Popular Science Monthly 



305 



Determining Brake Horsepower 



THE brake liur^rpowcr ol an ciigiiu.' 

 or motor is often determined i)y 

 means of a friction or proncy brake. 

 Make two wooden iiiocks A and B to 

 fit the face of (he iniiley on the machine 

 to l)e tested. The pieces C and D are 

 fastened to the two iilocks and the whole 

 clamped together by means of the two 

 bolts E and F with the nuts G and // to 

 tighten or loosen the whole. The end of 

 the arm D has an iron eye in it to hook 

 to the spring balance J which is hung 

 from some suital)le sup|)ort. When the 

 pulley is revolving in the direction indi- 

 cated at its best sfieed tiie nuts G and H 

 are gradually tightened imtil the friction 

 is increased on the pulley and the arm 

 pulls downward with considerable force. 

 This tendency to turn will be indicated 

 upon the spring balance. 



The net pull at the balance is obtained 

 by subtracting the net stationary weight 

 of the arm from the indicated weight at 

 the balance when the test is made. 

 This distance is represented as N. The 

 correct speed of the pulley or revolutions 

 per minute must also be known. After 

 all this data h;is been obtained the 

 brake horsepower of the machine can" be 

 calculated by the following formula: 



Brake Horsepower; 



X W RPM 



33,000 



— .3.1416 



N . Length of arm in leet. 



W . Net pull, in pounds, at the spring 

 balance. 



RPM. Pulley speed. 



This method, simple as it is, will be 

 found of great service in determining, 

 accurately, the brake horsei)ower of a 

 motor or engine. — B. F. Uashiell. 



The brake horsepower of a 

 motor can be accurately meas- /y^'\^)i\ 

 ured by means of a simple appar- j (^ p -^ 

 atus such as the one here shown 



Preventing Carriage Bolts from Turning 



C.\RRIAGK bolts are generally used 

 in fastening sheet-metal parts such 

 as dust-aprons, mud-guards, etc., to 

 automobile running-boards. While these 



/AJuminum Co>-e'rnq 



Wotxf Seen- L^-i 



An ordinary wood-screw will prevent bolts 

 from loosening and turning 



ha\"c a square shank to pre\ent them 

 from turning in the wood, if the running- 

 board is of soft material the bolts are 

 liable to cut away the wood surrounding 

 the .square shank and make it ditticult to 

 either remove or apply the nut. This is 

 not a serious matter if the bolt head is 

 exposed so it can be held by wedging, 

 or if it has been provided with a screw- 

 driver slot before assembling. When 

 the running-board is covered with lin- 

 oleum, which is nearly always shellacked 

 in place, or aluminum matting, which is 

 held by small screws and binding-strips, 

 it is difficult to get at the bolt head. The 

 usual installation, shown at A, can be 

 improved materially by following the 

 scheme shown at B. This can al.so be 

 used if the bolt has been installed and 

 the square shank has turned. A i/8-in. 

 or 5 32-in. drill hole is made in the bolt 

 head and a suital^le wood-screw inserted 

 and firmly set into the wood, as at B. 

 This is insurance against the head turn- 

 ing and prevents an upward movement 

 of the bolt when an attempt is made to 

 screw on the nut. — Victor W. Page. 



W 



A Celluloid Flashlight 



HKX a ruby light is not availa- 

 ble for developing photographic 

 prints an ordinary flashlight will serve 

 the purpose. Remo\'e the lens and fit 

 a disk of red celluloid in its place. Turn 

 on the light and the celluloid will redden 

 it, protecting the negatives from direct 

 light.— C. Id. Miixi-k. 



