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Grizzly G4003G Owner's Manual: Bearing Preload

Gunsmith's lathe.
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Place the chuck key in the cam-lock socket
and keep the spindle from rotating.
Using a spanner wrench, or hammer-and-
punch, loosen the outer spanner lock nut
(Figure 57) counterclockwise and remove it.
Figure 57. Loosening outboard spindle nut.
Loosen the inner spanner nut one turn.
Note: You may have to tap on the outboard
spindle tube as explained in Step 7 to help
unload the spindle and break the spanner nut
Place a wooden block over the outboard
end of the spindle, hit it soundly with a small
sledge or heavy dead blow hammer (Figure
58). Your goal is to slide the spindle forward
just enough to introduce spindle end-play that
you can feel by hand.
Figure 58. Introducing detectable end-play.
G4003G Gunsmith's Lathe
Spindle Nut
Place a dial indicator on the cross slide and
move the carriage toward the headstock until
the contact point of the indicator touches the
spindle face (Figure 59).
Figure 59. Dial indicator setup.
Move the carriage an additional 0.100" toward
the headstock.
10. Insert the chuck key into a cam socket and
prevent the spindle from turning. Tighten the
inner spanner nut until you see the motion
of the needle in the dial indicator just barely
stop moving (Figure 60). During the spanner
nut tightening process, rock the spindle back
and forth slightly with the chuck key to make
sure the spindle tapered roller bearings seat
properly in the tapered bearing races.
When the dial indicator needle stops mov-
ing, there will be no spindle end-play and no
bearing preload. It is essential that you find
this point without tightening the spanner nut
too much and inadvertently preloading the
spindle bearings.
Figure 60. Adjusting spindle bearings.


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