I'm hoping somebody might help out with my 1970 SB Fourteen.
I get spindle vibration at around 700 RPM spindle speed. I've tried a number of things (and spent a number of $$$) with no luck. At this point I am pretty sure it is in the spindle. Here's what I have tried that has led me to that sad conclusion:
- Started with 3-phase motor on static converter - switched to VFD to eliminate any motor vibration (and for other benefits too)
- Removed spindle drive belts - this leaves motor, transmission, and variable-speed pulley system from motor to transmission - NO VIBRATION
- Used variable pulley system and VFD to get 700 RPM spindle speed at different motor speeds - vibration corresponds with spindle speed
- Replace old V-Belts with Powertwist linked belts - STILL VIBRATES
I suppose I could rig up some sort of alternative setup to drive the spindle, but I don't think that's necessary at this point. I'm psyching myself up to tear into the headstock. I was wondering: Has anybody dealt with this kind of problem on this model before? What was your solution? Anybody torn down one of these headstocks? Any gotchas? Any special procedures related to reassembly of bearings?
Wally... first question which you must surely have done, but did not say so... are you measuring this vibration with the same three jaw and four jaw, or faceplate, or no load? What changes do you see under different load characteristics?
I should have mentioned that - it was same regardless of chuck, collet, faceplate, bare, etc. Notice I said *was* - I may have jumped out of the frying pan and into the fire.
I took the top off of the headstock and looked around. Pretty empty inside these beasts, but interesting. There is a (pretty chincy) little plunger pump that runs off of an eccentric on the spindle. Small copper tubing picks up oil from bottom of headstock and is supposed to squirt it on the bearings.
So I'm thinking "Eccentric, that would cause a vibration!". There is another eccentric that is supposed to act to balance the other one. There were 2 witness marks that were about 45 degress apart. Hmmm. Lined those up, thightened setscrew, and the vibration went almost completely away! Tried tweaking it but didn't get any real improvement.
Still, I was pretty happy. Yes, "was" again. Now my surface finish has gotten crappy at ALL speeds! Not horrible, but noticeably worse. Sigh.
Going to play around with different settings of the balancing eccentric...probably tomorrow.
This is the best proove, that the vibrations come from the spindle. You did remove the chuck/collet? Then the only thing left is either the bearing (preloaded? what type of bearing) or a big excentric mass on the spindle (did you clean it recently :-))
Looking through the photos does not tell me too much -- but I have a few questions. I'm presuming that you are running with the bare spindle nose, not with some possibly unbalanced load mounted on the spindle nose.
1) Can you look at the belt while it is running at 700 RPM? If so do you see vibration in (proably) the long run of the belt? (The likelihood of this is reduced by your having replaced the belt -- presumably a standard V belt with the link belt shown.) That is a long run between pulleys, and link belts have more stretch than standard V-belts, as indicated by the need to remove some links after a period of service.
If the long run *is* vibrating, can you toss in another idler pulley to help control that?
2) Is there something perhaps missing from the spindle which changes its balance? I note that this is a Camloc style spindle nose. Is it possible that one of the Camloc inserts is missing, or has been replaced with one which weighs either more or less than the other two?
Or perhaps the belt pulley on the spindle is designed for two setscrews -- one to lock the other in place, and the outer one is missing -- or even that you have a different length of setscrew than was originally used?
Does it have conventional back gears, or is this a gearhead lathe? I don't see enough levers on the front so I assume that it is a back gear equipped lathe. If so -- is there something lost from the pin which locks the bull gear to the spindle?
Or are there some teeth missing from the bull gear?
Anything else which might change the balance of the spindle?
3) Just off chance -- has there been any change in the stiffness of the mounting of the lathe bed to the pedestal, or the pedestal to the floor? It could be that you are missing enough stiffness to allow something to resonate at 11.666 Hz where it previously would not. The stiffness will determine how the other parts of the system relate to the frequency at which it will resonate.
If that is the case -- then the resonant frequency should change as you mount lighter or heavier chucks on the spindle nose.
4) What about play in bearings? If the bearings are loose or worn, you might have more play allowing an imperfect spindle balance to introduce the vibration.
Overall, 700 Hz seems to be a fairly low speed to get resonance in something this large and heavy. Again -- check the long run of the belt while it is vibrating.
Yee, Gods! What an insane drive system! It was originally supposed to have 2 belts, I guess. Is there any damage to the pulley flanges? If so, then the speed changes every time the dent goes round and belt rides higher and lower in the flanges.Maybe move the belt to the other pulley groove and see if there's any difference. That outer groove would be the one to get dented when moving, rigging, etc.
The headstock only has the backgears in it, all other reduction in the motor/gearbox unit? I doubt the problem is in the headstock, but I suppose a broken bullgear could unbalance the spindle enough. But, I'd expect the problem to be WAY worse at 1500 RPM than 700. Are the machine's feet properly adjusted to stabilize the machine?
Is there any possibility you can spin it up and then kick the belt off the pulleys or in some other way release the belt tension and let the spindle turn freely? This could be dangerous, so be sure you can do it safely before trying such a stunt! The idea is to isolate anything happening on the pulleys from the rotation of the spindle. I've seen belts with uneven wear or pulleys with bent flanges cause machines to rock or vibrate severely.
Is the vibration about 12 times a second? That is the rotation rate of the spindle at 700 RPM. If it is much slower, it is related to the worn spot on the belt going around one pulley, then the other. If much faster, it would be related to the drive pulley on the gearbox.
Don't even THINK about taking the headstock bearings on this lathe apart without proper tools. It is a high-end machine spindle, and the replacement bearings might cost more than you paid for the machine -- possibly MUCH more!
idea" in their late-model R-series lathes. They use the huge bull gear to whip up the oil and sling it up to the oil galley slung just under the top cover. So, there's no eccentric, and no mechanical pump.
Now, is your balance weight 45 degrees to the pump eccentric, or is that just the spacing between the setscrews? It would seem 180 degrees between the two weights would be the desired position.
Is it possible that this weight does something ELSE that counterweighting the pump eccentric? Funny that reducing vibration would WORSEN finish!
Anyway, unless this eccentric is really large, it shouldn't cause a whole lot of vibration if the machine is properly supported by its feet. On a 14" lathe, you should be able to walk up to the lathe and give it a HARD shove without it rocking at ALL! I know my Sheldon 15" just sits there like a ROCK, and I need a BIG prybar to budge it any. My Sheldon does vibrate just a bit at 900 RPM and above, especially if the chuck body needs to be offset a hair from dead center. I can't see any effect in the surface finish when it does that.
If you suspect bearings, I'd take a dial indicator and see if you can deflect the spindle any with a large pipe through the spindle bore to lean on. Then rotate the spindle very slowly while looking for +/- variation on the indicator. If you get a lot of bumpy changes in the reading, and the track on the spindle OD is smooth, then that does indicate serious bearing trouble. On a lathe this size, that is BAD news!
None of this is making ANY sense to me! A once-per-rev vibration shouldn't cause surface finish problems. And, reducing the vibration and getting worse finish is even more confusing. Is this lathe new to you? Have you done any work on it at all, or are you still testing it? Is it properly installed, or is it sitting on some 2x4's?
Well, the surface finish problem was a red herring - result of a chipped insert and (mostly) my fatigue from working out in a 95 degree garage all day. Things are actually looking pretty good at this point. There is still a hint of vibration at 700 RPM - I am guessing that the counterbalance eccentric could use a tad more weight on its' big end. But it is a lot better.
I cleaned up the tubing and the pump and it is oiling the bearings nicely now. I still haven't checked runout on the spindle - I will do that this week just to get a reference and make sure they are OK.
Thanks a lot for the input - I answered your questions below.
Wally
J> > I should have mentioned that - it was same regardless of chuck, collet,
What I meant there is that the eccentric alignment mark was about 45 degrees away from the corresponding one on the spindle. Yeah, the weighty ends are 180 apart. The eccentric had apparently moved somehow.
Again, sorry for the confusion.
This unit goes about 1700 lbs. - it doesn't move without a big pry bar either.
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