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- Dec 25, 2011
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First, in a used flat bed lathe, the ways will show the tarnish and wear pattern typical of these lathes when they have had at least a little usage in the past few years. The narrow tarnished band is on the part of the ways not touched by either the carriage or the tail stock. The front and rear parts of the top of both ways should show no tarnish, indicative of a lathe that has had at least some recent use. If the ways are tarnished across their full width, the lathe probably hasn't been used recently. And if the entire surface is bright and shiny, someone recently polished it (or it is new). If you need to evaluate the bed wear, do so by measuring the way thickness of front and rear ways about every 3 inches from the right end of the bed up to the front of the headstock. The nominal new readings for Atlas built lathes would be 0.375" from end to end for the 9", 10" and early 12", 0.438" for the 6" and .500" for the late 12". Establish the actual new thickness from the readings at the extreme right end of the ways or under the headstock. Do the same measurements of the width of the front and rear ways. The width of the front way usually shows minimal wear because the reaction force is mostly taken only by the rear way.
In a used lathe, there will be wear in the cross feed nut and maybe the screw as well. To evaluate the wear condition of the nut and screw, first crank the cross feed nut completely off of the screw. Then properly adjust the screw end float by differential adjustment of the two nuts on the visible portion of the cross feed assembly. One nut holds the crank on. The other may be just a thin pattern hex nut, a threaded collar or the visible part of an internally threaded shoulder bushing. This end-float should be as near to 0.000" as you can get it without there being much drag when turning the crank. Then pull the cross slide back toward you while turning the crank CCW until you can just see the end of the screw with the cross slide chip guard removed. Take the slack out by turning the crank a little CCW and zero the dial. Turn the crank CW until you just feel the thread in the nut hitting the thread on the screw. The dial reading is the normal running clearance plus wear on the nut alone (since one never operates the lathe with the cross slide that far away from the operator). With a new nut, this should be 0.000" to 0.002". Crank the cross slide back to about where it spends the most of its working life and repeat. Subtract the nut clearance reading from the new reading. This figure is screw wear. Check it in two or three cross slide positions. What you do next depends upon you and how deep your financial pockets are. But note that if you use normal SOP, a worn nut or screw should have no affect on the accuracy of your work.
In a used lathe, there will be wear in the cross feed nut and maybe the screw as well. To evaluate the wear condition of the nut and screw, first crank the cross feed nut completely off of the screw. Then properly adjust the screw end float by differential adjustment of the two nuts on the visible portion of the cross feed assembly. One nut holds the crank on. The other may be just a thin pattern hex nut, a threaded collar or the visible part of an internally threaded shoulder bushing. This end-float should be as near to 0.000" as you can get it without there being much drag when turning the crank. Then pull the cross slide back toward you while turning the crank CCW until you can just see the end of the screw with the cross slide chip guard removed. Take the slack out by turning the crank a little CCW and zero the dial. Turn the crank CW until you just feel the thread in the nut hitting the thread on the screw. The dial reading is the normal running clearance plus wear on the nut alone (since one never operates the lathe with the cross slide that far away from the operator). With a new nut, this should be 0.000" to 0.002". Crank the cross slide back to about where it spends the most of its working life and repeat. Subtract the nut clearance reading from the new reading. This figure is screw wear. Check it in two or three cross slide positions. What you do next depends upon you and how deep your financial pockets are. But note that if you use normal SOP, a worn nut or screw should have no affect on the accuracy of your work.