Did You Ever Have To Fix Your Lathe........

jackie schmidt

jackie schmidt

New member
One of our larger lathes went down two weeks ago, a 28 ft Kingston that we Bought new about eight yearsago. One of my machinist said he heard a loud "pop" in the feed quick change, and the Lathe stopped feeding.

We had to tear into the feed box. But in order to take the access cover off, (it's on top), you have to lift the entire headstock assembly up enough to get in there and work.

This we did , and found a gear broke in several pieces. Nothing else seemed amiss, so we ordered a gear from Kingston.

It arrived yesterday, and me and my younger brother have been putting the thing back together.

I talked to Kingston, inquiring as to why this gear broke. It looks awfully light or such a heavy application. In fact, every gear in the feed box quick change looks too light for this machine. Something like this really should not happen.

Anyway, I thought I would share some pictures. It should be up and running again this afternoon.

It's been a while since I tore into a machine like this. We called a machinery repair here in Houston, they said it would be three weeks. So we just decided to do the repair ourselves.

http://benchrest.com/attachment.php?attachmentid=21412&stc=1&d=1535565678

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Yes I did. Sort of...

I was getting a horrible surface finish with my old lathe, a Mori knock-off Cut King. I tried to get a "machinery repair expert" to come look at it, but he flaked. And I hate flakes, so off I went on my own. I couldn't feel any sort of vibration whilst running, and after checking the "obvious" (belts, pulleys, drive screws, gib tightness, tool post, etc.) culprits, I pulled the headstock off to ensure that where it mounted to the bed was debris free, cleaned it up, and put it back together. Didn't help. So I figger'd I had a bearing go south, so after taking numerous pictures of the inside of the headstock, I tore it down to Parade Rest, and replaced the bearings with high-grade, ABEC forty-eleven, expensive ones. Put everything back together, and still got a God-awful surface finish.

Panic time.

I had previously replaced the drive belts and checked the pulleys, and all appeared well. For some unknown reason, and running low on ideas, I adjusted the tension on the motor and drive belt assembly and "Presto!", the surface finish problem went away. Near as I can figure, they were adjusted just so to cause a harmonic vibration that played hell with the surface finish.

The machine ran perfectly after that, and later went to live at a friends machine shop where it is much loved, and gets used for any tight tolerance stuff he may have to do.

If anybody has a similar problem, remember my little adventure and try adjusting the belt tension. May save you a bunch of work, money, heartache, and bad language.

Justin
 
Those do not look as heavy as I would expect on a lathe that large.

While feed loading is not all that high an area large lathes are often used to make larger cuts.

The feed does provide a huge mechanical advantage but someone may have gone a little to far in the design.
Even when driving the carriage against its rack of the shaft.

They have effectively reduced some of those gears to hardly more than spur gears instead of helical gears with larger load/wear surfaces and the resulting smoother movement.

If you decide to keep that one I would reduce cutting depth to reduces loading on the carriage drive.
 
Drive belts changed them out with a Link Belt and one Motor. Reason I bring it up a friend has a pretty nice old 36" Jet. He had to pull out the gears and spindle just to replace a belt. Put it back together and the seals started leaking so I asked him why he didn't just get a link belt and about a five minute job to replace. Said he never heard of one before and he is a retired machinest who worked at Hershey as in candy.
 
brickeyee said:
Those do not look as heavy as I would expect on a lathe that large.

While feed loading is not all that high an area large lathes are often used to make larger cuts.

The feed does provide a huge mechanical advantage but someone may have gone a little to far in the design.
Even when driving the carriage against its rack of the shaft.

They have effectively reduced some of those gears to hardly more than spur gears instead of helical gears with larger load/wear surfaces and the resulting smoother movement.

If you decide to keep that one I would reduce cutting depth to reduces loading on the carriage drive.
Click to expand...

The gear that broke, as you can see in the photos, is very thin in cross section. Where the driving keyway is cut, it is only about 0.90 wall thickness in the hub.

This is not the first problem we have had with this Lathe. When we first bought it, a pinion gear on the main input shaft came loose on it's hub. Since we had the Lathe only a week, a factory mechanic came it. The gear was bolted to a hub with 6 socket head cap screws. We determined it was installed backwards.

That got by QC.

This is a rather heavy and robust machine as far as the bed, the headstock, the tail Stock, and the carriage are concerned. I am surprised how light the feed gear train is.

Another design flaw, (in my opinion), is the fact that you cannot access that gear train within the quick change box without lifting the entire headstock off of the Lathe. This is akin to having to pull an engine from a car to change a starter. The headstock has no locators. It is held flat down by 4 large socket head capscrews. I though there would at least be some locating dowels.

This means we have to align the headstock back with the tail stock, and square with the Lathe bed.

That's tomorrow's project.
 
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Jackie

The teeth in the photo remind me of a worn out syncro ring. Did the breakage occur while attempting a shift change under load. On the older lathes we had to feel our way in but I'm sure that is a moot point.

Please let me know how it goes.

Mort
 
jackie schmidt said:
This is akin to having to pull an engine from a car to change a starter.
Click to expand...

Mercedes did worse than that on one of their first 5 cylinder diesel car.

The back glow plug required lifting the motor and moving it forward to remove the plug.
The firewall transmission bell blocked it.
 
sunbeam tiger...
right rear plug (v8) was removed from the passenger footwell, if i remember correctly
a real pain.

brickeyee said:
Mercedes did worse than that on one of their first 5 cylinder diesel car.

The back glow plug required lifting the motor and moving it forward to remove the plug.
The firewall transmission bell blocked it.
Click to expand...
 
The Tiger

I think the original version was powered by a 260 instead of the later 289. I thought they were pretty cool but didn't know about any maintenance problems.
 
Jackie do you now have it back up and running and thank you very much for sharing this experience. One could only imagine how much impact this has had on your shop by it being down.
 
Riverwolf1 said:
Holy Moly, what does the 4 jaw chuck on that thing weigh?
Click to expand...

We had a 24 inch lx 20 feet lathe at work for a long time.
The chuck was over 2,000 pounds on that thing.

It was rarely removed for ANY reason.
You had to use the overhead hoist.

It had a special built 'cart' that you put on the ways that allowed the chuck to be turned to get it on and off.
It had a lot of large bearings on the cart top and on the ways.
 
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fourspear said:
Would you please share the steps you went through to realign the headstock. Thanks, Red
Click to expand...

The Lathe was cutting truly straight Before this episode, so this is what we did.

After lowering the headstock back down, we installed the four large holddown bolts, just snugging them. I then placed an indicator on the cross slide. And moved it from one ice of that 30 inch chick to the other. Whe moved the headstock untill the indicator read zero. We then tightened the bolts.

I then chuck up a piece of 1 inch wall thickness 30 inch aluminum tubing, about 8 inch diameter, that we had laying around. I took a couple of very light trial cuts on each end, measuring the turned spots. It cut dead straight in about 28 inches.

That will get it done.
 
Glad you got it done.
I assumed since there were no dowel pin holes, the hold down bolts had a ground shoulder fit. Evidently you had a little slack.

My alignment tools for heavy pieces were: A 3lb short handle slugging hammer, a 1 X 10" piece of brass round stock, a dial indicator and a little touch.

It all comes with practice.

Mort
 
mturner said:
Jackie,

Is there enough room to put a sleeve over the thin section?

Michael
Click to expand...

Michael, if you look at the picture, you can see that the hub of the gear barely clears the major diameter of the gear it meshes with when in fine feed mode. There simply is no room to increas the outside diameter.

Maybe another design flaw? I think it is. It would seem to me that common sense would dictate that any hardened gear asembly that is subject to any type of shock load would have to be as robust as possible.

Just an opinion from my lifetime as a machinist, but I see some serious problems. All of these sliding gear shafts should have been on splines, not single key ways and key seats. There Gould have been adequate room to insure each component had enough wall thickness to insure it could stand up to the rigors of operation without failure. Add the fact that there is little access to these parts without first doing a very labor intensive disassembly.

The Lathe is back in service. We have a lot of Rudder Tubes and Stern Tube assembly's to machine.

http://benchrest.com/attachment.php?attachmentid=21432&stc=1&d=1535987038
 

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What might be an alternative?

I guess if it were mine, I be thinking the machine my need a good dose of swap but what might be a better alternative?

Pete
 
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