perhaps 450 F ?

Many people use aluminum extrusions, and aluminum cans, and neither of these are very good for engine castings.
The best aluminum to use for casting engine parts is alloy 356, which is generally the material used for auto engine blocks, and aluminum auto rims.

To melt iron, it is easiest to use an oil burner, and forced combustion air is required.
And the burner has to be adjusted somewhat accurately in order to get iron to pour temperature, which is perhaps 2500-2600 F.

I was able to cast a second flywheel in gray iron, but I did not understand the iron casting process, or the correct burner settings, and was having great difficulty, and so after this second flywheel in iron, I cast the remaining parts for the green twin oscillator in aluminum 356.

At the time I made this flywheel casting, I was not sure if I would ever be able to make another casting of this quality.
I had a poor understanding of the entire casting process, especially the iron casting process.
I now cast iron routinely, and all my final engine parts are in gray iron.

I still cast permanent patterns in 356 aluminum sometimes, when I intend to cast multiple pieces, and want a more durable pattern.

This second flywheel turned out with no defects, and I was very proud of this.
I sent this flywheel off to my Canadian buddy for him to use on his green (he painted his engine gray) twin oscillator.

It took several more years of experimentation in order to find the correct burner setting in order to get consistent and high quality iron castings.
And I had to change to a bound commercial sand mold in order to get the quality I wanted.