05-10-2015, 08:49 AM
I was just thinking about the difference in drawbars I've used.
On turret mills (Brideports and their clones), all I've ever seen were 7/16-20UNF threads. A finer thread has less helix angle. Would that make it less prone to loosening?
The machines I've used with NMTB 40 and 50 tapers were Cincinnati, Milwaukee, Kearney & Trecker milling machines, beasts as compared to a Bridgeport. The drawbars on those were like Darren's, coarse thread 1/2-13UNC and 5/8-11UNC thread. The other difference was that the drawbars were not directly tightened against a shoulder. Instead, you screwed the drawbar into the holder until it bottomed out, back off by a 1/2 turn and snugged up a check nut under the end hex milled on the drawbar. Yes, you needed two wrenches and three hands to change a tool, and probably why DeVlieg and others developed "quick change" systems.
I wonder if this design had distinctly different characteristics of maintaining tension. Curious.
On turret mills (Brideports and their clones), all I've ever seen were 7/16-20UNF threads. A finer thread has less helix angle. Would that make it less prone to loosening?
The machines I've used with NMTB 40 and 50 tapers were Cincinnati, Milwaukee, Kearney & Trecker milling machines, beasts as compared to a Bridgeport. The drawbars on those were like Darren's, coarse thread 1/2-13UNC and 5/8-11UNC thread. The other difference was that the drawbars were not directly tightened against a shoulder. Instead, you screwed the drawbar into the holder until it bottomed out, back off by a 1/2 turn and snugged up a check nut under the end hex milled on the drawbar. Yes, you needed two wrenches and three hands to change a tool, and probably why DeVlieg and others developed "quick change" systems.
I wonder if this design had distinctly different characteristics of maintaining tension. Curious.