420 



MECHANICAL. 



CARPENTER'S WORK AND MEASU- 

 RING.— What is called Naked Flooring 

 in carpentry are the joists which support 

 the flooring boards and ceiling of a room. 

 There are different kinds, but they may 

 all be comprised in the three following — 

 viz. : Single joisted floors, double floors, 

 and framed floors. 



A single joisted floor consists of only 

 one series of" joists, sometimes every third 

 or fourth joist is made deeper, with ceil- 

 ing joists nailed across at right angles. 

 This is a good method, as the ceilings 

 stand much better than when the laths 

 are nailed to the joists alone. 



A double floor consists of binding, 

 bridging and ceiling joists; the binding 

 joists are the chief support of the floor, 

 and the bridging joists are nailed upon 

 the upper side of them; the ceiling joists 

 are either notched to the under side or 

 framed between. with chased mortices. 

 The best method is to notch them. 



Framed floors differ from double floors 

 only in having the binding joists framed 

 into large pieces of timber, called girders. 



Single joisted floors, when the bearing 

 exceeds 10 feet, should be cross-bridged 

 between the joists, to prevent them from 

 turning or twisting side ways, and also to 

 stiffen the floor ; when the bearing exceeds 

 15 feet, two rows will be necessary, and 

 so on, adding another row for each in- 

 crease of 5 feet bearing. 



Single joisting may be used to any ex- 

 tent for which timber can be got deep 

 enough ; but where it is desirable to have 

 a perfect ceiling, the bearing should not 

 exceed 18 feet, nor the distance from cen- 

 tre to centre be more than 16 inches; 

 otherwise the bearing for the laths be- 

 come too long to produce good work. 



To find the depth of a joist, the length 

 of bearing and thickness being given — 



Rule. — Divide the square of the length 

 in feet by the thickness in inches, and the 

 cube root of the quotient multiplied by 

 2.2 for pine, or 2.3 for oak, will be the 

 depth in inches. 



Example. — Suppose a joist whose bear- 

 ing is 10 feet, and the thickness 2 inches, 

 what will be the depth ? 



Here 10X10=100, divided by 2, the 

 thickness, =50, the cube root of which is 

 3,684X2.2=8.1048=8 inches, the depth. 



To find the scantlings of joists for dif- 

 ferent bearings from 5 to 20 feet, at sev- 



eral thicknesses, refer to the following 

 table : 



V< fl CO • 00 * CD 03* CD 



0**"* ■*•'•*.•• •'to *vrfl **» 



iffl S 





■5 -S 

 •2 S 



F * 



co 



h * 



11 



3 1 



o a 



5 ] 



Si o 



£ a 



■o a o 



a -a 



5 



6 



7 

 8 



9 

 10 

 11 

 12 

 13 

 14 



!2 



17 

 18 



19 



20 



6% 



V 



4% 



&A 

 &A 

 VA 



9H ^ l A 



9% 9 



10 9 % 

 io'A 9% 



11 io i A 



12 uk 



12^ "# 



13 12 



Girders are the chief support of a 

 framed floor, and their depth is often lim- 

 ited by the size of the timber; therefore,, 

 the method of finding the scantling may 

 be divided in two cases — 



Case i. — To find the depth of a girder 

 when the length of bearing and thickness 

 of the girder are given. 



Rule. — Divide the square of the length 

 in feet by the thickness in inches, and the 

 cube root of the quotient multiplied by 

 4.2 for pine, or by 4.34 for oak, will give 

 the depth required in inches. 



Case 2. — To find the thickness when 

 the length of bearing and depth are given. 



Rule. — Divide the square of the length 

 in feet by the cube of the depth in inches, 

 and the quotient multiplied by 74 for pine, 

 or by 82 for oak, will give the thickness 

 in inches. 



In these rules the girders are supposed 

 to be 10 feet apart, and this distance 

 should never be exceeded; but should 

 the distance apart be more or less than 10 

 feet, the thickness should be made pro- 

 portionate thereto. 



When the breadth of girders is consid- 

 erable, it is an excellent method to saw 

 them down the middle and bolt them to- 

 gether, with the sawn sides outward. This 

 not only gives an opportunity of examin- 

 ing the centre of the log, but also re- 

 duces the timber to a smaller scantling 



