. Electric railway journal . Probably the greatest advantage of the air-brushmethod of covering the interior of motor cases is theassurance of obtaining thorough results. With thehand method of painting, even though the motor casesmay have been cleaned with the utmost care, neverthe-less considerable carbon dust and copper dust will re-main lodged in the corners. If varnish is applied byhand this dust, which is a good conductor, gets mixedinto the varnish and it is very difficult to coat the motorcasing in such a way that the varnish will have anygreat value as an insulating medium. There are
. Electric railway journal . Probably the greatest advantage of the air-brushmethod of covering the interior of motor cases is theassurance of obtaining thorough results. With thehand method of painting, even though the motor casesmay have been cleaned with the utmost care, neverthe-less considerable carbon dust and copper dust will re-main lodged in the corners. If varnish is applied byhand this dust, which is a good conductor, gets mixedinto the varnish and it is very difficult to coat the motorcasing in such a way that the varnish will have anygreat value as an insulating medium. There are boundto be places where the carbon and copper will stickthrough the varnish. The air brush sprays the varnishfinely but with considerable force, and thus the copperand carbon dust are packed against the steel and thor- oughly covered. Also with this brush it is easy toreach behind the commutating poles and the field coils,and thus the whole interior right up to the coils willget a thorough coating. With hand work this prac-. Air Brush for Painting Motor Cases tice would be found difficult. The cost of this brushis insignificant compared with the saving in time andthe improvement in the work. MOTOR-DRIVEN PIPE-THREADER ON COLUMN In the Youville shops of the Montreal Tramways ad-vantage is taken of a building column for the mountingof a motor-driven pipe threading machine, as shown inthe accompanying half-tone. The machine is locatedabout 5 ft. above the floor on a wooden platform, at-
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