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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
I needed to securely hold a couple of 1/2" diameter brass balls with threaded blind holes, in order to enlarge and re-thread the holes.
What worked was a slightly undersize hole in a scrap of 1/4" aluminum plate. The ball was screwed onto some 10-32 threaded rod in the chuck of a drill press, then pressed into the plate. That held it, unmarred, with axis vertical for drilling and tapping. The second ball started to spin while being drilled, and re-pressing didn't fix it. Blue Loctite 242 thread locking fluid and some cyanoacrylate accelerator did an adequate job of gluing it in place for the rest of the job.
Why not buy correctly threaded balls to begin with? I only needed one, to replace a missing decorative finial on a fireplace screen. Minimum order quantity was five balls (for about $12) so I planned to replace the other three finials for matching appearance. Learned a lesson: this screen needs two balls with 10-32 threads and two with 1/4-20 threads! Fortunately, the thread I had measured and bought for was the smaller.
Just an idea - there are vises with V groves (don't know how it is called) - designed for gripping round objects.
Other solution is to use a piece of scrap aluminum a bit bigger than the diameter of the ball. Make a hole in it with a diameter as close as possible to the ball. Squeeze it tightly in the vise (the aluminum deforms and locks the ball).
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I use two plates, each with a hole in it of 0.7 or so the diameter of the ball, and clamp them together with several bolts spaced around the ball. That's the same clamping geometry as holds the 'elbows' of the 'any angle' bench clamps. Sort of like a circular V-block.
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[moved] Firm grip on brass balls
Fortunately, the thread I had measured and bought for was the smaller.
