by Jerry “Ozzie” Pryor
Many projects involve machining multiple instances of the same part, often involving changing tools one or more times for each piece. That situation may lead to a lust for a quick-change tool post, or better yet, a turret. A quick-change tool post is fast, but a turret is faster.
A while back, I guess because I harbored this unreasonable lust, I obtained a used turret on eBay. Originally used on a Hardinge Chucker Lathe, this turret was manufactured by Mag to very close tolerances. They can still be found on eBay occasionally.
The turret has eight positions, and repeatable accuracy is said to be .000050″. The locking mechanism is operated by compressed air, with the locking valve contained in the unit. Air pressure pushes two plates together, securing their 16 tapered surfaces in place for incredible holding power. Releasing the pressure allows springs to separate the plates, and in the relaxed state, the turret can be easily turned by hand to any of the eight positions. An adjustable spring loaded ball gives the operator a feel for approximate positioning.
Originally, it was used on the Hardinge in the flat position with the axis of rotation vertical. In my mind, that configuration is fine for a manually operated lathe, but limits the utility of the unit if one has CNC or electronic position indicators (DROs). The limitations include making parts that can be no more than a few inches long, and no easy height adjustment of the cutting tool other than shimming. Unfortunately, my mind seldom lets well enough alone.
I’d been thinking that mounting the turret with the axis parallel to the lathe Z-axis would cure those limitations, but I wasn’t sure this particular unit would work well in that position; it’s called procrastination. The unit gathered dust on a worktable in my shop. One day, while surfing the Web, I came across a discussion group post by a man that had worked for Mag, and “demonstrated the turret in various positions.” Wow! Adrenaline rush; I decided I wanted to try mounting it in the horizontal position, and to make the custom toolholders it would need. Photo 1 became a mental picture; that’s where I’m going.
“A Pneumatic Locking Lathe Turret ” appears in the upcoming November/December 2008 issue of The Home Shop Machinist.