Gear wear on my lathe

I clearly need to replace some gears on my lathe, the question is how many? There are four gears showing signs of wear, one of them really
bad. Replacing all four gets pretty expensive. The lathe is a 14 1/2" Southbend.
First, naming the gears. Here's a picture of the group:
http://users.frii.com/sos/Steve/Overall.jpg
Parts Works names them as follows: top gear in picture (this gear is on the spindle): "cone-pinion" two gears just below cone-pinion: "twin gears" gear which right twin gear drives (below R twin gear): "reverse gear"
Here is a top close up view of the cone-pinion:
http://users.frii.com/sos/Steve/Cone_Pinion.JPG
A close up view of the two twin gears:
http://users.frii.com/sos/Steve/Twin_Twin.jpg
The one on the right is clearly on its last legs.
A close up view of the right twin gear and the reverse gear beneath it:
http://users.frii.com/sos/Steve/Twin_Reverse.jpg
Again, the wear on the right twin gear is pretty serious.
I definitely need to replace the right twin gear. The cone-pinion doesn't look so good, I don't know how to tell on the other two. I will appreciate any recommendations and discussion .
Thanks, Steve
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Hey Steve, I only say this because it is what I am working on...have you considered trying to make them...there is a lot of info out there on cutting gears....just thought I would ask...might be a good learning thing as well as saving you some bucks.
John
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Good point. I'm keeping that as a backup plan. I really don't have enough time for current projects....
Steve
CAMCOMPCO wrote:

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Unless you're loading those gears heavily, I'd run them and not worry about it. I would imagine it has taken years for them to wear to the point shown, and were probably run far more then than you use them now. You could conceivably have years of service left. If you feel driven to do any replacing, I'd replace only the one(s) with the extreme wear, the ones with marking on them in the pics. The others have countless years of service life left in them, and there is no good reason to replace them, such as matching teeth to teeth.
The nice thing about this situation is if the gears fail, they're likely to do no harm aside from irritating you, unlike gears that run in an oil bath transmission, where pieces ruin other pieces. I'd expect one tooth to fail, and the gear assembly to come to a halt-----not much more. If the failure were to occur in the middle of a threading cut, that would cost you your project, but otherwise I can't think of anything bad that could occur.
Good luck
Harold
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    [ ... ]

    I would in general agree, except that there is one simple (and cost-free) step to postpone the day of needed replacement for quite a while.
    Note that of the twin gears, the one which is badly worn is the one which is *always* in mesh with the "cone pinion", and transmitting motion to the rest of the gear train, either directly, or (when in reverse feed) through the second gear of the pair.
    What I would consider doing is to interchange the two gears of that pair, which would put the most subsequent wear on the relatively un-worn one of the pair, and transmit power though the more worn one only during reverse feeds or LH threading.
    And -- make sure to keep them well lubed, of course.
    Good Luck,         DoN.
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about
shown,
Way to go, DoN! I didn't think of that, but it's sure to prolong the gear life.

Absolutely. I use Keystone 423, an open gear grease that comes in a spray can. I think it's obsolete now (bought it back in '67!) but there's likely a substitute on the market. Great stuff, doesn't run, and covers 100% without dispersing to the sides. Goes on like water and ends up like *very* sticky molasses.
Harold
.
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wrote:

Usually, I would not contradict Rose, but at least one of the names is incorrect. According to the SB manual, the upper gear in your pic is the Spindle Gear (PT30F2).
The Cone Pinion is a different part, located partially within the Cone Pulley (hence the name).
The "Twin Gears" are called that in the manual, although we call those the Reverse Idler Gears. For your lathe, they are PT27K32F2 and PT27K28F2. 'Course, if they are "twins", why different numbers?
The Reverse Gear is PT28F2.
As mentioned elsewhere, these may last a long time yet, but might also fail during a critical operation tomorrow.
I agree that the Twin Gear needs replacement at least. I don't know if you can swap them as mentioned by DoN, since they have different part numbers, but if so, that may prolong the life.
I respectfully disagree with Harold, that if they fail, they will not do other damage. I've seen it happen in Logan Lathes, and the tooth that gets kicked out CAN wedge into another gear damaging it and even the shaft or stud upon which it is mounted.
Of course, if you leave the Reverse Bracket in neutral, there is no load at all on any of these gears, and they SHOULD last forever. Kinda tough to thread that way, though.
Good luck!
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| Scott Logan - ssl "at" lathe.com |
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And most spindle gears on south bend lathes don't have any Hardinge parts attached!!
:^)
Jim
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snip----->

No problem with the disagreement, for I, too, have reservations about my comment, and I bow to your expertise as a manufacturer of lathes. My experience comes from running them, and I've never experienced such a failure.
My reservations come not only for the circumstance you described, but one whereby the gear is not made of cast iron, but steel, and the tooth folds over under load and wedges, much the same as you described. I shudder to think of the consequences. I was thinking optimistically, if not rationally.
My logic in this matter, based on many unknowns, is that the OP uses the machine for pleasure, likely well under capacity, so it's not stressed much, so it's unlikely to fail, and, given a little luck, should the cast iron (?) gear fail, it would toss the tooth, not wedge it. That would be a decision based on economics, and, with luck, would be a good one.
Yeah, I have heard of Murphy! I know him (or his law) quite well. <g>
Had I been armed with more information, such as the machine is used for gain, and must be up and running, I'd have likely suggested the replacement of the two gears, without giving any thought to anything less. It's really hard to know the circumstances of some folks. Could be the kids need shoes, the doctor bill remains unpaid for the last delivery, and the cupboards are bare. In that case, the gamble may be a rational option.
Harold
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Some day I'll figure out how email works.. ---------------- Don, this would be a great plan except that the two twin gears have differing number of teeth. The left one is 32, the right 28.
This threw me at first, but the gearing works out the same.
Thanks, Steve
DoN. Nichols wrote:

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Some day I'll figure out how email works.. ----------------
Thanks for much detail, Scott. I thought cone-pinion was a pretty strange name for the gear. I'm talking to a guy named Chris, who goes pretty much by the drawing and asking questions of someone else. I'll check into this further.
The twins have differing numbers of teeth, 28 on the right, 32 on the left. It looks likely this can be seen in the part numbers.
Much appreciated, Steve
Scott S. Logan wrote:

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Harold and Scott, Thanks for your replies. I lean toward Scott's answer that if one did break, it might be more serious. The one gear has me fairly worried as the teeth are so thin. It also makes a fair bit of noise, which is annoying.
Harold, you have reassured me as to wear on the other gears. I was expecting replies like "at the slightest bit of wear you should replace the whole gear train". I guess this comes from my delving into a Porsche 914 transmission and replacing some gears (twice actually, but we don't need to go into THAT).
I do use the lathe for pleasure, not a lot of hours or huge loads. I'll either replace just the one gear or add the spindle gear too. There is detectable wear on the other two, but much less.
Thanks again, Steve
Harold and Susan Vordos wrote:

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