View Full Version : Phase II 8"Rotary Table Question

03-27-2005, 12:25 AM
The rotary table and my lathe tailstock both have Morse 3 tapers so I want to use my chucks with both. The lathe tailstock has a keyway to hold the chuck shank tongue which prevents any spinning of the shank, but the rotary table does not have this. It is just a plain tapered hole. The chucks slide in snuggly, but there is no way to keep them from turning with any serious pressure which I am sure will occur with almost any job. What do I do? Are there any kind of after market fixes for this? Thanks,

Forrest Addy
03-27-2005, 07:21 AM
Correcting a mistaken assumption: You refer to a "keyway to hold the chuck shank tongue which prevents any spinning of the shank."

I believe you mean the "driving tang". This is used to remove the taper from its socket. The operator inserts a tapered drift in the "window" of a blind socket, engaging the driving tang on the small end of the taper. He gives the drift a sharp tap with a hard hammer thereby "driving" the taper free from the friction force holding it engaged.

The word "driving" has nothing at all to do with ensuring a positive drive to the spindle tooling. The driving tang's actual capacity to resist torque is but a small fraction of the torque capacity of the taper itself. When the taper is spun in its socket for any reason the driving tang is inevitably damaged if not twisted off completely.

Further, Morse tapers were intended for taper shank drills where the substantial thrust required to feed the drill's chisel point into solid metal keeps them solidly seated and capable of driving at the taper's full mechanical torque capacity. When the taper is solidly seated and the seat is maintained with drilling thrust the failure mode in the case of accident is: the drill either shatters or twists off at the un-hardened reduced diameter neck next to the big end of the shank without harming the spindle taper. Such is the genius of Steven Morse that in the 1850's he provided a "fuse" in his tooling system that prevented damage to drilling machines for the last 150 years.

Morse tapers are less effective in milling where there is little thrust or even a small extraction component in the cutting forces. Morse tapers frequently unseat in this service unless the taper fits well and is solidly seated with several blows from a copper hammer before cutting commences.

There are other standard methods for achieving a positive drive for Morse tapers. The most common is a pair of driving flats adjacent to the start of the large end of the taper. The spindle has corresponding driving flats. This standard configuration is discussed in Machinery's Handbook.

Usually damaged driving tangs are weld repaired to a blobby oversize and machined or free-hand ground back to configuration.

The morse taper in your rotary table is intended for a dead center for indexing work, holding a centering plug, and similar operations. A drill chuck has far too much overhang to provide sufficient rigidity of any but light cuts. If you install a drill chuck in the rotary table you can use it to hold small round for drilling or light milling but not significant stock removal.

Anything firmly seated in the Morse taper will not turn in the socket so long as there is no extraction milling forces you impose.

[This message has been edited by Forrest Addy (edited 03-27-2005).]

03-27-2005, 06:23 PM
Thank you for the reply. Very helpful for a newbie like me. I appreciate it.