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Thread: Headstock bearings
12-24-2004, 04:35 PM #1
I would like to have a lathe in order to thread and chamber rifle barels. While this is probably a dumb question your input will be appreciated. I assume that only a lathe with roller bearings on the headstock is suitable, I always figgured that the older lathes with plain bearings on the headstock would have too much play to make a precision chambering job feasible. Thanks Zoom
12-24-2004, 05:31 PM #2
I think that is a myth! Anti friction bearings in a lathe Headstock (Ball or roller) give the advantage of allowing higher spindle speeds over a plain bearing headstock. Some of the highest precision spindles used in demanding work such as the spindles of precision cylindrical grinders (Landis, Myford etc) are built with plain bearings. A plain bearing will tend to give a rounder part if all is setup corectly. The multi rolling elements of a ball and roller bearing tend to create "noise" in their rotation and that creates non perfect rotation. Now that said, high precision spindle bearings are made with very tight tollerences that help eliminate the added errors of all the elements,and produce very true rotation. With care a worn plain bearing spindle can be returned to accurate service. A precision ball or roller bearing once worn is not repairable short of replacement! ($$$)
A good plain spindle will produce very accurate rotation, and should, with care give acceptable results for your needs.
12-24-2004, 05:45 PM #3
Don't let the type of headstock bearing be a deciding factor when selecting a used lathe.
Once the "big enough to do the job and small enough to drag home" condition is met, the primary consideration should be physical condition of the machine with secondary consideration to the tooling included in the price.
In an everything-else-equal situation (which happens a thousand times more often in hypothesis than in real life), I'd personally prefer rolling-element bearings. But a lathe headstock with good plain bearings is very much superior to a similar headstock with poor-quality or damaged rolling-element bearings.
One other thing: Don't fall in love with a lathe brand or country-of-manufacture if you haven't won the lottery. Excellent lathes have been made in North America, Britain, Western Europe, Eastern Europe, Russia, and Asia, and lathes have been imported into the US from all of those places that are now available used. A high-quality lathe that's been babied from any of these countries is better than a beater from some other country.
12-24-2004, 08:42 PM #4
Sorry, never an owner but don't the "bearing cap" lathes have shims that can be removed to compensate for wear?
An old toolmaker once told me he preferred a plain bearing head, that the lathe he was thinking of would take cuts on material that made all others chatter....now this might have been the boat anchor construction of the machine but it sounded good and he was an ace toolmaker.
12-25-2004, 12:06 AM #5
Plain bearing machines had the happy characteristic of, in the hands of a gent that knew what he was doing, being adjustable to suit the work. He could snug up the bearings for exacting work requiring tops in roundness and fine finishes or he could make them less snug for lesser quality jobs requiring the highest speeds. Not that this was done regularly, but the feature of varying bearing tightness was there as needed.
I used to run my 1934 20" P&W Model B on the verge of making them hot simply because I liked the resulting work. This was the last of these fine Pratt & Whitney lathes so equipped.
12-25-2004, 02:12 AM #6
Your "biggest concern" should be the size of the hole in the spindle, followed by a steady rest.
Plain bearings have their limits versus rolling elements..but they do give better finishes as a whole
12-25-2004, 09:13 AM #7
I am not familar with plain bearings. Could someone bring me up to speed? What materials are they made from?
12-25-2004, 10:54 AM #8
The plain bearings being discussed here are in all likelyhood made of "babbit".Babbit is a realitively soft material consisting of mainly lead with other elements added for durability.It,babbit,is poured much like lead.Some babbit bearings are backed by brass/bronze and even their own cast iron shells.While babbit bearings may have their short comings durability isn't one of them.This type bearing is usually quite wide compared to ball or roller bearings.This makes for very good and precise spindle alignment and support.If I've left anything out the other guys here will pick it up.
12-25-2004, 01:58 PM #9
Of course the odds are that we all have a set of babbit bearings in the driveway or garage. As shown by automotive and motorcycle engines journal bearings can sustain quite high RPMs with adequate lubrication
12-25-2004, 03:46 PM #10
Not all lathe spindles have babbitt, though. Some are bronze bushed and my personal favorite intermediate sized lathe has cast iron plain bearings. All the old smaller South Bends, including my beloved 10L at work, have straight cast iron spindle bearings. There is no bushing. They just bored and finished the headstock to form the bearings.
As for high speed with plain bearings, not only in our driveways... Formula 1 cars (nearing 25,000rpms these days) run plain mains. Plain bearings, if properly lubed, can actually run faster than rollers! There is only one catch... it must be pressure lubed for high speed operation.
My big L&S has plain spindle bearings, but it is an older "dry head" model (referring to lack of an oil pump). The spindle bearings are oiled by catch cups and wicks that pick up oil slung around inside the case by the gears (basically a hands-off version of a South Bend where the oil cups are automatically filled). This limits the spindle speed to about 400-500rpm max. This can be tripled on a later machine equipped with a pump.
Also, the larger the diameter of the bearing, the slower it's top speed will be, relative to an otherwise identical smaller one.
12-25-2004, 05:16 PM #11
A very old [ and excellent] machinest once explained it to me this way . . . ball bearings ard designed to run with a constant metal to metal contact . . . plain bearings are designed to run on a thin film of oil, no metal to metal , and a properly adjusted plain bearing will produce a smoother cut because of this, his work was the proof . . .
12-25-2004, 06:55 PM #12
And plain bearings may make a come-back in machine tools. Already, as mentioned above, they are preferred over rolling element bearings for super-precise applications like grinders. But if you want to see the future, Google "hydrostatic bearing". This version of plain bearing supports the journal on a film of oil even at rest. There is NO runout. They are much stiffer and have much better damping for their size than is possible with a rolling element bearing. Also, there is no initial resistance to rolling as in properly adjusted roller bearings.
12-25-2004, 07:30 PM #13
Getting back to the posters original question, what's better for a first time purchase in a used lathe....IMO, go with anti-friction type bearings, roller or ball.
All the hydrostatic and other precison plain bearings aside, you're much more likely to have good luck with the anti-friction type.
12-25-2004, 08:09 PM #14
To cut through some of the possible confusion.....
There are, indeed, many makes of lathe which would do your job.....but there is only one which I would recommend to you, for practical serviceability, cost-effectiveness, and "operator-friendliness" for an inexperienced operator.
That one is the older South Bend, in the 13" or 16" size, and only in the later "toolroom" version, which was supplied with the hardened ways, D1-4 camlock spindle nose, large, easily read dials, 5C collet closer, and the taper-attachment.
The South Bend uses bronze sleeve bearings, which are provided with a sensitive adjustment, so the South Bend spindle runs very smoothly, and so will do very good workpiece finish.
The South Bend, of course, can never take the place of a heavy gear-head lathe for roughing out large steel parts, but, if you don't anticipate any heavy production work, that's not an issue.
The South Bend, with its sleeve bearings, is limited to an approximately 900-ish top spindle speed.....which is not a problem at all, for the generality of non-production fine work.
Fact is, for one-off parts, and such as rifle barrel work, you'll be running slowly and carefully anyway. Hogging the metal away rapidly with carboloy tooling at its optimal speeds is simply not likely to be part of your work.
One major advantage of the South Bend is its simplicity and ease of maintenence, and the ready availability of South Bend parts and tooling items, should they be needed.
Unfortunately, you may need to invest some time in looking for a nice late pattern South Bend.....there are many of the earlier types around, which can be bought for almost nothing, but they are the thread-spindle, soft-ways version, which will often be found with significant wear in the ways, near the headstock....if you can find an unworn one, and the price is right, you might "get lucky", but be careful, and get someone to show you how to inspect a lathe for wear....its not cost-effective to rebuild an older South Bend, considering the cost of re-grinding the ways, etc.
12-25-2004, 08:46 PM #15
it is a common misapprehension that babbitt, also known as white metal, has any lead in it. for very low speed bearings lead can be useful, but most babbitts in any machines we will see are about 90%tin, 7%antimony, and 3%copper. lead will be less that 1/3 of a percent. you'd have to look at a machinery handbook to get all the details; there are many types of babbitt, but the type we will see is called either original, or #2. it melts a little hotter than lead, but works about the same. don e.
12-26-2004, 01:06 AM #16
For Mike C - if you took off the bearing
caps on your 10L at work, you might be a bit
surprised at what you would find.
Those lathes typically do have cast iron caps
to the bearings, but the steel spindle journal
actually rides on a thin bronze shell that
fits inside the accurate bore of the headstock
and the cap.
There's an expander wedge on each bearing to
make it open up and fit into that bore. The
expander screws (two to a wedge) are under the
two 1/8 NPT pipe plugs that are seen in the
top of the cap.
Only the 9 and 10K lathes had steel spindles
that ran directly on the cast iron of the
headstock - in the modern versions, that is.
The really old machines used bronze inserts in
cast iron caps that were split in two pieces
But as far as the original premise of the
thread goes, as virtually every other poster
has pointed out, the plain bearing machines
can be every bit as accurate and rugged as
roller or ball bearing lathes - and there
are many who would *prefer* the plain bearing
There's no reason for Zoom to shy away from
12-28-2004, 05:52 PM #17
Well that is certianly a wealth of good information. I really appreciate all the good replies to my post. Carla, a taper attachment would be nice (although I would be buying bbls. that are already contoured, so I wouldn't really need one), and obviously the hardened ways would be an advantage (although in the used market one often takes what they can find). Could you explain the advantage of the camlock spindle? The significance of that is lost on me but I am sure there is a good reason for that and I am curious. Thanks again for all the good info
12-28-2004, 06:15 PM #18
Yes, I was wondering about that myself. Why is a camlock considered better than a threaded spindle. I need to know because I will be buying a lathe in the near future. Also could someone more knowlegable than me rehash the belt drive vs. gearhead debate. Is one better than the other, or, is it just personal preference. Thanks, Rojelio
12-28-2004, 06:31 PM #19
My 16" SB 2H Turret Lathe had spindle running directly in cast iron boxes. This was a single tumbler machine.
12-28-2004, 07:17 PM #20Yes, I was wondering about that myself. Why is a camlock considered better than a threaded spindle. I need to know because I will be buying a lathe in the near future.
Also could someone more knowlegable than me rehash the belt drive vs. gearhead debate. Is one better than the other, or, is it just personal preference.