Stellar
®
Heavy-Duty Telescopic Crane Owner’s Manual | Page 25
Rotation Gear Bearing Worm End Play & Backlash
Stellar
®
Telescopic Cranes have an integral base and worm drive rotation system.
Backlash is the shortest distance between non-driving tooth surfaces in mating gears. Measure
backlash using a feeler gauge at or near the pitch diameter and tangent to the gear.
Locate High Tooth
To set both Worm End Play and Backlash, first locate the high tooth on the gear. This spot is marked
by the manufacturer with light blue paint. If the paint mark cannot be found, use a dial indicator
with a magnetic base and a round steel pin large enough to contact the bearing near the pitch
line of the bearing tooth to locate the high tooth:
Step 1: Set the indicator base on the face of the bearing race with no teeth.
Step 2: Place the pin between two of the teeth.
Step 3: Set the indicator probe on the pin and adjust the dial to zero.
Step 4: Rotate the bearing, checking every third tooth until you find the highest indicator reading.
Step 5: Check three teeth in both directions in this area to determine the highest tooth. The
amount of run-out varies depending on the diameter of the bearing.
Step 6: Once you find the high tooth, mark it for future reference.
Set Worm End Play
Step 1: Locate the high tooth on the gear (See above)
Step 2: Screw a bolt into the threaded hole nearest the high tooth. Screw additional bolts into
threaded holes at 90º from the high tooth.
Step 3: Mount a magnetic base with an indictor attached on top of the worm housing and at the
opposite end from the motor mount.
Step 4: Adjust the indicator to read from the end of the worm shaft. Set the indicator to 0.
Step 5: Using two of the bolts as handles, rotate the outer race back and forth. Read the total
indicator movement. This measurement is the end play of the worm. The specification for
end play is +0.000/-0.004” (+0.000/-0.1016mm). If end play does not meet this specification,
remove the bearing retainer and add or remove shims from the unit. Repeat this procedure
until the end play meets specification.
Set Gear Bearing Backlash
Step 1: Locate the high tooth on the gear (See above)
Step 2: Rotate the bearing until the high tooth is engaged with the worm. Loosen the three bearing
retaining allen head bolts just enough to be able to move the bearing toward or away from
the worm. Screw a bolt into the threaded hole in the bearing nearest the worm.
Step 3: Set the magnetic indicator base on the worm housing with the indicator probe against the
bolt. Set the indicator dial to zero.
Step 4: Move the bearing back and forth. Watch the indicator dial and adjust the bearing in or
out of the worm until the total indicator movement is 0.005” (0.127 mm). Notice: Be sure to
deduct any end play in the worm from the indicator reading.
Step 5: Rotate the bearing 180º. Recheck the backlash. The total backlash should be 0.005” to
0.012” (0.127 to 0.3048 mm).
Step 6: After setting the backlash, torque the bearing retaining allen head bolts while watching the
indicator dial so the correct backlash setting is maintained. Use the Torque Data Chart and
Rotation Gear Bearing Thread Tightening Procedure for specifications.
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