Noisy Lathe Gearbox

My lathe gearbox has (over a few years) become increasingly noisy. It's bad enough that it has to doing some damage.

I have periodically changed the oil & carefully filled it to halfway up the little window.

In desperation, I over-filled it with EP90 car diff oil & it now sounds "not too bad" ( Very scientific)

It got warm after approx. 1 hours intermittent use, so heat may not be a problem. (car diffs get very hot).

I filled it so the gear that drives the main spindle gear was just picking up oil. It is the highest pickup gear in the box.

Is there a problem with too much oil?

Geoff

Not particularly comparable with a car differential - power transmitted is far higher for most cars, and also via a crown-wheel & pinion and differential gears - and they should not get particularly hot even though much smaller in comparison.

With a gearbox, such as this, there should be plenty of splash lubrication and possible pumped supply to bearings.

Over-filling will increase drag and therefore generate more heat, but also likely to leak from otherwise sufficiently sealed orifices.

Gear oils with ‘hypoid’ (extreme pressure) additives should not be used in the presence of yellow metals.

The manufacturers provide lubrication levels for a good reason.  Best to comply with those requirements.

Edited By not done it yet on 05/02/2020 10:11:45

A bit more info on the make, model and age of your lathe would be very helpful.

It it's an old lathe, it could be bearings worn out.

If it's a Chinese lathe, some of them have been known to come complete with casting sand inside the gearbox cavity that eventually chews the bearings out. And the bearings are not the world's best quality either.

Either way, adjusting the pre-load on the main spindle bearing may help. Or replacing the bearings with good quality such as SKF or Timken may help too.

The other thing with some Chinese lathes is the poorly made steel gears tend to wear and also tend to "ring" more than cast iron gears used on older lathes. Generally speaking, a lot of the Chinese lathes run very noisy in the gears for this reason. Some of the larger ones I have seen are almost painful to stand next to in operation. Yet some others seem to run reasonably quietly

It's unlikely overfilling the gearbox will do any harm other than a mess where it leaks out. It's a basic splash lube system, in accordance with the low speeds and loads involved (compared with say a 100hp car gearbox) so as long as the oil is up to the lowest rotating gear in the box, that should fling it all over the place and lube the bearings (which being rollers I presume, don't need a lot of oil) and gear teeth.

Did I see somewhere that the additives in EP oils are detrimental to bronze, a material which is sometimes used in geared headstocks?

Hi Geoff

I used to have a very old Colchester Student roundhead that was very worn and was horribly noisy( but very,very cheap!) I ran it on thicker oil. I can't remember what grade, but in a cold workshop it wouldn't pull the top speeds until it warmed up a bit. It did quieten it down quite a bit, before I had to wear ear defenders on the top speeds, it was bearable after.

I sold it to a friend ( even cheaper!) some twenty odd years ago who still uses it regularly, and I know he has never changed the oil since, or even cleaned it properly. Not advocating such practice but it's still going strong after many years use.

It is worth checking the suitability of your EP oil with any bronze or brass bushes, some makes do contain something that can degrade bronzes. There have been problems with Vintage vehicle gearboxes, I seem to recall reading that it's been superseded by synthetic replacement that no longer causes problems. Probably worth a Google search.

Hope this is of help

Dave

Most of the lathes I have worked on use a 32 or 46 viscosity hydraulic oil in the headstock - even very large capacity machines. A 1020mm swing Gildemeister at work uses 46 viscosity oil & a similar sized, but heavier duty, DS &G uses 32 viscosity oil.

On a machine without a circulating pump, the parts not immersed are lubricated by splash - the machined groove you can see around the lid joint face collects oil splashed onto the lid & directs it towards the spindle bearings via the machined slots that guide it down the vertical face & into the bearings (some have wicks sitting in the groove to regulate the flow via drillings instead). It is important that the oil you use can be splashed onto the lid & you can check this with a piece of perspex in place of the lid - the fast running input shaft & gears should be able to produce enough splash to be seen hitting the lid & if the groove isn't being continuously refilled, you won't be getting much oil to the spindle bearings. You can usualy see dirty marks on the underside of the lid where the oil has being hitting it on older, well used, machines.

Too much oil saps power to move it around.

I have heard of people using the "Timesaver" lapping compound to quieten noisy gearboxes but have not had to resort to that myself.

Nigel B

Does it have an adjustable back gear like the colchester student. if that is not adjusted right it makes a lot of noise

I bought a Myford 280 with a noisy gearbox, one of the interference fit gears had come loose and could slide left and right (correction, it could slide left, it shouldve been up against a shoulder on its right), I rebuilt the gearbox and there wasn't anything else wrong I could see (correction, something else was wrong, I don't recall what but you could "rub" gears together by pushing the selectors in certain directions, something wasn't aligned or secured or something). I used dab of special Loctite for very close fitting parts requiring a high bond while immersed in oil. It's smooth and has been whispering along for years now.

(The gear top left should have been against that shoulder)

I also recall the spindle bearings (Gamet Super Precision) required an end float of a 10th of thou off the top of my head (2um ish) and it was probably 5 times that although I couldn't see or feel anything moving! it was such a small number I'm sure even the 1000lbs of casting could flex that much if I pulled and pushed them!!

I think we need to know what lathe you've got, and if the noise is related to the input or output speed of the machine. I can see from that photo you have 3 ratios that you can transmit from the input shaft the layshaft under it but It's unclear to me what happens after that, I'm guessing another 3 position selector and perhaps a seperate backgear but I don't count enough gears or envisage enough throw on the selector for that to work, more info needed.

Where are you located, if you're local I could take a look/listen which counts for more than a thousand words!

Edited By Russ B on 05/02/2020 14:41:49

Calls for a careful inspection. Any teeth missing, or worn, loose or badly meshing gears (sideways and/or vertically)? Misplaced selectors, foreign objects, or damaged bearings? Anything moving that shouldn't, or jammed? Is the noise worse in one particular ratio? I'd expect the cause of scary noises to be fairly obvious when the gearbox is rotated by hand. Anything causing loud damage is unlikely to be fixed by simply adding a lot more oil.

If nothing obvious, sound can be deceptive - perhaps it's not coming from the gearbox. Check absolutely everything and try to isolate the noise by disconnecting stuff. May be worth investing in a stethoscope or making one from a wooden rod.

Gearboxes are funny things - a damaged box can last years despite sounding like a demented coffee-grinder. With luck it's either easily fixed or can be tolerated.

Dave

I would suggest ear defenders when using the lathe, I have a Chinese geared head lathe which is loud due to inaccurately machined gears, way too much backlash.
Dave W

Thanks for all the advice. It's a typical Chinese lathe, 38mm spindle bore with huge taper roller bearings. No back gear, 6 speed gearbox & 2 speed pulleys. Overall, I am very happy with value for money & don't regret my purchase.

I hadn't considered EP oil attacking bronze bushes. The only bronze would be in the selector pivot bushes. (although they may just run in the cast iron casing)

I will investigate a 90 weight manual trans oil, which I don't think has the EP additives. The noise reduction is so good I would sacrifice any pivot bushes.

Russ B, Thanks for your diagnostic offer. Chances of being close enough are slim, but here goes. I'm in Drysdale, Victoria, Australia. That's about 100 km south of Melbourne. And yes, it's still smokey.

Regards, Geoff.

Geoff, I'm only 17,000 km away, I'll drop in if I'm passing!

If you want to use high viscosity oil, and the lathe can run without the splash lubrication provided by "thin" oils, normal SAE 90 gear oil should be free of the surfactant additives present in EP oils, likely to attack yellow metals.

The bronze wormwheels in Leyland rear axles seemed to manage OK for many thousands of miles using such lubricants.

EP oils were developed for Hypoid axles where the high pressures and sliding action of the teeth made for strenuous working conditions.

Howard

The attack of bronze typically happens when acidic combustion by-products are present alongside the EP additives. So the thing you typically should avoid is using an EP oil in an engine.

In a gearbox there shouldn't be combustion by-products present, so no problem.

Rather like not brushing your teeth too close to eating!

What about other additives such as moly or Redex?

I remember being advised to push a pair of old nylons through the filler hole of the noisy diff on my Cortina estate.

I got stopped by a copper, thought he'd spotted me doing 70 in a 60 zone, but he just said my diff sounded like a jet fighter and to get it sorted before it seized.

Oddly enough a workmate had the diff seize on his escort resulting in an unplanned 180 around the same time ...

The label should say if the EP90 oil is ok for yellow metals. Almost alk are safe these days. GL1 to 4 rated gear oil is ok. Then early GL5 rated was not good for yellow metals . But these days most manufacturers have added a stabilizer that makes it yellow metal compatible and say so on the label.

You could even try the EP140 that is available these days. Could be a bit thick if your gearbox has small needle roller bearings on those layshafts. Or not.

Edited By Hopper on 07/02/2020 00:20:19

Noise from a gearbox can be from different beginnings.

Carp gears/metallurgy is generally down to the initial manufacture and worn gears are not going to get quieter as they wear further

Carp bearings will cause noise - and then wear gears - but can be prevented from further destruction by swapping them out (often for better quality items).

Analysing the sediment in the box can be revealing. White metal usually means bearings, steel might be from gears. Any sand was in there from manufacture!

A magnet on the drain plug can collect a lot, even all of ferrous particles, if the drain is positioned properly in a well designed gear case (not one with a flat bottom). But it does need checking if large quantities of metal filings are being generated.

Most certainly, a gearbox getting noisier ovee time/use needs diagnosing and fixing if longevity is required.🙂

Noise from a gearbox can be from different beginnings.

Carp gears/metallurgy is generally down to the initial manufacture and worn gears are not going to get quieter as they wear further

Carp bearings will cause noise - and then wear gears - but can be prevented from further destruction by swapping them out (often for better quality items).

Analysing the sediment in the box can be revealing. White metal usually means bearings, steel might be from gears. Any sand was in there from manufacture!

A magnet on the drain plug can collect a lot, even all of ferrous particles, if the drain is positioned properly in a well designed gear case (not one with a flat bottom?). But it does need checking if large quantities of metal filings are being generated.

Most certainly, a gearbox getting noisier with time/use needs diagnosing and fixing - IF longevity is required.🙂

Perhaps consider a dual rated slideway / (low speed) bearing oil.

I use Castrol Magna BD 68 as my slideway, low speed bearing, banjo gear train and general purpose oil can oil. Castrol tech department advised using Magna for the slideways maybe 40 years ago when I asked about oils for my SouthBend 9" as it's less sticky than a full on slideway oil. They also said Hyspin AW32 for the spindle. The pairing seems to be fine on every lathe I've had.

The Magna is very effective at quieting down banjo gear train oils and hangs on well so it creates little mess. I imagine it might well be OK in your headstock.

Clive