08-25-2013, 11:06 PM
Hello All,
Nowadays we think of thread cutting in a lathe and the first thing that comes to mind is probably single point cutting or maybe using a die holder in the tail stock, but how do you make thousands of identical parts? CNC of course.
The following images are of the "Production tool" used before carbide threading inserts and CNC control.
Behold; The Herbert "Automatic" Die box,
Held either in the Turret of an automatic lathe or "Capstan" attachment or sometimes in the tailstock or in a holder mounted on the back of the cross slide, the latter would ensure the device was centered with an indexing pin or similar.
Once set the tool would simply be applied to the rotating shaft and the thread cut as with a normal die holder, but with a difference. when the operator stops feeding the tool or when the shaft reached an internally set stop the threading cutters would spring back clear of the work.
The above photos show the tool in the "set" position with the cutters closed in ready to cut the thread and the "open" position with the cutters right back out of the way,
The short protrusion on the top of the barrel is the adjustment screw which allowed for the cutting of tight or loose screws and allowed adjustment for wear etc.
The longer lever is the arming or "closing" lever simply rotate this lever and it brings the cutters back to the previously set position.
The cutting tools were made to an extraordinarily high standard using the best tool steels available and sharpened using special fixtures that were sold to production shops allowing very precise resharpening of the tools in minutes per set, the sharpening was done on a basic tool and cutter grinder. it was not unheard of to get 500 threads out of a single sharpening of a set of cutters in steel and I heard an account of 5000 threads being cut in a particular job making brass thumb screws, the story went that after 5000 threads they sharpened the cutters despite the fact that they were still working fine.
I hope this brings something new to the attention of our less experienced machinists.
Regards
Rick
Nowadays we think of thread cutting in a lathe and the first thing that comes to mind is probably single point cutting or maybe using a die holder in the tail stock, but how do you make thousands of identical parts? CNC of course.
The following images are of the "Production tool" used before carbide threading inserts and CNC control.
Behold; The Herbert "Automatic" Die box,
Held either in the Turret of an automatic lathe or "Capstan" attachment or sometimes in the tailstock or in a holder mounted on the back of the cross slide, the latter would ensure the device was centered with an indexing pin or similar.
Once set the tool would simply be applied to the rotating shaft and the thread cut as with a normal die holder, but with a difference. when the operator stops feeding the tool or when the shaft reached an internally set stop the threading cutters would spring back clear of the work.
The above photos show the tool in the "set" position with the cutters closed in ready to cut the thread and the "open" position with the cutters right back out of the way,
The short protrusion on the top of the barrel is the adjustment screw which allowed for the cutting of tight or loose screws and allowed adjustment for wear etc.
The longer lever is the arming or "closing" lever simply rotate this lever and it brings the cutters back to the previously set position.
The cutting tools were made to an extraordinarily high standard using the best tool steels available and sharpened using special fixtures that were sold to production shops allowing very precise resharpening of the tools in minutes per set, the sharpening was done on a basic tool and cutter grinder. it was not unheard of to get 500 threads out of a single sharpening of a set of cutters in steel and I heard an account of 5000 threads being cut in a particular job making brass thumb screws, the story went that after 5000 threads they sharpened the cutters despite the fact that they were still working fine.
I hope this brings something new to the attention of our less experienced machinists.
Regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.