CRANE INSTALLATION NBT40 SERVICE MANUAL
9-22 Published 8-01-2017 Control # 287-11
10. The NBT40 needs an after frame of about 92 inches
(233 cm).
Calculate the weight distribution of the complete
machine in order to determine where the crane center of
rotation is in relationship to the center of the rear axles.
A typical mount positions the crane centerline of rotation
from 20 to 24 inches (50 to 61 cm) behind the center of
tandems. At this location, an after frame (AF) length
(distance from center of tandems to back of truck frame)
of 90 to 94 inches (228 to 238 cm) is required. If the AF
is too long, cut off the excess and remove any
crossmembers from back of truck frame.
If the AF is too short, the frame needs to be lengthened.
Use channels fabricated from 100,000 psi yield material
that are the same size as the truck frame. Weld these
channels to the ends of the existing truck frame
channels. Bevel the ends of the channels to get 100%
weld joints with Grade 90 weld material. Fabricate an
inner channel of the same thickness as the truck frame
channels to span the weld joint for at least 12 inches
(30 cm) on each side of joint. Plug weld this channel to
the inside of the truck frame, then skip weld the inside
edge of the top and bottom flanges to the truck frame
flanges.
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5
2
6
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6"
6"
6"
6 "
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FIGURE 9-14
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12 - 6
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