Design Considerations

weld on profiles design considerations

The following are a list of important subjects to consider when specifying timing belt profiles:

  • Weld-On Position
  • Maximum Profile Thickness “s”
  • Weld Beads
  • Profiles with Relief
  • Profile Pairs
profile opposite tooth
profile welded opposite tooth

The flexibility of a timing belt is primarily achieved in the area of the tooth gap. In order not to impede the flexibility of the timing belt necessary to grant a smooth running performance, even with small pulley sizes, the weld on position of profiles opposite the tooth is preferred. In this case, the belt tooth also supports the profile.

profile design considerations
profile design considerations

The flexibility of a timing belt may be reduced by the weld-on profiles. As a general rule, the profile thickness should be selected as small as possible. In the table below, the recommended maximum profile thickness is given in millimeters. The recommended profile thickness is in direct relation to the number of teeth on the pulley. See the chart below.

Example: To determine the profile thickness ‘s’ for a BRECOflex H pitch timing belt in conjunction with a 20 tooth pulley:

  • For weld-on position “opposite tooth” the maximum profile thickness should be less than or equal to 8.
  • For weld-on position “opposite tooth gap” the maximum profile thickness should be less than or equal to 4.

NOTE: for in-between pulley sizes (i.e. 22 teeth) we recommend selecting the next lower maximum profile thickness.

The first number in the chart shows the maximum profile thickness “opposite tooth” / the second number shows the maximum profile thickness “opposite tooth gap.” All thicknesses are represented in millimeters. 

Pitch20 Tooth Pulley25 Tooth Pulley30 Tooth Pulley40 Tooth Pulley50 Tooth Pulley60 Tooth Pulley100 Tooth Pulley
T55 / 26 / 26 / 38 / 49 / 610 / 812 / 10
T108 / 39 / 410 / 412 / 614 / 915 / 1220 / 20
T2012 / 513 / 515 / 618 / 820 / 1223 / 2030 / 30
AT55 / 26 / 26 / 38 / 49 / 610 / 812 / 10
AT108 / 39 / 410 / 412 / 614 / 915 / 1220 / 20
AT2012 / 513 / 515 /618 / 620 / 1223 / 2030 / 30
XL5 / 26 / 26 / 38 / 49 / 610 / 812 / 10
L6 / 37 / 38 / 410 / 5 / 512 / 713 / 1016 / 16
H8 / 49 / 510 / 612 / 714 / 1015 / 220 / 20
XH12 / 514 / 515 / 618 / 820 / 1223 / 2030 / 30
profile with weld beads
timing belt profile with weld beads removed

A bead develops between the profile and the belt back due to the welding process. The polyurethane bead may reach a radius of 0.5 to 1.0 mm (0.020 to 0.040). Should the bead impede your operation, please specify weld bead removed.

profile with releif - drawing
profile with releif

When using wide profiles it is helpful to choose or design a profile with relief. Two examples are shown above. The first shows relief at the base of the profile, known as weld feet. The second provides relief through its angled and hollow design which helps retain the flexibility of the timing belt.

As with regular profiles, the preferred welding position for the best support is opposite the tooth, though a weld opposite the tooth gap is acceptable if necessary.

profiles with beads removed

Profile pairs (profile pockets or brackets) are used in conveying applications primarily for positioning of parts and for feeder insert operations. The manufacturing tolerance for the clear measurement between a profile pair is +/-0.5mm (+/-0.02 inches). A reduced tolerance of +/-0.2mm (+/-0.01 inches) is possible but may require additional set-up or tooling. Please consult Applications Engineering.

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