Dangerous chuck mounting? 12" South Bend chuck

Look at this picture:
http://yabe.algebra.com/~ichudov/misc/ebay/South-Bend-12inch-Lathe-Chuck/South-Bend-12inch-Lathe-Chuck-4545.jpg
This is a 12" lathe chuck for South Bend lathes.
My question is that the mounting seems to be a simple thread. There is no "lock" like there is on L type mounts, or on camlock chucks etc.
So, it could happen that the big chuck would unscrew itself during stopping if RPM was too high, the brake was applied too vigorously, or something broke inside the gearbox. The chuck weighs about 100 lbs, so having it bounce around the shop would not necessarily be a great experience.
Am I missing anything?
i
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That's the old style mount. When you had shaft drive with overhead pulleys there was not any fast breaking or reverse so no problem. But a quick reversing motor will certainly send it across the room. I've seen it done with a 6" 3 jaw on a Sheldon Lathe. It's not QUITE as bad as it looks: the longer you use it on one setup, the tighter is sets itself on the spindle.
Ignoramus11200 wrote:

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...
Simply the fact that such mounts are not intended for use with braking or reversing - at most slow speed light cut reverse if any reverse at all. I've got a couple - a 2 x 6 on one and a 2-1/2 x 6 on another, IIRC. Lathes that will swing 20 and 17 inches, respectively, with flat belt drive and Babbit bearings, about 130 years old.
If you do anything stupid, they will bite you. You either learn to not do stupid things, or you learn that you need a more modern lathe with a more idiot-resistant chuck/faceplate mount.
--
Cats, coffee, chocolate...vices to live by

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Well, I am glad that on my Clausing, I can use brake, reverse etc and the chuck will never unscrew itself, due to a keyway.
With a 12" chuck, it is plainly a scary thought to use a lathe if it has a brake, or an ability to power reverse.
i
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Can you put in a spindle lock ?
Something like a C5 threaded tube. Locks by pulling on the inside of the chuck and on the far end of the spindle a compressing thread, locking it in.
Martin
Ignoramus11200 wrote:

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http://yabe.algebra.com/~ichudov/misc/ebay/South-Bend-12inch-Lathe-Chuck/South-Bend-12inch-Lathe-Chuck-4545.jpg
No brakes. And if the gearbox breaks, duck. <g>
Threaded spindles are the traditional design for engine lathes. My 1945 SB has a threaded spindle. It works fine. Billions of parts have been made using them, in production and in toolrooms.
Newer locking designs are better. The threaded spindle is an old approach, as is the rocker-type toolpost, the plain-bearing spindle, plain dead centers with white lead for lubricant, and so on. They work. They're capable of really fine machining. Hobbyists will be using them for years to come.
But doing commercial work with one of these lathes today is like delivering parts in a Model A truck.
-- Ed Huntress
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The old lathes didn't run very fast. I saw a WW2 vintage lathe that had a top speed of 400 RPM and it was a gear head lathe.
Richard W.
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Ignoramus11200 wrote:

http://yabe.algebra.com/~ichudov/misc/ebay/South-Bend-12inch-Lathe-Chuck/South-Bend-12inch-Lathe-Chuck-4545.jpg
Its difficult to tell from this photo. My little Grizzly benchtop lathe has two clamps that are held on to the chuck with some bolts. The spindle has a grove into which the clamps engage.
The requisite threaded holes might not show up if the photo was taken at the wrong angle.
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http://yabe.algebra.com/~ichudov/misc/ebay/South-Bend-12inch-Lathe-Chuck/South-Bend-12inch-Lathe-Chuck-4545.jpg
You're probably missing the delightful experience of trying to remove a threaded chuck after it's been on a while! :-) Some have had to take a parting tool to the back plate to get their chucks off the spindle. I had a South Bend with a broken back gear tooth, most likely a result of someone trying to remove the chuck. My 13" South Bend had a D1-4 Spindle that I much prefer to threaded spindle.
RogerN
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I would prefer anything to threaded spindles... L mounts or D mounts are both great. I would think that D mounts (camlock) are the best, due to not being prone to mating surface contaminated with chips.
i
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Ignoramus11200 wrote:

One of the guys I was in high school metal shop enjoyed spinning up the chucks on small Southbends and putting the lathe in reverse, causing the chuck to unwind and drop off and roll across the floor at speed. After a few occasions he was warned and didn't do it again. Would have seemed a good idea to not provide reversing on a threaded spindle lathe for novices.
When in Wichita I recall the lecturers mentioning an occasion when a student had a chuck come loose and roll down between all the subsequent lathes, causing the students to jump out of the way. All the lathes were in line and the chuck rolled down the line until it hit the far wall IIRC. Those lathes were Rockwells, not highly regarded by the instructors IIRC, but not fitted with threaded spindle either.
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I locked out reverse on our 13" Enterprise Lathe for exactly that reason. It's a cam lock spindle but the forward/off/reverse lever is not marked for direction nor is it intuitive. I've had novices try to cut in reverse, even tried for reverse myself in a moment of inattention after switching from a different lathe.

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Hey Iggy,
It will be OK, except if something dumb happens at the higher spindle speeds. My friend says if it doesn't hit you, it will have a sharp whistling noise as it flies through the air. That may be an old OSHA requirement, warning everyone else in the shop to "duck & cover".
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXX
On Thu, 21 May 2009 10:27:47 -0500, Ignoramus11200

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http://yabe.algebra.com/~ichudov/misc/ebay/South-Bend-12inch-Lathe-Chuck/South-Bend-12inch-Lathe-Chuck-4545.jpg
The disadvantages have been pretty well covered. One advantage is that it is a fairly straight forward machining job if you need to make a dummy spindle, backplate, faceplate, etc..It is therefore also a lower cost system.
Don Young
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No. Turning backwards is dangerous as well.
The threads must be clean - and the back ring. It seats for a flat and mounts the chuck in precision.
Martin
Ignoramus11200 wrote:

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    It is probably the most common style of chuck mounting around for lathes. The various other systems were produced as improvements for just such reasons.

    It would not be a great experience -- but consider that the machines which use these are typically not supplied with a gear-driven headstock. Instead, they are belt driven (except in back-gear, where the speed is too slow to pose a problem, except when doing a deep cut in reverse).
    And the South Bend lathes tended to use flat belts, so the slip on plug reverse and the like is much greater -- offering a safety factor.
    Also -- in the home they are often fitted with single phase motors, so plug reversing is not an option anyway. :-)
    That said -- a friend who used to be a machinist in the Navy plug reversed a lathe with a *big* chuck and a big workpiece, and it started to unscrew. He quickly re-plug reversed it which caught up with the chuck -- but made it *very* difficult to remove that chuck later. :-)
    Note that some chucks -- for example some for the Myfords which are screw thread spindles -- come with provisions to tighten a clamp on the register of the spindle to allow turning in reverse without the excitement of a chuck going walkabout.
    But you have identified one of the reasons why I converted my Clausing from 2-1/4x8 threaded spindle to L-00 (by replacing the spindle with one from eBay.)
    Enjoy,         DoN.
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On May 21, 4:27pm, Ignoramus11200 <ignoramus11...@NOSPAM. 11200.invalid> wrote:>

Most lathes that will take a 12 inch chuck will not have a very high spindle speed. Assuming you have more than one lathe, you would use a much smaller lathe when turning something under 4 inches in diameter and are using a fairly high spindle speed.
Assuming you are turning a 6 inch diameter part at 180 sfm, that would be about 120 rpm.
Dan
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