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Wanted: Metal Lathe

Dabbler

Well-Known Member
#82
The old wisdom was SAE 50 or greater in the apron. Nowadays it is different. If you call the Grizzly tech department (I did) they will tell you to not follow the directions, and go AW32. It is not to save money. it is because of the particle suspension problem as I mentioned above. The recommended change interval has gone to 100 hours of use or 1 year, to minimize wear and maximize life. Oil is cheap - rebuilds are expensive...

What you are looking for is an oil that conforms to ISO standard 11158

I know this flies in the face of these offshore manuals, copied from manuals written in the 60s and 70s. The King one must be updated. Modern Tool (millwright), King (help line), and Grizzly (technical staff) and Precision Matthews (millwright) all recommend AW32 for cold climates and AW 46 for very warm ones in the apron. I'm really trying to help you get the longest life out of your lathe. There is no more lubricity using SAE50 Gear versus AW32 because of the anti-wear additives. I did spend 2 weeks almost every day researching this and talking to technical staff and lube experts. Still, do what you think is best!

I got my BB lathe in 1981 and they recommended 85/150 oil in the apron, but I used (then) SAE 50 gear oil, because it was what I could get easily in 500 ml bottle. I am going to rebuid my apron and I'll post the results in the next month or 2. I will be changing it to AW32 as well. I figure a rebuild every 37 years is in order!

Johnwa, AW32 is similar to an SAE 20 oil in viscosity, but with the antiwear, it should lubricate like an SAE50 gear oil, if that helps. As long as none of these oils have EP additives! Both the free-sulfur and the zinc-based Extreme Pressure additives will etch and destroy the bronze components in time: they leech the copper out of the bronze leaving it porous and weak, and the surface flakes away.

Last point: I'll be putting a rare earth magnet or 2 in the sump of teh apron to try to catch particles in suspension; just a thought!
 
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Johnwa

Active Member
#83
My SM starts fine in the cold, but I do have it on a vfd that ramps it up relatively slowly. I’ll never wear it out regardless of the oil but am following this thread with interest.
 

Tom Kitta

Active Member
#84
OK let me put on my geek hat with a dab of oil on it :)

The main purpose of oil is to provide lubrication and the main characteristic of oil is its viscosity.

Viscosity is selected based on load, speed and temperature. The higher the speed the more load an oil can support, the thinner (lower) viscosity the less load oil can support.

Thus a fast moving part with thin oil can support the same load as slow moving part with thicker oil.

EP additives should be used for spur / hellical gears. (EP == extreme pressure). EP should be not used on worm gears as it can attack brass and there is no rolling action which EP is for. Because the sulphur in the Extreme Pressure additive can corrode yellow metals, corrosion inhibitors are added to the oil. Some bearings dislike EP. First EP additive was lead.

Oil is also used to cool bearings, it is better then grease at low/ high temps and is needed at very high speeds.

Now as we do have bearings in the machine we must note that too low of a viscosity will cause the oil to escape the bearing too quickly thus small lathe == higher viscosity oil in the headstock. Faster speed also means lower viscosity. Roller bearings = 50% more viscosity.

I went through this little book: http://correctlubricant.co.za/Correct_lubricant.pdf

So what does it all mean? Well for starters there is a reason why we have all these oil types in different viscosity grades. Old big lathes should use much thicker oil then a bit smaller but much faster lathes. Oil in the headstock should be lighter then oil in the apron (unless it is some kind of older slow lathe) as headstock moves much faster. This way they can both support same load.

Of note is the fact that you better not have any water in your oil as well as you don't want your oil to foam too much.

If anyone wants to read more this 1000+ links about oil should fill your day: http://correctlubricant.co.za/web_book.php

I am not saying my conclusion is 100% correct - but I think it is - unless someone can look at it all and point out some hole.
 

Dabbler

Well-Known Member
#85
Tom you invited friendly debate, so, respectfully, is a different view.

Thus a fast moving part with thin oil can support the same load as slow moving part with thicker oil.
The choice of oil Is far more complex than that. The loads on a small lathe, including medium sized lathes are very small compared to, say a car differential or transmission. Loads in the apron are seldom over one hundred pounds for the spur gears. For the size of the gears this is a tiny % of the maximum load.

The purpose of the oil is to both lubricate and remove contaminants from the gear. Thicker oils only do this well if they have sufficient radial velocity and oil exchange to do so. This is not the case in an apron gear set.

EP additives should be used for spur / hellical gears. (EP == extreme pressure).
Never us EP in the presence of brass no matter what the gear combination is.

Now as we do have bearings in the machine we must note that too low of a viscosity will cause the oil to escape the bearing too quickly thus small lathe == higher viscosity oil in the headstock. Faster speed also means lower viscosity. Roller bearings = 50% more viscosity.
This is a serious over-generalization, as many short pamphlets do. Bearings that are lubricated by oil can be oil bath, splash or flow lubricated. The viscosity in the headstock isn't solely for the bearings, or you would need dual lubrication in the headstock.


Oil in the headstock should be lighter then oil in the apron (unless it is some kind of older slow lathe) as headstock moves much faster. This way they can both support same load.
That is simply not how the apron works. You are right in saying the gears move slowly, but the speed of the gears has *nothing* to do with the required lubricity.

It is the combination of the temperature speed, pressure profile, and oil circulation characteristic that is crutial in choosing oils for anything. In my case, operating a lathe with 50wt oil in the apron at 7 deg C would be silly. it would not be within it's performance range. (that means that it is below it's critical temperature, and would provide significantly less lubrication than at 20 deg C). A few synthetic 50 wt oils can do this, but they probably have EP additives - catch-22.

SUMMARY

Any oil is better than none.

ISO 50 will work - for the service life in a hobby lathe - probably fine.
AW32 is recommended because of superior characteristics including lubricity, removal of contaminants, and oil circulation.

In no case will the pressure profile in the apron require heavy oil.

I'm going with what my vendor uses when he is paid thousands $ to rebuild machines. He uses AW32 in the apron of their 14 - 24" lathes - because of these superior characteristics, not because of some cost saving measure.
 

PeterT

Ultra Member
Premium Member
#86
Here is a visual cross reference chart to correlate oil viscosity by common oil types we encounter. At least we can all agree on that :)

Attaching lubrication chart for my '97 King 14x40 which calls for pretty high viscosity in the head stock gear case - but I cannot honestly answer why. I'm running something less than that but not for any good reason other than availability & seemed about right. As others mentioned, I've seen equivalent lathes with lower viscosity factory recommendation.

I suspect temperature plays a bigger role, but its rarely quantified. For example have a look at the attached ISO vs Temperature chart. If you go to the intercept of ISO-32 oil at 10C it yields a kinematic viscosity of 150 mm2/sec (1 mm2/sec = 1 centistoke = viscosity of water). Now take this identical 150 cSt & run across horizontally. It equates to ISO-68 oil at 22-23C. So maybe my Taiwan lathe assumes a non air conditioned Taiwan shop at 25C ambient and extended gear meshing adds another 5C. So that operating oil bath temperature could be 30C. The same lathe in a Canadian winter shop conserving heat could be 10C + intermittent use + 2C = 12C. I'm just pulling numbers out of my ass but you see what I mean. You can't talk viscosity without also referencing temperature, they go hand in hand. Interesting discussion. And this is only viscosity! :)
 

Attachments

Tom Kitta

Active Member
#88
Technology we are dealing with here is very old. It is very well understood. Thus any changes to it are very suspect. Does your vendor has any scientific study not done by them (i.e. impartial) or more than one suggesting change is in order? Otherwise I simply assume the vendor is simply incorrect and their reasoning has no basis at all.

Just b/c the vendor is big doesn't mean what they do is correct just b/c they are big - they need to say why and point to research that is plentiful and impartial.

So lets research how does one remove contaminants from oil - water and particulate matter. Water is a bit beyond small system AFAIK. See https://www.pumpsandsystems.com/top...water-and-particulate-contaminants-oil?page=2

So that leaves small metal particles in the oil, microns in size, and metal shavings.

Small metal particles in oil would not benefit from thinner oil at all - you can use a filter to help with this to a point - they you need to replace oil. So that leaves metal shavings. Metal shavings will settle at the bottom and are removed via magnet - I fail to see how viscosity of oil helps here.

http://www.uslube.com/contamination.html "There are two ways to deal with contamination: prevent it or remove it. "

I found zero articles pointing to a thinner oil as a solution to dealing with particulates and extending machine life. Lathe aprons are not special in any sense - there are other slow gear systems yet there is no information on simply dealing with the dirt by using thinner oil!

I suspect this big company is simply saving $$$. They determined that extra wear of ISO 32 (if more then negligible) in apron is within tolerance when compared to ISO 68 or even ISO 100. Thus at a price of little more wear they unified their oil to use same one everywhere. It can also be the case that the little load that apron has makes oil choice between ISO 32 - ISO 100 of no practical value - i.e. old manual recommendation is an overkill.

In summary:

Any oil is better than no oil

For the apron AW32 may be OK for service of a hobby lathe in the apron in temps it sees in most workshops.

AW68 is a better choice but may be an overkill - i.e. there may be minimal if any benefits of its use over AW32.

Thus if one only has AW32 b/c they got it at 40CAD at PA I would not say sacrilege if they used it everywhere. If they got AW68 on sale & don't mind starting issues with their lathe if not using VFD & its OK with the bearings & some wasted electricity is OK - use it everywhere.
 

Tom Kitta

Active Member
#89
Here is a visual cross reference chart to correlate oil viscosity by common oil types we encounter. At least we can all agree on that :)

Attaching lubrication chart for my '97 King 14x40 which calls for pretty high viscosity in the head stock gear case - but I cannot honestly answer why. I'm running something less than that but not for any good reason other than availability & seemed about right. As others mentioned, I've seen equivalent lathes with lower viscosity factory recommendation.

I suspect temperature plays a bigger role, but its rarely quantified. For example have a look at the attached ISO vs Temperature chart. If you go to the intercept of ISO-32 oil at 10C it yields a kinematic viscosity of 150 mm2/sec (1 mm2/sec = 1 centistoke = viscosity of water). Now take this identical 150 cSt & run across horizontally. It equates to ISO-68 oil at 22-23C. So maybe my Taiwan lathe assumes a non air conditioned Taiwan shop at 25C ambient and extended gear meshing adds another 5C. So that operating oil bath temperature could be 30C. The same lathe in a Canadian winter shop conserving heat could be 10C + intermittent use + 2C = 12C. I'm just pulling numbers out of my ass but you see what I mean. You can't talk viscosity without also referencing temperature, they go hand in hand. Interesting discussion. And this is only viscosity! :)
Yes temps are important - but one assumes that the headstock and apron are about same operating temperature - at least for initial use - i.e. after few hours I would get the lathe warmed up and significantly hotter - by more than 10C then the apron - at least some gears are moving at few hundred RPM.

As for your lathe the oil choice is quite thick and may suggest that they are assuming operating temp of over 20C. What is of interest is that they unified the oil - everything is the same grade! If you drop to thinner oil in your headstock it will be easier to start & you use less electricity in addition to having more spindle power. There is also something called oil flow point - with a thicker oil you will cause a lot of wear if you start it when very cold - if your bearings use drop lubrication from the top of the housing then the oil will not flow down to well when cold causing bearing to overheat.

Now I bet no one will change their oil from summer to winter in their lathe. So as you can see there is some build in tolerance - at least 25 deg. In engine oil we have double grade to take care of the problem - clearly not that of a big deal in a lathe. Also the chart doesn't mention temps the oils are at - its only our guess they need to be high.

In practice we use AW32 in the headstock - or at least most people are OK with it - due to cold Canadian winters and temp of around 5 deg at which starting a lathe with say AW68 without VFD would be an issue - I experienced this myself. This is the thinnest oil recommended for speeds around 1750 rpm.

It would be interested if someone bothered to run an actual test checking wear with different grades of oil at say few standard temps. However, for hobby machines & anything up to max they sell at grizzly it seems of little interest. I mean people have very old lathes and when gears were made properly they last for many decades - far longer then industry needs them to last (i.e. did anyone heard of a lathe with worn out gears but say a good bed? Not broken gears, worn out. On a quality machine.). I mean when was the last time someone paid for oil test on a small lathe oil? Even for small commercial stuff like F350 it is very rare its common for bigger machines through.
 
#92
I guess a note on temp. Everyone is worried about a cold canadian winter.... so they prolly have a cold shop.
This is going in my basement....so...... 21c all year.
 
#93
Well at least everyone seems to agree on 32 in the headstock which is my biggest concern right now. The Apron and gearbox can be removed and transported without being drained.
 
#96
ok, so 32 everywhere :) and I have seen that the headstock takes about 7L. Anyone know roughly how much is needed in the gearbox and apron?
And Thanks Tom, I didnt think about PrincessAuto for the oil. Their AW32 in a 5Gal pail is going for 39.99 right now.
I have basically the same lathe as yours, (a bit older and different face plate is the onlty difference I can see from photo) I fill my apron gearbox until the oil runs out of the gear clearance hole in the back of the box. Personaly I think the Chinese manufacturers recommend heavier oil in the aprons so that the pin/shaft/ operating lever cut-outs don't have to be as precice...heavier oil seeps slower than light viscosity. Headstock boxes are very well bearinged & sealed to maintain true-ness so lighter oil that turns easier until it warms up is sufficient.
 

Tom Kitta

Active Member
#97
You should be fine with AW32. Through AW46 may be better at constant over 20C temps. Then again wear difference is probably not something you would notice. I.e. we are a bit of hair splitting here.

I was wrong about no multi-grade oils for hydraulics - they just call it "all season" and have extended pour point at cold temps so you can use the same oil for winter and summer. https://www.hydraulicspneumatics.co...s/Article/False/6526/TechZone-HydraulicFluids

In large industrial setting they do indeed change oil from AW22 in winter to AW46 in summer or use expensive multi-grade.

Obviously multi-grade / all season is more $.
 

Tom Kitta

Active Member
#98
I have basically the same lathe as yours, (a bit older and different face plate is the onlty difference I can see from photo) I fill my apron gearbox until the oil runs out of the gear clearance hole in the back of the box. Personaly I think the Chinese manufacturers recommend heavier oil in the aprons so that the pin/shaft/ operating lever cut-outs don't have to be as precice...heavier oil seeps slower than light viscosity. Headstock boxes are very well bearinged & sealed to maintain true-ness so lighter oil that turns easier until it warms up is sufficient.
Yes it may be part of the recommendation they use, after all if we ignore any bearing issues the consequences of thicker oil then needed is lost power and energy but no loss in lubrication. Thus it is "safer" to use thicker oil then to use thinner oil - within a sanity limit. Since these are small machines a tiny bit of energy lost to thicker oil is no big deal.
 
#99
Well I just removed the gearbox and I think I got it down to the point where four people can just man handle it.
It is still bolted to a skid so I can forklift it onto a truck. If Dabbler is still fine with me using his engine hoist then I can use that to offload into my garage. Then just four guys, brute and beer get it down stairs. Then use the hoist again to position it and boom, done and pray I dont blow my back out.

I know everyone is talking about ramps and winches but it is not practical for the design of my house and stairs.