Smithy Midas 1220 LTD - Manual (Page 49)

mandrel. When removing a mandrel, drive it back out of, instead of through, the hole.
You can purchase hardened steel mandrels, which have a slight (0.003") ground taper
and an expanding collar, to facilitate mounting and demounting (Figure 10.13). Mandrels
with compressible ends for holding single or ganged pieces are also available. When a
workpiece is mounted on a mandrel, machine it as you would a solid shaft. You can drill
eccentric centers in mandrel ends to permit eccentric turning.
Figure 10.12 Mount workpieces too long for a chuck on a mandrel.
Figure 10.13 Hardened steel mandrels have a slight ground taper and expanding collar.
Steady Rests and Follow Rests
Rests are for setting up (1) work that is relatively long in proportion to its diameter or (2)
work whose dead end must be left free for boring or other operations. You can also use
rests to machine slender shafts that are apt to spring out of alignment from the thrust of
the tool. The purpose of a rest is to support the workpiece and maintain it in accurate
alignment for machining. Rests are classed as steady rests or follow rests.
Steady Rests
Steady rests mount on the lathe bed (Figure10.14). Clamped over the ways, they provide
three bearing surfaces. These surfaces bear down lightly but rigidly against the surface
of the shaft and keep it from moving out of the line without interfering with the
operation.
To set up a steady rest, first center the work in the chuck and true it up. Then slip the
steady rest into position and tighten it to the bed. With the bearing jaws clearing the
work, close the top of the rest and tighten the locking screw. Now, with the lathe
running, adjust the three bearing jaws to touch, but not push, the workpiece. Finally, test
again for alignment, making sure the axis of the workpiece coincides with the axis of the
lathe. Otherwise, the end will not be square and the surfaces and boring will be untrue.
The tips of the jaws are bronze and require lubrication.
10: Setting Up with Centers, Collets, and Chucks
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