Thursday, November 12, 2009

One thing leads to another - Ring Roller interlude

Some friends asked me to design a gate that incorporated calligraphy in the design. I thought I would do the calligraphy inside a circle and I started working on a prototype. I usually make circles by wrapping some 1" x 1/8" bar stock around a cylinder of some kinds a piece of pipe ora paint can for small ones or a trash can for big ones. This circle was about 12" in diameter and nothing in the shop was the right diameter. I thought about cutting a piece of MDF in a circle but didn't want to cover all my machines to protect them from the sawdust.

'It's only a prototype' I thought and being lazy, I quickly made the circle using my Diacro #2 bender. This is a beautiful piece of equipment for making precise, discrete bends. I made a small bend every 1" around the circumference and while my friends liked the design, all I could see were the bends, each one a precise angle. I did not want discrete bends, I wanted a smooth circle. In short, I needed a ring roller!

My first stop was the web where I saw lots of expensive ring rollers for sale, and some cheap imports. I went to Harbor Freight prepared to buy one but when I actually saw the way it was made -- not well -- I could not bring myself to purchase it. I wound up designing and building a ring roller with enough capacity to handle up to 1 1/4" wide bar stock, 1/8" thick. Several trials, about five weekends, and I had some education in how to design and fabricate (or rather, how not to d & f). Just as important, I had a new tool and some rings.

I took pics of the design and will post them eventually - too many to put on this blog. As for the gate, I am still working on the overall design.

Sunday, September 13, 2009

Three steps backward but four foward!

Every year I make a ceremonial bowl. As a result when I discovered rotary tables I became enamored. Not only could I make gears but I could finish bowls. Apart from that, they are beautiful machines.

I looked at rotary tables, used a big one on a Bridgeport, and realized the only practical size was an 8" table which can hold a piece that is 5" - 6". They weigh 70 to 80 pounds which is about what I can lift onto the mill. After lusting for about a year I got finally nabbed a nice used table. Perfect - except most of my bowls are larger than 8" and I needed at least a 12" table.

A solution is to extend the size of the table by finding a big disk of plate steel and fastening it to the table. The only problem is that I did not have the steel and, depending on the thickness, it too could weigh another 70 pounds. Because my acquisition of a rotary table was aligned with the Universe (apologies if this is too California) I soon came across a posting by someone who had a similar problem and solved it with an extender. This is four pieces of rectangular steel, each with a protrusion that fits exactly into one of the slots of the table. It has some countersunk holes so it can be fastened to the table, and sticks out a few inches so a large work piece can be held down.

The progression is bowl -> rotary table -> project. The project consisted of four pieces of steel, exactly the same size, with a protrusion that just fits the slots in the table, and countersunk holes right down the middle to hold it down with T nuts. I also drilled an tapped two additional holes so I could screw in pieces from a clamping kit. I can not tell you how many mistakes I made. At least three major mistakes and they were so embarrassing that is all I am going to say about them. Fortunately, I found a way of fixing all of them and making it all work.

The first photo shows the extender in action. There are three extenders (hidden) that are used to hold the various clamps and the mill is cutting a nice arc in 1/4" plate. The work piece itself is about 18" long.

The next photo shows how one of the extension pieces fits in the groove. There are two countersunk holes for bolts that fit the T nuts. The last photo shows this piece turned on its side and one T nut is shown. The extensions convert the 8" table into a 12" table.

Thursday, August 13, 2009

Lost Foam Casting 2 - Foam, Surfaces, and Sand

What foam to use? Almost all foam sold in building supply stores contains fire retardant. The right property for home insulation but the wrong property for casting. The fire retardant makes it hard to cut with a foam cutter and increases the thermal mass which in turn increases the risk of a short pour; i.e. a pour where the aluminum freezes before vaporizing all the foam.

Styrofoam pieces sold at craft stores work fine however the grain is coarse and the price is wrong. The best foam is from packing materials such as boxes that contain appliances, electronics, or computers - fine grained foam, no fire retardant, free.

Surfaces and sand: I like foam casting because it is quick. Make the piece, plonk it in some loose sand, pour. This, however, leaves a rough surface with embedded particles of sand. I like this surface for some of my art but it is terrible for anything that will be machined.

The topic of surfaces depends upon the sand. Using fine sand such as petrobond or green sand will produce a surface that matches the foam surface.

When you use a tool such as a grinder, rasp, or even sandpaper not only does it leave foam dust everywhere but the surface is coarse. A hot wire tool such as a foam cutter or an inexpensive soldering iron seals the surface as it melts foam. Other techniques I have read about, but never tried, are dipping the piece in molten wax and coating with latex paint. Reportedly these leave a smoother surface however as these materials get exposed to molten aluminum they burn.

Wednesday, August 12, 2009

4 holes, 4 pieces of steel, 4 machinists

I am making a kind of tool which consists of four bars of steel, each with four holes drilled in it. The holes do not need to be precisely located but they do need to be on center and straight. 4 holes, 4 pieces, no problem.

According to the book, the proper way of drilling a hole is to use a spot drill, then to drill a relatively small diameter pilot hole, and then to drill the full diameter hole. There will be a machine screw put in the hole so I also need to drill a countersink so the top of the screw will be flush with the bar of steel. Let's see -- 4 holes, 4 pieces, 4 drill bits - that comes out to 64 separate operations.

I made a pilot piece and discovered it is a pain to change from spot drill, to pilot drill, to full size drill, to countersink. The other way is to do all the spot drilling, change to the pilot and do all of them, then do all the full size drilling, and then all the countersinks. This too is a pain because it takes awhile to keep lining up each operation on center. And there are 64 operations.

Which is faster - or might there be a different and better way? The books, at least the ones I have, are no help for this basic a question. It takes experience - and so I turned to my favorite machining forum on the web. One reason it is my favorite is that if I am polite even the dumbest question is answered.

I asked, and I got four different and better alternatives to the two methods I had inquired about. With one basic question I received insights that will serve me in my future machining. Throughout my adult life I have learned to value experience and here was yet another proof.

This started me musing on book learning vs. experience, and how this particular body of knowledge is vanishing. Manual machining is almost dead due to computer controlled machining. My lathe is sixty years old and works fine now but in another forty years it will either be scrap or be in a museum. As for today's machinery - which are almost all too big to fit in a home shop - there are already 3D computer printers that print solids. It is fairly easy to see that printing metal, nanotechnology, or something else will whisk away today's computerized machining equipment if not within twenty years, certainly within forty years. Manual machining knowledge is destined to become a tiny niche, much the way there are a very few people who preserve the knowledge of making wooden wagon wheels.

Machining is very interesting to me, and I am so appreciative of experts who share their knowledge, it makes me sad to think of the future. Then I realize this is not knowledge of eternal truth, it is knowledge of the real and material world. Its very nature is to change, perhaps to die, perhaps to morph into something else. The proper response is not sadness but gratitude and enjoyment and even as I type this I am back in that place, in those emotions.

This weekend it's back to the shop. One of those new suggestions would reduce the 64 operations to 20. Hmm....

Friday, August 7, 2009

Lost Foam Casting - 1 Foam Cutter

All of this treatise on lost foam casting of larger pieces will begin with the same title so, if you are not interested, you can skip these blogs.

The first thing one needs is a foam cutter. A hot wire is superior to cutting, sanding, or grinding foam to a desired shape. It leaves a clean, sealed edge The only downside are foam vapors which can not be good for one's health so I wear a mask when I cut.

There are tons of plans for cutters on the web and the prevailing aesthetic seems to be to make them as much as possible with scrap from your shop. You need a power source, a wire that can get hot, and a way to hold it together.

Power source: A/C is dangerous although some folks use bell transformer. I had a computer power supply that had enough power but shut off as soon as I connected it. My theory is that it was smart enough to sense a short circuit and shut off to not damage the computer. I wound up buying an inexpensive battery charger that puts out 10 amps at 12 Volts. Beware, the more expensive automatic shutoff models do not work because you can not control them. Get the less expensive fixed charge model that produces at least 8-10 amps. I have seen very inexpensive models that put out only 2 or 4 amps and they are not enough.

Wire: Since I weld, I have MIG wire available. Inexpensive, easy to replace, lasts a surprisingly long time. If you do not weld you can get a small spool at Home Depot. I use .023 or .025 wire; .030 works but needs more power to get hot enough so I prefer thinner wire. You do not need expensive wire such as nichrome.

Hear Control: A light dimmer works fine with the battery charger.

Assembly and wiring: As the wire gets hot, it will stretch. In order to keep it tight, the top arm of the cutter is on a pivot (a bolt) and there is a spring at the back to keep it pulling upwards. The bottom picture shows this assembly and a black alligator clips from the battery charger. The red clip is connected to the bottom of the post to a piece of lamp cord that runs underneath the base.

Lamp cord runs from the top out across the arm, and is wrapped around a bolt - you can see it in the top picture. The MIG wire is twisted on to the other side of the bolt. At the bottom there is a hole in the base for the MIG wire to pass through to connect around another bolt to the lamp cord.

To provide clearance for the wiring on the bottom, I glued some wood strips to raise it about an inch.

Bill of Materials: scrap wood; four bolts and nuts; battery charger; light dimmer; outlet box for light dimmer; about 4' of lamp cord; plug; MIG wire.

Design Feature and Flaw. In the middle picture you can see that the top arm is angled. The spring is off to the side so it tilts the arm. As a result the wire is not perpendicular to the base. I will fix this some day but it is only an issue when cutting a very thick piece of foam.

The feature can be barely seen in the bottom photo - a line of holes extending at 1/2" intervals from the wire to the front of the base. These holes are just big enough for a small finish nail. When I want to cut a circle, I run the nail through the center of the foam and put it in the appropriate hole. Turn on the power, rotate the foam, and you have a nice disc of foam.

Sunday, August 2, 2009

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.

Wednesday, June 10, 2009

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."

Tuesday, May 19, 2009

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.

Tuesday, February 17, 2009

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?

Saturday, February 7, 2009

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.

Friday, January 30, 2009

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 ...

Thursday, January 29, 2009

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)