Sunday, May 16, 2010

Boring Head - doing it right (for me)

I decided to stretch my machining skills by making a boring head that would extend to bore up to 3" diameter holes. I found the plans on the web created by Joe Worthy for an engineering program - unfortunately I have lost the link.

As a learning experience it was a success and the good news was that the many mistakes I made -- several of which are part of the final result -- do not interfere with the function.

The first issue encountered was figuring out how the boring head actually works, something obvious to the designer but not to me. Next up were improving my techniques for centering, for measuring, and for milling dovetails and removing broken taps. Then there was deciding when a component had so many mistakes it should be discarded and redone rather then fixed. Painful but not too difficult because it is something done in sculpture all the time.

The most creative challenge, however, was modifying the plans to fit the materials I had available. I well understand that it is not in my character to be a good machinist but I have been trying to do the best I can. It was a kind of breakthrough to successfully figure out how to change a design and make my machining skill limitations work for me rather than try to overcome them. Working with strength rather than overcoming weakness is something I practice as well as teach and, as is so often the case, seeing it in yourself is much harder than seeing it in others.

There is someone who posts on one of the lists I read with the signature, "If you can't do it right then don't do it at all." There is a truth in that however there is also a truth in getting it done even if you can not do it right.

Friday, January 15, 2010

I love it when a plan comes together!

I wanted to make a set of fire place tools and was inspired by some parts made by King Architectural Metals. They are called baskets and are traditionally made by blacksmiths to demonstrate their skills. These are machine made and I thought they would make nice handles. The photo shows all the ingredients; some sheet metal, a basket, some 1/2" EMT left over from a project, and a steel ball which is also from King.

Although EMT is galvanized and one needs to take care of the fumes when welding the inside dimension is 1/2". This works nicely with the basket which is designed to fit into a 1/2" diameter.

I had the design pretty firmly in mind and so did not make any plans. The next photo shows the results, exactly as I had pictured it. While my welding still needs a lot of improving my grinding has gotten pretty good to compensate.

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.