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T–69 SECTION 18    DOUBLE-SIDED BELT TOLERANCES This type of belt was introduced briefly in Section 5.1, page T-10.  As previously described, this type of belt has teeth on both sides to provide synchronization from both driving surfaces.  This special  feature  makes  possible  unique  drive  designs,  such  as  multipoint  drives,  rotation  reversal with one belt, serpentine drives, etc.  It may also provide solutions to other difficult design problems. Double-Sided  Belts  are  similar  in  construction  to  regular  synchronous  belts,  including  nylon- faced  teeth  on  both  sides.    This  construction  uses  essentially  the  same  design  parameters  as standard synchronous belts.  Their torque ratings are the same as conventional PowerGrip Belts of identical pitch and width. Double-Sided  Belts  are  available  in  MXL,  XL,  L,  3  and  5  mm  HTD  and  T5  and  T10  pitches from stock. See "Timing Belts and Pulleys Locator Charts" in the product section. Double-Sided Construction Tensile  members  of  the  PowerGrip  Double- Sided  Belt  are  helically-wound  fiberglass  cords providing the same load-carrying capacity as single sided  PowerGrip  belts.    The  body  is  Neoprene rubber  providing  oil  and  weather  resistance  and protection for the fiberglass cords.  Both sides of the belt have a specially treated nylon tooth facing that provides a tough wear-resistant surface with minimal friction. Double-Sided Tolerances Since Double-Sided Belts are manufactured and cut to the required width by the same method as   standard   PowerGrip   belts,   the   same manufacturing  tolerances  apply,  except  for  the thickness and center distance tolerances listed in Tables 38 and 39. Overall  thickness,  opposing  teeth  symmetry and  pitch  line  symmetry  are  closely  controlled during Double-Sided Belt manufacture. Specifying Double-Sided Belts The available Double-Sided Belts and other double-sided belts from stock can be found from the Timing Belt Locator Chart, on page 1-2 of the product section. Double-Sided Drive Selection Double-Sided Belts can transmit 100% of their maximum rated load from either side of the belt or in combination where the sum of the loads exerted on both sides does not exceed the maximum rating of the belt.  For example, a Double-Sided Belt rated at 6  lb×in  could  be  used  with  50%  of  the  maximum rated on one side, and 50% on the other;  or 90% on one side, and 10% on the other. Fig. 37    Double-Sided Belt Tolerances 15 to 20 20.01 to 30 30.01 to 40 40.01 to 50 50.01 to 60 60.01 to 70 over 70 ± .020 ± .024 ± .026 ± .030 ± .032 ± .034 To be specified Table 39    Center Distance Tolerances Fig. 38    Double-Sided Belt Application Belt Length (in) Center Distance Tolerances (in) Belt XL (.200") 3 mm HTD 5 mm HTD MXL L T5 T10 Table 38    Belt Thickness Tolerances T (in) .120 ± .007 .126 ± .006 .209 ± .007 .060 ± .004 .180 ± .012 .130 ± .010 .268 ± .014 W (in) Ref. .020 .030 .045 .020 .030 .035 .071