I frequently am asked, “What are those threads on a 5C pullback collet chuck for?”
For this answer, a bit of a history lesson is in order: Back in the day when Hardinge was the number one manufacturer of precision lathes, they designed their spindles with the 2-3/16-10 threaded nose and the 4° tapered nose. For those of you who are old enough to remember, almost every machine shop had a Hardinge chucker or tool room lathe on their production floor. These machines either had the 2-3/16-10 thread or the 4° tapered nose. The reason for this was to accommodate the closing rings that could be used with their 5C Step Chucks. Being that a standard 5C collet closes on the 5C taper, Hardinge developed the 5C step chuck and closing ring. Instead of the collet closing on the 5C taper, it was designed to close on the OD of the collet head.
The reason for this is that when you spin a larger collet head, it is more likely the collet will open up due to the centrifugal force that is generated by the higher rpm causing the collet to open and for the part to come flying out!
When CNC lathes became popular in the early 1980’s a 5C collet chuck was developed by a gentleman named Dewey Riggins. The first 5C collet chuck didn’t have the 2-3/16-10 threaded nose on it. Then a man named Bill McMurphy (who was a partner with Dewy Riggins) bought out Dewy’s portion and created ATS Workholding as it is known today.
Bill had several requests from customers who wanted to be able to use the 5C Step Chucks on his 5C collet nose pieces AKA/5C Collet Chucks, prompting him to add the threads. So this is the tale of how the 5C collet chuck came to have those 2-3/16-10 threads that are now available on almost every manufacturer of 5C pullback style collet chucks!
Click the following link to purchase: Hardinge 5C Step Chucks
