I asked to hear a 14-inch gear-head Chinese lathe running at a dealers today. Even at top speed (1800 rpm) it was really quiet, and I commented on it. Yep, he said, we used to run them on 68 grade hydraulic oil, but they were pretty noisy, so now we use 220 grade hydraulic oil.
This seems like a heck of a step up in viscosity. My knowledge of safe oil practice and substitution is about zero, so... Is the change to 220 safe/good-practice/going-to-cause-problems/void-waranties, etc, etc??
Interesting. I am rebuilding a 1972 Sheldon 15" lathes, a very high end machine. The oil specs in the book really had me wondering if there was a typo, but there is a plate on the machine with the same info. Basically, they run way oil in the headstock, and gear oil on the ways! I had to read the info a dozen times, and I still keep thinking I'm reading it wrong, somehow!
The only likely place you'd have a problem with the change in the Chinese lathe is possible overheating at the highest speed. The ISO 220 hydraulic oil is not all that much higher viscosity than the ISO 68. These ISO numbers are roughly 3.5 times higher than the SAE oil "weights".
I'm not an expert on this stuff by any means, but I still wonder about the shear properties of hydraulic oil vs a good gear grease. Now it probably wouldn't be an issue in a home shop, but if you were using most of the horsepower of your motor taking big cuts, wouldn't there be a problem with gear wear?
Having ridden a motorcycle for a few years and having experimented with different motor oils (which, BTW also serve as the transmission grease as well), I found that it was best to stick with purpose-formulated lubricants rather than what ran the most quiet at idle.
I can't answer for the original poster, but this is what was recommended by the manufacturer. The particular Sheldon headstock has no gears meshing except when in the back gear range. (All the rest of the gears are in another gearbox, that is lubed with heavy gear lube.) The back gears are very big, 3/4" wide at least, and so may not need a very heavy gear lube.
Motorcycles are another animal entirely, as they try to make the gearboxes (and everything else) as small as possible, and running very hot at high speeds. That makes them need a very high performance lube. (Running the clutch in that lube puts them in a double bind - too good a lube and the clutch will slip, not a good enough EP lube and the gears grind themselves to bits.)
What exactly does the plate recommend for the headstock? I was confused the first time that I saw Mobil Vactra specified for a gearbox til I did a little digging and found out there are two Vactra lines. The numbered series (No.2, for example) is waylube, the named (e.g., medium- heavy) are general purpose oils.
If the ISO 220 oil in the original post is indeed hydraulic oil, it's unusually heavy. I think it's more likely a gear lube. ISO 220 would correspond approximately to SAE 50 engine oil or SAE 90 gear oil.
Ok, spoke to the dealer's engineer today, and yes, it is ISO 220 oil, but not hydraulic oil - it's Shell OMALA 220 gear oil. There are plenty of references on the web for this product. He said that in their presses, guillotines, larger lathes, etc (anything that has force-feed lube pumps) they use the normally recommended grades, but in the small splash systems they use this 220 grade stuff. They move a lot of product, and carry the warranty themselves (at least on this smaller equipment), so I guess they don't see any problems when using it.
Like I said, it was the quietest 14 inch lathe I've ever heard - it was like a big powerful sewing machine.
has a few interesting words, some of which I have extracted here:
"The Society of Automotive Engineers (SAE) is a viscosity grading system for oils used in the automotive industry. To avoid confusion it is divided into two subclasses, one for gear oils and one for engine oils. A high number (greater than 60) means that the oil is formulated for a gear type component while a low number corresponds to oil which is used in the engine."
"Unlike the ISO system, the SAE system does not give the viscosity of the oil in centistokes at 40°C, although the higher the number, the higher the viscosity."
"SAE gear and engine numbers cover the same range of viscosities; for example, an SAE 30 engine oil has approximately the same viscosity as a SAE 85W gear oil. This is because the formulation of engine oils is very different to that of gear oils in the automotive industry. An engine oil is far more stressed than a gear oil because it must cope with combustion by-products and blow-by gases which severely degrade the oil. As a result engine oils contain a much wider variety of additives than gear oils. Although not ideal, an engine oil will function in a gearbox while a gear oil will destroy an engine."
Heavy trucks used to use grease in their wheel bearings on the front wheels and trailer wheels, and axle oil lubricated the drive wheel bearings. Owners found that the oiled bearings outlasted the greased bearings, as the grease just got thrown off or squeezed out, and the bearing was dry. Front and trailer axles have used oil now for nearly 30 years. Grease is just oil with thickeners to keep it stuck to something. It really doesn't have any more EP qualities than a good oil. If an oil bath is possible, it's far better to use it.
What makes a good engine oil does not make a good gear oil, even though the viscosity is the same. The differences are more in the additives then the base oils, though there are different types of base oil. When the SAE number system was invented, pre-metric, they need easy numbers to remembers (verse SUS "something"-universial-seconds), and they picked 10,20, 30, 40, and 50 "weight" to call motor oils, and 80, 90 and etc to call gear case oils so some "gearhead" did not use the wrong oil.
The ISO 220 or 68 oils (there are quite a few numbers) are based on the metric systems viscosity number, and is easier to remember.
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