# SAE 68 gear oil for PM-932M gear box



## 9t8z28 (May 30, 2020)

I am sure this has been discussed but the search feature says my search is too short so, 
I just got as PM-932M-PDF and am about to do the break in procedure for the gear box.   What kind and brand of SAE 68 oil are you all using?  I have heard that its better to use non synthetic but not sure if that's true.  I do not know much about oils other than what I put in my cars and am seeing conflicting info.  I have searched for SAE 68 and I get results for ISO 68 which appears to be different.


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## darkzero (May 30, 2020)

SAE are viscosity grades commonly used in automotive. ISO is commonly for hydraulic oil. ISO 68 would be what you want, not SAE 68. I use Mobil DTE in my PM-45 but any good brand hydraulic oil will work if that is all you have access to.


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## Ulma Doctor (May 30, 2020)

i wouldn't be worried about using synthetic oils on a lathe, especially in the gear train
oils are usually compatible between synthetic oil and mineral oil, small contamination of either doesn't cause problems
but conversely, you don't want to mix synthetic grease and non- synthetic greases- often bad things happen quickly when greases are mixed

most hydraulic fluids in the ISO68 range would suffice, i wouldn't get too hung up on brand name- all will meet minimum specifications


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## 9t8z28 (May 30, 2020)

Thats interesting thats its hydraulic fluid.  So Mobil DTE "26"?  I see the DTE in "24" and "25" ?  
Why would Precision Matthews be recommending SAE 68 if its not even the right kind of oil?  


darkzero said:


> SAE are viscosity grades commonly used in automotive. ISO is commonly for hydraulic oil. ISO 68 would be what you want, not SAE 68. I use Mobil DTE in my PM-45 but any good brand hydraulic oil will work if that is all you have access to.


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## RandyWilson (May 30, 2020)

To further muddy the waters, most of the synthetic oil on the market today isn't. It is cracked mineral oil that the US government allows to be called synthetic. The EU does not. That is why you have $5 "synthetic"  and $12 Euro-synthetic. In truth, there is little to no difference in performance between true synthetic and hydrocracked mineral. But Marketing gotta market.


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## 9t8z28 (May 30, 2020)

I am not worried about the non synthetic and synthetic oils being mixed in the mill gear box, I have read that the synthetic oils with detergents do not do well without filtration.  
I ask for a particular brand because its just easier to search for a specific product then I don't have to worry about the small differences between the products like how darkzone recommended Mobil DTE but there are different variations of it, IE 24, 25 and 26.  




Ulma Doctor said:


> i wouldn't be worried about using synthetic oils on a lathe, especially in the gear train
> oils are usually compatible between synthetic oil and mineral oil, small contamination of either doesn't cause problems
> but conversely, you don't want to mix synthetic grease and non- synthetic greases- often bad things happen quickly when greases are mixed
> 
> most hydraulic fluids in the ISO68 range would suffice, i wouldn't get too hung up on brand name- all will meet minimum specifications


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## RandyWilson (May 30, 2020)

9t8z28 said:


> Thats interesting thats its hydraulic fluid.  So Mobil DTE "26"?  I see the DTE in "24" and "25" ?
> Why would Precision Matthews be recommending SAE 68 if its not even the right kind of oil?



There is no such thing as SAE 68.  ISO 68 is about the same as SAE 80/90 gear oil. If I was to go the gear oil route, I would definitely avoid GL5. GL1 would be the ticket.


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## RandyWilson (May 30, 2020)

I found the PM manual online. I don't know how the Mobil DTE Heavy/Medium stacks up against the numbers. 

"""
Lubrication Oils are classified according to their viscosity. There are several viscosity indexes, the main ones being ISO (International Standards Organization) and SAE (Society of Automotive Engineers). SAE adds another complication with different indexes for engine and gear oils, further sub-divided into lists with and without the suffix W, meaning "multigrade". Mistaking SAE engine oil for gear oil can be an issue; for instance, SAE 20 engine oil has about the same viscosity as SAE 80 gear oil, both roughly equivalent to just one number on the ISO scale, ISO 68. Recommended lubricants Gearbox: ISO 68, such as SAE 80W90 auto gear oil, or Mobil DTE Heavy/Medium circulating oil (about 3 qts.) Ball oilers (X and Y leadscrews): ISO 32 oil, such as 3-IN-ONE (the "motor oil" version of this brand is heavier, about ISO 68, but it can also be used) X, Y and Z axis ways (dovetails): ISO 68 oil, such as Mobil Vactra No. 2, or equivalent Power feed (visible gears), quill rack and pinion, Z-axis helical gears: light general purpose grease, NLGI No. 2, or equivalent X and Y leadscrews: ISO 68 oil, such as Vactra No. 2 or 3-IN-ONE Motor Oil Z leadscrew: ISO 68 oil or NLGI No. 2 grease
"""


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## darkzero (May 30, 2020)

9t8z28 said:


> Thats interesting thats its hydraulic fluid.  So Mobil DTE "26"?  I see the DTE in "24" and "25" ?
> Why would Precision Matthews be recommending SAE 68 if its not even the right kind of oil?



For ISO 68, Mobil DTE 26 or Mobil DTE Heavy/Medium is the equivelent. I use either or depending on what my local MSC has in stock at the time.

DTE 24 & 25 are different viscocities. 24 is ISO 32 & 25 is ISO 46. You can use a lighter viscocity if you live in a very cold climate.

I'm not sure why they would tell you SAE 68. Did they actually tell you that or was it printed somewhere? It's a misprint if the latter. I have a a lathe & mill from PM, they never told me SAE 68, they told me ISO 68. But I bought my machines before they had manuals for their machines created.


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## 9t8z28 (May 30, 2020)

I'm not sure where you got that info but the manual that came with the machine states SAE 68.  It definitely doesn't say ISO.  I'm not debating what you read, I'm just telling you whats in my book.    
So M


RandyWilson said:


> I found the PM manual online. I don't know how the Mobil DTE Heavy/Medium stacks up against the numbers.
> 
> """
> Lubrication Oils are classified according to their viscosity. There are several viscosity indexes, the main ones being ISO (International Standards Organization) and SAE (Society of Automotive Engineers). SAE adds another complication with different indexes for engine and gear oils, further sub-divided into lists with and without the suffix W, meaning "multigrade". Mistaking SAE engine oil for gear oil can be an issue; for instance, SAE 20 engine oil has about the same viscosity as SAE 80 gear oil, both roughly equivalent to just one number on the ISO scale, ISO 68. Recommended lubricants Gearbox: ISO 68, such as SAE 80W90 auto gear oil, or Mobil DTE Heavy/Medium circulating oil (about 3 qts.) Ball oilers (X and Y leadscrews): ISO 32 oil, such as 3-IN-ONE (the "motor oil" version of this brand is heavier, about ISO 68, but it can also be used) X, Y and Z axis ways (dovetails): ISO 68 oil, such as Mobil Vactra No. 2, or equivalent Power feed (visible gears), quill rack and pinion, Z-axis helical gears: light general purpose grease, NLGI No. 2, or equivalent X and Y leadscrews: ISO 68 oil, such as Vactra No. 2 or 3-IN-ONE Motor Oil Z leadscrew: ISO 68 oil or NLGI No. 2 grease
> """


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## 9t8z28 (May 30, 2020)

If its supposed to be ISO 68 I would rather stay with this than use SAE gear oil even if it is almost the same thing.  Like I said, I don't know much about oils so I would rather know what brand and model I need than understand the differences I guess.  Thank you for the info tho.  
I guess I'll go with the Mobil DTE 26 unless someone tells me the 24 or 25 or whatever what number is better.  


RandyWilson said:


> There is no such thing as SAE 68.  ISO 68 is about the same as SAE 80/90 gear oil. If I was to go the gear oil route, I would definitely avoid GL5. GL1 would be the ticket.


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## RandyWilson (May 30, 2020)

Then, sorry to say, your manual has a misprint. There is no such thing as SAE 68.  That quote is straight from the manual on PM's website.

https://www.precisionmatthews.com/wp-content/uploads/2017/01/PM-932M-10-3-2018-v13-web.pdf

pg 17


For more information than you can possibly use:

https://www.bobistheoilguy.com/putting-the-simple-back-into-viscosity/


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## darkzero (May 30, 2020)

9t8z28 said:


> I'm not sure where you got that info but the manual that came with the machine states SAE 68.  It definitely doesn't say ISO.



Maybe you have an older manual? They have made a number of revisions to their manuals as they improved them. I helped proof read & make changes to the PM1236 manual. I've never heard of one of their machines specify SAE oils. SAE 68 doesn't exist.

I just looked at the current manual for the PM-932. It does say ISO.


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## RandyWilson (May 30, 2020)

Ah crossing posts. Go fetch the newest manual online that matches your machine, and get the recommended Mobil.


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## reds (May 31, 2020)

Detergent oils will attack any brass or bronze on shafts or gears. Beware.
There are synthetic gear oils available.


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## mksj (May 31, 2020)

Detergent oils do not attack brass/bronze shafts, the primary purpose of detergents are to keep particles in suspension so they can be removed by a filter, which requires a pressurized lubrication system. Almost all engine oils these days have a detergent, one reason why they are a poor choice for splash lubrication systems. Multi-viscosity oils are designed to operate over a wide range of temperatures, so one will see a range of rated viscosity such as gear oil 75W90 or motor oil 5W30.  Extreme pressure (EP) anti-wear additives can damage yellow metals, softer materials such as clutch packs. etc. Most EP additives these days are inactive at lower temperatures and need heat to be activated. Oils are also designed for specific applications, so something like a limited slip differential oil has very different properties then standard gear oil of the same viscosity. As pointed out by others, in the US we have SAE viscosity index which is a bit mixed up as to the application and the viscosity. The rest of the world primarily uses the ISO system which is a single viscosity nomenclature.  Many oils these days will list there ISO viscosity in addition to their SAE, but a comparison chart is worth noting.  So viscosity wise an ISO 68 oil is equivalent to a SAE 20 motor oil and a 80W gear oil.

Many of the "gear oils" for machinery such as lathes and mills are based on mineral oil, and typically are a single weight viscosity. The higher the operating speed of the bearings/gears usually requires a lighter weight (lower ISO/SAE) oil. The type of gears and if there are any hydraulic components/clutch packs also factor into the oil properties and additive packs. Typically for manual mills and lathes, gear oil and hydraulic oils of the same viscosity are used pretty much interchangeably. There are small difference between the two, but not something that would make a difference in the lubricating properties of the oils.  Some oils are also designed to emulsify water contamination while others are designed to separate it out, almost all oils have anti-rust and anti-foaming agents. True synthetic oils have a much more uniform molecule size are are less prone to degradation and have a more constant viscosity index over a wide temperature operating range. As an example in air piston compressors the rated change time for a mineral based oil is ~200 hours, where a synthetic oil is around 1000-2000 hours. So if you have a high usage compressor, it makes sense to use a synthetic oil, but the oil still needs to be changed at regular intervals (6-12 months) due to water/particle  contamination.

So specific to gear head mills, any oil is better than no oil, and in general the design (straight cut gears) and operating stress of a gear head mill is low. So just about any non-detergent oil of the proper viscosity will work for a long time. There is no "best" oil for this application, other than having the proper viscosity. Mobil just seems to be the most frequently sited oil these days were older manuals seemed to have sited Shell oils, and is is synonymous with equivalent oils of the same viscosity/overall characteristics. These days Mobil ISO 68 oils that would be used would be the DTE 26 hydraulic oil and the Heavy-Medium gear oil.

So now for a bit of the finer details from my own experience with gear head mills and oils having had one in the past. As indicated any good gear/hydraulic oil without EP additives will work quite well, and with regular oil changes (at least annually) you should see no differences between oil brands. The factory oil in most gear heads should be changed probably after the first 50 hours of use if not sooner. Most lower priced gear head mills come with probably the cheapest crappiest oil possible and often there is a lot of casting residue as well as metal particulate crap in there. If your gear head gets hot at the higher RPM's and/or you plan on using it at higher then stock RPM, then I would recommend a synthetic gear oil. I switched my gear head mill to synthetic after being broken in, I picked up 100 RPM top speed (2900 -> 3000 RPM), had significantly less foaming, and the head ran significantly cooler. The difference was very noticeable. I ended up using Amsoil Marine 75W90 gear oil, which although is designed for high speed marine drives and high gear pressures, will not damage yellow metals.








						AMSOIL Synthetic Marine Gear Lube 75W-90
					

Shop AMSOIL Synthetic Marine Gear Lube 75W-90 at AMSOIL. Find premium synthetic oil, filters and more online. Fast, free shipping available.




					www.amsoil.com
				



* Mobil dte heavy medium equivalent | Mobil DTE heavy medium cross reference | Hydraulic oil cross reference chart      *

DTE Heavy = ISO 100
DTE Heavy Medium = ISO 68
DTE Medium = ISO 46
DTE Light = ISO 32

*Brand* *Hydraulic Oil ISO VG 32* *Hydraulic Oil ISO VG 46* *Hydraulic Oil ISO VG 68
Mobil* DTE 24 Light DTE 25 Medium DTE 26 Heavy
*Shell* Tellus 32 Tellus 46 Tellus 68
*Chevron* AW Hydraulic Oil 32 AW Hydraulic Oil 46 AW Hydraulic Oil 68
*Exxon* Humble Hydraulic H32 Humble Hydraulic H46 Humble Hydraulic H68
*Texaco* Rando HD 32 Rando HD 46 Rando HD 68
*Sinopec* AW 32 Hydraulic Oil AW 46 Hydraulic Oil AW 68 Hydraulic Oil
*Castrol* Hyspin 32 Hyspin 46 Hyspin 68


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## 9t8z28 (Jun 2, 2020)

Thanks guys.  I got a gallon of Mobil DTE 26 and another gallon of way oil.


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## 9t8z28 (Jun 3, 2020)

this is very informative especially about switching to synthetic and seeing the rpm increase and cooler temp.  Thanks


mksj said:


> Detergent oils do not attack brass/bronze shafts, the primary purpose of detergents are to keep particles in suspension so they can be removed by a filter, which requires a pressurized lubrication system. Almost all engine oils these days have a detergent, one reason why they are a poor choice for splash lubrication systems. Multi-viscosity oils are designed to operate over a wide range of temperatures, so one will see a range of rated viscosity such as gear oil 75W90 or motor oil 5W30.  Extreme pressure (EP) anti-wear additives can damage yellow metals, softer materials such as clutch packs. etc. Most EP additives these days are inactive at lower temperatures and need heat to be activated. Oils are also designed for specific applications, so something like a limited slip differential oil has very different properties then standard gear oil of the same viscosity. As pointed out by others, in the US we have SAE viscosity index which is a bit mixed up as to the application and the viscosity. The rest of the world primarily uses the ISO system which is a single viscosity nomenclature.  Many oils these days will list there ISO viscosity in addition to their SAE, but a comparison chart is worth noting.  So viscosity wise an ISO 68 oil is equivalent to a SAE 20 motor oil and a 80W gear oil.
> 
> Many of the "gear oils" for machinery such as lathes and mills are based on mineral oil, and typically are a single weight viscosity. The higher the operating speed of the bearings/gears usually requires a lighter weight (lower ISO/SAE) oil. The type of gears and if there are any hydraulic components/clutch packs also factor into the oil properties and additive packs. Typically for manual mills and lathes, gear oil and hydraulic oils of the same viscosity are used pretty much interchangeably. There are small difference between the two, but not something that would make a difference in the lubricating properties of the oils.  Some oils are also designed to emulsify water contamination while others are designed to separate it out, almost all oils have anti-rust and anti-foaming agents. True synthetic oils have a much more uniform molecule size are are less prone to degradation and have a more constant viscosity index over a wide temperature operating range. As an example in air piston compressors the rated change time for a mineral based oil is ~200 hours, where a synthetic oil is around 1000-2000 hours. So if you have a high usage compressor, it makes sense to use a synthetic oil, but the oil still needs to be changed at regular intervals (6-12 months) due to water/particle  contamination.
> 
> ...


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## deadbunny (Dec 13, 2021)

pretty sure hyd, oil is high detergent (dirt stayes in oil without filter) this could wear gears, just saying


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## 7milesup (Dec 13, 2021)

Correct.  First two sentences of post #16.


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