Pantograph Engine
A machine or instrument for copying on the same, an enlarged or a reduced scale.
Making a Pantograph. In beginning a pantograph attachment we must have an arbor chuck to make our cutter on and to use it on after it is made. It would also be advisable to get a micrometer reading in thousandths of an inch. For the material for the machine we will first get a piece of soft steel 1/8 inch by 3/4 inch wide and 3 inches long. At 3/4 inch from one end we will bend it at right angles, then find the center of its length from the inside of the bend to the other end. Then drill an 1/8 inch hole with its center about 1/8 inch from the upper edge as shown at A, Fig. 245. Next make the two oblong holes B C. A line drawn through their center should come 9/32 inch from a line drawn through the center of A.
Then drill and tap the hole E for the screw that is to hold the index arm. At 2 is shown a plan view of the piece shown in elevation at 1. The blocks shown at F and G are held to the plate, 1, by the knurled screws and steady pin made solid with the block. Now it will be seen that for the different thicknesses of cutters which we wish to make, it will be necessary to move the blocks in order to have the center of our cutter blank come in line with the forming bar shown at H, 2. The hole to take the arbor chuck in block G should be bored out at 20 degree angle; that is what most first-class lathes are in the front end of spindle; with its center on a horizontal line with the center of the hole for the knurled screw.
The block F is drilled on the same line to take the steel center, I. The blocks F and G can be made of hard brass. The block G should not fit the arbor chuck back of the 20degree angle but should be loose, so as to depend wholly on the angle and the steel center at the end of the chuck. Have the arbor chuck accurately centered before taking it out of the lathe. The index at J, 2, can be obtained from any material house of lathe manufacturer. We can mount the index plate in our Universal head and bore it out to take the collar, about 7/32 inch outside diameter. Then bore out the collar to fit the arbor chuck. The index is fastened on to the chuck by a set screw the end of which fits the chuck spline. About sixty (60) divisions is what we need for making cutters from 1/2 inch to 5/8 inch diameter. The knurled screws (2) can be purchased from any large hardware house. The index arm K, 2, should be of steel with a spring to keep it on the index. It will be seen from the drawings, that we are preparing to make <??> pinion cutter of 40 diametrical pitch.
We will now refer to 5. We have a universal joint which gives the free movement of our forming bar, H, 2. The joint is made of two steel rings 1/8 inch wide and 1/16 inch thick; the larger one being 3/4 inch in diameter outside, and the smaller one 1/2 inch in diameter outside. The piece T, 5, is turned to fit the T rest post; see M, 3.
Now drill and tap the larger ring U, 5, and screw in the piece T, having a very tight fit. Next drill and tap the ring U at 90 degree each side of the piece T. The smaller ring has four holes drilled 90 degree apart; two of them being smaller and reamed at a 60 degree taper to take the screws that are screwed through the outer ring and turned at 60 degree taper. The other two holes are tapped to take screws same as in the outer ring; these two screws fit into 60 degree taper holes drilled opposite each other in the forming-bar at 1/8 inch from the shoulder where it is screwed into the plate. (2.) The small forming cutter shown five times enlarged at 6 can be made of a piece of Stubb's wire .05 in. diameter and 3/4 inch long. To turn the taper, set the slide-rest at 6 degree and turn it down till it measures 0.3 inch at .03 inch from the end which is made slightly concave. Then cut ten teeth on it and harden and temper, after which it is ready to be used in a wire chuck in the head stock of the lathe.
The piece P that is fastened to the bed of the lathe to hold the form can be made of cast brass planed to fit the lathe-bed and held in position by a cam lever, as the head stock is. It is made with a step on the end to fit the lower end of the form O; this form is held in place by the screw R. Another view of the form, which is for a pinion cutter of forty pitch, is shown at S, 4; for convenience this is made of hard brass 1 1/2 inch wide and 1/16 inch thick. First draw a vertical line through the center; then make the sides of the form 12 deg. from the center line as in Fig. 246. The lines are connected by a semi-circle and the curves below the pitch line are arcs of 0.3 inch circles; the width of the form at the pitch line is .47 inch, and the length from pitch line to the end is 0.5 inch.
Now it will be seen that the form is ten times larger than the cutter we wish to make and the part of our forming-bar that we move over the form is ten times longer from the universal joint than the distance from the universal joint to the center of our cutter blank, so that everything is ten to one. If we wish to make a cutter of different form it will only be necessary to make an exact form ten times larger than the cutter we wish to produce. If we wish to use a smaller forming cutter than .03 it will be necessary to reduce the end of the forming-bar accordingly, or if we wish to use a forming cutter of .05 diameter to be moved over the form.