This Homemade Rheostat Has a Capacity of One-Half to Five Amperes, on a Six-Volt Circuit
A rheostat made as shown in the sketch has been used successfully for calibrating a large number of ammeters and wattmeters. One of the general designs suggested will be useful for many other purposes. The dimensions given were used for obtaining a variation of from ¹⁄₂ to 5 amperes with a 6-volt source of electromotive force. For other capacities the proportions may be increased or decreased proportionately. A piece of pine, 7 by 9¹⁄₂ in., forms the base. For resistance wire No. 16 gauge “Climax” was used, but wire of any material which will carry the maximum current without excessive oxidation may be employed instead. Nails support the resistance wire, which should be soldered to the nails to insure good electrical contact. Leads of flexible cord are arranged as shown. These are soldered to the first and last nails in the series. To provide connection between the free ends of the cord and the resistance wire or the nails, 5-ampere test clips are soldered to the cord ends. The teeth of the clip jaws are filed off, and in their stead a short piece of brass wire is soldered to each jaw, as indicated in the detailed view. A nick is filed in each of the brass wires so that they will hold firmly onto the resistance wire or nail. Suspender or display-case clips, suitably modified, may be substituted for the commercial test clips.
In using the device, one clip is moved along the front span. The other is gripped to a nail in the rear row. Sliding the front clip along the span wire insures a fine adjustment of resistance. Gripping the rear clip on the different nails provides the coarse adjustment—R. F. Binney, La Vina, Calif.
¶Glue applied to door-knob screws will prevent them from loosening easily, yet they may be removed without difficulty.
Roll-Paper Feed for Typewriter
Typewriter paper may be fed from a roll where only one copy is necessary and where maximum speed of production is essential. Sections, not to exceed about 11 in. in length, of the typed paper are torn off as necessary. This practice is followed often in newspaper offices. The roll paper can be purchased at any paper-supply house, cut to the width required by the user. The construction of a roll-feed attachment which may be mounted on any of the standard typewriters will be described.
A Paper-Roll Holder for Typewriters That can be Attached to Any Standard Machine
First make the two uprights. Both are cut from ¹⁄₆-in. sheet brass, as shown. After cutting, heat the pieces to anneal them before bending. A hole is provided for the paper-roll rod in the right-hand upright and a slot in the left-hand one. A rod, threaded on one end and equipped with two nuts, constitutes the paper holder. For a guide plate and cutter, cut a piece of sheet brass, 1¹⁄₂ in. wide and of a length equal to that of the carriage, as detailed in the drawing. Bend it as shown. A ¹⁄₈-in. slot is cut almost the entire length of the guide.