VOL.5, NO. 10
AN IMPROYED HOT-WIRE GLASSCUTTER
1289
AN IMPROVED HOT-WIRE GLASS CUTTER J. ALLEN BAKER AND HARRY H. &J.DEMAN,SIMPSON COLLEGE, INDIANOLA, IOWA
Inspired by the difficulty encountered by students of elementary chemistry when doing an experiment which required an 8-inch test tube with rim cut off, the authors sought for some means of cutting glass tubing other than the triangular file method. Various glass cutters of the hot-wire type were considered, with the result that a piece of apparatus was assembled which combined the better features of several instruments, such as portability, simplicity of operation and construction, low cost, and wide applicability. The authors wish to claim no credit for discovering a new principle or inventing a new apparatus. The hot-wire glass cutter has long been used in many institutions, and its principle is familiar to all; but we have never seen such an instrument which combined portability, simplicity, and general usefulness to a like degree.
Construction The apparatus is assembled upon a base of asbestos composition board ("Transite") 12 X 24 inches in size. To support this base, No. 1 onehole rubber stoppers (K) are slipped on stove bolts passing through holes in the four comers. The resistance coil D-Eis wound upon a 3 X 6 inch piece of Transite which is fastened to the base by stove bolts and separated from the base by a tap or washer on each bolt between the two parts. The wooden trough G-H (made in two pieces), acting as a support for the article t o be cut, is also bolted t o the base, and has the end nearest the hot wire covered with asbestos paper which may be glued on with waterglass. F represents a single-contact knife switch, arranged so as to work very easily-at a touch. The hot wire A-B consists of abont 18 inches of No. 21 American Standard Gauge Nicbrome wire, attached a t A and B to binding posts. The post a t B is screwed into a wooden handle, which may be made conveniently from a broom stick. The resistance wire BCDE consists of abont 130 inches of No. 18 A. S. G. Nichrome wire, the length varying between certain limits to be given later. B-D should be long enough to allow plenty of slack wire for easy manipulation of the handle B. At C the wire passes through a hole in the base, going along the lower side of the latter until i t reaches D. The remainder of the resistance wire is wound upon D-E. The apparatus operates on 110 volts, a. c. or d. c.
Operation A piece of glass to be cut is first sqatched lightly with a triangular file at the point where the break is to be made. This scratch need not be deep, nor does it need to encircle the glass. With very large tubes i t is some-
times best to make two scratches on opposite sides of the tube, but this is seldom necessary. After being snatched the tube is laid in the trough G-H and a loop of the wire A - B drawn around it. The scratch on the tube should be on top, while the crossing of the two branches of the loop is below. Adjusting the position of loop and wire so that the loop is directly over the scratch, with the right band the operator holds the wire A - B taut by means of handle B, meanwhile steadying the glass with the other hand and turning on the current by closing switch F with one finger. The wire A - B becomes red, and in a very short time the tube cracks under the loop. There are two precautions to be observed: first, that the hot wire is not stretched too tight and, second, that the two branches of the loop are not
DIAGRAM OP HOT-WIRE GLASSCUTTER
A-B-hat wire, 18 in., $21 ASG. B-C-D-E-resistance wire, 130 in., $18
A.S.G.
C-D-wire runs an lower side of base coil D-E-17 turns (102 in,) resistance (base of Transite) F-single mntact knife switch
G-H-wooden trough ~ . ~ - ~paper ~ b averjug ~ ~ end t of ~ ~ trough (water glass used for glue) B-wooden handle, binding post in end K-$1 rubber stoppers attached by stove bolts for supports
allowed to touch while the current is turned on. Should either error be made, the wire will break, hence i t is well to have one or two extra wires cut, and perhaps attached to the bolts K on the under side of the base for safe-keeping. I n cutting very large pieces, such as large bottles, the glass is scratched as usual, but instead of encircling the bottle, the wire-with loop straightened out-is laid across the top of the glass, and the current turned on until a crack is made. The bottle is then rotated a little and the process repeated until the crack extends around the bottle, when a gentle tap will break the glass along the crack. I n this way almost any size bottle may be cut off.
VOL 5, NO.10
AN IMPROVED HOT-WIRE GLASSCUTTER
1291
The apparatus described above has been found useful about the laboratory for cutting off test tubes, large tubing, broken condensers, bottles, and other things. Of course, it cannot be used with Pyrex glass. In assembling the cutter, a little difficulty may be experienced in getting the right proportion between the relative lengths of the resistance and the hot wires. The dimensions given above were found by trial and error to be effective, although some other lengths may do just as well. An improvement recently made is a new handle with a built-in switch which may be operated by the thumb, leaving the left hand with only one function to perform-that of holding rigid the article heing cut. However, it is hardly possible for everyone to obtain such a switch, lacking good shop facilities, while the simple knife switch is obtainable anywhere, and performs very well.
