A positive cross-slide stop ( not a lock) is almost a necessity for threading on a lathe.  Unfortunately, almost none of the newer lathes come equipped with this accessory.  

The most generally accepted method of manual threading is to set the compound [top] slide of the lathe to 1/2 of the included angle of the thread form.  This causes almost all of the material to be removed from the leading side of the thread.  This gives the effect of a few degrees of positive rake with a zero rake tool, and because the chip width is cut in half, chatter is greatly reduced, and the tendency of the chips to jam in the cut is also prevented.  The cross slide is used only to rapidly withdraw the tool at the end of a cut, and possibly for the last 1 or 2 thousandths of cut.

A positive thread stop allows the cross slide to be rapidly returned to the correct position without the need to count revolutions and read an index, thus eliminating a continuing source of error and greatly speeding the threading process.  Quality and quantity are both improved which seldom occurs.

The thread stop shown below was designed, laid-out, and machined by Keith Morris.  The stop is mounted on the rear of the top slide for internal threading and the front of the top slid for external threading.  1 inch square cold drawn steel was used for the for the arms, and 7/16 X 20 "Allthread" was used for the stop screw.  A 3/8 UNC SHCS was used to fasten the arms.  7/16 X 20 "Allthread" was used primarily because some was on-hand, being left over from the construction of parallel jaw clamps which was an earlier class project. [Two of these are shown in other photographs.]

The cold drawn bar, used in this and several other projects, was generously donated by Steve Williams, a member of the FPC Board of Regents. 

Positive stop shown installed at rear for internal threading

Positive stop show installed at front of cross slide for exterior threading.  The stop screw will have to be changed to avoid interference as will the hold down bolt.


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last updated by GmcD on 27-May-14 14:59
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