The cylinder on the far left is the acrylic stock for the handle. To prepare it, you need to face the ends (scrape off the rough edges made by sawing it off from the rest of the stock) and drill the central hole for the blade to go into. Both those steps are done using the lathe (drilling on the lathe will always feel odd to me, since it's the part that is spinning, not the drill bit). Next you use the lathe to carve out the cone. The milling machine then bores out the six flutes along the length of the handle, and it's back to the lathe to file the dome on the end into shape.Finally the entire thing is polished -- first you sand it with coarse-grit sandpaper, then with two or three finer grades of sandpaper until you finish off by rubbing it down with toothpaste using a sock. If you do it right and put some elbow grease into it you'll get nearly a mirror finish to the plastic which is quite remarkable to see: scratches from machining the handle make the surface of the acrylic very cloudy and it looks like it will never again be as clear as the stock you were given.
The blade is placed into a holder that keeps it at the proper angle for machining the tip, the mill is used to take off the material from one side of the blade and then you flip the whole thing over in the jig to machine the other side. The other end is then faced to length on the mill and a tiny hole is drilled right in the very center of the blade near one end. A matching hole is drilled in the handle and the blade slides in and is held in place with a small pin. Before assembling the screwdriver, the blade is heat treated to increase its hardness and toughness and then polished in a sandblaster.
The hammer, shown disassembled with each piece next to a piece of stock where available, is a much more demanding tool, owing mostly to its increased complexity.
This is a machinist's hammer, not a claw hammer, and it has two faces: a soft face made out of nylon for easily-damaged pieces and a hard-face for driving nails and other more traditional hammer tasks. The first piece I made was the hard face. The hard face is made of AISI 4340 carbon steel and machined entirely on the lathe. After machining it is heat treated just like the screwdriver blade. The 4340 steel is quite hard to begin with and is much more difficult to machine than any of the other materials we use in this class.After working with the hard face, machining the nylon for the soft face felt like butter. There wasn't much to do for this beyond facing it and reducing the diameter. The only noteworthy part was tapping the hole drilled in the back side so that we can easily thread a set screw into it to hold it on to the hammer head.
The hammer head required quite a bit of machining, both on the lathe and the mill. It's made of AISI 1015 steel, though, and is much easier to work with than the hard face. First it must be faced and the smaller diameters must be reduced on the lathe. Then a hole must be drilled and tapped and a "spotface" (very small washer-like indentation against the face of the piece) produced for the nylon soft face to attach to. The other side is drilled out, then reamed to a very tight specification so that the hard face can press-fit into it and hold without slipping out. That hole has a countersink bored into it to make room for the chamfer on the hard face between the two diameters. The head is transferred to the mill where the flats are cut on the sides and the slot for the handle is bored.
Finally, the handle is worked from a piece of wood and the entire thing is assembled. To hold the handle in the head a slot is cut in the top of the handle and a wedge driven between the two pieces of the slot. The spec-sheet says that the wedge is made out of "Red Devil #4" which has defied my preliminary attempts to define.
Moral of the story: take a machine shop class. It's fun, and amazingly useful even if you never step inside a shop again.
~Kyle Marsh
Posts
No comments:
Post a Comment