7 face of the disc. After this film is deposited, a disc of abrasive paper is then held tightly against the surface while it is revolving. For the model engineer who lives in a small flat, with little available space for a workshop, the outfit described in the following paragraphs will be of great interest. It ·1-6" 0.0 B HANDLE Fig. 36-Showing the front of the cabinet is a description of a portable lathe cabinet that may be kept in the living room when not in use, and when put on the kitchen table, opened and connected to the electric light socket, forms a complete motor-driven lathe equipment capable of wood turning, metal turning, polishing, grinding, drilling, and numerous other lathe operations. The capacity of the lathe is small and the work that may be done on it is somewhat limited, though sufficient for model making. The cabinet is made of cedar, 3/4 inch thick, the boards having been secured by tearing apart an old cedar chest. that had been discarded. This made it possible to pro vide an exterior shellac finish that presents a good appearance when the cabinet is closed. Iron strap hinges are used for hinging the end, top, and front pieces. Brass handles are provided at the ends to facilitate handling it, and incidentally, they add to the general appearance. Brass dowel pins are used to hold the ends of the cabinet in perfect alignment with the top when it is closed. These are not shown on the drawing. Iron brackets are used to stiffen the back. It will be found desirable to provide four small rubber feet to prevent marring the table upon which it is placed when in use. The lathe used is a "Goodell Pratt," No. 29. It has a swing of 5 inches and the extreme distance between centers is 32 inches. The appliances used with it are as follows: Face plate. Three-jaw scroll chuck. Saw arbor. The cone pulley has two steps for a 34-inch flat belt. The speeds of the lathe spindle range from 1,800 to 2,700 R.P.M. The motor is a small one of the universal type. This makes possible the use of alternating or direct current at 110 volts and develops 20th H.P. The maximum speed of the motor is approximately 1,200 R.P.M. When first placed in the cabinet, the high speed at which it operates caused it to be noisy and it was found necessary to mount it on rubber to reduce this noise. The countershaft is 3 inches in diameter and has ball-bearings mounted in wood pedestals. The ball-bearings are of a standard type and fit into counter-bored holes in the pedestals. The hubs of the pulleys on the shaft fit against the ball-bearings, thus holding them in place. The pulleys are of standard manufacture, there being a grooved pulley 4 inches in diameter which is connected to the 1-inch motor pulley with a round leather belt, and two 3/4-inch face pulleys 111⁄2 inches and 2 inches in diameter from which the lathe 'spindle is driven. The countershaft and motor are mounted on a wood base which is bolted to the base board of the cabinet. The bolt holes are slotted, thus making it possible to take up slack in the lathe belt by moving the countershaft and the motor. The rheostat is just behind the lathe where it can be reached conveniently by the operator. Near it is a snap switch which controls the entire current supply to the motor. Either this or the rheostat, or both, may be used as the operator wishes. If the builder desires, he can arrange a small rack on the back of the cabinet to hold various tools and attachments for the lathe. If such a rack is made, it will be necessary to so design it that the tools will be held in place while the cabinet is being taken from place to place. CHAPTER III DRILLS AND DRILLING Marking work for drilling—How to sharpen drills for various metalsSpeed of drill for different work—Description of twist drills and names of parts—Using the V-Block. Drilling generally forms an essential operation in the construction of anything the model engineer makes, and knowing how to drill accurately and properly is a distinct asset that every amateur mechanic should avail himself of. In the following paragraphs will be found a short but practical treatise on the subject of drilling which has been prepared for that class of readers who have never had the opportunity of becoming learned in general machine shop practice. Unless the holes are to be drilled promiscuously, measuring and marking constitute the first operation in drilling any object. As a means of illustrating, we will assume that we have a brass plate 3 inches square and 1/4 inch thick to be drilled with holes of various sizes. With the exception of the method of sharpening the drills, the drilling of a piece of brass is no different than the drilling of any other metal. The tools necessary for marking are a rule, a pair of dividers, a center punch and a scribe. The scribe, which is merely a sharp-pointed piece of steel used to scratch marks on metallic surfaces, can be made from an old round file ground down on a wheel. A center punch can also be made in the same way. The rule is a steel one of the machinists' type and the dividers need not be larger than four-inch. |