Casting failure on the way to success

I did a lot of work in July and took lots of photos with the idea of writing about my adventures with lost foam casting. There is a lot of good material in the backyard metalcasting forum however I seem to have gone beyond what others have posted about -- although I am sure others have succeeded at what I am attempting.

Now that the hook is baited, what am I attempting? To make bigger castings. My goal is to be able to make a piece with as much aluminum as I can handle myself - about ten to twelve pounds.

With small pieces, lost foam is a piece of cake. You make the foam piece, hot glue a sprue and a vent, plonk it in some loose sand, and pour away.

When the piece gets bigger, everything changes. There is too much thermal mass for the molten aluminum to vaporize the foam. Acetone dissolves foam but then the loose sand collapses into the void. The first technique I tried was to put the piece in petrobond sand, ram it up, and then drip the acetone. Acetone and the vapors are very flammable - probably explosive - so I do this the day before pouring so the vapors have a good time to escape. . There is a flask with petrobond in the photo above sitting in the wagon and you can just see the red color of the sand. No explosions so far

When the piece gets bigger than the flasks on hand the options are to build a bigger flask or do something else. My pieces are often odd shapes, my petrobond is limited, my space for flasks is limited, so I opted for the something else - investment casting. This is simply investing, i.e. coating, the piece with a liquid material that becomes solid. Contemporary investment materials are expensive and require firing in a kiln. The process is designed for lost wax rather than lost foam so it will not work. As a result I have been trying a material that worked for sculptors for centuries - sand and plaster. In the photo above I am pouring a small piece in this investment.

So far the investment casts have mostly failed, however I am learning from each failure so it has been a positive experience. More to come.

Full circle

One of the machinist forums I read had a posting from someone who made a Geneva drive. The disk at the top rotates and the pin, which you can just see at the top left side, catches in the one of the grooves of the elegant piece at the bottom. As it catches the groove it turns the bottom piece, which then pauses until the next groove is caught. There are some animated illustrations of how it works on Wikipedia.

After reading comments of admiration on the machining skills one person asked what use anyone would have for such a thing. I wondered myself and checking Wikipedia discovered the purpose is to change a continuous rotary motion into an intermittent rotary motion. It was first used in clock and watch making where you need to convert a continuously wound spring into intermittent ticks.

Kind of interesting but what caught my attention is that this drive is also used in CNC machines (aka computer driven mills and lathes). Aha! I had a morsel of machining knowledge that my more experienced confreres perhaps did not know. I zipped back to the forum to post and discovered someone already posted they had been using one on a lathe. "I had no idea that's what that was called. Turret on big Warner Swasey VTL uses that for indexing the tools."

Visual inspection.

My day job has been intense the past few months but a month ago I did get some time in the shop. I did some clean up chores and was finally ready to do some art. Plugged in my trusty foam cutter and it did not heat up. Got out the multimeter and everything seemed fine so I decided my power source, an el cheapo battery charger, had died. I was getting 12 volts, but the multimeter does not measure amps so I concluded something was wrong and I needed a new power source.

Another week and I scored a laptop charger - 15 volts and 4.6 amps or 69 Watts. Close enough to my battery charger which is 12 volts and 6 amps or 72 Watts. Plugged it in and nothing.

Now there is absolutely nothing to foam cutter circuitry. My cutter is a piece of MIG wire, tensioned by a spring, that goes to two terminals. Hook up the battery charger and the wire turns red - what could be simpler? The laptop charger by itself produced 15 volts, but when connected to the cutter produced 0 volts! Then I remembered when I first built the cutter several years ago I tried to use a power supply from a computer. It too did not work and I concluded that the power supply 'saw' the foam cutter as a short circuit and shut itself off. Maybe the laptop charger was smart enough to do the same thing. Another week at work went by.

Back in the shop, I remembered a posting on the Miller welding site. Someone had a problem with their welder, lots of people chimed in with solutions, and it finally turned out there was a loose connection. The guy with the problem had wasted everyone's time trying to analyze the problem and one of the experts in frustration posted, 'Never ask for help until you have performed a visual inspection!'

I carefully examined the foam cutter. Everything was fine. Then I looked at the battery charger and noted that the ground clamp had some corrosion. I was ready to throw the thing out so, what the hell, I cut off the clamp and hooked up the bare wire to the cutter. Mirable Dieu, it worked perfectly.

One step backwards, one step sideways, I was finally ready to make some art. So I did, went to take some pictures, and the camera batteries and the two sets of spares were all dead. Maybe the universe is trying to tell me something.

Bruce, Imogen, and me

If you do not know him, Bruce Beasley is an internationally exhibited sculptor who lives in Oakland. The picture shows him standing by one of his smaller bronze sculptures. Awhile ago I heard him speak at a retrospective exhibit at the art museum in Oakland.

He wandered through the exhibit which was arranged more or less chronologically talking about what he was thinking when he made various pieces. The amazing thing I discovered was we think alike about the creative process; how a stray thought or image comes to awareness, gets developed, changed, and finally manifested. How the resulting piece of sculpture triggers others that refine, develop, and take the original impulse into new directions.

Now to Imogen Heap, a more or less pop singer and music creator from the UK. I like her voice and, even more, I like the way she creates most of the accompaniment by playing bits and pieces on a piano and using sampling to create a larger sound.

Last week I came across her web site filled with video blogs. In this vblog she rambles on about a song on an album she is creating and talks in almost exactly the same way about creating music as the way I think about sculpture. I know nothing about music but there was instant communication about the creative process. I felt that if I were working in music that I would be working in exactly the same way that she does.

Does this pretty random sample of three make a trend?

Pouring again

What a relief to get back to casting and art! The first photo shows three castings right out of the furnace. One is a shallow round bowl and the other two are pieces of art. To be more precise, a blob and a piece of art. I also cast a rectangular bowl which is not in this photo. The blob in the middle actually came out the way I designed it but now, I can not imagine why I thought it was any good! The nice thing about aluminum is you can always melt down and recycle your failures.



The next photo shows the rectangular bowl in the mill. I like the contrast of highly machined surfaces with the rough surface that results from sand casting. Those long lines at the bottom of the bowl are caused by the end mill and are variations of, perhaps, several millionths of an inch. You can not feel them - the bottom is perfectly smooth to the touch.

The last photo shows the finished rectangular bowl and the bottom of the round bowl. There is a tremendous joy in using all the machines; saw, lathe, mill, grinder, and wire brush and having them all work in a harmonious way to make the pieces that I envisioned.

Weldors, machinists, and diversity - Part 2

One problem with horizontal band saws is the vise that holds pieces of metal that are being cut. It does not work well and it only holds pieces of metal that are at least 4 or 5 inches long. What do you do when you want to cut a piece that is only 2 or 3 inches long?

Machinists have three solutions. One is a kind of vise jaw extender. It sits inside the vise, but is longer and extends right out to where the saw cuts. The second is to use milling clamps, which all machinists with a mill have on hand. You have to drill and tap holes in the table of your saw and then you can bolt the clamps down to hold the metal you want to cut in place. The third is a pretty neat idea which involves putting a smaller vise inside the larger vise in such a way that the small vise sticks out to where the saw cuts. The photo shows the small vise holding an odd shaped aluminum casting. The jaw of the saw vise itself is on the Left side of the small vise.


The weldor's solution was to take a piece of angle, drill a couple of holes through the angle into the bandsaw base to make a small shelf that sticks out. Then he just used a Vice-Grip 'C' clamp to hold the small piece of metal. This probably took ten minutes.

The weldor may have thought of this solution because weldors have lots of these clamps in their shop - it is the most used method of holding pieces of metal together to be welded or ground. On the other hand, machinists do not have these kind of clamps in their shop. Even if they did I think they would be uncomfortable with the lack of elegance. These clamps do not hold as well as a machinists vise or milling clamps which are designed to exert thousands of pounds of force. Of course the Vice-Grips hold just fine for the bandsaw but I that might well be irrelevant to a machinist.

I was explaining this to my wise wife who told me there is a lot of research on how people form mental models, and how difficult it is to think 'outside the box.' It is one of the strengths of diversity she said.

Maybe I should join a jewelers forum, and an auto body forum, and a sheet metal forum, and ...

Weldors and machinists - Part 1

I have mainly learned everything about metal work from trial and error, and the web. I am a member of a welding site, machining site, and horizontal band saw site. When you work in metal you need to cut it. For several years I used a chop saw which uses a big, thin, movable grinding wheel that grinds through the metal. Works just fine but it throws metal sparks, dust, and grit everywhere. Worse, it is not very precise -- especially when cutting angles that have to fit together.


A nicer way to cut metal is with a horizontal band saw which is quiet, much more accurate, and makes very little mess. They come in two flavors; small, really cheap, and poorly made or big and expensive. I did my research by lurking on the horizontal saw site which is devoted to methods to make poorly made saws work well and to improve them.

This is rambling background coming to the point that both welders and machinists use band saws. However their approaches to modifying and improving their band saws could not be more different.

Welders are to the point; make something that works and be done with it. It may be because many of the welding site members are professional weldors, and in many cases, time is money.
Oddly enough, their solutions, usually involve welding!

You might think this unremarkable, however machinists rarely think of welding anything! If they have to put two things together they mill them so they fit within a few thousandths of an inch, drill precise holes and tap them so they can be screwed or bolted together. Machining is a hobby for almost all the site members and many are retired. Designing, machining, and assembling an elegant modification that takes hours or even days strikes them as the natural way to do things.

That is why I was struck by a welder's elegant, simple solution to the problem of holding pieces of metal that are too small for the band saw vise. The machinists have at least three different solutions to this problem but none of them of come close to the weldor's solution. (to be continued)