MOTHER's Fluorescent Glass Tube Cutter

A dowel rod, some wire, a few screws, a switch, and a car battery are all you need to make this simple glass tube cutter. You probably already have most of the materials at hand.
By the MOTHER EARTH NEWS editors
September/October 1978
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The completed fluorescent glass tube cutter looks something like this.

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The principle of this amazing little glass tube cutter is quite straightforward: A stainless steel wire, which can be heated electrically, encircles the tube. When the current is on, the wire heats and melts into the glass. Then, when the power is turned off, the glowing wire immediately cools, causing the glass to cool unevenly and break apart on the melted "score line".

You can build your own cutter in about an hour with a drill, some assorted bits, a handsaw, a hammer, a center punch, a tap and die set, a chisel, a hacksaw, a pair of wire cutters, and a screwdriver.

Start by cutting the 1 1/4" X 7" wooden dowel exactly in half lengthwise. Then temporarily nail a short scrap of wood to the rounded side of each dowel half and clamp them, one at a time, in a vise so that the flat side of each half faces up.

Now take your handsaw and cut a 1/8"deep lengthwise groove down the center of each half-dowel's flat side. Then use a wood chisel, carefully, to open one end of each of these grooves into a wider and deeper (5/16"-wide, 3/8"-deep, and 1 1/4"-long) slot.

Next drill four 3/16" holes through the dowel halves (one hole 1/2" in from each end of each half). And use a 3/8" bit to bore two holes (each about 1/4" deep but not all the way through the wood) into the flat faces of the half-dowels about three inches from their "unslotted" ends and to one side of the center grooves.

Now drill two 5/32" holes—one 3/16" from the end and the other 3/8" from the opposite end—through each of the two 1 1/4" X 5/16" X 5/16" square steel rods. Cut threads into each of these four holes with a 10-32 tap. Then put the square rods—one at a time—into the vise "short-end" (the end with the hole drilled through it 3/16" back) out and bore a 1/16" hole lengthwise into each block 3/32" from the edge, until the drill bit pierces through into the first tapped hole.

Next, stick a length of .032" or .034" stainless steel wire into the 1/16" hole and thread a 10-32 machine screw into the end of the tapped hole closest to the wire until the screw touches the wire's edge. Cut the rest of the screw off flush with the side of the square rod, then lock the sawed-off "stop" that is left in the hole firmly in place by nicking the cutoff stub with a center punch where it meets the face of the square rod.

Line the two wooden handle halves up with each other, tape them together, mark and drill the four 3/32" hinge-mounting holes in the handle's butt, screw the hinge firmly in place, and remove the tape.

Then take a length of good lamp cord, separate one end of its two insulated strands for about nine inches, and peel a half inch or so of insulation from the end of each strand. One of these separated and peeled wires should then be threaded "in" through the 3/16" hole on the butt end of each half of the tube cutter's wooden handle and run up through the groove sawed into the flat face of the handle half so that its bare end can be seated under—and directly in contact with—the square steel block which mounts into the "business end" of each half of the handle. Slip the two steel blocks into position ("stopped" sides facing each other) and secure each one in place with a 10-32 machine screw.

Note that the steel blocks—and all metal hardware in each assembly—are recessed into the wood so that neither block or any of its components can create a short circuit by touching the other. Electrical current can ONLY travel down one strand of the lamp cord to the steel block on its end, through the loop of stainless steel wire connecting the first steel block to the second, and then back through the second strand of the lamp cord.

Finally, cut a 5" length of .032" or .034" stainless steel wire. Stick one end of the wire into the 1/16" hole in the end of one of the cutter's square steel blocks, secure the wire tightly in place with a 10-32 machine screw, and then form the stainless wire into a circle and clamp its other end into the other square block in the same way so that the ends of the handle will never quite touch when the loop of stainless steel wire is squeezed around a fluorescent tube.

When the above adjustment has been made, separate the handle halves and insert the small compression spring into the holes that were drilled for it.

At this point you're ready to hook your cutter up to a 12-volt car battery, a transformer, or an automobile cigarette lighter tap. In any case, the unit's on/off switch is nothing more than an automobile headlight dimmer switch. These are available from any wrecking yard for pennies or from an auto supply house for about $2.00.

Cut a notch, if necessary, into the end of a piece of scrap 2" X 6" lumber and mount the dimmer switch to the board. Then connect one lead (it doesn't matter which) on the cutter to one pole on the battery (or to one of the cigarette lighter tap leads), and the other wire from the cutter to one terminal on the dimmer switch (use a butt connector).

It's then easy to run a length of wire from the dimmer switch's other terminal (use another butt connector) to the remaining pole on the battery or the other cigarette lighter adapter lead. That's it! You're ready to cut fluorescent tubes, bottles, jars, even water glasses.

Just hook up your power source (alligator clips work fine), fit the loop of stainless steel wire around the tube of glass you want to cut, and depress the foot switch. Then, when the wire glows red hot, depress the switch again. The hot stainless wire will cut the cylinder of glass "to order." The wire, of course, will break from time to time (due to its constant expansion and contraction) but it's easy to replace ... certainly a whole lot easier than trying to cut glass tubing with a conventional glass cutting tool!

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