AMATEUR VACUUM TUBE MAKING
COMMON FIXTURES USED IN TUBE MAKING
A fixture is a specialized tool. Some are used to hold glass, some to hold wires, some to position parts of a tube together. Fixtures can be used to make tubes. It is not as convenient as having a glass lathe but it can be done and is a viable alternative to having a lathe. Using fixtures is not to be considered a desirable alternative but it is possible if a lathe is not practical to make. Here we examine a set of fixtures that are needed to make basic tubes.
The roller stand is one of the most basic of glass holding tools. It is made of wood, metal, or plastic.
One of the most common tasks in glasswork is cutting off pieces of glass tubing to size. The roller stand is used to hold the tubing while the diamond saw makes the cut. Two sizes of roller stands are needed. One for small diameter tubing (1/2 inch to 1 inch) and one for large. (1 inch and up) Tubes smaller than 1/2 inch can be broken by hand.
For the small diameter tubing, a simple V groove in blocks of wood or plastic are satisfactory. For larger diameters of tubing the friction of the V grooves becomes excessive so rollers are desireable. Wheels robbed off of casters work fine, or you can cut disks of plastic from a piece of bar stock. The diameter of the disks should be about 1 1/2 inches. Be sure the hole in the center for the screw is closely centered so the wheel doesn't wobble. Space the wheels apart so that a piece of 3/4 inch diameter glass will not fall through while a 2 inch piece will ride smoothly. The spacing of the blocks should be about 8 to 12 inches. Provisions for moving the far block closer can be made so that shorter pieces of tubing can be supported. This can be as simple as using double sided carpet tape to hold the block to the base. Simply replace the tape when it gets too weak to be satisfactory. Or, you can put multiple pairs of screw holes in the base and use screws to hold the movable block. The V or roller should hold the glass tube about 3 inches above the table.
A simple 2 jaw chuck design that has capability of on center or off center positioning. The jaws are shown in two positions for a small diameter tube and a large one.
Above is shown a simple design for a 2 jaw chuck that is used to hold glass. The radius of the arms is made such that the V blocks are always on center. The V blocks are mounted on 1/4 inch dia. shafts protruding from the arms and are free to swivel to match the position of the glass. It can be seen that the tube can be set to be either on center or off center. This can allow centering or off-centering of the tube, a proceedure that is sometimes needed. The arms are fastened to the faceplate with screws with wing nuts to allow tightening them in place. Centering is done by hand. The jaw blocks are about 3/4 inch square with the V cut about a third the way in. They should be made of teflon because they do get hot sometimes! A chuck like this could be made entirely using hand tools.
Above is a small lathe that is made using the chuck design. This was used to successfully make tubes before the glass lathe was built. The main disadvantage is that when joining two parts one of the parts must be held by hand, demanding a steady hand!
A possible solution is to mount a clamp arm to the column that can be positioned to hold the second part.
This lathe has the ability to rotate from vertical to horizontal depending on which position is desired to work on the piece. The bearing is a large surplus bearing that is available online. The motor is gear driven to the bearing but it could just as well be friction driven since there is no force on the parts. Using this simple-to-make lathe you can successfully blow great looking spheres and other vacuum tube shapes from glass tubing.
The glass flare must be held while the pinch seal is being made. Since the entire flare will be at high temperature the holder must be able to repeatedly take the hot flame near it. Here are two designs of flare holder. The top design was a first attempt. It uses three spring loaded arms with grooved disks to hold the flare. It is very difficult to get the flare into the disks so that design was abandoned.
The lower design is much simpler. It uses a spring loaded "sissor" arrangement of two arms. The arms are U shaped with a V notch cut in the end to accept the edge of the flare. The design works great and is used for all the seal making operations. The shaft of the holder is held in the lathe chuck.
Above are shown two models of wire holders. The shaft on each is 1 inch in diameter for size reference. The top holder has a spring loaded clamp. To make one, a paper clamp available at most office supply stores would work fine. Get a small one since the total width doesn't need to be wider than about a half inch. The lower model has a swivel joint inside the shaft. This allows the wires to be centered more easily in the lathe. The clamp is a piece of spring steel that clamps down on the wires using the thumb nut.
Putting slight pressure inside a glass item while hot is done to expand the glass. To do this, a blow hose is used. A rotary joint makes the hose useable with the lathe. To make a rotary joint, get a 1/4 by 1/2 shielded ball bearing. Make a tube and a cup like the drawing. The bearing can be glued in place with super glue. Be sure not to slop glue into the bearing itself. The free end of the bearing tube is pushed into a rubber stopper (get on ebay) that plugs into the glass tube end.
Tube can be held vertical or the head can be rotated horizontal
Above is a small fixture that is used to assemble a tube. The rods slide horizontally to position the parts and hold them in place while the glass is sealed. To get to all sides, the entire fixture is simply laid over on its side. This fixture has one side with a gear driven slide but that is not necessary if you can't find a drive unit like that. Simply make both sides slide through a block like the left hand one. The rods are made according to the type of tube being made, and may have wire slots like these, or carbon holders, or cup holders with set screws. This can take the place of a glass lathe for assembly and is used even now to make tubes.