GB653742A - Improvements in drafting machines - Google Patents

Abstract

653,742. Draughting-machines. CELLOPHANE SOC. ANON. Dec. 31, 1947, No. 35071. Convention date, Jan. 15, 1941. [Class 97 (iii)] The head of a draughting-machine comprises a frame 10, Fig. 4, arms 21 rotatable relatively to the frame 10 for carrying the scales 11, a knob 13 carried by the arms 21, a locking device 14 also carried by the arms 21 for rotation with the knob 13 and adapted to engage the frame 10 at selected angular positions, a friction clutch device within the knob for holding the knob to the frame when the clutch is engaged, whereby the scale arms 21 are fixed against movement, and a member 16 rotatably carried by the knob 13 and provided to operate the clutch. Preferably the clutch device comprises a cone clutch having one member 22, Fig. 6, fixed to the frame 10 and a second member 23 carried by the knob, a spring 24 holding the cone members apart and the member 16 is threaded on a spindle 25 within the knob so that it moves axially thereon when rotated to engage together the clutch members 22, 23. The locking device 14 comprises a plunger B, Fig. 2, having a conical end adapted to engage in one of a series of recesses in the protractor plate H and mounted to slide in a vertical support in which it can be lifted by the engagement of a pin D with a lever E pivoted at F against a spring G. The undersurface of the lever E acts as a ramp N for a pin 7 carried by the operating lever A which is mounted to rotate about a pin I against a spring J. Rotation of the lever A in the direction of the arrow L lifts the lever E about its pivot F and thus raises the plunger B from its engaged position. The ramp N terminates in a recess O wherein the pin M may be held so that the lever A may be secured with the locking means in the inoperative position. The micrometer screw 26 which normally engages a rack 30 carried by the scale carrying means for fine adjustment is provided with a pivot at its end remote from its nut 28 so that it may be swung out of engagement with the rack for coarse-adjustment purposes. The scales 11 are secured to tapered plates 33 adapted to enter dove-tailed grooves in the scale-carrying arms 21, each arm having a hole 34 lying opposite the inner end of the plate to receive a key by which the end of the plate may be engaged and levered out of the groove when a scale is to be removed.